Building control guide to extending your home

Building control guide to extending your home
Building control guide to extending your home
Your home is likely to be one of your biggest assets, it is a major long-term investment
and over the course of your occupancy your home will have to adapt to the changing
needs of you and your family.
Within England and Wales most construction work is covered by the Building Regulations.
These are minimum technical standards set by the government and all but the most
minor building work carried out must conform to these standards.
The standards cover many aspects of health and safety within buildings as well as energy
consumption and accessibility. The Building Regulations are detailed technical standards
set to ensure that the building stock within England and Wales is built to a reasonable
standard and that it meets the needs of the population.
The Building Regulations are minimum standards, they do not cover quality of
workmanship beyond that required to ensure the basic safe construction of the building.
It is possible therefore that a building
which complies with the Building Regulations may not meet the finishing standards that
you require and you should be mindful of this when you are entering into contractual
arrangements with your builder.
There is a legal requirement on both the builder and the owner of the building to make an
appropriate Building Regulations Application and to comply with the Building Regulations.
Failure to do so can result in prosecution through the Magistrates' Court.
Purpose of this guide
This guide will take you through the Building Control process. It is not a substitute for
professional advice but it aims to show how your project will be affected by the Building
Regulations. The guide is divided into chapters that contain advice about typical building
projects and it is hoped that when you have read the guide you will have a better
understanding of what is involved in a domestic building project.
Domestic projects that may require Building Regulations consent include:
Extensions (http://thanet.gov.uk/publications/building-control/guide-to-extendingyour-home/domestic-extensions/)
Garage conversions (http://thanet.gov.uk/publications/building-control/guide-toextending-your-home/garage-conversions/)
Loft conversions (http://thanet.gov.uk/publications/building-control/guide-toextending-your-home/loft-conversions/)
Cellar conversions (http://thanet.gov.uk/publications/building-control/guide-toextending-your-home/domestic-cellar-conversions/)
Structural alterations e.g. removing load bearing walls
Drainage, hot water or heating systems alterations
New or replacement windows
Electrical work
Replacement roof coverings
Cavity wall insulation
Some garages
Some conservatories
If you are considering a building project and you are unsure as to whether it will require
Building Regulations consent please feel free to contact us and we will be happy to advise
you.
The Building Regulations process
If your project needs Building Regulations consent you will need to make a Building
Regulations application (http://thanet.gov.uk/publications/building-control/guide-toextending-your-home/building-regulations/) .
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How to proceed
Unless you are experienced in construction you will need to get some professional advice.
There are a number of ways of obtaining this including:
1. Appointing an architect/technician or building surveyor: these will prepare drawings
and designs for your proposal, obtain the necessary approvals and if required they
will also help you to find a suitable builder and manage the project for you.
2. Appointing a design & build company: these companies offer a onestop shop for
construction projects, their design department will prepare the necessary drawings
and obtain the necessary approvals and their construction departments will
translate these drawings into reality.
3. Using an experienced builder: some builders have experience in carrying out
domestic projects and may be able to offer you a package similar to the design &
build companies.
Whatever type of project that you are undertaking we will arrange to carry out a series of
inspections of the work in progress.
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Guide to extending your home - Home owners and
projects
Home owners, Your Project needs you!
We know that taking on a building project can be very stressful and that sometimes it
feels best to leave it to others but in our experience the most successful building projects
involve good communications between builder, building control and you the client. So to
help you we have produced some guidance about what you can do to help your project
run smoothly:
Choose the right builder/architect/ surveyor/designer
When choosing a building contractor you should consider your choice very carefully. You
are advised to check them out before employing them. If you employ a good reputable
building contractor in terms of price, reliability and workmanship, the potential for
problems will be greatly reduced. An architect, surveyor, or designer can not only provide
the drawings and information your builder often needs to produce an accurate quote but
can offer on site supervision to ensure that your contractor's work gives you the quality
you want as well as value for money.
Understand the role of building control
The Councils' Building Control Officers are not there to act as your clerk of works; they
are there to check that the work undertaken satisfies the Building Regulations, which are
simply minimum health and safety standards.
You, as well as your builder, are legally responsible for making sure that all works comply
with the relevant regulations.
What you can do to help when the building work starts
Make sure that:
You have a valid Building Regulations application before works start. Building
Regulations approval is completely separate to Planning consent. Most building
projects require both.
Your builder has contacted building control when work starts, so that we are aware
and can make the necessary site visits. When we send out our decision notices we
include a commencement notice which you should complete and return to us.
Alternatively you can always telephone or e-mail us.
If you haven't employed a professional to supervise the work on your behalf then
keep a sum of money as a retention, which you withhold until you have received the
Building Regulations completion certificate
(http://iweb.thanet.gov.uk/edit/ILINK%7C15446,%7C) . The certificate is not a
guarantee of quality but it does demonstrate that the work, (as far as we can
reasonably tell - after all we are not on site all day every day), does meet the
requirements of the Building Regulations.
You have received the completion certificate. Should you ever wish to sell the
property or raise a loan/mortgage against the property you will need it.
You understand the basis for our charges. We will charge you only what it costs us
to process your application and carry out the various site visits. The charge is
calculated by multiplying our published hourly rate by the overall time that we
anticipate we will spend in relation to your project.
You have a reasonably competent builder carrying out the work;
You have a construction period that does not exceed one year. So if we have to
spend a lot of time on
site because you/your builder: needs guidance or we need to re-visit because you
are not ready or we need to re-inspect work that is not correct the first time or if we
have to spend time trying to contact you/ your builder to arrange site visits then we
may have to charge you extra for this additional time. We of course monitor how
much time we are spending on each job and will contact you in advance to let you
know if any additional charge is required.
Any electrical work or the installation of heating appliances should be carried out by
an installer registered under the Governments Competent Persons Scheme. This
allows them to self certify their work. The installer registers the installation with their
accredited body who then notify us of the registration electronically. Once this is
received we will issue our completion certificate for the whole project.
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Building Regulations
Making a Building Regulations Application
There are two ways of making a Building Regulations application:
Full Plans Application
This is often thought of as the traditional way of applying for Building Regulations
Approval. The building designer will draw up detailed plans and supporting information for
the proposed scheme and will send them to us together with an application form and the
necessary fee. We will then check the details and following any necessary consultations
and liaisons with the building designer a Building Regulations Approval will be issued.
Work can start any time after the application has been received although it is wise to wait
until the scheme has had its initial check under the Building Regulations, this usually takes
between two and three weeks. Our team of surveyors will liaise with your builder and
inspect the work in progress on site. When the project is satisfactorily completed a
Building Regulations Completion Certificate will be issued showing that the project has
been independently inspected and that it complied with the Building Regulations.
Building Notice Application
This system is best suited to small projects carried out by a competent builder and is not
recommended unless your builder and designer are very experienced in the type of
project that you are undertaking and are fully aware of the requirements of the Building
Regulations. Under this scheme no formal Approval of plans is issued and work is
approved on site as it progresses.
To use the Building Notice process you or your agent will need to submit a Building Notice
application form together with a site location plan and the required fee. Work can
commence 48 hours after the notice has been accepted. When work commences one of
our surveyors will meet with your builder to discuss your intentions, to agree how the
work should be carried out, agree when the work will need to be inspected and to
establish whether any further information will be required e.g. structural calculations or
drawings.
When the project is satisfactorily completed a Building Regulations Completion Certificate
will be issued showing that the project has been independently inspected and that it
complied with the Building Regulations. The forms for making a Building Regulations
application can be obtained by telephoning or calling into our offices, or can be
downloaded from your Council's website.
Self Certification
To help you to gain Building Regulations approval more easily the government have
allowed certain trade bodies to self certify their members' work and to issue Building
Regulations certificates. Currently the bodies
which can issue these certificates are:
1. FENSA – Contractors registered with FENSA can issue certificates for replacement
windows.
2. CERTASS – Contractors registered with CERTASS can issue certificates for
replacement windows.
3. GAS SAFE – Registered contractors can issue certificates for installations and
alterations to gas, hot water and heating systems so long as the contractor is a
registered installer and not just a service engineer.
4. OFTEC – Registered OFTEC installers can issue certificates for installation of and
alteration to oil burning boilers and appliances.
5. HETAS – Registered HETAS installers can issue certificates for installation of and
alteration to solid fuel burning boilers and appliances.
6. Part P – Electrical Contractors registered under one of the Part P schemes can issue
certificates for domestic electrical work.
For a comprehensive and up-to-date list go to the Communities and Local
Government website
(http://www.communities.gov.uk/planningandbuilding/buildingregulations/competentpersonsschemes/existingcompetentperson)
Tips for using Self Certified Contractors
1. Always ensure the contractor is registered for the work they are undertaking, eg. If
you are having a new heating system installed ensure the contractor is a registered
installer not a service engineer.
2. Always ensure that at the end of the job the contractor issues you with a Certificate
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confirming that the work complies with the Building Regulations, you may need this when
you come to sell your property.
3. If you are in any doubt about anything either contact the relevant trade association or
contact your local Building Control Office for advice.
Other permissions you may require
Planning Permission
Many domestic alterations will also require Planning Permission, further advice is available
from the Planning Portal http://www.planningportal.gov.uk/
(http://www.planningportal.gov.uk/) or to confirm whether Planning Permission will be
required for your project please contact your local Council's Development Management
section
Details on CCC 01227 862000, DDC 01304 821199 or TDC 01843 577000 or follow the
links from the web pages which can be found on the rear cover of the guide.
Party Wall Act
If your proposal affects a Party Wall or if you will need to excavate foundations close to
your neighbour's house you may need to give them notice under the Party Wall Act. This
is a Civil Act and Dover, Canterbury and Thanet Council's do not have any enforcing
power under the Act.
Further details of this can be found on the Planning
Portal http://www.planningportal.gov.uk/ (http://www.planningportal.gov.uk/) or
contact us for the latest guide to the Party Wall Act.
The inspection process
Whatever type of project that you are undertaking we will arrange to carry out a series of
inspections of the work in progress. Whilst we cannot be on site all of the time the
inspections will be carried out at key stages so that we can be reasonably sure that the
work carried out complies with the Building Regulations. We will tailor the inspections
carried out to suit your individual project and we will generally arrange these inspections
with your builder.
If during the project you have any concerns, if you want something specific inspecting, or
if you would like to meet to discuss any issues please contact us and we will make the
necessary arrangements.
Completion Certificates
When your project has been satisfactorily completed under the Building Regulations we
will issue a Completion Certificate. This is a legal document that you will need if you want
to sell your house, you may also need it for re-mortgaging or insurance purpose
Please ensure that we are called in to carry out our final inspection at the end of the
project to ensure that your Completion Certificate is issued.
Make sure your building project receives its Building
Regulations Completion Certificate
The Building Regulations completion certificate is the document that tells you that the
work on site meets the minimum health and safety standards required by the Building
Regulations. It is an essential document when/if you come to sell your property or raise a
secured loan/mortgage.
In some cases if building work is finished but no Building Regulations completion
certificate has been issued your building's insurance can be invalidated. Although the main
responsibility for ensuring work complies with the Building Regulations rest with your
builder, there are a number of things you can do to ensure that we can issue the
completion certificate promptly:
Discuss the matter with your builders so that they know you are expecting to
receive a Building Regulations completion certificate
Check with your builder that copies of the various documents we need to see before
we can issue a completion certificate have been given/shown to us at/before the
completion inspection, (examples include Part P electrical certificates and benchmark
certificates for boilers)
Where you have agreed this in advance with your builder, withhold a retention sum
until you have received the Building Regulations completion certificate.
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If you are in any doubt please just contact Building Control.
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Domestic Extensions
If you need more space and you do not want to move house you may wish to consider
extending your home.
Your home is probably your most valuable asset so it is important that your extension
project is carefully planned.
This guide is not a substitute for professional advice but has been written to provide you
with useful information about how the Building Regulations will affect your extension.
Suitability: most houses are suitable for extending, providing that you have the space.
When you are thinking about whether your house is suitable for extending you might like
to consider:
1. How will you access your extension?
2. What effect will your extension have on the circulation in and around your home?
3. What effect will your extension have on your existing house and garden? W ill it
block out light from existing rooms or make some rooms unusable? W ill you still be
able to get into your garden?
4. Is your existing house built from an unusual construction for example prefabricated
panels, concrete frame etc? If you can resolve all of these issues then your house
may well be suitable for extending.
How to proceed
Extensions are complex projects and unless you are experienced in construction you will
need to get some professional advice. The introduction contained advice about obtaining
this and with this in place we can now consider some of the technical issues that affect
domestic extensions.
Technical Issues
Foundations
The foundations are one of the most important parts of your extension and often one of
the most expensive. For domestic extensions trenchfill foundations are the most
common, these should be taken down into firm natural ground and should generally be a
minimum of 1m deep. In areas with clay subsoil trees up to 20m away can have a
significant effect on foundations which generally means that they need to be deeper,
sometimes as deep as 2.5m. If you are concerned about any trees please get in touch
with us and we will give you some advice regarding foundation depths.
Ground Floor
The ground floor of your extension performs a number of tasks: it must support the
floor loading, keep out damp and provide thermal insulation. Generally a ground floor is a
multi layer structure, the top soil under the extension floor area is removed and a layer of
compacted stone is placed over the site. This is blinded with sand and a layer of 1200g
polythene is then placed over the sand and lapped in with the damp proof course in the
wall. A layer of insulation is then provided and a concrete slab at least 100mm thick is
poured over the insulation (some insulation may require an additional membrane). The
concrete can either be float finished or a screed applied at a later date. On some sites
where the ground floor is significantly higher than external ground level or where the site
has been affected by trees, a suspended floor may be needed, these can be formed from
either concrete or timber and if you need any guidance regarding suspended floors,
please get in touch with us for advice.
Walls
The walls of your extension must carry the loads from the floors and roof, keep the
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weather out of the extension and provide thermal insulation. Cavity walls are commonly
used for domestic extensions. These are made up from bricks and blocks and the cavity
is filled with insulation as the work proceeds. When building walls remember to ensure
that you have adequate buttressing at the corner of your extension, lintels over all
openings, wall ties to join the leaves of your cavity wall together and a suitable damp
proof course. If you are building up against your neighbour's house you will also need to
ensure that your wall provides adequate sound resistance.
First Floor
Two storey extensions will require a first floor, these are generally made up from timber
floor joists which span between load bearing walls, they support floor boarding above and
plasterboard is then fixed to the underside of the joists to provide a ceiling finish and fire
resistance. The size of the floor joists will depend on the span so please contact us for
advice on the joist size required. The floor will also need to include sound insulation and in
domestic extensions, 100mm of sound deadening mineral wool placed between the joists
is generally sufficient.
The Roof Structure
The roof of your extension will need to be designed to keep out the rain and snow and
may need to cope with some light loft storage loading. Generally two types of roof are
used for domestic extensions:- Flat Roofs: this is the simplest type of roof structure and
for some extensions, generally single storey, a flat roof can provide a practical and
economic solution. Timber joists are used to span between the load bearing walls and
beams and these are covered with a plywood decking laid on firring strips to provide a
fall. Thermal insulation is then placed over the roof and it is generally finished with a
waterproof covering of three layers of bonded roofing felt.
Critical things to consider in this type of roof are the size and support of the roof joists
and the way that the roof will be insulated and, if necessary, ventilated. Pitched Roofs: if a
flat roof is not suitable for your needs you are likely to require a pitched roof. These are
generally more substantial structures that are finished with roof tiles or slates. The
supporting structure of the roof can be formed in two ways:
1. Trussed Rafter Roofs: these are quick to construct, measurements are taken from
site and roof trusses are made up in a factory, they are then delivered to site ready
for installation. Each roof is individually designed by the roof truss manufacturer
using specialist computer software and the carpenter's time on site can be
significantly reduced.
2. Traditional Roofs: A carpenter cuts a traditional roof on site. The roof structure will
generally be designed by an architect or structural engineer and the timber is then
delivered to site where the carpenter will set out the roof and cut each of the
individual timbers to size before installing them. This type of roof offers the greatest
flexibility in roof shape and is often the only way of roofing complicated extensions
especially where the new roof must join onto an existing structure.
The size of the timbers and supporting beams required in a roof will depend on the
loadings and spans involved in each case, complex roofs will require a structural
engineer's design but our Building Control Surveyors will be happy to assist your
builder in designing simple roof structures. Once the support is in place the roof
must be covered to provide weather protection, pitched roofs are generally finished
with tiles or slates with a layer of roofing membrane or felt under them. The tiles are
supported by the rafters via a series of timber battens.
To provide adequate weather resistance the tiles overlap each other and they must have
an adequate pitch. For extensions it is common to use tiles or slates that match the main
house although this is not always possible if the extension roof has a very low pitch. Our
Building Control Surveyors will be happy to assist you with any enquiries that you have
about roof finishes.
Stairs
If your extension has more than one storey you may need to install a staircase and
careful design of this can be critical to the success of the extension. If a stair is installed it
should be designed in accordance with the following guidance. Width: there is no
minimum width for stairs in the Building Regulations however they will need to be useable.
Generally stairs are 850–1000mm wide. Pitch: the maximum pitch for the stair should not
exceed 42 degrees. Rise and Going: the maximum rise of each tread of a domestic stair
should not exceed 220mm and the going should be at least 220mm. Headroom: the clear
headroom over the stair should be at least 2m.
Handrails and Balustrades
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The stair should be provided with a handrail at least 900mm high and any exposed edges
of stairs or landings should be provided with balustrading at least 900mm high. Fire
Precautions: it is important that you consider fire precautions when you are designing
your extension. The most dangerous fires generally occur at night when everyone is
asleep and to give you awareness of a fire the Building Regulations suggest that mains
operated smoke detectors should be installed on each floor of the house when it is
extended.
To prevent people being trapped by a fire all rooms that do not open directly onto a hall
and all first floor rooms should have a window or door that is large enough for people to
escape through. If you are using a window as your secondary fire escape it should have
a clear opening of at least 0.33m2 at least 450mm wide with a cill height of between 800
and 1100mm above floor level. Fire is a very dangerous thing and careful design and
planning are required to ensure that the risks it poses are minimised.
Ventilation
Fresh air is essential to healthy living and the Building Regulations require your extension
to have adequate ventilation, generally an opening window with a 'trickle vent' is all that is
required, the window should have an openable area equivalent to at least 1/20th of the
floor area of the room that it is ventilating. The trickle vent is a small slot type vent that
you can leave open to allow some background ventilation without the need to open the
window, generally these are found in the top of the window frame. If your extension
contains a kitchen, utility room or bathroom you will need to provide an extract fan in
these areas and your Building Control Surveyor will be pleased to provide you with more
detailed advice when they call on site.
Drainage
It is usually possible to connect drainage from extensions into the existing drainage
systems. Drainage can be divided into two types, foul water and rainwater and generally
speaking the drainage systems should be kept separate. Foul drainage is generally
discharged through a series of pipes and manholes to a public sewer although some
properties will have septic tanks or private sewage treatment plants. When planning your
extension look for manholes and try and find out where your drains are running so that
you can work out how any new drains will connect to them.
Consent may also be required from Southern Water Services if you intend to build over
and/or within 3 metres and/or connect to an adopted sewer, manhole lateral drain. You
are advised to check with them direct as this consent must be obtained before work
commences. It is important that all new underground drain pipes have a diameter of at
least 100mm so that they do not block or freeze, are watertight and have manholes or
access points so that any blockages can be cleared. Where possible rainwater drainage
should not be discharged to foul sewers as this can cause problems with flooding, the
preferred solutions are to discharge rainwater to soakaways located in your garden at
least 5m from any building or to storm water sewers if they are available.
Heating
Most extensions will need to be heated and you will need to check with your heating
engineer that your existing system has sufficient capacity to heat your extended house.
You may also need to move your boiler, if for example, your extension will cover the flue
outlet. Any alterations to your heating system should be carried out by a suitably qualified
plumber or heating engineer registered with Gas Safe for gas fired boilers or OFTEC for oil
fired boilers. Any new boilers will need to be highly efficient condensing boilers and the
new radiators that you install in your extension should be fitted with thermostatic radiator
valves so that you can ensure that they use heat efficiently.
Thermal Insulation
CO2 emissions are a major concern in today's environment and you will need to provide a
high level of insulation within your extension. Your extension should provide an insulated
envelope so that the amount of heat escaping is minimised. The roof, walls and floors of
your extension should all include thermal insulation; walls generally have insulation placed
within the cavity, roofs generally have insulation in the loft area and sheets of insulation
can be placed beneath the concrete of your ground floor.
Another major area where heat is lost from buildings is the windows and these require
special attention: 24mm double glazing units incorporating low emissivity glass are
generally required and, unless energy improvements are carried out in the existing house,
the window area of your extension is limited by the Building Regulations to 25% of the
floor area plus the area of any existing openings covered by the extension.
High levels of insulation can result in problems with condensation and care must be taken
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to ensure adequate ventilation is available to rooms and particularly in roof voids. As well
as insulating your extension you will need to consider the efficiency of any services you
put into it.
Low energy light fittings should be used where possible and any new heating systems
should work to high levels of efficiency and have suitable thermostats and controls.
Sound Insulation
To reduce unwanted noise the walls and floor around bedrooms will need to be insulated
to reduce sound transmission, this is generally achieved by placing 100mm of sound
deadening quilt in the floor void and in the partitions around the bedrooms.
Electrical Installations
As part of the Building Regulations process you will need to supply British Standard Test
Certificates for most new electrical installations, when selecting your electrical contractor
please ensure that they are competent to provide you with these test certificates as
otherwise you are likely to incur additional costs for testing the circuits. Glazing: to reduce
the risk of people injuring themselves, glazing in and around doors and all glazing within
800mm of floor level should be either toughened or laminated glass.
Conclusion
Whereas a well designed and constructed extension is a definite asset to your home that
can provide useful extra space and add value to your property, a poorly thought-out
extension can reduce your property's value and in some cases compromise your safety
and the structural integrity of your home.
It is important to ensure that you plan your extension carefully and get the work carried
out by an experienced contractor. The Building Regulations exist to ensure that buildings
are constructed to a reasonable standard; Building Control will be pleased to provide you
with any further assistance that you require during the design and construction of your
extension.
It is important to ensure that you plan your extension carefully and get the work carried
out by an experienced contractor.
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Loft conversions
Most houses have a large space under their roofs normally known as the loft or attic, this
space is often under utilised and in some instances can offer an ideal opportunity for
expanding your home.
This guide has been written to provide you with useful information about how the Building
Regulations will affect your loft conversion project.
Suitability
Not all lofts are suitable for conversion and as a first step it is wise to go into your loft
and carry out a brief survey before you get too far into the planning of your project.
When carrying out your survey check:
That there is enough height within your loft to stand comfortably, bearing in mind
that your new floor is likely to be around 200mm higher than your existing ceiling
joists.
That the loft space is large enough to provide a useable room.
That there aren't any chimneys or services passing through the loft space that will
need moving.
That your roof has felt under the tiles or is fully weathertight. If the answer to all of
these questions is 'Yes' then your loft may well be suitable for conversion.
How to Proceed
Loft conversions are complex projects and unless you are experienced in construction
you will need to get some professional advice.
The introduction contained advice about obtaining this and with this in place we can now
consider some of the technical issues that affect loft conversions.
Technical issues
The roof structure
The roof of your home is currently designed to keep out the rain and snow and to cope
with some light loft storage loading. After a loft conversion your roof will have to cope
with significantly different loadings, a new floor structure will be required and it is likely
that a number of the structural elements will need to be altered to allow for circulation
within the room, roof windows etc. Roofs can generally be divided into two types.
Trussed rafter roofs
These have been common since the 1970s, and roofs of this type are difficult to convert.
Roof trusses are complex pieces of engineering and they should not be altered without
the advice of a structural engineer. When converting this type of roof it is common for a
series of beams to be installed to provide support to the new floor and to strengthen the
rafters, this allows the bracing sections of the trusses to be cut out to create a clear floor
area.
Traditional roofs
These are generally made up from a series of rafters and purlins spanning between load
bearing walls. These roofs are less complicated to convert than trussed rafter roofs,
however, beams are often required to provide support to the new floor structure and the
existing purlins and a structural engineer's design will be required for all but the simplest
conversions. When considering a loft conversion don't be tempted to simply board over
your existing ceiling joists and rafters, this can adversely affect the value of your property
and in some circumstances can cause overloading and endanger the structural stability
of your home.
Accessing your loft conversion
If you want to convert your loft for habitable use you will need to install a staircase and
careful design of this can be critical to the success of your conversion. If there is enough
headroom it is often best to continue the stair in the existing stairwell as this saves space
and gives a feeling of continuity within the home, alternatively part of a room will have to
be partitioned off to accommodate the new staircase.
Wherever the stair is installed it should be designed in accordance with the following
guidance. Pitch: the maximum pitch for the stair should not exceed 42 degrees.
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Rise and going
The maximum rise of each tread of a domestic stair should not exceed 220mm and the
going should be at least 220mm.
Headroom
The clear headroom over the stair should be at least 2m, for some loft conversions the
Building Regulations allow a reduced headroom of 1.9m over the centre of the stair and
1.8m on the outside edge.
Handrails and balustrades
The stair should be provided with a handrail at least 900mm high and any exposed edges
of stairs or landings should be provided with balustrading at least 900mm high.
For loft conversions where space is very limited and only one room is created, a specialist
alternating tread staircase can be used, these are steeper than standard stairs and can
provide valuable space in some circumstances.
Fire precautions
House fires can kill and fire precautions are a major concern for the Building Regulations.
The most dangerous fires generally occur at night when everyone is asleep and to give
you awareness of a fire it is important that you install smoke detection. When converting
your loft you will need to ensure that you have mains powered, interlinked smoke
detectors in the hall/landing areas on every floor of your house.
Two storey houses
The Building Regulations requirements for fire precautions in two storey housing are quite
simple as it is generally felt that if you couldn't get out down the stairs you could jump or
be rescued from a first floor window. If you are converting the loft of a bungalow you will
need to ensure that you have mains powered interlinked smoke detection at ground and
first floor level and that all habitable rooms at first floor level have an 'escape window'.
Escape windows
As their name suggests, are windows that are large enough to allow people to escape or
be rescued through them. They need to have a clear opening area of at least 0.33m2 and
a clear width of at least 450mm. The bottom of the opening light should be no more than
1100mm above floor level and they should allow people to escape to a place free from
danger. Escape windows need to be fitted with escape hinges that allow the window to
fully open. Some of the standard hinges fitted to UPVC windows do not achieve this so it
is wise to check this with your glazing supplier when you order your windows.
Three storey houses
When you convert the loft of a house and create a third floor the Building Regulations
require you to look at the fire precautions within the house a lot more seriously. Mains
operated smoke detection needs to be fitted to give you awareness of a fire and as, due
to the height of your new floor, you can no longer rely on escaping through the windows
the only safe way out of the house is down the stairs. It is therefore vital that the stair is
protected from fire. To protect the stair all of the doors that open onto the stair need to
be half hour fire doors and the stair should end up in a hall with a door direct to the
outside. Generally, unless a sprinkler system or alternative escape stair is provided, stairs
cannot discharge into other rooms in three storey properties.
Four storey houses
If your house already has three storeys, loft conversions become more complicated. You
are likely to need to install a sprinkler system or a second escape stair and the project will
need specialist design. Please contact us and we will be happy to provide you with more
detailed advice if you are considering one of these projects.
Fire is very dangerous and careful design and planning is required to ensure that the risks
it poses are minimised.
Bathrooms
It is often a nice idea to include a bath or shower room in your loft conversion, the best
place for this is generally directly above your existing bathroom as this should ensure
that you can connect into the existing drainage and water supplies without the need for
Page 12 of 25
excessive pipework. Any bath or shower rooms will also need to be fitted with an extract
fan to improve ventilation. It is a good idea to decide on the location of any bathrooms at
an early stage in your space planning process.
Thermal insulation
CO2 emissions are a major concern in today's environment and you will need to provide a
high level of insulation to your roof as part of your loft conversion. The most common
way of achieving this is to place a high performance insulation board in between and
below the rafters. Unless your roof has a breathable felt you will need to leave a void
above the insulation and ensure that you have effective roof ventilation to prevent the
build up of condensation.
Sound insulation
To reduce unwanted noise the walls and floor around bedrooms will need to be insulated
to reduce sound transmission, this is generally achieved by placing 100mm of sound
deadening quilt in the floor void and in the partitions around the bedrooms. If you are
converting the loft of a semi-detached or terraced property you will need to ensure that
the sound resistance of the Party Wall is upgraded so that sound transmission to your
neighbours is reduced.
Heating
To maximise the usability of the room you will probably want to install heating, in most
instances the most effective way of doing this is to extend the existing central heating
system. You will need to check with your plumber or heating engineer to ensure that your
existing boiler has sufficient capacity to serve any additional radiators and any new
radiators should be fitted with thermostatic valves to control the room temperature.
If it is not possible to extend the existing system or if you prefer an alternative method of
heating, e.g. electric panel heaters, careful consideration should be given as to how these
can be switched and controlled to ensure that they function efficiently.
Electrics
You are likely to require some electrical alterations as part of your conversion. Depending
on the age and condition of your existing electrical system it is sometimes possible to
extend existing circuits but sometimes new circuits and even a new distribution board will
be required. It is a good idea to get advice from a competent electrician at an early stage.
When appointing an electrician please ensure that they are able to issue you with BS7671
test certificates when they have completed their installation as these will be required
before your Building Regulations Completion Certificate can be issued and you will incur
additional costs if the test certificates have not been provided.
Windows and ventilation
Any new habitable rooms will need to be ventilated. Generally this is achieved by providing
an opening window or roof light equivalent to 1/20th of the floor area of the room with a
trickle vent at high level. All new windows must be fitted with highly efficient double glazed
units. In bath or shower rooms an extract fan should be fitted and in rooms without
opening windows extract fans should be fitted that are triggered by the light switch with
overrun timers that allow the fan to remain on after the light is turned out.
Conclusion
A well converted loft is a definite asset to your home, it can provide useful extra space
and add value to your property. However a poorly converted loft can reduce your
property's value and in some cases compromise your safety and the structural integrity
of your home. It is important to ensure that you plan your conversion carefully and get
the work carried out by an experienced contractor.
The Building Regulations exist to ensure that buildings are constructed to a reasonable
standard; your local Building Control Office will be pleased to provide you with any further
assistance that you require during the design and construction of your project.
Page 13 of 25
Garage conversions
Garage conversions
If you need more space and you do not want to move house you may wish to consider
converting your garage. Your home is probably your most valuable asset so it is
important that your conversion project is carefully planned. This guide is not a substitute
for professional advice but has been written to provide you with useful information about
how the Building Regulations will affect your conversion.
Suitability
If you have a brick or block garage attached to your house it is probably suitable for
converting. When you are thinking about whether your garage is suitable for conversion
you might like to consider:
Whether there are any known problems with your garage, are there any cracks in
it? Is it damp?
Does the roof leak? Has the floor been contaminated with fuel or oil?
How will you get into the new room? Have you got or can you put a doorway
through to the garage from the house?
Will you have enough parking and storage area if you convert your garage?
Is there enough room in your garage to provide the accommodation that you
require or would you be better extending the property?
Is your existing garage built from an unusual construction? For example,
prefabricated panels, concrete frame etc.
If you can resolve all of these issues then your garage may well be suitable for
conversion.
How to Proceed
Garage conversions can be complex projects and unless you are experienced in
construction you will need to get some professional advice. The introduction contained
advice about obtaining this and with this in place we can now consider some of the
technical issues that affect garage conversions.
Technical Issues
Infilling the Garage Door Opening
This tends to be the most visible part of your conversion from the outside and whatever
you choose to infill the opening it will need some support. Some garages have a
foundation that runs across the garage opening which you can use to support your infill.
Unfortunately the only real way to tell if the front of your garage has an existing
foundation is to dig a hole and find out. If there is no foundation under your garage door
opening there are two main options.
You can either:
1. Dig a foundation 1m deep or to the same depth as the foundations of the existing
garage, call us to inspect the foundation and then fill it with concrete.
or
2. If the opening is only the width of a single garage door install two 150mm deep
concrete lintels across the opening supported by the existing foundations.
Your Building Control Surveyor will be happy to provide you with more advice about which
is the best option for you when we get to site. With the foundations in place the garage
door opening can now be filled in. There are several options for how this can be done.
The opening can be filled in with brickwork to match the house and a window.
People generally narrow the garage door opening slightly as a full width window can
appear out of proportion. To keep the damp out and to provide insulation it is best to use
a cavity wall and your new window should be double-glazed.
Other options include installing a lightweight timber framed panel with a weatherproof
external surface and insulation, this can be quicker and cheaper and has the advantage
that it is easier to remove if you, or any future owners of the house, ever wanted to
reinstate your garage.
Whichever option you choose it is important that the infill panel provides adequate
weather resistance and insulation and that all of the new work is tied into the existing
Page 14 of 25
construction. Y our Building Control Surveyor will be happy to provide you with advice
about this.
Raising the Floor Level
Garage floors are generally lower than the floor in the main house and they often slope
towards the garage door. For these reasons garage floors are generally raised as part of
a conversion. There are two main ways of raising a garage floor. Whichever way you
choose it is important to consider insulation and damp proofing.
Option 1
Concrete: using this method a polythene membrane is placed over the garage floor, floor
insulation is laid down, a second polythene membrane is installed and the floor level is
brought up to the same level as the house using concrete or sand and cement screed.
Option 2
Timber: this method involves placing treated timber floor joists onto a damp proof
membrane placed over the existing concrete floor, placing floor insulation between the
joists and covering the floor joists with floor boards or tongued and grooved chipboard.
The floor can then be finished with carpet, laminate or any other decorative surface.
Lining the External Walls
The walls used to construct garages are not normally up to habitable standards, they are
sometimes formed from a single thickness of brickwork and even when built from cavity
masonry they are often un-insulated. When converting your garage the walls will need to
be upgraded.
There are three main areas of concern when upgrading walls in a garage conversion:
weather and damp resistance, insulation and sound resistance. The upgrading scheme
that you choose will be influenced by the original construction of your garage walls, these
can be broadly divided into two categories. Cavity Walls: if your garage is built from cavity
walling, weather resistance and damp proofing are unlikely to be a problem.
These walls generally have damp proof courses and providing that your wall is in good
condition and is not showing signs of water ingress or rising damp, the wall will simply
require insulating and a plaster finish ready for your decoration.
There are two options for insulating the wall: either the cavity can be injected with cavity
wall insulation or an insulated lining board can be fixed to the inner face of the wall prior
to plaster boarding or plastering. Various boards are available and your Building Control
Surveyor will be happy to provide advice as to which boards are suitable for your project.
Solid Brick Walls
In garages these are generally only a single brick approximately 100mm thick and they
often have intermediate piers that buttress the walls and give them additional strength. A
single brick wall will not provide adequate weather resistance to a habitable room and a
supplementary wall will need to be provided behind the original wall. This can be done
either by building an additional skin of masonry to form a cavity wall, the cavity can be
insulated as the wall is built, and the wall can then be dry lined or plastered.
Alternatively an independent timber framed wall can be constructed with a cavity between
the new framing and the existing wall. The frame should be constructed from treated
timber and insulation should be provided between the timber studs. Once the frame is in
place an insulated plasterboard finish can be applied ready for decoration.
Occasionally garages are built with 225mm thick solid brick walls. If they are in good
condition and have a damp proof course they will normally provide adequate weather
resistance but they will need to be lined with an insulating board to improve their
insulation.
Party Walls
If any of the walls of your garage are shared with a neighbour it is considered to be a
Party Wall. These walls will need to be upgraded to reduce sound transfer between your
new room and your neighbour's property. Your Building Control Surveyor will be happy to
provide you with advice as to how you can upgrade any Party Walls.
The Ceiling
Page 15 of 25
Unless your existing garage has an adequate ceiling you will need to provide one as part
of your conversion. Plasterboard is the most common material used for ceilings as it
offers good fire resistance and flame spread properties. Other materials can be used but
they will generally need to be treated to improve their fire performance.
If the garage is open to a roof you will need to provide insulation above the ceiling and the
roof void will generally need to be ventilated above the insulation to reduce the risk of
problems with condensation. In a pitched roof fibreglass insulation will normally suffice
but with flat roofs, where space is confined, high performance insulation boards are often
required.
Your Building Control Surveyor will be happy to discuss this with you.
Heating
To maximise the usability of the room you will probably want to install heating; in most
instances the most effective way of doing this is to extend the existing central heating
system. You will need to check with your plumber or heating engineer to ensure that your
existing boiler has sufficient capacity to serve any additional radiators and any new
radiators should be fitted with thermostatic valves to control the room temperature.
If it is not possible to extend the existing system, or, if you prefer an alternative method
of heating, e.g. electric panel heaters, careful consideration should be given as to how
these can be switched and controlled to ensure that they function efficiently.
Drainage
If you are looking to include a sink, bathroom, shower room or cloakroom in your
conversion it is important that you consider drainage at an early stage. Any new
appliances will need to connect to your existing foul drainage system as they are not
allowed to be connected into rainwater drains. When planning your layouts make sure
that there are suitable routes for pipes to run to a point where they can connect to
existing drains.
Windows and Ventilation
Any new habitable rooms will need to be ventilated. Generally this is achieved by providing
an opening window equivalent to 1/20th of the floor area of the room with a trickle vent at
high level. All new windows must be fitted with highly efficient double glazed units and it is
wise to make sure that they contain an opener with a clear area of at least 0.33m2 and
450mm wide which should be large enough for you to escape through in the case of fire.
This is essential if the door out of your garage opens into a room other than your
entrance hall. Special fire escape hinges should be fitted to this window to ensure that it
can be fully opened if you ever need it.
In bath or shower rooms an extract fan should be fitted and in rooms without opening
windows extract fans should be fitted that are triggered by the light switch with overrun
timers that allow the fan to remain on after the light is turned out. Fire Precautions: when
you are investing money in your home it is a good opportunity to review the fire
precautions that are available in the existing house.
Mains operated smoke detection significantly improves fire safety in the home and the
Building Regulations require that it should be installed where garages are converted to
habitable rooms.
Electrics
You are likely to require some electrical alterations as part of your conversion. Depending
on the age and condition of your existing electrical system it is sometimes possible to
extend existing circuits but sometimes new circuits and even a new distribution board will
be required. It is a good idea to get advice from a competent electrician at an early stage.
When appointing an electrician please ensure that they are able to issue you with BS7671
test certificates when they have completed their installation as these will be required
before your Building Regulations Completion Certificate can be issued and you will incur
additional costs if the test certificates have not been provided.
Conclusion
A well designed and constructed garage conversion can be a definite asset to your home
that can provide useful extra space and add value to your property. A poorly thought-out
conversion can reduce your property's value and in some cases compromise your safety
and the structural integrity of your home. It is important to ensure that you plan your
conversion carefully and get the work carried out by an experienced contractor.
Page 16 of 25
The Building Regulations exist to ensure that buildings are constructed to a reasonable
standard; your local Building Control Office will be pleased to provide you with any further
assistance that you require during the design and construction of your project.
Page 17 of 25
Domestic cellar Conversions
If you are fortunate enough to have a cellar beneath your house and you need more
space you may wish to consider converting your cellar. Your home is probably your most
valuable asset so it is important that your conversion project is carefully planned. This
guide is not a substitute for professional advice but has been written to provide you with
useful information about how the Building Regulations will affect your conversion.
Suitability
If you have a cellar beneath your house it may well be suitable for converting. When you
are thinking about whether your cellar is suitable for conversion you might like to
consider:
Is there sufficient headroom in the cellar, bearing in mind that the ceiling and the
floor treatments that you will have to install are likely to reduce the available
headroom?
Does the cellar ever flood?
What is the access like? Is there a place for a staircase?
Will you have enough storage area if you convert your cellar?
Is there enough room in your cellar to provide the accommodation that you require
or would you be better extending the property?
Is there any ventilation to your cellar or could any be provided?
If you can resolve all of these issues then your cellar may well be suitable for conversion.
How to Proceed
Cellar conversions can be complex projects and unless you are experienced in
construction you will need to get some professional advice.
Technical Issues
Lowering the Cellar Floor
If there is not sufficient headroom in your cellar it is sometimes possible to lower the
cellar floor. This is not however a simple operation and careful consideration needs to be
given to whether lowering the floor will undermine the house or the neighbour's house
foundations and whether the floor will end up below the water table and make the
property more vulnerable to flooding. Specialist advice should always be taken before
considering lowering cellar floors.
Waterproofing
As most cellars are set within the ground they tend to suffer from problems with damp. If
it is to be converted to a habitable room your cellar will need to be damp proofed. A
number of systems are available for damp proofing cellars and most of them use a
proprietary waterproof render system known as tanking. This is applied so that it forms a
continuous damp proof layer across the floor and up the walls and is generally installed
by specialist companies who will offer an insurance backed guarantee for the installation.
Protecting your cellar from damp is an important part of the cellar conversion process
and we will need to approve details of the system that you are using and the installer prior
to installation.
Access
Some cellars already have good stepped access to them, whether the existing stairs will
provide suitable access to a habitable room is a matter of judgment and our Building
Control Surveyors will be happy to offer advice. If there are no steps, or if the existing
steps are inadequate, a new stair will need to be installed.
Careful consideration should be given to the best location for the stair and this will be
influenced by a number of factors including the layout of the existing house and cellar,
the headroom available and whether a secondary means of escape can be provided from
the cellar area.
Wherever the stair is installed it should be designed in accordance with the following
guidance.
Pitch
The maximum pitch for the stair should not exceed 42 degrees.
Page 18 of 25
Rise and Going
The maximum rise of each tread of a domestic stair should not exceed 220mm and the
going should be at least 220mm.
Headroom
The clear headroom over the stair should be at least 2m, for some loft conversions the
Building Regulations allow a reduced headroom of 1.9m over the centre of the stair and
1.8m on the outside edge.
Handrails and Balustrades
The stair should be provided with a handrail at least 900mm high and any exposed edges
of stairs or landings should be provided with balustrading at least 900mm high.
Fire Precautions
Your cellar will need to be provided with suitable escape routes in case of a fire. If your
cellar has a light well it may be possible to upgrade this so that as well as providing
ventilation to the room it can provide a secondary fire escape. To be considered as a
secondary fire escape it would need to be fitted with a door or window with a clear area
of at least 0.33m2 and 450mm wide.
Special fire escape hinges should be fitted to this window to ensure that it can be fully
opened if you ever need it and you should be able to easily climb up from the light well to
ground level. If you cannot provide a secondary fire escape the staircase will need to end
up in a fire protected hallway with a door direct to outside.
When converting your cellar it is a good opportunity to review the fire precautions that
are available in the existing house. Mains operated smoke detection significantly improves
fire safety in the home and the Building Regulations require that it should be installed
where cellars are converted to habitable rooms.
Drainage:
If you are looking to include a sink, bathroom, shower room or even a washing machine
in your conversion it is important that you consider drainage at an early stage. Any new
appliances will need to connect to your existing foul drainage system and the drains are
usually above the level of the appliances that you wish to install.
You are likely to need to install a pumped drainage system and various package systems
are available that macerate the drainage and pump it via a small diameter pipe to the
existing drainage system. When planning your layouts make sure that there are suitable
routes for pipes to run to a point where they can connect to existing drains.
The Ceiling:
Unless your existing cellar has an adequate ceiling you will need to provide one as part of
your conversion. Plasterboard is the most common material used for ceilings as it offers
good fire resistance and flame spread properties. Other materials can be used but they
will generally need to be treated to improve their fire performance.
If either your cellar or the room above is to be used as a bedroom you will need to install
100mm of acoustic quilt within the floor void between the rooms.
Heating:
To maximise the usability of the room you will probably want to install heating, in most
instances the most effective way of doing this is to extend the existing central heating
system. You will need to check with your plumber or heating engineer to ensure that your
existing boiler and pump has sufficient capacity to serve any additional radiators. Any
new radiators should be fitted with thermostatic valves to control the room temperature.
If it is not possible to extend the existing system, or, if you prefer an alternative method
of heating, e.g. electric panel heaters, careful consideration should be given as to how
these can be switched and controlled to ensure that they function efficiently.
Ventilation:
Any new habitable rooms will need to be ventilated and this can sometimes present a
problem for cellar conversions. Where the cellar contains a light well this can sometimes
be adapted to include an opening window equivalent to 1/20th of the floor area of the
Page 19 of 25
room with a trickle vent at high level. In any bath or shower rooms an extract fan should
be fitted and if they do not have opening windows extract fans should be fitted that are
triggered by the light switch with overrun timers that allow the fan to remain on after the
light is turned out.
Where natural ventilation through windows is not practical a mechanical ventilation
system will need to be installed and various package systems are available on the market.
Ventilation should be considered early in the design stage as, if mechanical ventilation is
required, the duct work will need to be accommodated.
Thermal Insulation
CO2 emissions are a major concern in today's environment and you will need to provide a
high level of insulation within your conversion. Your cellar should provide an insulated
envelope so that the amount of heat escaping is minimised. The walls and floor of your
cellar are generally lined with insulating boards and the windows should include 24mm
double glazing units incorporating low emissivity glass. As well as insulating your
extension you will need to consider the efficiency of any services you put into it. Low
energy light fittings should be used where possible and any new heating systems should
work to high levels of efficiency and have suitable thermostats and controls.
Electrics
You are likely to require some electrical alterations as part of your conversion. Depending
on the age and condition of your existing electrical system it is sometimes possible to
extend existing circuits but sometimes new circuits and even a new distribution board will
be required. It is a good idea to get advice from a competent electrician at an early stage.
When appointing an electrician please ensure that they are able to issue you with BS7671
test certificates when they have completed their installation as these will be required
before your Building Regulations Completion Certificate can be issued and you will incur
additional costs if the test certificates have not been provided.
Conclusion
A well converted cellar can be an interesting space and can be a great way of getting
extra room in your house.
Cellar conversions are often not simple projects and a poorly thought-out conversion can
reduce your property's value and in some cases compromise your safety and the
structural integrity of your home. It is important to ensure that you plan your conversion
carefully and get the work carried out by an experienced contractor.
The Building Regulations exist to ensure that buildings are constructed to a reasonable
standard; Canterbury, Dover and Thanet Building Control will be pleased to provide you
with any further assistance that you require during the design and construction of your
project.
Page 20 of 25
Other alterations
A number of home improvement projects are covered by the Building Regulations and
this chapter sets out to explain how the Building Regulations affect some of the projects
that you may be considering. This guide is not a substitute for professional advice but
has been written to provide you with useful information about how the Building
Regulations will affect your project.
Removing Internal Walls Internal walls have a number of functions, some are fundamental
to the structure of the house, some offer fire protection to the stairway and others
merely divide up the space within the house and can be altered or removed with very few
issues.
Load bearing walls are fundamental to the structure of the house and careful
consideration needs to be given before they can be altered or removed. Alteration or
removal of load bearing walls requires Building Regulations consent and generally
speaking a structural engineer should be commissioned to design the alteration.
Supporting beams over padstones
Load bearing walls are fundamental to the structure of the house and careful
consideration needs to be given before they can be altered or removed.
Building control
The structural engineer will consider what loads the wall is taking and will design a beam
and, if necessary, other supporting structure to ensure that the loads the wall was
carrying are safely transmitted to the ground. We will then inspect the work as it
progresses and then issue a completion certificate to show that the work complied with
the Building Regulations.
The walls around your staircase offer you some protection to allow you to escape if your
house catches fire and the alteration of these walls requires Building Regulations consent.
If these walls are removed it is essential that your house is fitted with mains operated
smoke detection and that all of your rooms have windows suitable for fire escape
purposes (see Fire Precautions (http://thanet.gov.uk/publications/buildingcontrol/guide-to-extending-your-home/domestic-extensions/) – Domestic Extensions).
If you wish to remove one of these walls contact us and we will arrange to visit you to
establish whether the walls are essential to the fire protection within your house and
advise what, if any, additional work is required to allow the alterations to take place.
Bay Windows and Chimneys
In Building Regulations terms these are basically small extensions. They require Building
Regulations consent and much of the guidance in the Extensions
(http://iweb.thanet.gov.uk/edit/ILINK%7C15434,%7C) chapter is relevant albeit on a
somewhat smaller scale.
Chimneys require lining with a flue liner that is suitable for the fire that they will serve and
the installer should test the flue prior to commissioning the fire.
We will carry out a series of inspections on these projects and issue a completion
certificate when the works are satisfactorily completed.
New Drainage
Replacement kitchens and bathrooms do not generally need Building Regulations consent
but where new drainage is installed to serve a new bathroom or other appliance Building
Regulations consent is required. With these projects we will carry out a series of
inspections to ensure that the drainage and ventilation is satisfactory and issue a
completion certificate when the works are satisfactorily completed.
Replacement Boilers and Alterations to Electrical
Systems
These alterations require Building Regulations consent although in practice most of this
work is carried out by contractors who can self certify their work.
Details of the self certification scheme are given in the introduction to this guide and, if
your contractor is able to self certify, you will not need to make a separate Building
Regulations application.
Page 21 of 25
If you wish to use a contractor who is not registered with a self certification scheme
please contact us and we will arrange for the necessary application to be submitted, carry
out the relevant inspections and issue your completion certificate when work has been
satisfactorily completed.
Whichever scheme you use make sure that you get the completion certificate as you will
need this if you wish to sell your house.
Page 22 of 25
Radon
Radon is a natural radioactive gas. You cannot see, smell, hear or feel it. It comes from
minute amounts of uranium that occur naturally in all rocks and soils and the air in all
buildings contains a degree of radon.
The gas can move through cracks and fissures in the subsoil and eventually to the
atmosphere. Most of the radon will disperse harmlessly but some will pass from the
ground and collect in spaces under or within buildings.
Some areas of the country might have unacceptably high concentrations unless
precautions are taken; the granite areas of South-West England is one of these area
The level of radon protection required to your extension depends on the location of your
property. This can be determined either by consulting your local East Kent Council
Building Control Services office or by accessing the maps on the Building Research
Establishment website (http://www.bre.co.uk/radon) . The maps indicate the highest
radon potential within each 1-km grid and determines whether full or basic radon
precautions are required or if radon protection is not needed at all. More accurate
information is available from the Health Protection Agency (http://www.ukradon.org/)
or the British Geological Survey (http://www.bgs.ac.uk/radon) .
Radon protective measures can be included relatively easily and cost-effectively within
extensions to dwellings.
All extensions to dwellings which fall within a full or basic radon protection area will be
required to incorporate an appropriate level of radon protection if a new ground floor is
provided.
Full radon protection:
The damp proof membrane (minimum 1200g) acts as the radon barrier. It is important
that the membrane extends through the cavity and is linked with a cavity tray.
A subfloor sump is also required. Where the existing house has a solid floor the sump
could be used to reduce the level of radon in both the extension and the existing building.
Basic radon protection:
Only the continuous damp proof membrane is required.
The detailing in both cases will depend on the type of construction used and the
positioning of the damp proof membrane, your local surveyor will be able to give you
further guidance, alternatively examples are provided in our online guide to radon or the
BRE website (http://www.bre.co.uk/) .
Wherever possible the construction joint between the new floor and the existing house
should be sealed. Where radon barriers have been incorporated in both the new floor and
the existing floor, the aim should be to joint the two barriers where they meet within the
wall of the house. This is difficult to achieve in practice without damaging the existing
barrier and a simpler alternative is to cut a chase in the wall slightly above or below the
existing barrier in which to tuck the new barrier.
If the existing house has a beam and block or suspended timber floor, care should be
taken to ensure that the provision of subfloor ventilation is maintained.
It is recommended that you have your house measured for radon before plans are
prepared. Ideally measurement should be over at least 3 months; the Health Protection
Agency (HPA) can provide detectors for this purpose. If your dwelling is found to exceed
the current recommended action level, appropriate protection measures can be
incorporated into your building project.
Figure 1 Routes by which radon enters a dwelling
Page 23 of 25
Key:
1.
2.
3.
4.
5.
6.
7.
Through
Through
Through
Through
Through
Through
Through
cracks in solid floors
construction joints
cracks in walls below ground level
gaps in suspended floors
cracks in walls
gaps around service pipes
cavities in walls
Useful contacts
HP A – Radon Studies Group
Radiation Protection Division,
Health Protection Agency,
Chilton, Didcot,
Oxon, OX 11 0RQ
http://www.ukradon.org (http://www.ukradon.org/)
Building Research Establishment
Garston,
Watford, WD25 9XX
www.bre.co.uk/radon (http://www.bre.co.uk/radon)
British Geological Survey
Keyworth,
Nottingham, NG12 5GG
www.bgs.ac.uk/radon (http://www.bgs.ac.uk/radon)
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Mining
Part of East Kent's industrial history creates problems for developers in relation to ground
stability, foundation design and contaminated land.
For new buildings and areas of concern, initially a desk study is required to assess the
risk to the development. A desk study is carried out by a suitably qualified person and
investigates the possible risks associated with mining using maps and archive records.
This report will then provide recommendations and a conclusion.
The recommendations will normally say either that there is minimal risk from mining
activity or that further investigations are necessary.
If further investigations are required this will involve site investigations. Depending on the
nature of the ground the investigations can range from the inspection of the foundation
trenches to a full trench survey of the site. The investigations can reveal the following
problems:
Filled Ground – In areas that have been mined it is usual for mine waste to be used
to fill over natural ground. These areas are not obvious as they may have been filled
many years before. This is a common problem and can usually be overcome.
Suitable load bearing strata can usually be found but at greater depths. This may
impact on the amount of concrete used to fill the foundations and thus increase the
cost of the substructure. Trial holes taken at an early stage can assist in planning
and costing the scheme.
Shafts – These are vertical features found frequently in mined areas. Most are in
known locations and are noted on the desk study, however, others can be
discovered during the site investigations. Shafts are normally capped under the
guidance of a structural engineer. The structural caps can usually be built over,
however, guidance will be required from the structural engineer.
Adits – These are horizontal features found infrequently. Adits will require
investigations by a suitably qualified mining engineer to ascertain the extent and
nature of the feature. They will then advise on the best possible course of action.
Trial holes – These are features where shafts and adits have been started but never
completed. Trial holes are frequent in these areas and usually easily dealt with. The
holes can usually be excavated and backfilled with concrete once a suitable base is
located.
Contaminated land – The filled material is usually excavated mining waste. This
material can be contaminated with arsenic and sulphates. If high levels of sulphates
are found they can affect the concrete mix that is required.
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