A Detailed Guide to Insulating Your Home.23249.shortcut

A Detailed Guide to Insulating Your Home.23249.shortcut
The energy for life…
Energy is essential to our daily lives. It heats our homes, fuels our transport and supplies our electricity. At the moment, most
of the energy we use comes from fossil fuels such as oil, gas, coal and peat. Unfortunately there is a limited supply of fossil
fuels in the world and we are using them up at a very fast rate. The other downside to fossil fuels is that burning them for
energy also produces CO2, a greenhouse gas, which causes climate change. That’s where sustainable energy comes in.
So what is sustainable energy?
Sustainable energy refers to a way we can use and generate energy that is more efficient and less harmful to the
environment. Another way of explaining sustainable energy is that it will allow us to meet our present energy needs
without compromising the ability of future generations to meet their own needs. We can do this by being more efficient
in how we use energy in our daily lives and also by increasing the amount of energy that comes from renewable sources
such as the wind, the sun, rivers and oceans.
What are the benefits of sustainable energy?
The good news is that being sustainable in how you use energy has immediate benefits:
It will save you money on your electricity and heating bills
Your home will be more comfortable and convenient
And you will also be making a vital contribution to reducing climate change
Believe it or not, the small actions you take to be more energy efficient in your home can have a very significant impact
on improving the environment. The collective efforts of individuals can often be the most powerful of all.
Who is Sustainable Energy Ireland?
Sustainable Energy Ireland (SEI) was set up by the government in 2002 as Ireland’s national energy agency with a mission
to promote and assist the development of sustainable energy. SEI’s activities can be divided into two main areas:
Energy Use - Energy is vital to how we live our daily lives but most of us don’t use energy as efficiently as we could.
By assisting those who use energy (mainly industry, businesses and householders), to be more energy efficient, SEI
can help to reduce the amount of energy we use overall.
Renewable Energy - Energy that is generated from renewable sources such as wind and solar power is clean and
doesn’t produce harmful greenhouse gases. By promoting the development and wider use of renewable energy in
Ireland SEI can help to further benefit the environment, in particular reducing the threat of climate change.
SEI is also involved in other activities such as stimulating research and development, advising on energy policy and
producing energy statistics.
Sustainable Energy Ireland is funded by the National Development Plan 2000-2006 with programmes part financed by
the European Union.
Did you know…
• Energy use is responsible for two-thirds of Ireland’s greenhouse gas emissions.
• Irish homes use around a quarter of all energy used in the country– that’s even
more than industry.
• The average home consumes almost 40% more electricity than it did in 1990.
• Renewable energy currently accounts for just 2% of Ireland’s energy supply.
An Introduction
Roof, Attic and Attic Room Conversion
Wall Insulation
Ground Floor Insulation
Draught Sealing
Appendix U-values
Many Irish houses, particularly those built before 1980,
are very wasteful of energy. Various cost-effective
energy saving opportunities exist which, through
reducing fuel and electricity bills, can pay for themselves
in a relatively short time. The implementation of energy
conservation measures can also make the house
warmer, more comfortable, and eliminate cold draughts
and condensation.
Areas of Heat Loss in Homes
Flue Loss
Roof Loss 30%-35%
Loss through
Loss 25%
By conserving energy in our homes, we can
• save money
• help to conserve fuel resources
• promote a cleaner environment.
On a wider scale, conservation can reduce polluting
emissions, provide employment, and reduce Ireland’s fuel
imports bill. Most of our energy currently comes from oil, coal,
natural gas and peat. These resources are finite, and if we
continue to use them at current rates, they will run out within
a small number of generations. In the meantime, the burning
of these fuels releases pollutants into the atmosphere,
contributing to smog, acid rain and, in the longer term, climate
Energy Conservation measures in the home include:
• design and shape of the building
• insulation of the building fabric
• energy-efficient heating and lighting systems,
and controls
• energy-efficient appliances
Heat loss through the fabric of the building can be substantial,
and in this booklet we are going to look at methods of
insulating the building fabric of your home to reduce this loss.
Insulation of the Building Fabric
Insulation evenly distributed over all your home generally
produces better results than additional insulation applied to
only one or two areas. It is better to have a good overall level
of insulation than, for example, a highly insulated roof with no
wall insulation.
Window Loss 15%
Floor Loss 7%-10%
Since increasing insulation thickness does not produce a prorata reduction in U-value, there comes a point where the
economic return on additional insulation for any one element
will be virtually nil.
When selecting insulating materials, choose those that have
an Irish or British Agrément Board Certificate. This Certificate
will give you information on the Technical Specification,
Design Data and Installation recommendations for the
material. For the purpose of U-value calculations, it will give
you the thermal conductivity of the thickness of the material.
Good workmanship and attention to detail are most
important when insulating your home, to avoid thermal
bridging and other related problems, and could have greater
impact on overall heat loss than simply increasing the
thickness of insulation. Use only approved installers.
Some measures are more cost-effective than others and you
will recover the cost in reduced energy bills more quickly than
others. These could be undertaken first and are outlined
throughout this guide.
What is Thermal Bridging?
Thermal bridging occurs in small areas where the insulation
level is reduced significantly compared with the remainder of
the element.
Once you have decided to adopt energy-saving measures in
your home and start investigating issues more deeply you
may find yourself coming across unfamiliar measures and
concepts. One of those is the thermal transmittance, or Uvalue, of a construction.
Reducing Heat Loss
Insulate Attic
at joist level
What is a U-value?
WALLS ~ Max U Value 0.27
FLOORS ~ Max U Value 0.25
ROOFS ~ Max U Value 0.20
To put it simply, it is the measure of the rate at which heat is
lost through a wall, for instance. As it is a measure of heat loss
then the lower the U-value the better it is for your home
Hot Water Cylinder
One of the quickest and simplest ways to save energy in your
home is to insulate your hot water cylinder and pipes. Hot
water will stay hot longer and you will save money on heating
it by fitting a lagging jacket. An 80mm jacket can cut heat loss
by 75% and could pay for itself in just a few months. Even if
your cylinder is already insulated, if the jacket is less than
75mm thick, it is worth getting a new one. Care should be
taken not to cover the cap of the electric immersion heater
with the lagging jacket.
If you need to replace your cylinder, choose one with a preformed foam insulation jacket. This is more efficient and less
bulky than a cylinder with a separate jacket.
Conservation of Energy and the Building
Regulations 2002
The Building Regulations 2002, Part L Conservation of Fuel
and Energy, require that all new buildings achieve minimum
standards of energy efficiency. Existing houses should be
refurbished to achieve these standards also. Levels of
insulation higher than those required in the Building
Regulations are in many cases worthwhile, since a house
being built or refurbished today can be expected to be
occupied for 60 years or more, and an energy-efficient design
can yield considerable savings over its lifetime.
Part L gives maximum values which should be met to comply
with the Building Regulations Standards of energy
Maximum Average Elemental U-values
Fabric Elements
Pitched roofs,
insulation horizontal
at ceiling level
Pitched roofs,
insulation on slope
Flat roof
Ground floors
Other exposed floors
External doors,
and rooflights
New buildings and
extensions to
existing buildings
Material alterations to,
or material changes of
use of, existing buildings
Roof Insulation
Heat Loss
Through the Roof
You put a hat on your head and keep
your body heat in. Thermal
insulation in your roof will do the
same for your house!
If you do not have insulation in your roof,
up to 30% of your heat could escape,
costing you money and contributing to
atmospheric pollution and global
If you have already insulated your roof,
you may want to replace it or add
another layer to improve its
performance and bring it up to current
Building Regulations Standards.
Another method is to have shredded glass fibre, mineral fibre
or cellulose fibre blown into the attic between and above
ceiling joists. This method requires a
professional contractor. Be careful not
Insulating Attic
at Joist Level
to compress fibreglass insulation,
otherwise it will lose part of its
insulating value. So if boarding is to
be put down in some areas of the attic
for storage, it should not compress
the insulation.
After the attic is insulated at joist
level, its temperature is reduced, so
you must insulate the water storage
tank and pipes.
The water storage tank can be
insulated with any semi-rigid insulating board and the pipes
with closed cell neoprene, polyethylene, glass fibre and
mineral fibre in pipe section form.
Insulating the 50 sq.m. (540 sq.ft.) attic space of a typical
house costs around m400 and could save approximately m130
a year (up to 20% of your fuel bill) so it would pay for itself in
about three years. Insulating a flat roof of the same size could
cost about m1,000 and will pay for itself in around five years.
As well as saving your money, you will be helping to reduce
the emission of carbon dioxide and other environmentallypolluting substances.
Types of insulation suitable for different
types of roofs
Pitched roof with
an attic space
Pitched Roof with
Attic Space
If you have a pitched roof with
an attic space, it can be
insulated in many ways.
Probably the simplest is to lay
quilt, such as glass fibre quilt or
mineral fibre quilt in a roll
between the ceiling joists and a second layer in the opposite
direction over the joists.
Insulating a Water Tank
closely fitting
cover with
air inlet
pipework in
roof void
overflow kept
below loft
turn up
loft insulation
insulate rising
main above ceiling
heat rising from
below prevents
Conversion to an attic room
When converting your attic into
Conversion to Attic Room
a room, insulation is placed in
between the rafters. The
insulation can be semi-rigid
insulation boards such as
expanded polystyrene board,
extruded polystyrene board,
glass fibre batts, mineral fibre
batts, urethane foam board or phenolic foam boards. Some
contractors also offer a spray-on cellulose fibre or
polyurethane foam insulation system between rafters. If a first
layer of insulation is placed between rafters, a second, thin
layer applied to the underside of the rafters avoids thermal
bridging. Glass fibre quilt and mineral fibre quilt can also be
used. A vapour check should be installed on the warm side of
the insulation and ventilation above.
Flat roof
The type of insulation used in
Flat Roof
new flat roofs is dependent on
the roof structure. On a new
concrete slab, with a screed,
semi-rigid insulation boards
such as expanded polystyrene
board, extruded polystyrene
board, glass fibre batts, mineral fibre batts, urethane foam
board or phenolic foam board are laid under the roof
covering. In a new timber structure, glass fibre quilt and
mineral fibre quilt can be laid between the joists.
Flat Roof - Concrete Deck
These materials can be held in place by a plaster lining board
which also provides the necessary fire protection.
Flat Roof - Timber Deck
Insulation and
Lining Board
Lining boards can have integral
insulation backings, such as
glass-fibre-backed insulated
plaster and urethane-foambacked insulated plasterboard,
often lined with aluminium foil.
If you have an existing flat roof,
insulation can be increased
externally with extruded
polystyrene or foamed glass, or
internally with an insulated
lining board such as mineral
fibre or polyurethane foambacked plaster-board.
Can you do it yourself?
Pitched Roof with
Attic Space
Pitched roof with an
attic space
The majority of Irish houses
have a pitched roof, which is
the easiest type to insulate and
with a little care and guidance
can be insulated by yourself.
Conversion to Attic Room
Guidelines for laying quilt insulation in a
pitched roof attic space
Before you insulate your attic, read the manufacturer’s
Some insulation materials irritate your skin and throat, so
wear a mask, rubber gloves and goggles and tuck in your
clothes when handling
these materials.
Stretch a long board
across two or three
joists to walk and kneel
on. Do not stand on the
section between the
joists or your foot is
likely to go through the
Check the depth of the
joists. If the insulation is
going to be higher than the joists or if you are going to lay
a second layer of insulation across the joists, you may need
to fix timber battens to some joists to raise the boarding in
the area of the attic where access will be needed, thereby
avoiding compression
of the insulation.
Fill any cracks or holes
in the ceiling to
prevent warm, moist air
rising into the attic as
Open and unroll the
insulation in the attic.
Lay insulation between
joists in widths sized to
fit tightly between the joists and a second layer over the
joists in the opposite direction.
If possible, fit insulation over the wallplate to abut with the
wall insulation while leaving the necessary air gap around
the eaves and soffits. This will help to avoid cold bridging.
Attic room
Attic conversions are more
complicated as the roof
structure has to be insulated, so
the appointment of a building
contractor is advised.
Flat Roof
Flat roof
The insulation of new and
existing flat roofs should be
carried out by a roofing
Guidelines for choosing insulation
Insulation is available from builders’ providers, DIY and
hardware stores and specialist contractors.
Buy insulation from a reputable supplier who can help you
choose the most suitable insulation for your roof type.
If using glass or mineral fibre wool insulation, specify a
minimum thickness of 100mm between joists and 150mm
across joists. To find out how much insulation you need,
check the measurements between the joists, their length
and the number of joist spaces in your attic.
If installing the insulation yourself, check if special
precautions should be taken when handling the material.
To ensure that there is
adequate ventilation at
the eaves, cut the ends
of the insulation in a
specially shaped plastic
eaves pieces to ensure
that the insulation does
not block the eaves
It is essential to cross-ventilate the attic space to prevent
condensation by leaving a continuous air gap along the
eaves at each side.
In attic room conversions, it is essential to ventilate the
roof structure between the insulation and the roofing felt
with continuous air gaps along the eaves and at the ridge.
Special ventilation tiles are available for ridge ventilation.
Don’t bury electric cables under the insulation. Leave
cables clear and avoid compressing. Keep plasticinsulated cables away from polystyrene insulation.
Leave clearance for recessed lights to avoid them
The use of combustible insulation is not recommended
for attics.
At the gable wall,
insulation should be turned up 225mm above ceiling
After you insulate the attic, its temperature will be
reduced. Therefore it is essential to insulate water storage
tanks and pipes to prevent them from freezing. Do not put
insulation directly under the water storage tank as the
warm air from below will help prevent it freezing.The tank
sides and top should be insulated, as should the pipes, to
prevent them freezing
in the cold attic.
Insulate the hatch by
cutting a piece of
insulation and sticking
it onto the hatch.
Up to half of the heat loss from a house occurs through
the walls. This can be reduced by two-thirds by
insulating the walls.
Most houses built before about 1980 have no wall insulation.
Many (though not all) houses built during the 1980s have
some wall insulation. Houses built since the 1991 Building
Regulations came into effect are required to have wall
Cavity wall insulation
The walls of many houses consist of two ‘leaves’ of brick or
concrete block with a cavity or space between them to resist
rain penetration.
Insulation may be placed on the outside, in the cavity or on
the inside of a wall, without altering the overall insulation
Outer masonry leaf
Inner masonry leaf
Cavity Wall
What is Thermal Response?
External or cavity insulation allows the internal wall to act as
a thermal store, absorbing heat during the day and releasing
it at night-time, reducing fluctuations in room temperature
throughout the day. Internal insulation isolates the thermal
mass from the room. This reduces both the response time of
the heating system and the energy required to reach comfort
levels in the room. Occupancy patterns, the response time of
the central heating and its controls, and the optimal thermal
mass of the building will determine the appropriate action.
When considering wall insulation, first you should find out
whether your house has cavity walls or solid walls. A building
contractor or architect will be able to tell you if you have
cavity walls in your new or older house. If you have cavity
walls, then cavity insulation is likely to be the most costeffective insulation method. If cavity insulation is not an
option, then the more expensive options of either internal or
external insulation may be considered. It is not possible to fill
the cavity in a wall constructed simply of 9-inch hollow blocks.
New Housing
It is standard practice when building new houses to insulate
this cavity as the wall is being constructed, either with full-fill
batts or partial-fill boards.
For cavity walls a minimum of 78mm rigid insulation board,
with a thermal conductivity of 0.25W/mK must be used, unless
there is additional insulation outside the cavity.
Initially the architect or installer will carry out an assessment
of the walls to check their suitability for cavity insulation,
particularly for full-fill insulation. This assessment will
determine the degree of exposure of the house to winddriven rain and the construction details of the walls.
Fully Filled Cavity
100 mm external leaf
Variable cavity with
100 mm internal leaf
13 mm plaster
(or drylining)
Specify stop ends to all cavity trays
Avoid raked joints.
Partially Filled Cavity
100 mm external leaf
50 mm residual air cavity
80 mm rigid insulation
100 mm internal leaf
13 mm plaster
(or drylining)
• Specify a minimum of
50 mm clear residual cavity
• Specify drips on wall tiles to
be in the centre of the
residual air cavity
• Specify rigid insulation boards
• Hold insulation boards tight
against inner leaf with retaining
clips and avoid gaps between
the boards.
When full-fill cavity insulation is being used it is essential that
such walls are designed and constructed to incorporate the
normal precautions to prevent moisture penetration.
Insulation thickness should remain constant and should any
change in vertical thickness occur, a horizontal damp-proof
cavity tray should separate each thickness change.
It is important to ensure during installation that wall ties are
fitted correctly and cleaned, excess mortar is cleaned from the
inside faces of the wall, mortar droppings removed from the
cavity and cleaned from the exposed edges of the insulation
slabs. All insulating materials should be installed in
accordance with manufacturers’ instructions and procedures.
Materials used for cavity
House with Insulated
insulation include mineral
Cavity Walls
wool (glass or rock),
granules and cellulose fibre.
The thermal properties of
these materials do not differ
greatly (in technical terms,
their thermal conductivities
tend to fall within the range
0.025 to 0.04 W/m K). Insulating the cavity with such materials
will typically reduce heat loss through the wall to one-third of
its original value. Such cavity insulation materials are generally
water-repellent and rot-proof and some are non-combustible.
It is most important before deciding to insulate existing cavity
walls that you check their suitability for cavity insulation. This
assessment will take account of the degree of exposure of the
house to wind-driven rain and the construction details and
condition of the walls. Any ventilation openings in the wall will
also be checked to ensure that these will not be blocked by
the insulation. If the walls suffer from rain penetration at
times, this problem must be remedied first. In some cases, the
walls may be found to be unsuitable for cavity insulation or
may require some remedial work beforehand.
The Irish Agrément Board (IAB) provides independent
certification of cavity wall insulation systems and maintains a
register of approved installers for certified systems. These
installers should be able to show you an IAB certificate for the
insulation system they propose to use and proof of their
reputation as approved installers.
Older Housing
In older houses insulation
can be injected into this
cavity through holes drilled
through the outer leaf, by
means of a blowing or
pumping machine.
Insulating From Outer Wall
Since the work is done from
the outside, it causes
inside. The drilled holes,
which are typically about 25
mm (1 inch) in diameter and
spaced a metre or so apart,
are then filled to match the wall appearance as closely as
possible. The job typically takes less than a day.
The cost of cavity wall insulation depends on a number of
factors, including the width of the cavity, but is typically in the
region of m5 to m7 per square metre. For a typical semidetached house, this gives a total cost of about m550 - £700.
With annual fuel savings of m100 to m160, the pay-back
period will be in the region of 4 to 7 years.
You may be able to negotiate a lower price if you can
persuade some of your neighbours to have their walls
insulated at the same time.
Internal insulation
involves fixing insulation
Internal Insulation
to the inner surfaces of
Solid masonry
external walls (insulated
dry lining). One method
involves fixing insulation
boards to the wall and
Vapour barrier
covering with a vapour
barrier and plasterboard.
Alternatively, composite
boards of plasterboard
backed with insulation
and incorporating a
vapour barrier may be fixed to the wall. The work is quite
labour-intensive, involving the repositioning of skirting
boards, any electrical sockets or switches and other wall
Interstitial Condensation
Types of insulation material used include expanded
polystyrene, fibreglass and polyurethane boards.
Polyurethane tends to be more expensive, but its thermal
performance is approximately 50% better than polystyrene or
fibreglass, so a 25 mm (1 inch) thickness of polyurethane will
have roughly the same insulating performance as a 38 mm
(1.5 inch) thickness of polystyrene.
A disadvantage of internal insulation is that it reduces room
space. This limits the permissible thickness of insulation in
existing buildings. If room space is a factor, high-performance
insulation may be preferred.
Some brands of insulation (e.g. polyurethane foams) use
ozone-damaging substances (e.g. HCFCs) in their
manufacture. From the point of view of environmental
protection, it is preferable to select an insulation product
which does not use such substances (e.g. expanded
polystyrene, fibreglass). Sometimes a balance between
conflicting aims (cost, thermal performance, environmental
impact) is required.
Internal insulation costs more to install than cavity insulation,
and because it is generally installed in smaller thicknesses,
energy savings will be lower. It is most cost-effective to install
internal insulation when the inside of the house is being
refurbished.The additional costs will depend on the particular
circumstances, but annual fuel savings of m75 to m150 can be
expected for a typical semi-detached house.
If warm moist air from inside the house were to pass around
or through the insulation to the colder wall surface behind, it
would condense on the wall. This invisible or ‘interstitial’
condensation is undesirable and is prevented by installing a
vapour barrier (e.g. a polythene sheet) on the warm (room)
side of the insulation. Composite boards for internal insulation
generally incorporate a vapour barrier. It is important that the
vapour barrier be well sealed at wall, floor, ceiling, door and
window junctions, around light switches and at all other
breaks in the insulation. The avoidance of interstitial
condensation problems depends on good workmanship in
sealing the vapour barrier, so a reputable installer should be
Electrical wiring
Polystyrene insulation should not be placed in contact with
PVC-coated electrical wiring, otherwise the PVC may degrade.
Also, steps should be taken to ensure that any electrical wiring
covered by the insulation does not overheat.
Cold bridging
When installing internal insulation, the junctions of internal
walls and floors with external walls may ‘short-circuit’ the
insulation, allowing heat to escape. The presence of such
‘thermal bridges’ will reduce the effectiveness of internal
insulation. In so far as is practical, insulation should be
installed so as to minimise thermal bridging.
Thermal Bridge at Junction of Internal
and External Walls (plan view)
heat loss
External wall
Internal insulation
Thermal bridge
Internal wall
External insulation
External insulation involves fixing insulation materials such as
mineral wool or expanded polystyrene slabs to the outer
surface of the wall. This insulation is covered with a special
cement-based render to provide weather resistance. A steel
or fibreglass mesh is embedded in this render to provide
strength and impact resistance. It may be necessary to extend
eaves and sills and relocate downpipes. A thin layer of
insulation may be applied around the edges of window and
door openings to minimise thermal bridging. The technology
is well-established in northern Europe, where it has been in
use for many years, but is not yet widely used in Ireland.
External Insulation
External render
Steel mesh
At a cost of up to m150 per square metre, the cost of insulating
a typical semi-detached house could amount up to m15,000.
Annual fuel savings would be similar to cavity insulation, i.e.
about m100 to m160, so the pay-back period based on energy
savings alone would be more than 30 years. However, if work
on the outside of external walls is already required, the
economics of external insulation may be improved.
Since external insulation may change the appearance of
the house, planning permission may be required.
An approved installer or architect should help with this.
Cavity insulation and external insulation are jobs for
professional contractors. It is possible to fit internal
insulation as a DIY job, but anyone undertaking such a job
should be fully aware of the required precautions
(see internal insulation section above).
Solid masonry wall
Note on costs and savings
Mechanical fixing
It is worth asking the installer if the proposed external
insulation system has independent certification, for example
from the Irish Agrément Board or equivalent. Such
certification means that the system has been tested by an
independent body and found fit for the purpose for which it is
In relation to energy savings alone, external insulation of
existing buildings is expensive. However, if the walls are
vulnerable to rain penetration or frost damage, external
insulation may be one means of solving these problems. An
additional benefit may be an improvement in the appearance
of the house.
Costs given in this leaflet are indicative only - quotes may be
obtained from installers. Savings are estimated assuming
initial annual space-heating fuel costs (excluding standing
charges) of m650. Particularly in colder houses, some of the
savings may be absorbed in higher temperatures and
increased comfort, offsetting the reduction in fuel bills.
Of all the components in a building, it is through the
windows that most heat is lost. This is because glass
allows heat to escape more readily than most other
building materials.
Double Glazing
For example, given the same area of wall and window, the
window will allow up to eight times more heat to escape. For
this reason, it is important that your windows are as efficient
as possible.
Single Glazing
Different types of glazing
air gap
To meet the current regulations a minimum standard of
double-glazing with a 12mm air gap and soft low-E glass is
necessary. This change is due to the need to reduce energy
consumption and the desire to improve comfort.
While standard double glazing is a great improvement over
single, even more advanced glazing systems are now available
on the market at affordable prices.Two examples include gasfilled double glazing and low emissivity glazing.
In gas-filled double glazing the cavity between the two panes
of glass is filled with an inert gas (usually argon) which
conducts less heat than air, therefore improving the window’s
energy efficiency.This type of system generally costs about 10
- 20% more than standard double glazing, but will vary from
one manufacturer to another.
The low emissivity or low-e type system is more complex. The
outside face of the internal glass pane is coated with a special
material, which allows light to pass in through it while very
little heat is allowed to pass out. When light hits an opaque
surface much of its energy is turned to heat. Heat is similar to
light in that they are both forms of energy which travel in
waves. However, heat has a much longer wavelength than
light. The specially applied coating on the glass prevents the
long wave heat energy from escaping. It also prevents much
of the heat generated in a home heating system from
escaping. In short, it acts as an invisible layer of insulation.
double glazing
filled space
So why do double glazed windows prevent more energy from
escaping? It’s mainly because of the space between the two
panes of glass. This gap is filled with air, which is a poor
conductor of heat, thereby making it more difficult for the
heat in the room to bridge the gap to the outside pane.
Argon filled
double glazing
This will generally cost between 10-15% more than standard
double glazing but is very energy-efficient. In both Denmark
and Germany this form of glazing is fast becoming the
standard installed in all buildings and it is possible that in
Ireland it will also become the norm in the not too distant
future. Other combinations of glazing systems include low-e
gas-filled double glazing or triple glazing.
Window frames
In addition to the glazing, the window frame must be
considered when addressing the energy efficiency of a
window. When viewed in terms of overall heat loss the
difference in performance of these materials is not significant.
Air leakage through gaps in window frames can also lead to
considerable heat loss. By selecting a well-designed system,
further energy and cost savings can be made. All proprietary
systems should have draught strips built into the frame.
Finally, other points to consider include ease of opening for
ventilation and cleaning, the security features and provision
for controllable ‘trickle’ ventilation. The durability of the
window frame is also important as poor quality will result in
higher maintenance.
What to do if you are thinking of replacing
your windows
With such a selection of new glazing systems it can be difficult
to know which one to choose. If you are thinking of replacing
your existing windows you probably have single glazing - up
to just a few years ago this or poor quality double glazing was
still being installed in most houses. In recent years, however,
the cost of double glazing has dropped considerably, making
it much more affordable. Good quality double-glazed
windows should have an air gap of 12 mm or greater.
If you are replacing your windows you should consider
installing double glazing as a minimum. Not only will you save
energy but you will also increase your comfort levels
immediately. When selecting double glazing you should shop
around. There are numerous reputable window
manufacturers in Ireland who can supply, and in many cases
fit, good quality double-glazed windows.
The extra cost of double glazing with a low-e coating is not a
whole lot and could save you even more money. If your
budget allows, you should give this option serious
consideration. Not all window manufacturers or installers will
be familiar with low-e glazing. However, it won’t be long
before most manufacturers and installers will be offering it.
Who will install them? The manufacturer from whom you will
buy them will probably recommend an approved installer.
Otherwise you will need to find one. Remember, this is a job
for a professional.
If replacement windows are beyond your budget then there
are also secondary glazing systems available on the market.
These are normally installed inside your existing windows,
creating an air space between this and the new ‘window’.
There are a number of different designs - for example those
with sliding frames. While these systems can help to reduce
heat loss and save you money if installed correctly, provision
for the ventilation of the air gap is important. Otherwise,
condensation could become a problem.
What to do if you are buying a new home
Reduced Energy Loss of Different
Glazing Systems Relative to Single Glazing
In a new home, nothing but double glazing, as a minimum, will
do. However, since you have to install windows anyway, why
not consider low-e double glazing, and start saving from day
one? In years ahead, it may even add value to your home. Talk
to your building contractor as early as possible to assess the
(with argon) (low-e) (with argon
& low-e)
If you are changing from old single-glazed windows to more
modern double-glazed systems it is likely that draughts will
be greatly reduced. While this will help to save energy it can
cause moisture levels in your house to increase. You should
always ensure that there is some controllable means of
ventilating all inhabitable rooms.
Heat loss through the ground floor of a two-storey
house typically accounts for about 10% of total heat
loss. For a one-storey house the figure is about 15%.
However, if a house is well insulated everywhere except
for the ground floor, the percentage will be higher.
The amount of ground floor heat loss depends on the type of
soil – houses built on wet soils tend to lose more heat through
the ground than those on dry soils. Also, detached houses
tend to lose more heat through the ground floor than
terraced houses because their ground floors are exposed on
all sides. So if you plan to live in a bungalow built on damp
soil, floor insulation merits special attention.
Acrylic or silicone sealants for small gaps. The more
flexible silicone sealants are better for gaps where
shrinkage, settlement, or expansion/contraction may
Expanding (polyurethane) foam for large gaps.
Polymer-modified cement mortars for large gaps in areas
which are to be walked on.
Suspended timber ground floors require sub-floor ventilation
to avoid dampness and wood rot. Ventilation openings to the
sub-floor space should not be blocked.
The 2002 Building Regulations, Part L, Conservation of Fuel
and Energy, recommends that the U-value (a measure of the
rate of heat loss) of the ground floor in new houses should be
no greater than 0.25 W/m2K. Compliance with this
requirement can in most cases be achieved with the
insulation thicknesses given below (indicative only).
Thicknesses greater than these can reduce heat loss further
and are recommended.
The insulation methods illustrated below for new houses may
also be implemented in existing houses. In some cases this
would be disruptive and costly, but if work needs to be done
on the floor anyway, this is a good time to consider an
insulation upgrade.
The insulation thickness depends on the material used.
Typical thicknesses for different house types would be:
Examples of insulated ground floor constructions are given
below. Other configurations are also used. In all cases the
insulation manufacturer's instructions should be followed.
Detached two-storey house
Detached bungalow
Semi-detached two-storey house
Mid-terrace two-storey house
103 mm
90 mm
90 mm
60 mm
This insulation should cover the full floor area, not just the
perimeter as was sometimes done in the past. Note that for
houses with irregular perimeters (e.g. extensions), greater
thicknesses may be required. Also, if underfloor heating is to
be used, an additional 30 mm or so can help to avoid
increased heat loss from the warmer ground floor.
Existing houses
A relatively simple way to reduce heat loss through the
ground floor is to lay a carpet with foam backing or a foam
underlay. Both carpet and underlay should be ‘wall-to-wall’.
Sealing of gaps in the ground floor will help to reduce
draughts, and also radon levels in houses with radon
problems. Gaps commonly exist at skirtings, at cracks in the
concrete slab, and at service (pipework) entries. Sealing may
be done as a DIY job using:
New houses
Concrete floor with insulation under slab, cavity
The insulation material chosen should have a high moisture
resistance and compressive strength. Rigid insulation board is
positioned on the damp proof membrane, which is laid over
sand blinding on hardcore. There should be no gaps between
the insulation boards. A strip of insulation is placed vertically
at the slab perimeter to minimise thermal bridging via the
inner blockwork leaf. Extending the cavity wall insulation
down to the level of the horizontal floor insulation, and/or
using insulating blocks between the wall insulation and floor
perimeter insulation, will further reduce thermal bridging.
Radon is a naturally occurring radioactive gas, which enters
buildings from the underlying soil, and in some areas can
accumulate in a building to such a concentration that it is
deemed to be a health hazard.The 1997 Building Regulations,
Part C, requires that a radon barrier be provided under new
dwellings in parts of the country worst affected by radon. This
barrier must bridge the cavity in cavity walls. Care is required
in design to ensure a good radon seal while avoiding thermal
bridging at floor-wall junctions.
In cases where interstitial condensation on the damp-proof
membrane may be a problem, suitable types of insulation
may be placed below rather than above the damp proof
membrane (or radon barrier).
Good overlap of cavity and edge insulation
Insulating blockwork
Edge insulation
Concrete slab
Radon barrier
or dpm
Hardcore with
sand blinding
In all cases, the designer/builder should try to minimise
penetration of the insulation by pipework and wiring, and
to keep heating pipework above the insulation in order that
heat loss from the pipework contributes to heating the
room above.
Insulation materials
Insulation materials commonly used for floors are given
below, along with typical thermal conductivities. The thermal
conductivity of an insulation material is a measure of its
resistance to heat flow – the lower the number, the smaller the
thickness required for a given insulating performance.
Concrete floor with floating screed, hollow-block
or solid walls
Rigid insulation board is laid over the concrete slab. A strip of
insulation is placed vertically at the screed perimeter to meet
the wall insulation. The screed should be at least 65 mm thick
with reinforcing mesh. Wood-based flooring boards may be
used instead of screed, in which case a vapour control layer
may be required.
Wall insulation behind
Edge insulation
Typical thermal conductivity
Expanded Polystyrene board (HD)
Expanded Polystyrene board (SD)
Extruded polystyrene board
Glass fibre / wool quilt
Glass fibre / wool batt
Phenolic foam
Polyurethane board
Concrete slab
Dpm or radon barrier
Hardcore with
sand binding
Suspended timber floor
The insulation is laid between the joists, supported on
polypropylene netting. The netting is first draped over and
between the joists and stapled to the side of each joist, low
enough to accommodate the full thickness of insulation. Air
should not be allowed to circulate around the insulation.
Floor boards
Insulation between
Polypropylene netting
Ventilated airspace
Ensure there is no danger of pipes below the insulation
Design to avoid dampness problems associated with
interstitial condensation, construction moisture and
Minimise thermal bridging and associated condensation
Provide sub-floor ventilation if required.
Check that materials in contact are compatible,
e.g. polystyrene should not be in contact with PVC
electrical wiring.
Electrical wiring buried in insulation may need to be
derated (ask an electrician).
All houses need a supply of fresh air, but overventilation in the form of draughts can be undesirable,
particularly in cold, windy weather. For many homes,
draught-sealing doors, windows and other gaps can be
an inexpensive way of improving comfort and reducing
heating bills while helping to protect the environment.
The key to applying draught seals to doors and windows is to
seal the gap without making the door or window difficult to
close. In many cases, a perfect seal is neither practical nor
desirable, and it is sufficient to form a seal which excludes
most of the draught.
This section provides an overview of the various types of
draught-sealants available, their suitability to various
applications and a quick guide to determining whether
draught-sealing is likely to prove a financially worthwhile
exercise. The ‘Precautions’ section, which should be consulted
before commencing work, highlights the importance of
ensuring that the house does not become ‘over-sealed’, as
inadequate ventilation may result in a stuffy atmosphere and
condensation problems and may even pose a safety hazard if
the air supply to combustion appliances is insufficient.
Sources of draughts
In older houses, more than half of the cold outside air entering
the house is admitted through the windows and doors. Other
sources of draughts include attic hatches, suspended wooden
floors, and spaces between window- and door-frames and
wall openings. There may also be gaps around pipes
penetrating external walls, floors and ceilings.
New windows and doors are generally supplied with draughtseals, but many older units are unsealed. If the opening part of
the door or window does not fit tightly against the frame,
draughts can enter or leave through the gap. Large gaps can
generally be detected by inspection, and in cold, windy
weather, it may be possible to feel a cold draught entering the
house. (Bear in mind, though, that cold draughts will enter
only on the upwind side of the house. On the downwind side
and at the top of the building, warm air will tend to exit
through gaps.)
The width of the gap around windows and doors may not be
uniform. Gap sizes of up to 8 mm around wood-frame
windows and 10 mm for wooden doors are not uncommon.
The larger the gap, the more worthwhile draught-sealing is
likely to prove.
Draught-sealing products
The main categories of draught-sealing products available are
compression and sliding seals, both of which are available in
hidden or visible options, and fillers or sealants. Compression
or sliding seals are often used for gaps between moving
components, for example, the opening part of windows and
doors. Fillers or sealants are generally more convenient for
fixed openings, for example, at skirting boards. Examples of
each type are illustrated in this leaflet. Some guidance on
installing draught-stripping is also provided, though
manufacturers’ instructions should be followed for particular
Hidden compression seals
The most common hidden-type compression seal product
available is a self-adhesive foam tape. This sometimes comes
with a backing that is peeled off as the tape is stuck on to the
frame. Surfaces to which the strip is to be applied should be
clean and dry. Generally, the strip is applied to the frame stop
opposite the closing face of the door/ window. The closing
face should compress the foam rather than slide across it and
pull it off. If the gap at any part of the opening is too wide to
be sealed by one layer of the tape, another may be applied
over the first layer. On the other hand, in places where the gap
is less than a millimetre or so, no tape should be applied, since
it could make the door or window difficult to close.
Hidden Compression Seal
top framework
frame stop
opening part
of window
Visible Compression seals
Wiper seals
Visible compression seals are usually soft rubber or plastic
mouldings mounted on a rigid support, which can be
attached to the frame. They form a seal as they are deflected
by the closing window/door and remain visible after closure.
They may be attached by screws, tacks or adhesive, and, in the
case of a metal frame, clips. It is important that the attachment
used is of a weather-resistant material, for example brass or
stainless steel. When fixing the strips in position, pressure
should be applied gently to the soft moulding. If the moulding
is applied too tightly, it may become difficult for the unit to
close. For wooden windows/doors, the moulding should be
compressed enough to allow for small seasonal changes in
gap width.
Wiper seals form a seal by sliding, normally against the closing
edge of the window or door. They offer relatively little
resistance to closure, and, thus, are particularly suited to large
windows and doors involving a long length of seal, where the
use of compression seals could make closure difficult.
Visible Compression Seal
top framework
Hidden wiper seals are generally metal or plastic strips and
can be used if a sufficient gap (e.g. 3 mm) exists between a
closing edge and the frame. If the gap is insufficient and if the
visual appearance of seals is acceptable, visible wiper seals
may be used. These are attached to a closing face and slide
over the frame to form the seal.
Hidden Wiper Seal
top framework
frame stop
opening part
of window
frame stop
(inward opening)
Other seals
For sliding sash windows,
compression or wiper
seals may be used at the
frame stop ends. Purposemade seals are generally
required to seal along the
sliding window edges and
at the junction between
sashes; various types exist.
Special seals are also
thresholds, and brush
seals are a common
choice. Seals used to keep
out wind-driven rain will
also help to exclude
Door Threshold - With Brush Seal
Draught-sealing is generally a DIY job, and sealing products
may be purchased at DIY stores. Costs vary depending on the
type and quality of product. Self-adhesive foam is generally
inexpensive, though rubber mouldings on rigid supports,
while more expensive, will be more durable. If the job is to be
carried out by a contractor, it is worth investing in a highquality, long-lasting product.
In many cases, draught-sealing will pay for itself through
reduced heating bills in a matter of months rather than years.
In other cases, more comfortable conditions rather than
reduced bills may be the priority.
Letterbox - With Brush Seal
As a rough guide to determine whether it is worth draughtstripping your house, ask yourself the following four
Letterboxes with just one inward-opening flap will tend to
admit draughts, particularly when the wind is blowing directly
on the front door. Brush seals are commonly used to reduce
draughts through this type of letterbox.
Suspended wooden floors must be vented from underneath
to prevent rot. This is often achieved through the use of airbricks at the base of the outer walls.These vents should not be
blocked; instead the room should be sealed from the space
under the floor. Linoleum or carpet with underlay will help to
prevent draughts between the floorboards, and a filler or
sealant may be used to fill gaps around the skirting.
Attic hatches may be sealed with compression or wiper seals
in the same way as windows and doors. If the hatch does not
sit tightly against the seal, it may be weighted or bolted down.
Other gaps in the top-floor ceiling, for example where pipes
penetrate into the attic and around ceiling-mounted light
fittings, may be sealed with filler or sealant. This will also help
to avoid condensation problems in the attic.
Unused chimneys may be blocked with baffles or closed up,
but a small opening should be left to air the chimney.
Are windows and doors poorly fitting with gaps around
the edges?
Are there obvious draughts?
Is the house sited in a location exposed to wind?
Is a high level of heating required (i.e. must the house be
warm for most of the day)?
Are your fuel bills high?
For DIY installation, draught-sealing is likely to be worthwhile
if the answer to at least one of the above questions is yes. For
contractor installation, two yes answers should make it
Adequate ventilation
Combustion air supply
Adequate ventilation is required in all houses for the following
Adequate ventilation must be provided for combustion
appliances that draw their air supply from the room. Examples
of this type of ‘open-flued’ appliances include open fires, fueleffect gas fires, and most stand-alone gas, oil, and solid fuelfired room heaters. Ventilation is required not only to supply
combustion air, but also to remove combustion products.
to provide fresh air for occupants
to remove odours
to remove pollutants eg. cigarette smoke
to remove water vapour – persistent condensation can
result in mould growth and damage to furnishings and
the building materials.
The amount of ventilation required varies with the number of
people present and related issues such as whether or not they
are smokers. Ideally, ventilation should be provided through
controllable ventilation openings such as slot ventilators, and
the house should be well sealed to keep uncontrollable
infiltration and draughts to a minimum.
In rooms where these appliances are used, a lack of
combustion air could lead to a build-up of carbon monoxide
in the room, with potentially fatal consequences.
Open-Flued Heater
room heater
air supply from room
In cold, windy weather for a house with only one or two
occupants, infiltration may fulfil all the ventilation
requirements even in a well-sealed house, so slot ventilators
can be closed fully. In calm weather with several people
smoking in the house, slot ventilators (and windows if
necessary) can be opened.
Before draught-sealing, check for signs of inadequate
ventilation such as persistent condensation and mould
growth. If such problems exist, they should be addressed first,
since draught-sealing may make the problem worse.
Leave a minimum of ventilation in every room. If a room does
not have a vent, air brick, chimney or other ventilation source,
part of the window can be left unstripped.
Building Regulations require that permanent ventilation
openings are provided in such rooms. Provided adequate
vents exist and are not blocked off, the room’s windows may
be draught-sealed. If in doubt, seek professional advice.
Air supply concerns do not apply to radiators, since no
combustion occurs in these heaters. Nor do they apply to
balanced flue heaters or balanced flue boilers, since these
units draw their combustion air directly from the outside and
are sealed from the room.
Evaporation of water in kitchens, bathrooms and toilets
produces moist air. Windows in these rooms may be left
partially or fully unstripped (depending on gap width and
window perimeter length) in order to help vent moist air to
the outside.
Balanced Flue Heater
air supply
room heater
Air always contains some invisible water vapour. The
amount of water vapour that the air can hold depends
on its temperature - warm air can hold more water
vapour than cold air. When warm moist (humid) air
comes into contact with a cold surface, it will cool and
may become saturated. If it cools further, some of the
water vapour will condense out on the cold surface.
The people living in a house add to the water vapour in the air
simply by breathing (picture your breath on a cold morning)
and through activities such as cooking and bathing. Normally,
this moist air leaves the house through ventilation.Ventilation
not only removes moisture, but also provides fresh air for
occupants to breathe, and removes pollutants and odours.
However, if moisture is allowed to accumulate in the house,
some of it may condense on cold surfaces within the building,
particularly in winter. Examples of such cold
surfaces include
Single glazed windows
Cold water pipes
Uninsulated external walls and ceilings, particularly at
corners and at the north side of the house
External walls behind large items of furniture and within
built-in wardrobes
Frequent condensation on windows in winter, with pools
of water collecting on window-boards
Mould growth on walls, ceilings or cupboard spaces
located on outside walls
A musty, damp smell, even though there may be no visible
signs of dampness.
Types of condensation
Surface and Interstitial
condensation where
moisture appears on
visible surfaces within
the building is called
surface condensation. It
may be seen to occur at
amounts of moisture
are being produced in
the house or room,
especially during cold
weather when windows
and vents are closed.
Interstitial condensation
Around the edges of window and door openings, where
surface temperatures may be lower due to an uninsulated
part of an otherwise insulated wall (a ‘thermal bridge’).
In many houses, the inside surfaces of single-glazed windows
often become damp due to condensation. This is particularly
noticeable in the mornings in unheated rooms in an
otherwise well-heated house. However, the same process can
take place on any relatively cold surface such as an outside
wall. Provided the amounts of moisture are small and
infrequent and that they evaporate fairly quickly, this will not
usually harm the building. However, if dampness due to
condensation persists for lengthy periods, it can damage the
building’s structure and interior decor. Signs of condensation
problems include the following:
This is condensation that occurs within external walls, floors
and roofs. It occurs when warm moist air from inside the
house passes through gaps in the internal surface and
condenses at colder parts within. Since it cannot be seen, it is
more difficult to identify. It may give rise to a damp, musty
smell, and possibly mould growth on the inside surface.
However, other causes of dampness can produce similar
effects. Internally insulated walls with a deficient or damaged
vapour barrier are particularly vulnerable to interstitial
Interstitial Condensation in
Internally Insulated Wall
Cold wall
Internal insulation
Vapour barrier
Gap in vapour barrier
Interstitial condensation
Cross-section of wall
Effects of condensation
Controlling surface condensation
Persistent dampness due to condensation can have the
following effects:
To reduce condensation, do one or both of the following:
Reduce the amount of water vapour in internal air, by
removing moisture at source and/or increasing overall
ventilation rates.
Increase internal temperatures, by insulation and/or
additional heating.
Wood and other building materials may decay, giving rise to
structural and other damage.
Mould grows in damp, humid, warm conditions. If a wall or
ceiling is frequently damp with condensation, mould may
form on it. Mould usually appears initially as spots or small
patches, usually grey-green, brown or black in colour, which
grow in size and number with time.
Heat loss
The effectiveness of some insulation materials will be
seriously reduced by dampness. If insulation becomes damp,
either through condensation or by other means, heat loss
from the house will increase. In addition, the insulation and
the room surface inside it will then be colder, increasing the
likelihood of further condensation.
Sources of moisture
A typical four-person household (two adults and two children)
may produce in the region of 5 to 12 kilograms of water
vapour per day. The main sources include breathing (exhaled
air contains more moisture than inhaled air), cooking, bathing,
clothes drying and the use of free-standing (i.e. flueless) gas
and paraffin heaters.
Typical Breakdown of Moisture Generation
Rates for Four-person Household
Washing clothes
Drying clothes
(e.g. by
hanging up)
kg per day
Remove moisture at source
When cooking, particularly when generating lots of steam,
open windows and vents in the kitchen to let out the steam
and close the kitchen’s internal door to prevent the steam
from entering the rest of the house. If there are vents or open
windows in two walls, this will help to provide ventilation
across the room even on days with only a slight breeze.
An extractor fan or cooker hood will help to remove steam
and moist air. Since such fans extract heat as well as moisture,
closing the kitchen’s internal door will prevent heat from
being extracted from the rest of the house. Air extracted must
be replaced by air intake somewhere else, so another vent in
the kitchen may need to be opened to allow replacement air
to be drawn in.
When bathing, close the door and open the fly window a little
while bathing or more immediately afterwards. In internal
bathrooms mechanical or stack ventilation is required. This
should be controlled so that it is not left switched on for any
longer than required, since it extracts heat as well as moisture.
Removing Moisture at Source in the Kitchen
or extractor
Insulation of the building will raise internal surface
temperatures, reducing the likelihood of surface
condensation. Also, whatever condensation does occur will
evaporate more quickly. Similarly, the use of double glazing or,
better still, low-emissivity double glazing, rather than single
glazing, will reduce the likelihood of condensation on
windows. If aluminium window-frames are to be installed,
these should have a ‘thermal break’, otherwise condensation
may occur on the frame itself.
Dry clothes outdoors whenever possible. If hanging clothes
up to dry in a utility room, close the internal door and open a
window or vent slightly (not too much, otherwise the room
will cool down, reducing the drying rate). Always vent tumble
dryers to the outside.
Additional heating will have a similar effect to insulation - it
will raise internal temperatures and reduce the incidence of
condensation. Ventilation will still be needed to prevent the
accumulation of moisture.
Controlling Condensation
Insulated external walls, roof, etc
Moisture generation
Free-standing heaters (i.e. those with no flue to the outside)
burning fuels such as gas or paraffin release water vapour into
the room as they operate. Burning one litre of paraffin will
produce about one kilogram of water vapour. In rooms with
such heaters, adequate ventilation is always required not only
to remove water vapour and other combustion products
(fumes) from the room, but also to supply combustion air to
the heater. In buildings vulnerable to condensation, a heater
with a flue to carry fumes to the outside is preferable.
Ensure adequate ventilation
The ventilation rate should be high enough to prevent the
build-up of moisture (and pollutants) in the indoor air, but
should not be so high that it causes excessive heat loss.
The optimum ventilation rate will vary depending on
what activity is going on and the weather conditions on
the day. In well-sealed houses (e.g. those with draughtstripped doors and windows, blocked-off chimneys, etc.),
ventilation should be provided through controllable
openings such as trickle vents or windows that can be
secured in a marginally open position. These can be
adjusted by occupants in response to ventilation
requirements. For example, they might be opened on
calm days when large amounts of moisture are being
generated in the house, and closed on windy days when
little moisture is being produced. Signs such as misting up
of windows indicate the need for increased ventilation.
Controlling interstitial condensation
If interstitial condensation is suspected, check for any gaps or
holes in the surfaces of external walls, the ground floor and
the top-floor ceiling, and seal these to prevent moist air from
getting inside. The methods for reducing surface
condensation described above will also help. If the problem
persists, seek professional advice.
Condensation in the attic
Further tips
If there are gaps in the ceiling of the top floor, warm humid air
from the house may pass through the ceiling into the attic,
where it may condense on cold surfaces. This may cause
rotting of timber or, if it drips down onto insulation, reduced
effectiveness of insulation and increased heat loss.
When cooking by boiling, keeping lids on pots will reduce
steam generation as well as saving energy.
Do not allow water that has condensed on cold water
pipes to run down to where it may cause damage or
present a safety hazard.
If condensation occurs within cupboards mounted on
external walls, leave the cupboard doors open to ventilate
the affected surfaces. Insulate the wall at the back of the
cupboard to prevent recurrence.
Some new buildings can take time to dry out. Extra heat
and ventilation may be needed to evaporate moisture
during the first winter after construction and care may be
needed in mopping up condensation.
Controlling Condensation in the Attic
No gaps
in ceiling
attic hatch
Adequate ventilation
at eaves
Other causes of dampness
To avoid attic condensation problems:
Apart from condensation, other possible causes of dampness
in buildings include
(a) Ensure that there is adequate ventilation in the attic. In
conventional pitched roofs (unconverted), there should
be a gap at the eaves on opposite sides of the roof to allow
cross-ventilation above the insulation. It is recommended
that the area of these gaps should be equivalent to a
continuous opening of not less than 10 mm (about a halfinch).
Rain penetration through walls, roofs or around window
and door openings.
Rising damp, i.e. moisture from the ground rising up
within a wall or floor.
A leaking pipe, tank or gutter.
(b) Seal any gaps in the ceiling below the attic.The attic hatch
should be draught-sealed (light-weight hatches may need
to be clamped or weighted to ensure adequate pressure
against the seal). Gaps around pipes or light fittings
penetrating the ceiling and cracks at wall-heads should be
Drying out of a newly-constructed house or a house that
has recently been flooded.
(c) Ensure that the water tank and pipes in the attic are
insulated to avoid condensation on them.
If the dampness problem is not solved by the measures
described in this leaflet, it may be due to a cause other than
condensation, and professional advice should be sought on
how to deal with it.
The Building Regulations Technical Guidance Document Part
L defines two types of U-value, the elemental U-value as
detailed below and the overall U-value (Um). The latter is
given by:
To calculate the U-value of this wall we must first calculate the
combined thermal resistance of the various layers to account
for heat lost due to conduction.
Thermal resistance or R is:
The sum of each elemental U-value
multiplied by its respective area
Total building area
Total AU
The heating energy performance of a new building design
can be predicted using a standardised method called the Heat
Energy Rating Method (HER).The result is usually expressed in
kilowatt-hours per square metre of floor area per year
(kWh/m2). A U-Value calculator for walls, floors and roofs is
also provided in the HER software. The range of energy
consumption of a dwelling house under the new 2002
Building Regulations is designed to fall in the range of 80 to
102 kWh/m2y. However, it is possible to achieve a fuel
consumption much lower than this through measures
referred to in this booklet.
The Technical Guidance Document L incorporates a provision
whereby an energy rating procedure can be used to
demonstrate compliance.
How to Calculate the U-value of a Wall
The U-value of a building element (wall, floor, roof or window)
is simply one divided by the total resistance of
that element or:
U-value (U) =
Thickness of the material
= m2K/W
For a wall made of numerous layers:
+ etc.
For our example:
R =
3.49 m2K/W
Rigid Foam
+ 3.2
Note the difference in the resistance of the insulation when
compared to the other materials.
Now we can include the thermal resistance of the surfaces:
Outside surface 0.06 m2K/W
Inside surface
0.12 m2K/W
Air cavity
0.18 m2K/W
The total thermal resistance of the wall is:
R = 3.49 + 0.06 + 0.12 + 0.18
= 3.85
Therefore, the U-value is
Element Resistance (R)
U =
By way of example, let us consider a typical wall:
Brick (102mm)
Air Cavity (40mm)
Rigid foam
insulation (80mm)
Concrete block (100mm)
Plaster (12.5mm)
Cavity Wall
= 0.259 W/m2K
Building Regulations Technical Guidance Document Part L
indicates that the elemental U-value of a wall should be a
maximum of 0.27 W/m2K. Therefore this wall complies.
Useful contacts for further information
SEI, Glasnevin, Dublin 9. Energy Hotline: 1850 376666
Irish Agrément Board, Glasnevin, Dublin 9. Telephone: (01) 8073800
National Standards Authority of Ireland, Glasnevin, Dublin 9. Telephone: (01) 8073800
Insulating Contractors Association
Irish Home Builders Association
Roofing and Cladding Contractors Association
Irish Window Association
Construction Industry Federation, Federation House,
Canal Road, Dublin 6. Telephone: (01) 4977487
Relevant Standards
Irish Standards
IS 260:1984, Mineral Fibre Material for Thermal Insulation of Buildings
IS 298:1987, Thermal insulation of Pipes, Ducts and
Storage Vessels
Irish Building Regulations 2002
Technical Guidance Document Part L, Conservation of Fuel and Energy
Technical Guidance Document Part F, Ventilation
Technical Guidance Document Part B, Fire
Technical Guidance Document J: Heat Producing Appliances.
Irish Agrément Board Certified Products
The Irish Agrément Board assesses, tests and certifies insulation products for compliance with the requirements
of the Building Regulations. An index of certified products is available from the Irish Agrément Board.
Source Text
Energy Research Group UCD
This leaflet is printed on paper produced from 50% recycled
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Read our other publications:
A Detailed Guide to Home Heating Systems
Your Guide to Renovating an Older Home
Your Guide to Building an Energy Efficient Home
Your Guide to Renewable Energy
A Consumer Guide to Sustainable Energy
How to make your Home more Energy Efficient
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SEI, Glasnevin, Dublin 9
tel: +353 1 836 9080
fax: +330 1 837 2848
[email protected]
SEI InfoLine
8 to 8, Mon to Fri, 1850-376 666
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