STRENGTHENING STANDING CHIMNEYS The task is to strengthen

STRENGTHENING STANDING CHIMNEYS The task is to strengthen
ADVICE NOTE 3
STRENGTHENING STANDING CHIMNEYS
The task is to strengthen and/or repair a standing chimney in such a way that it retains its
original design integrity and to make sure that its junctions with the rest of the building
remain waterproof.
The challenge is to enhance the underlying strength of the stack as a unit and also to
hold its various components together. A number of possibilities are discussed below.
These are intended to keep the chimney stack intact or to help it move as a single
element under earthquake load, rather than disintegrating or breaking off. As with
reconstruction, it will generally be necessary to obtain professional engineering advice to
design the structural support and it will be necessary to obtain a building consent for that
structure.
Structural diaphragms can be used to distribute the horizontal loads from the chimney to
the various supporting elements of the building, then back down to ground. These
diaphragms can be formed by plywood fixed fo the existing or new timber framing that lies
in the plane of the roof and ceiling, or diaphragm action provided by existing floors, if they
have sufficient strength and stiffness. Generally, metal strapping and/or blocking is
required to distribute the load from the chimney into each diaphragm. Note that where the
chimney shaft extends well above the roof plane and the chimney stack is over one or
more storeys, support for the chimney requires at least two diaphragms spaced well apart
vertically. These spaced diaphragms form a couple to stabilise the upper section of the
chimney shaft where if projects above the roof.
As a general principle, it is better not to think of filling a chimney with concrete as this will
change its behaviour in an earthquake and will increase the weight in the upper part of
the shaft.
The following methods describe a range of approaches to strengthen an existing chimney
flue. All require specific professional design with varying degrees of complexity.
Metal sleeve inserted into the flue
Support for the chimney is provided by a metal tube
(eg. galvanised steel tube) fitted info the chimney flue.
This tube ties the stack together through its height and
carries the horizontal inertia loads from the chimney to
the supports such as a masonry wall, or diaphragms or
hearth breasting or foundations.
The tube is to be sufficiently strong and stiff to carry
the inertia loads from the chimney to the supporis by
shear and bending in the tube, and limit the flexing of
the chimney to within the capacity of the brickwork.
However, diurnal movement of the brickwork should
not be restrained so that excessive tensions do not |
develop in the brickwork. И
metal tube
inserted
info flue
To inhibit the brickwork from breaking away from the
inner tube, stainless steel wire hoops (or Helifix*
threaded rods) can be fitted into say every third
horizontal mortar joint, and held in place by new
pointing into the perimeter of the joint.
a. A metal tube — say 200mm diameter — is
supported in the flue while a small amount of
cement mortar is placed to close the flue at
the base of the tube (a pneumatic tube placed
around the tube and inflated, will support the
wet concrete).
10096 Canterbury Earthquake
REVISION 21 JANUARY 2011 — page 12
ADVICE NOTE 3
b. The space between the steel tube and masonry is back-filled with either granular
‘pea’ gravel or weak grout (Centricrete MV)'. This helps stiffen the shaft, without
reducing its flexibility to diurnal effects, and dampens the earthquake actions.
с. The top portion of the cavity is to be sealed with non-shrink grout to stop water
entry between brickwork and the steel {ube.
d. As required, horizontal hoops should be provided in the horizontal mortar joints of
the brickwork.
This method enables the chimney to ventilate the room or the interior. Where itis
intended that the chimney will continue to function in conjunction with a fireplace, a
proprietary product with multiple concentric stainless sfeel fubes can be inserted. This
allows cooler air to circulate around the central flue.
If may also be advisable to connect such a metal flue to a new enclosed metal firebox,
either by welding on site, or with the use of a fabricated metal collar.
Tension rods within the flue
An alternative to the above method utilises the high compressive strength of the
brickwork, but is dependent on the age and strength of the chimney bricks and the mortar
used. The instaliation must be professionally designed by a structural engineer.
a. Fix atleast two, preferably four, threaded metal
anchors in the base of the firebox, down into the
foundations of the chimney and well bedded in
epoxy adhesive. Locate the anchors as far apart
as possible but with a clear vertical fiue cavity
above, through to the top of the chimney.
Alternatively, for a large cnimney where the
brickwork is sound on a vertical line for the full
height of the chimney, core down through the
height of the brickwork to insert each anchor in
the foundation of the chimney. The coring of the
holes for the full height of the chimney, placing,
anchoring and stressing of the ties requires the
services of a specilist contractor.
tension'yods
anchoredimo
chimney base
structural
diaphragm
formed in roof
structure
b. Make up and fit a stiff metal plate to cover the top
of the flue, and drilled for the ends of the tension
rods (if it is intended to continue to have fires, this
plate will need to have an opening for smoke to
pass through).
с. Locate threaded rods or tensioned wires into the
anchor points and through the top plate, and
tension these as directed by the engineer.
A method where the tie rods or wires pass up through the flue is more invasive as it
requires a strong anchorage to be formed at the base of the flue within the hearth area
and therefore depends on this part of the chimney retaining its structural integrity.
! Supplied by Building Chemical Supplies, Wellington
tree phone 0800 22 55 62
10096 Canterbury Earthquake
REVISIÓN 21 JANUARY 2011 — page 13
ADVICE NOTE 3
Also, because the metal fies required will be exposed, it will inadvisable to use the
chimney for its original purpose as the heat of a fire will weaken the tension rods.
If it is intended to continue to have fires, then the metal sleeve systems described above
will be preferable, used in conjunction with a metal firebox.
Where the tie rods or wires pass up through holes cored in the brickwork, each rod or
wire should be greased and encased in a plastic tube, The tie assembly is fitted into the
cored hole, fixed at the base, stressed and grouied into the hole.
The grease filled plastic tube protection can also be used where the ties pass up the flue.
External strapping
This is likely to be a fairly visible repair, in which case some thought should be given to its
design and assembly and to finishing the metalwork with either a paint to match the
chimney material or perhaps, where the design of the strapping has been carefully
considered, with a contrasting paint colour (e.g. black). Where external strapping is used,
it should be installed in conjunction with a structural system that inhibits the externally
strapped section of the chimney shaft breaking away below the strapping, and tipping
over as a whole.
The benefit of this method is its capacity to restrain
the masonry over the strapped height from
disintegrating under earthquake forces. mein cool
structure
a. Galvanised pre-formed steel straps placed
around the shaft both vertically and horizontally a
tie it together as if in a cage. ‹
b. Metal work should be bolted together so that it
can later be removed if necessary.
c. May also require some direct attachment into
the masonry siructure of the chimney.
Bracing back to roof framing
This may be undertaken in association with sirapping the chimney shaft, and is likely to
be quite visible. Consequently this may be used only as an interim measure or, if itis to
be permanent, then the design and location of the bracing element should be carefully
considered.
a. Locate a robust fixing point in the adjacent roof structure and attach a structural
anchor designed by a structural engineer.
b. Locate a support position on the shaft and fit a galvanised steel collar around the
shaft with connection to the brace.
c. Connection to the roof structure will require penetration of the roof covering, leading
to a risk of water entry. Therefore special care shouldbe taken with the design of
flashings to exclude moisture.
de Diaphragms fitted to the underside of the roof framing may be required to support
the chimney stack where it passes through the roof plane and at the brace fixing
points to the roof. Earthquake loads from the chimney are to be carried back into the
supporting structure without causing excessive stress or deflection of the supporting
members.
Note that the braces are to carry inertia loads from the chimney in two directions at right
angles to each other. Therefore the braces should be splayed to take components of load
in each load direction.
10096 Canterbury Earthquake
REVISION 21 JANUARY 2011 — раде 14
ADVICE NOTE 3
Near-face tension reinforcing
This method makes use of modern materials to increase the horizontal bending strength
of the brick masonry. It relies on reinforcing strips set into slots cut in the masonry to
achieve an effect similar to that of the external strapping. This technique will work well in
rendered (plastered) chimneys, as the cuts made can be replastered to disguise their
existence.
a. Open up the roofing around the perimeter of
the chimney so that the saw cuts can be
taken to below the roof plan.
b. Saw cut vertical slots in the face of the flue
at intervals from the top of the chimney to
below where bending tension will be
generated in the brickwork due to horizontal
earthquake loads.
c. Insert carbon-fibre strips into the saw cuts
and bond these into the slots with epoxy
resin.
d. Re-point the joints with mortar to match the
existing construction.
e. Form structural diaphragm within roof structure as noted above, and make good
the roofing.
This method is less suitable for exposed brick masonry as it will require saw cuts to be
made across the face of the bricks, and will be difficult to conceal, even using coloured
mortars.
proprietary anchor systems
A number of modern anchor systems are available
to locally augment the strength of a flue in
conjunction with any of the above techniques.
These systems rely on the use of slender threaded
reinforcing rods which can be drilled though
masonry to pin pieces together. These can be used
in horizontal strips or on an angle and must be used
with reference to their specifications.
They can be used to repair cracks, to join separate masonry skins (such as veneers)
together and as reinforcement set into mortar joints. Examples include the Helifix
system”. Other manufacturers may also offer equivalent systems.
2 see: http://www.helifix.com.au/crack_stitching.html
hitp://www.helifix.com.au/masonry repair details .html::BRF
10096 Canterbury Earthquake
REVISION 21 JANUARY 2011 — page 15
ADVICE NOTE 3
OTHER METHODS
The above methods are intended for use where the repair to the chimney is intended as
a full restoration as a part of the whole building. Other techniques which replicate the
shape or form of the chimney using light-weight or synthetic materials, alone, or in
combination with parts of original materials, are aiso possible.
Such techniques are beyond the scope of this Advice Noie.
SUMMARY
Repair or reconstruction of chimneys is not a simple matter.
it will be important first to consider structural stability and safety.
Always consult with the local authority before embarking on repair.
It is strongly recommended, in all cases, that professional engineering advice is taken.
For heritage buildings, it is strongly recommended that professional heritage advice is
taken. In the first instance this may come from the NZHPT or the local Council and a list
of heritage specialist can be provided.
If it is intended that the chimney will continue to be used for fires, then particular care is
required to design and construct a repair option which will be fit for the purpose and
function efficiently for many years with minimum maintenance.
This Advice Note has been produced as general introduciory guidance
for those involved in the repair and reinstatement of heritage buildings,
His not intended fo provide specific solutions far individual projects but,
rather, to set out available options that are in accordance with accepisd
conservation principles,
It is strongly recommended that appropriate skilled professionals with
proven conservation experience and qualifications should be appointed
fo specify repairs on a case by case basis.
Copyright of this document remains with Salmond Reed Architects Lid
and the contents should not be reproduced in part or whole without full Printed: 7 February 2011
acknowledgement to Salmond Reed Architects.
10086 Canterbury Earthquake
REVISION 21 JANUARY 2011 — page 16
New Zealand Historic Places Trust Pouhere Taonga
Sustainable Management of Historic Heritage Guidance Series
Repairing Historic Brickwork after an Earthquake
Repairing Historic Brickwork after an Earthquake
Brickwork damage can occur during earthquake events and may continue
during aftershocks. Bricks have little inherent strength on their own but
require a system of mortar, reinforcing and ties to hold them together.
In countries with minor seismic activity, masonry can be constructed, brick
upon brick, and remain stable for centuries. In New Zealand, however, the
sideways and vertical thrusts of earthquakes strain the brickwork. If strong
enough, the earthquake forces eventually cause damage.
Unreinforced brickwork is particularly prone to collapse but partly
reinforced or partly strengthened brickwork can also suffer failure. Cracks
might appear, bricks or whole walls of bricks fall away, brick walls might
lean or move out of alignment, or mortar between the bricks might be lost. If
brickwork was compromised before the earthquake, the cracking or loss of
bricks may be exacerbated.
First, Make Your Place Safe
In the first days after an earthquake you will hopefully have had initial
assistance in deciding what degree of damage has been caused. For severe
damage, you may have been advised to evacuate and tape off or barricade
the building or undertake urgent work to hold the bricks together. It may
have been necessary to contain or remove loose bricks to prevent them
falling on people, or waterproof your building where brick loss makes it
open to weather.
How to Repair
All building owners will be keen to resolve their damaged building as soon
as possible and there are a range of matters to consider. Many of the
decisions to be made are complex. For heritage building owners, there are
further issues of long-term importance to consider that owners of other
buildings may be unconcerned with.
Heritage Buildings
Heritage buildings have historical, architectural, cultural or other values that
make them important. The loss of brick material may have been devastating
and subsequent restoration may be necessary for the understanding of the
building. For instance, a house that is important for its architectural values
should have aspects of architectural design repaired. Otherwise the sense of
the building is changed — even diminished. Most importantly, apparent
damage is not a reason to unnecessarily alter or demolish the heritage
building until all avenues and options are considered.
For information about
conservation principles
that inform works such
as repairing historic
brickwork, see the NZ
ICOMOS Charter 2010:
WWW.icomos.org.nz
See also the NZHPT”s
Sustainable
Management of
Historic Heritage
Guidance Series
Information Sheet No.
1
http://www historic.or
g.nz/ Publications/Susta
1
6 December 2010
Every part of a Heritage Building is Important...
But some parts may be more important than others. As a heritage owner you
may be well aware of the significance of your building and its fabric, or you
may be contemplating removing brickwork because it looks too hard to
repair.
The New Zealand Historic Places Trust (NZHPT) can work through with
you any dilemmas of damage and options for appropriate repair. The
NZHPT’s experience in many issues of heritage repair nationwide means it
is well placed to offer advice for seemingly unsolvable problems. You can be
sure that when the NZHPT confirms your direction it will be based on
sound best practice heritage principles.
You Are Not Alone
As a heritage building owner confronted by extraordinary circumstances
you have the goodwill of New Zealand's heritage community. Please contact
the NZHPT anytime during working hours to discuss options about
repairing your heritage building.
It may be the first time you need to engage a structural earthquake engineer
or architect with conservation knowledge. They will have had experience
with other brick buildings around the country. A list of heritage
professionals experienced in repair of heritage buildings is available on the
NZHPT's website:
://www.historic.org.nz/en/ProtectingOurHeritage/F AOs-
Earthquake.aspx
You will need to check with your insurer and EQC before proceeding with
the employment of consultants or the carrying out of work.
Determine the structural cause of the failure
A structural engineer is needed to determine the cause of the material
failure. An engineer will be able to look at the building in terms of the
strength of its component parts and see which gave way and how. The
engineer will observe the building — perhaps over a period of time — looking
at the types of failure and where they occurred.
Designing Repairs
The design and repair of damaged buildings will involve a comprehensive
look at the strength of the building. There is no point in putting back a brick
walls and chimneys if they are not adequately strengthened. Repairing to be
able to withstand another earthquake is the aim. An engineer will not only
look at the areas that were damaged this time, but will look to ensure it will
survive as a whole in the future. A conservation architect, heritage
consultant or contractor skilled in heritage work can help design the repairs
so that they don’t impact adversely on the special features that your place
has. Some of the repairs that will be considered are:
e New mortar & reinstating individual bricks.
Resource consent is
required under the RMA
from your local
authority to demolish or
alter any listed heritage
building.
Always check with your
local authority before
carrying out any repair
work to heritage
buildings.
The demolition or
partial demolition of any
pre-1900 historic
building requires an
archaeological authority
from the NZHPT.
Special emergency
procedures exist for the
post-earthquake
situation in Canterbury
in relation to
archaeological
authorities. See the
NZHPT's website:
http://www historic.org,
nz/en/ProtectingOurHer
itage/FAOS-
Earthquake.aspx
o Re-building walls.
e Re-seating lintels.
e Structural tying of gable ends, towers.
e Strengthening of wall-to-wall joints.
e Strengthening of wall-to-roof joints.
e Strengthening of the two or more layers of brickwork and tying
together.
e Methods of strengthening brickwork for the entire height into the
ground. Further information
е Tying floors and ceilings into walls. — it is
e Reinstating chimneys with increased strength. available from the
NZHPT:
Ian Bowman, Historic
In undertaking repairs to damaged buildings, the local authority will also Brick Structures,
often require earthquake strengthening and other NZ Building Code Conservation Bulletin
requirements. These requirements ensure that buildings are “built-back- No.2, NZHPT, 1992
better’ to be more resilient for the future. The NZHPT has prepared a draft
guide for earthquake strengthening of heritage buildings:
Pre-existing Conditions
Repair work can be complicated by pre-existing conditions and earthquake
damage may have been exacerbated by these conditions. These may have
been part of an ongoing maintenance programme for your building or they
may have been there undetected for some time. These matters may include:
e Crumbling or decayed mortar.
e Crumbling or decayed bricks.
e Rising damp.
e Water penetration from above.
e Settling of the brickwork or movement.
e Efflorescence (that white stuff!).
e Damaged or inadequate lintels or other structural members.
e Existing but inadequate structural strengthening.
Now is the time to also look at these issues as well. Your engineer and
conservation architect/expert can advise you on how to proceed.
Repairing Mortar
Taking professional heritage advice about repair of mortar joints is
recommended. Inappropriate materials or methods can cause problems very
quickly.
3
6 December 2010
The presence of water or damp can move soluble salts through the bricks
and mortar, which over time can be left on the surface as the moisture
evaporates. The salts can expand and spall away the wall material.
The choice of mortar composition is vital. The commonly-used high-cement
mortar is harder, more impervious and allows little movement. It is also
likely to crack, allowing in moisture which then becomes trapped because
the mortar will not allow evaporation. As a general rule the mortar mix
should be weaker that than the bricks themselves to prevent the bricks
breaking in any future event.
Mortar has a colour, composition and textural appearance both in the mix
and the pointing methods used. For a heritage building, the match is
important and skilled tradespeople with experience on heritage buildings
need to be used. Advice from a conservation architect/heritage expert on the
mortar ‘recipe’ and application is recommended. See the list of heritage
professionals on the NZHPT’s website:
://www.historic.org.nz/en
Earthquake.aspx
Is the damage too serious?
By their nature heritage buildings are worth keeping because of their
heritage values. If an entire building is seriously compromised, it may need
to be partially rebuilt or demolished in only rare circumstances. This is a
difficult decision for any building owner and requires guidance. A heritage
building, or part of it, may hopefully be restored and may be deemed
inappropriate for demolition.
This is not a decision to be taken quickly but after discussion and advice
from engineering consultants, insurers, the Earthquake Commission, the
local Council, and the NZHPT. There are usually several options for the
future of the building, and there are normally engineering solutions that can
assist in the economical retention and strengthening and repair of heritage
buildings.
Consultation
A building and/or resource consent may be required for any repair and
strengthening work and this needs to be clarified with you local authority.
The Christchurch City Council has its own dedicated heritage team that will
need to be consulted in conjunction with NZHPT about significant
brickwork repairs.
Is there funding to support owners of heritage buildings?
The government, NZHPT and local authorities have established the
Canterbury Earthquake Heritage Building Fund as a source of assistance for
owners to repair damaged heritage buildings. Information about this
funding campaign is available from the NZHPTs website:
http://www historicplaces.org.nz/donationForm.aspx
Further information
and advice can be
obtained by contacting
the NZHPT.
Contact details are
available from the
NZHPT's website:
http://www historic.or
g.nz/ContactUs.aspx
O Copyright, NZHPT,
December 2010
4
6 December 2010
New Zealand Historic Places Trust Pouhere Taonga
Sustainable Management of Historic Heritage Guidance Series
Repairing Historic Stonework after an Earthquake
Repairing Historic Stonework after an Earthquake
Stonework damage can occur during earthquake events and may continue during
aftershocks. Stone block walls may have little inherent strength unless well
mortared or tied to other wall structure.
In countries with minor seismic activity, masonry can be constructed, stone upon
stone, and remain stable for centuries. In New Zealand, however, the sideways
thrusts of earthquakes strain the stonework. If strong enough, the earthquake forces
eventually cause damage.
Unsupported stonework is particularly prone to failure or collapse. Cracks might
appear, individual stones or whole walls of stone fall away, walls might lean or
move out of alignment, or mortar between the stones might be lost. If stonework
was compromised before the earthquake, the cracking or loss of stones may be
exacerbated.
First, Make Your Place Safe
In the first days after an earthquake you will hopefully have had initial assistance in
deciding what degree of damage has been caused. For severe damage, you may
have been advised to evacuate and tape off or barricade the building or undertake
urgent work to hold the stonework together. It may have been necessary to contain
or remove loose stones to prevent them falling on people, or waterproof your
building where stone loss makes it open to weather.
How to Repair
All building owners will be keen to resolve their damaged building as soon as
possible and there are a range of matters to consider. Many of the decisions to be
made are complex. For heritage building owners, there are further issues of long-
term importance to consider that owners of other buildings are unconcerned with.
Heritage Buildings
Heritage buildings have historical, architectural, cultural or other values that make
them important. The loss of stone material may have been devastating and
subsequent restoration may be necessary for the understanding of the building. For
instance, a house that is important for its architectural values should have aspects of
architectural design repaired. Otherwise the sense of the building is changed — even
diminished. Most importantly, apparent damage is not a reason to unnecessarily
alter or demolish the heritage building until all avenues and options are considered.
Every part of a Heritage Building is Important...
But some parts may be more important than others. As a heritage owner you may
be well aware of the significance of your building and its material fabric, or you
may be contemplating removing stonework because it looks too hard to repair.
For information about
conservation principles
that inform works such
as repairing historic
stonework, see the
NZHPT ICOMOS
Charter 2010:
WWW.icomos.org.nz
See also the NZHPT's
Sustainable
Management of
Historic Heritage
Guidance Series,
Information Sheet No.
1
http://www.historic.or
nz/Publications/Susta
inMgtSeries.aspx
1
6 December 2010
Repairing Historic Stonework after an Earthquake
The New Zealand Historic Places Trust (NZHPT) can work through with you any
dilemmas of damage versus importance. The NZHPT’s experience in many issues
of heritage repair nationwide means it is well placed to offer advice for seemingly
unsolvable problems. You can be sure that when the NZHPT works with you to
confirm your direction it will be based on sound best practice heritage principles.
You Are Not Alone
As a heritage building owner confronted by extraordinary circumstances you have
the goodwill of New Zealand's heritage community. Please contact the NZHPT
anytime during working hours to discuss options about repairing your heritage
building.
It may be the first time you need to engage a structural earthquake engineer or
architect with conservation knowledge. They will have had experience with other
stone buildings around the country. A list of heritage professionals experienced in
repair of heritage buildings is available on the NZHPT's website:
http://www.historic.org.nz/en/ProtectingOurHeritage/FAQs-Farthquake.aspx
You will need to check with your insurer and EQC before proceeding with the
employment of consultants or the carrying out of work.
Determine the structural cause of the failure
À structural engineer is needed to determine the cause of the material failure. An
engineer will be able to look at the building in terms of the strength of its
component parts and see which gave way and how. The engineer will observe the
building — perhaps over a period of time — looking at the types of failure and where
they occurred.
Designing Repairs
The design repair of damaged buildings will involve a comprehensive look at the
strength of the building. Repairing to be able to withstand another earthquake is the
aim. An engineer will not only look at the areas that were damaged this time, but
will look to ensure it will survive as a whole in the future. There is no point in
repairing one corner after this quake only to have the opposite corner damaged if it
happens again from a different direction. A conservation architect can help design
the repairs so that they don’t impact adversely on the special features that your
place has.
Some of the repairs that will be considered are:
e Reinstating individual stones.
e Repairing mortar.
e Re-built walls.
e Re-seating stone lintels.
e Structural tying of gable ends, towers.
e Strengthening of wall-to-wall joints.
e Strengthening of wall-to-roof joints.
e Strengthening of the two or more layers of stonework and tying together.
Resource consent is
required under the RMA
from your local
authority to demolish or
alter any listed heritage
building.
Always check with your
local authority before
carrying out any repair
work to heritage
buildings.
e Methods of strengthening stonework for the entire height into the ground.
e The problems of rubble-filled cavities.
In undertaking repairs to damaged buildings, the local authority will also often
require earthquake strengthening and other NZ Building Code requirements. These
requirements ensure that buildings are ‘built-back-better’ to be more resilient for
the future. The NZHPT has prepared a draft guide for earthquake strengthening of
heritage buildings:
http://www historic.org.nz/en/ProtectingOurHeritage/ConsultingOn.aspx
Pre-existing Conditions
Repair work can be complicated by pre-existing conditions. These may have been
part of an ongoing maintenance programme for your building or they may have
been there undetected for some time. These matters may include:
e Crumbling or decayed mortar.
e Crumbling or fractured stones.
e Incorrect stone combinations or orientations.
e Rising damp, soiling.
e Water penetration from above.
e Settling of the stonework or movement.
e Efflorescence (that white stuff!) or subflorescence.
e Damaged or inadequate lintels or other structural members.
e Existing but inadequate structural strengthening.
Now is the time to also look at these issues as well. Your engineer and conservation
architect can advise you on how to proceed.
Repairs
Taking advice about repair is well worthwhile as for heritage buildings repair is not
as simple as it might seem. Inappropriate materials or methods can cause problems
later. After an earthquake, masonry often has structural failure, related to the strain
of the movement that the building has been subjected to as its root cause. Repairing
the mortar may not itself fix the structural fault. The presence of water or damp
which may have brought soluble salts into mortar and porous stone may have
spalled away the wall material.
A heritage building needs skilled tradespeople with experience, and advice from a
conservation architect is essential. The rebuilding may be a matter of relaying intact
stones but also may involve cutting stones out of and into sound stonework. The
selection of stones and the way in which they are reattached and mortared in place
is a skilled piece of work. Careful stone placement and the use of original pointing
techniques should match the original wall.
The demolition of
any pre-1900 historic
building requires an
archaeological
authority from the
NZHPT.
Special emergency
procedures exist for
the post-earthquake
situation in
Canterbury in
relation to
archaeological
authorities. See the
NZHPT's website:
http://www.historic.o
rg.nz/en/ProtectingO
urHeritage/FAQs-
Earthquake.aspx
Mortar has a colour and textural appearance both in the mix and the pointing
methods used. The choice of mortar composition is vital. It should not be stronger
than the stone itself. Ideally, the original mix should be tested and re-used.
Advice from a conservation architect/heritage expert on the mortar ‘recipe’ and
application is recommended. See the list of heritage professionals on the NZHPT's
website:
http://www historic.org.nz/en/ProtectingOurHeritage/FAQs-Earthquake.aspx
Is the damage too serious?
By their nature heritage buildings are worth keeping because of their heritage
values. If an entire building is seriously compromised, it may need to be partially
rebuilt or demolished in only rare circumstances. This is a difficult decision for any
building owner and requires guidance. A heritage building, or part of it, may
hopefully be restored and may be deemed inappropriate for demolition.
This is not a decision to be taken quickly but after discussion and advice from
engineering consultants, insurers, the Earthquake Commission, the local Council,
and the NZHPT. There are usually several options for the future of the building,
and there are normally engineering solutions that can assist in the economical
retention and strengthening and repair of heritage buildings.
Consultation
A building and/or resource consent may be required for any repair and
strengthening work and this needs to be clarified with you local authority. The
Christchurch City Council has its own dedicated heritage team that will need to be
consulted in conjunction with NZHPT about significant stonework repairs.
Is there funding to support owners of heritage buildings?
The government, NZHPT and local authorities have established the Canterbury
Earthquake Heritage Building Fund as a source of assistance for owners to repair
damaged heritage buildings. Information about this funding campaign is available
from the NZHPT's website: http://www.historicplaces.org.nz/donationForm.aspx
Further information
about repairing
historic stonework is
available from the
NZHPT:
lan Bowman, Historic
Stone Structures,
Conservation Bulletin
No.3, NZHPT, 1992
Further information
and advice can be
obtained by contacting
the NZHPT.
Contact details are
available from the
NZHPT's website:
http://www historic.or
g.nz/ContactUs.aspx
© Copyright, NZHPT,
December 2010
New Zealand Historic Places Trust Pouhere Taonga
an Earthquake
Sustainable Management of Historic Heritage Guidance Series
| Repairing and Rebuilding Historic Chimneys after
Background
Chimneys were a ubiquitous feature of pre-1960 buildings in New Zealand. It was
extremely unusual for a domestic dwelling to be constructed without a chimney.
The majority of chimneys were built using unreinforced brick masonry. The
Canterbury earthquake (4 September 2010), and its subsequent aftershocks, caused
significant damage to a high proportion of unreinforced masonry chimneys in the
region.
Technology and social factors, such as the availability of cleaner heating devices
and a desire of the community to live in a less polluted environment, have made
chimneys increasingly functionally redundant and as a consequence many property
owners have had their chimney stacks removed over the past half century. The
incremental erosion of our chimney stock, combined with the loss attributable to a
destructive earthquake, leaves the future of the chimney hanging in the balance.
Chimneys are often vital components of a building's composition and it would be
regrettable to lose these architectural elements from the skyline. Not only are
chimneys aesthetically pleasing, they serve as tangible reminders of a previous way
of life.
The New Zealand Historic Places Trust (NZHPT) strongly recommends that, where
possible, chimneys damaged or destroyed as a result of an earthquake, should be
repaired, restored or reconstructed in the most authentic manner feasible.
However, safety must be prioritised and seismic strengthening may require
significant intervention.
No two chimneys, and the damage they have sustained, are identical - nor will one
approach be the solution to all the various scenarios. Although repairing or
rebuilding a chimney to its original form, using original materials is the most
heritage sensitive solution in a conservation sense, in some instances replacement,
using lightweight materials, may be an option. Each chimney needs to be dealt with
on a case by case basis.
Following an earthquake the NZHPT suggest you:
1. Ensure your building is safe:
(a) Chimney appears (visually) undamaged
e Record (photograph, draw and measure as appropriate) damage
even if chimney appears undamaged to the naked yet.
Aftershocks may have an unknown effect on the structure.
e Check the structural integrity of the chimney both above and
below roof level.
e Consider seismically strengthening the chimney to ensure the
structure will withstand any future seismic activity. The New
Zealand Historic Places Trust (NZHPT) strongly recommends
strengthening all chimneys.
For information about
conservation principles
that inform works such
as repairing historic
chimneys, see the NZ
ICOMOS Charter 2010:
WWwWw.icomos.org.nz
See also the NZHPT's
Sustainable
Management of
Historic Heritage
Guidance Series
“Heritage Provisions
for earthquake-prone
buildings policies
under the Building Act
2004
http://www.historic.or
g.nz/ProtectingOurHer
itage/-/media/Corporat
e/Files/Submissions%2
Oand%20research/Revi
sedDraftGuide Earthq
uake.ashx
1
6 December 2010
Repairing and Restoring Historic Chimneys
(b) Chimney partially destroyed - bricks missing, displaced or
destabilised
e
(с) Chimney destroyed — shaft fallen, possible damage to the chimney
Record remaining structure (photograph, draw and measure as
appropriate). Photographing where the bricks fell can provide
useful information also.
Remove bricks which have become detached from the structure
(check ceiling cavity).
Stabilise the chimney shaft by tying, propping or cladding.
Ensure building is temporarily weatherproof.
Check structural integrity of the chimney below roof level.
Ensure all infact bricks (and/or other important building
materials) removed from the chimney are stored on site.
breast
Record damage (photograph, draw and measure as
appropriate).
Remove bricks which have become detached from the structure
or those which could imminently fall thereby posing a risk to
personal safety (check ceiling cavity).
In some instances the damage may be so extensive and pose
such a risk to personal safety that the building is deemed
uninhabitable until remedied.
Check the structural integrity of the chimney below roof level.
Check structural roof members have not been affected.
Where the building is open to the weather, make as
temporarily weatherproof as soon as possible.
Ensure all intact bricks (and/or other important building
materials) removed from the chimney are stored on site.
2. Repairing/rebuilding/replacing a damaged chimney
All work must comply with the Building Act 2004.
Given the risk inadequately repaired chimneys can pose,
skilled and professional building practitioners should be used.
Do not rush building work. All options should be carefully
considered before building begins. Generally it takes a
considerable amount of time for EQC and insurance companies
to assess the property and to pay out claims.
A structural engineer will be required in most instances to: (a)
determine the reason for the chimney failure and (b) to provide
Resource consent is
required under the RMA
from your local
authority to demolish or
alter any listed heritage
building.
Always check with your
local authority before
carrying out any repair
work to heritage
buildings.
a design to strengthen the chimney against future earthquake
damage.
The NZHPT recommends strengthening all chimneys. The
NZHPT has prepared a draft guide for earthquake
strengthening of heritage buildings:
urHeritage/Consulti
All work should be done in accordance with the ICOMOS New
Zealand Charter (2010):
://WWw icomos.org.nz/NZ Charter.pdf (Guidance can be
provided by NZHPT and Council staff).
REPAIRING (using original or like materials)
Repair will be appropriate when the chimney has sustained minimal damage and the
structure is relatively intact.
When repairing a chimney it is important to preserve the
original appearance so much as possible. Where feasible,
original materials should be used or if this is not achievable
identical or closely similar material should be utilised.
The repair of mortar joints should be carefully considered.
The type of mortar used will depend on the age of the chimney
and when/if any repair work has been undertaken.
Lime-based mortars (crumbly in consistency and paler in
colour) were most often used on buildings pre 1900. Cement-
based mortars (harder and more impervious in consistency and
darker in colour) have typically been used in buildings post
1900. Each mortar type has inherent strengths and weaknesses.
Lime mortars behave very differently to cement mortars and it
is vital that the mortar used is consistent throughout the
structure.
New mortar joints should not be stronger than the bricks. In
the event of future earthquakes it is preferable that the mortar
joints give way before the bricks fail. This encourages
“stepped cracking” of the brick structure rather the entire unit
failing.
Brick Chimneys - Original bricks should be reused wherever
possible. Physically damaged, or severely weathered, bricks
should be discarded. Bricks must be cleaned of all mortar and
mortar dust. Immediately prior to relaying the bricks should
be pre-wetted to ensure the new mortar re-adheres to the brick
surface. Caution should be exercised when reusing bricks from
chimneys with unlined flues - bricks which lined the inner
surface of the chimney should not be reused because their
performance may be compromised due to the accumulation of
salts from flue gasses. Experienced brick masons should be
Further information
about repairing
historic brickwork is
available from the
NZHPT:
Ian Bowman, Historic
Brick Structures,
Conservation Bulletin
No.2, NZHPT, 1992
REBUILDING
Rebuilding is appropriate where the chimney has sustained serious damage. For
example, when a number of bricks have fallen or the structural integrity has been
compromised to such an extent that the chimney needs to be carefully taken down to
engaged to repair chimneys as they will be fully conversant
with various mortars and how reused bricks will perform
when used in a rebuilt structure.
a level where it is structural stable and reassembled back to the original form.
When restoring a chimney it is important to preserve the
original appearance so much as possible. Where feasible
original materials should be used or if this is not achievable
identical or closely similar material should be utilised.
In order that the chimney is able to withstand future seismic
events a new internal structure may be required. Various
options are available. The appropriate solution will depend on
a number of variables, i.e. height of chimney, degree of damage
and whether the chimney will be functional or not.
If the chimney is to be functional a triple skinned flue may be
inserted — this allows functionality while also providing
structural strength.
Threaded tension rods or wires may be anchored at the base of
the fireplace and drilled to run the entire height of the chimney.
A plywood diaphragm surrounding the chimney shaft in the
roof space may be necessary to provide lateral strength.
A lightweight steel frame may be utilised. Affixed to the frame
is a suitable substrate to which the original bricks are affixed.
Hebel™(lightweight aerated concrete panel), Hardiebacker™
or marine plywood are two of the substrates available.
Brick Chimneys - Original bricks should be reused where
possible. (See final bullet point under the section titled
‘Repairing’ above).
REPLACING (Using lightweight materials)
Replacement is considered the least desirable option from a heritage conversation
However, there will be occasions when it may be necessary to
reproduce discrete elements within a building which have been lost or destroyed due
to a destructive event (i.e. earthquake). Using lightweight replacement materials
would be unlikely to be an acceptable option for buildings with the highest heritage
value. Solutions for each building/chimney must be carefully considered on a case
perspective.
by case basis.
Any reconstruction should be accurately replicate the visual
appearance of the original chimney.
Photo: H eritage Replica Chim Heys
Timber frame fabricated to
original form with brick slips
providing the skin.
e In order to ascertain the form of the original structure
architectural plans (if available) should be studied.
Photographs taken pre-damage will also provide valuable
information.
Ls ir
ко.
В
RET BE aT
e If sufficient information is not available to accurately replicate
the original form rebuilding should not proceed. In such cases
it may be deemed most appropriate to remove the chimney
altogether. Use of conjecture is not considered acceptable on a
heritage building.
Photo: Reflex
e Using original materials which have been modified. Instead penis Siege
of replacing chimneys with bricks laid two or three deep, cut
down bricks (brick slips) can be affixed to a suitable substrate
to create a lightweight brick ‘skin’. The substrate must be
formed in such a way as to replicate the original structure of
the chimney. The original bricks or matching bricks, carefully
cleaned and prepared, should be used for the slips. Note — it is
important to consider that this technique is new and issues
such as longevity are yet to be proven.
e Lightweight composite materials. A number of companies are
now manufacturing fibreglass replica chimneys. Fibreglass can
potentially reduce the weight of a chimney from more than
1300kg down to approximately 60kg. This approach should be
treated with caution. There is an enormous variation in the
quality of replication provided by various companies. It is
essential the colour matches the existing bricks, the form is
accurate and the detailing is authentic as possible.
Maintenance
Some of the damage chimneys suffered as a result of the Canterbury 7.1
magnitude quake could have been lessened had they been properly maintained.
In many instances mortar had decayed and the shaking action caused the mortar
to crumble and bricks to dislodge and fall. Deep re-pointing of the brickwork
can increase the strength and flexibility of the structure.
Consultation
If your building is listed as a Heritage or Character building on the City or
District Plan or it is registered with the New Zealand Historic Places Trust
(NZHPT) you must consult with Council Planners and/or the Heritage Advisor
of the NZHPT to comply with the requirements of the Resource Management
Act 1991.
Is there funding to support owners of heritage buildings?
In response to the 4 September 2010 Canterbury earthquake the government,
NZHPT and local authorities have established the Canterbury Earthquake Heritage
Building Fund as a source of assistance for owners to repair damaged heritage
buildings. Further information and advice can be obtained by contacting the
NZHPT.
Heritage Specialists
A list of heritage specialists experienced in the repair and reconstruction of heritage
buildings (including chimneys) is available on the NZHPT's website:
http://www .historic.org.nz/en/ProtectingOurHeritage/FAQs-Earthquake.aspx
Contact details are also available from the Christchurch City Council. Note - You
will need to check with your insurer and EQC before proceeding with the
employment of consultants or the carrying out of work.
Additional Sources of Information:
New Zealand Historic Places Trust — Sustainable Management Series — Information
Sheets: http://www historic.org.nz/Publications/SustainMgtSeries.aspx
Christchurch City Council Earthquake Damaged Buildings Guidelines for
Building Owners:
Guideline 3 — Reconstruction of Elements
Guideline 4 —- Strengthening of Buildings
Spiroloc Tubing (manufacturers of custom built, lightweight flue systems)
http://www .spiroloc.co.nz/
Reflex (manufacturers of custom built fibreglass chimneys)
http://reflex.co.nz/industrial/architectural
QSC [Quake Safe Chimneys] (manufacturers of custom built fibreglass chimneys
Ph. 0800-saferhomes [0800-723 374], [email protected]
Contact details are
available from the
NZHPT's website:
http://www historic.ore nz
ContactUs.aspx
O Copyright, NZHPT,
December 2010
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement