What are the best materials to use for traditional
building repairs?
Modern buildings use cavity walls, damp proof courses and plastic membranes
to completely separate the inside living space from damp conditions outside.
Traditional buildings, however, work on a different principle. They use solid
walls built of materials that are porous to varying degrees and will absorb
and release moisture as the weather and internal temperature and humidity
constantly change. This is what is meant when it is said that old buildings need
to ‘breathe’ in order to provide comfortable and healthy living conditions.
It has been recognised that the inappropriate combination of modern and
traditional materials has caused problems, including timber decay and damp.
Modern materials, such as cement and waterproof sealants can act as a barrier
to the wall’s natural ability to breathe, trapping moisture within the wall which
can cause erosion and breakdown of stone. Therefore, in recent years, there has
been a return to the use of lime for plasters, mortars and renders and an interest
in natural insulation materials that will help to regulate internal humidity.
INTERNAL FACE
EXTERNAL FACEB
WIND DRIVEN RAIN
VAPOUR IN
In a lime bonded
mass wall, moisture
will move into and
be released by
the wall, leaving
WETTING
LINE
the structure dry.
DOMESTIC
B
VAPOUR LOADING
B
Problems arise when
modern materials are
VAPOUR RELEASE
introduced which act
as a barrier to the
walls’ ability
to breath.
VAPOUR OUT
B
GROUND
Damp
Traditional houses, with open fires and looselyfitting doors and windows were deliberately
well ventilated. Reducing unwanted ventilation
by draughtproofing is the most effective way of making a house more comfortable in winter and reducing the energy bills, and it is usually
possible to make considerable improvements
without encountering any problems. However,
dampness caused by condensation and the
black mould that accompanies it can occur in
winter with all houses that are inadequately
insulated, heated and ventilated. It happens
when warm moist air is cooled by contact with
cold surfaces and the water vapour that it is
carrying condenses as liquid water.�
Although it may not be possible to eliminate it entirely, there
are some common sense measures that can reduce the risk of
condensation occurring such as:
�
• reducing the amount of moist air inside the house
�
• keeping the outside of the house in good repair, as
damp walls retain less heat and so are more susceptible
to condensation
• if possible provide a constant low level of background
warmth to keep the surface temperature of the walls high
enough to avoid condensation
• Ventilate the house regularly
• If the problem is severe consider the use of de-humidifiers,
however, be aware that unless they are used in a well-sealed
room they may be ineffective
Maintenance
Checklist
All buildings require regular maintenance as well as periodically needing
more substantial repairs. If regular maintenance is not carried out this can
result in further costly damage being caused. It is therefore a good idea to
regularly assess a building thoroughly and systematically, starting with the
roof and working downwards. The table below provides some guidance as to
what to check when examining your building, this is not however intended
to be a fully comprehensive list and it is advisable for all repair works to be
carried out by a suitably skilled tradesperson.
Sometimes it is not possible to make a permanent repair immediately
because of cost, difficult access or bad weather. Therefore, it is usually better
to make a quick temporary repair that keeps the building weathertight rather
than allow more serious problems to develop because timbers have become
saturated or water has begun to enter the walls. Bitumen coatings and other
solutions that may make the re-use of materials and permanent repairs more
difficult should be avoided, but temporary works using roofing felt, plywood,
flashband or plastic guttering can be effective in keeping the weather out.
What should I
check for?
How often
should I check?
Suggested
repair
What will happen
if I leave the issue
unattended?
Date
Inspected
WINDOWS AND DOORS - see Windows and Doors section for more details on repairs
Condition of paintwork,
putty and sealants to
external joinery and
cast iron, including any
dormer windows and less
accessible areas
Touch up any defects
and fill any gaps
Yearly summer
Draught seals around
doors and windows are in
good condition
If it is more than about five
years since the joinery and
ironwork was last painted,
preparation and complete
re-painting may be needed
Water could
enter and rot
the timber
Repair or replace
ROOF DRAINAGE – see Rhones and Downpipes section for more details on repairs
Blocks or leaks
Staining or damp
patches on walls
Broken brackets,
missing end caps, rust,
splits in downpipes
Every 6
months,
particularly
after
autumn
Clean out leaves and
other debris
Repair or replace if
required with matching
materials and design
Leaks can
eventually wear
away mortar
and can cause
damp, rot or even
subsidence
ROOFS – see Roofs and Gable Detailing sections for more details on repairs
Slipped, broken or
missing slates
Missing or damaged
ridge tiles
If there are cast-iron
rooflights - missing
putty, cracked glass, or
corroded frames
If there are lead flashings
- check to ensure they
are not loose or cracked
Yearly
and
after
storms
Re-fix, repair
or replace with
matching if
necessary
Water could
enter loft space,
damaging timbers
Action
Date
What should I
check for?
How often
should I check?
Suggested
repair
What will happen
if I leave the issue
unattended?
CHIMNEYS - see Chimneys and Gable Detailing sections for more details on repairs
Eroded stonework or
pointing, cracked render,
or cracked mortar around
chimney cans
Damaged chimney pots
If chimney has been
sealed ensure that
the flue (lumb) is still
adequately ventilated
Every 6
months
from ground
level, with
a close
inspection
every year
to five years
depending
on
accessibility
Wide or recent cracks
should be investigated
further by professional
Replace with similar
Consider the use
of vented cowls or
Chinese bonnets to
keep rain and birds out
of the flue
Water ingress,
which could
cause damp
EXTERNAL WALLS - see External Walls section for more details on repairs
Check the outside walls
(stone or render) for
cracks, bulges and areas
of eroded or cracked
pointing or render
Not usually a cause for
concern, however, if any
changes are noticed
between inspections seek
professional advice
Yearly after winter
Check the condition of
lime harl to establish
whether re-limewashing is
needed
If cement harl is cracked
a temporary repair may
be achieved using mineral
paint to close small cracks.
If cracking is extensive a
long-term repair may involve
removal and replacement
with a lime harl or render
Water could be
drawn into the wall
behind, causing
damp issues
Re-coat if necessary should only be needed every
few years, depending on
exposure to the weather
EXTERNAL ELEMENTS
Clear leaves and other
debris
Rainwater gullies at ground
level are functioning
Ground levels around the
house are higher than the
inside floor levels
Yearly
Airbricks providing ventilation
are clear
If levels are higher
outside consider whether
it might be feasible to
lower them
Water could rise up
the walls and cause
damp
Ventilation under
the floor will not be
adequate
Clear any debris
LOFT SPACES & INTERNAL SURFACES
Damp in the loft,
particularly on timbers
Yearly
Damp patches on
bedroom ceilings
If there are woodworm
holes check for fresh
wood dust, which would
be evidence of an active
infestation
Yearly spring
Could indicate the roof
has been leaking, a
problem with chimneys or
a condensation problem
Seek professional advice
A high incidence of wood
boring insects is often
an indication of raised
humidity levels and
additional ventilation may
be needed
Timbers could rot/
damp issues
Date
Inspected
Action
Date
repairs
Gable detailing
Many roofs in Orkney have skews at the gables rather than having the
slates overlapping the wall. This helps to protect the roof from wind
damage, but does create a more complicated junction between roof and
wall. Early buildings have a crowstepped parapet wall half the width of
the gable wall below, rising above the roof. The slates are carried partway across the top of the gable wall and butted up against the inner
face of the parapet, with mortar used at the junction. Many of these
buildings had their walls, including the crowsteps, finished with lime
harl and limewash, which made it easier to make the junction watertight.
In many cases a shallow slope on the crowsteps in the direction of the
roof minimised streaking and staining on the gable wall.
Later buildings have plain stone skews at the gables, partly overlapping
the slates and bedded on mortar. Today many of these have been
replaced by concrete, cast in-situ using timber boards as shuttering.
Although this is an easy solution, thermal movement means that some
cracking is likely over time and repairing or replacing cast concrete
skews may be difficult.
Gable detailing when
re-roofing
CHIMNEY CANS
HAUNCHING
CHIMNEY COPE
Details for stone
skew copes
CHIMNEY STACK
SKEW COPE
KNEELER
GABLE END
SKEW PUTTB
Details for a skew cope and
adjacent leadwork
SLATES
VAPOUR
CONTROL
LAYER
SARKING
DRIP MOULD
LEAD COVER
FLASHING
SECRET
GUTTER
5 DEGREE SLOPE
LEAD
DRIP
GABLE
TILTING FILLET
ROOF SIDE
GABLE
SIDE
The skew copes will need to be removed and
then re-bedded if a building is re-roofed.
New sandstone copes can be provided if the
originals are missing, and they should overlap
the top of the wall slightly, have their top
surfaces slightly sloped away from the gable,
to discourage water from running down the
wall. As well as being bedded in mortar, hidden
stainless steel fixing pins must be used to
hold them securely in place. Some nineteenth
century buildings have skew putts or kneeler
stones at the bottom of the copes, preventing
them from sliding down the roof slope. These
need to be securely built into the wall and if
there is any doubt about their stability may
need the addition of hidden fixings.
It is now common to install leadwork to
waterproof the junction between the skews
and the roof. One way is to create a small lead
gutter at the side of the skews. This alters the
appearance of the roof and if the building is of
historic interest alternatives, such as the use of
hidden lead soakers, should be considered.
sources
of further
information
Orkney Islands Council
www.orkney.gov.uk
Development Management
Building Standards
Kirkwall Townscape Heritage Initiative
Historic Scotland
www.historic-scotland.gov.uk
Free downloadable publications on
conservation, repair and maintenance
‘Inform’ Guides
Technical papers
Technical conservation knowledge base
Information on Listed Buildings
The Building Conservation Directory
www.buildingconservation.com
Products and services, articles on
conservation issues
The Society for the Protection of Ancient
Buildings
Includes SPAB in Scotland
www.spab.org.uk
National amenity society providing
technical advice. On-line shop includes
technical pamphlets and guides.
The Lead Sheet Association
www.leadsheetassociation.org.uk
Trade body that provides guidance on the
use of lead for flashings and roofing and
has technical officers who can provide
advice on specific projects
National Library of Scotland Map Images
maps.nls.uk
Includes high resolution images of early
maps of Orkney.
Institute of Historic Building
Conservation
www.ihbc.org.uk
A professional body representing building
conservation practitioners, including
local authority staff. Web site includes a
technical bibliography and a searchable
archive of ‘Context’ magazine.
Orkney Heritage Society
www.orkneycommunities.co.uk/ohs
A charitable body with wide-ranging
objectives that include the encouragement
of high standards of architecture and
planning in Orkney.
If you require this document in another format please contact the
Kirkwall Townscape Heritage Initiative on 01856 873535.