Practical Conservation Guide for Heritage Properties
Insulation
In this guide:
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Typical Energy Problems
Typical Energy Solutions
Planning & Assessment
Types of Insulation
 Batt Insulation
 Rigid Foamboard Insulation
 Blown-in Insulation
 Polyurethane Spray Foam
Insulation
Risks Posed by the Addition of
Insulation
Initial Areas to Focus Thermal
Efficiency
 Attic Insulation
 Windows & Doors
Considerations for Insulating Brick
Walls
 “Breathing” Buildings
 Thermal Mass
 Environmental Influences
 Damp
 Thermal Bridges
Solid Brick Wall Insulation
 External Insulation of Solid Brick
Walls
 Interior Insulation of Solid Brick
Walls
Brick Cavity Wall Insulation
 Adding Insulation to Brick Cavity
Walls
 Insulating the Cavity
Masonry Deterioration
Financial Implications and Payback
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Introduction
Many of the Region of Waterloo’s heritage buildings
were constructed before modern heating, ventilation
and air conditioning (HVAC) systems were invented.
Older buidlings were built to “breathe” as opposed to
the current method of construction that aims for airtight
structures with mechanical air circulation. Although, the
use of insulation was limited, many old buildings
incorporated passive energy features to help structures
hold heat in the winter and stay cool in the summer.
Heritage property owners wanting to improve the
comfort and energy conservation of an older building
can often do so by cafefully upgrading the thermal
efficiency of a historic building’s envelope. Increasing
the thermal efficiency of a building envelope may be
achieved by adding insulation to walls and roofs. It is
important, however, that modifications that improve
energy efficiency do not alter the historic character of a
structure and that methods and materials used do not
create future maintenance problems. Traditional
building assemblies that breathe (transpire) require a
different approach from modern ones that are sealed
and need help to breathe. New technologies offer ways
to improve the performance of old building envelopes,
while retaining their character and improving energy
performance.
This Practical Guide provides advice on the various
methods that can be undertaken to add insultation to
your heritage building. It should be noted, however, that
heritage conservationists have differing opinions about
the best methods and materials used to insulate older
buildings.
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More research is needed to fully understand the passage of moisture thorugh buildings and how
certain forms of construction and materials can mitigate these risks. Primarily, English Heritage’s
Energy Efficiency and Historic Buildings guides were relied upon given the heritage expertise of the
organization and the recent publication date. A number of additional sources were also consulted and
are included in the references list at the end of this guide to help you choose the most informed
approach to insulating your heritage building.
Typical Energy Problems
Addressing the typical energy problems experienced in detached structures built pre-1950 could
significantly increase the thermal performance of your building. Common sources of heat loss include:
 Large air leaks (i.e. around windows and doors)
 Poor attic insulation
 Walls with little or no insulation
 Uninsulated foundations
 Uneven heating of rooms
Typical Energy Solutions
Typical energy solutions to heat loss in detached structures built pre-1950 include:
 Air sealing. Ask a certified energy advisor to show you how your home is performing using a
blower door test, an effective and affordable way to visualize air leakage. Fix leaks by sealing
and caulking.
 Improve attic insulation
 Add insulation to walls (options are discussed throughout this guide based on construction
type)
 Insulate the top of the basement wall
 Close fireplace dampers when not in use
 Upgrade duct work
You can use the Green Home Planner, an online calculator that allows you to compare the cost of
savings of various renovation types. This is a helpful tool to use to determine how much energy
savings you can accumulate through improving the insulation in your heritage building and if it will be
worth the effort and expense.
Planning and Assessment
Before you decide to improve the thermal performance of your heritage building by adding insulation,
it is important to asses the structure to determine:
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The heritage significance of the building and the anticipated impact of the intervention on its
heritage value
The construction and condition of the building
The existing hygrothermal (movement of heat and moisture through buildings) behaviour of
the building
If the effort and impact of improving energy performance will be worth the cost
The technical risks associated with the chosen method
Considering each of these points will help to identify if insulation should be added to your building
externally or internally, and will ultimately reduce the risk of accidently creating long-term
problems.
Types of Insulation
There are a number of different types of insulation to choose from when improving your heritage
building’s insulation. The three most common are batt, rigid and blown-in. All three are typically
inserted into the air space between the inside or outside surfaces of wood or masonry walls.
Another frequently used type is polyurethane spray foam. Each is quite different and should be
explored to determine which has the propreties best suited to your particular building.
Batt Insulation
Batt insulation is made from fiberous material attached to a paper or foil backing. Manufactured
and green options for batt insulation are discussed below.
Manufactured Options
Two readily available manufactured batt insulation products
include:
1. Fibreglass. Commonly found, this pink, white or yellow
material is composed of finely woven glass. It is often faced
with kraft paper, and in some products asphalt is added to
the paper and coated with foil in an effort to stop the
movement of moisture.
2. Roxul mineral wool insulation. This material is made from
basalt rock and slag. Roxul (the company name) has good
fire proofing capabilities and is considered by some
professional heritage conservationists to be the best
candidate of all batt insulations to recover after being
saturated with water.
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A Note on Health and
Safety Precautions
Health warnings accompany
both fibreglass and Roxul
insultations due to the potential
inhalation of these materials.
An approved catridge type
respitator (rated for lead and
asbestos) should always be
used when handling these
materials.
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Green Options
Recycled denim, sheep’s wool, hemp and flax represent ‘green’ options
for batt insulation. Although these options are effective alternatives they
are also expensive and can be difficult to obtain.
Rigid Foamboard Insulation
Rigid foamboard insulation is made from expanded polystyrene and other
materials. Due to the thin, compact nature of this type of insulation, it is
best used in the attics of one-and-a-half storey houses or on walls where
there is little room for ventilation once the insulation has been added.
Two types to look for are Dow’s Blue and Owens Corning’s Pink. These
products have an insultating factor of R5 per inch and can be effectively
used in newer, air tight buildings.
R-value is a term used to describe the thermal resistance to heat flow. The
higher the R-value of an insulation product, the more effective the
insulation properties.
Blown-in Insulation
Blown-in insulation is made from loose fiberglass or cellulose, along with a
growing variety of alternative natural materials. These materials are
blown into the cavity of a wall through small holes drilled on the exterior.
When the work is complete the holes are patched using in-kind materials.
A draw back of loose insulation, particularly the type that is blown in,
stems from its tendency to settle and pack down over time, leaving a void
near the tops of the wall cavity where heat can escape. Two types of
blown-in insulation are discussed below.
Image: Types of insulation
(District of Columbia, 2010, p. 6)
Blown-in Cellulose
Blown-in cellulose is simply shredded paper product. It easily fills hard-to-reach voids due to its
composition of light, puffy particles. The problem with this material is that air moves through it
easily as it is low-density. If there is any condensation as air passes through the walls, water will wet
the cellulose and it will no longer function well as insulation. For this reason, blown-in cellulose
should generally only be used in very dry locations, such as attics, where it can be easily removed if
necessary. There have, however, been some positive reviews of this type of insulation that
incorporats a borax additive to help the cellulose from slumping in the wall cavity.
Blown-in Fibreglass and Vermiculite
Similar to cellulose, these materials are non-combustable, effective insulators. Blown-in fibreglass is
very light and puffy, composed of glass fibers that use a high percentage of air space. Vermiculite is
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a flaky, natural rock expanded to a pebble-sized mix that insulates similiarly to blown-in fibreglass.
Both of these materials allow for air to pass through them easily, like celluslose. As a result, they too
have the potential to become watterlogged if exposed to condensation, although to a lesser extent.
Polyurethane Spray Foam Insulation
Polyurethane spray foam is a commonly used alternative to traditional building insulation, such as
fiberglass batts. It is a two-component mixture of isocyanate and polyol resin that is combined and
applied through the tip of a gun to form an expanding foam. It can be sprayed continuously at the
floor joists, floor slabs, wall cavities and around window and door perimeters to ensure the
continuity of the air barrier and insulation system.
Risks Posed by the Addition of Insulation
Altering the thermal performance of an older building
can include some risks, most notably the creation of
condensation on a building’s surfaces or between walls
(interstitial). This can cause health problems for
occupants as it can lead to mold formation and decay of
the building fabric. Avoiding the risk of condensation
can be a challenge as a number of variables must be
considered.
Many heritage practioners recommend the addition of
insulation that has hygroscopic properties (a substance
that readily absorbs moisture), which acts as a buffer
during flucuations in temperature and vapour pressure
and reduces the risk of surface and interstitial
condensation.
In addition to consideration being given to the
movement of water vapour through a building, other
factors to be considered to determine the best
approach include the type of heating system and the
orientation and exposure of the structure.
The impact on the existing materials must also be
considered. The addition of some types of insulation
(i.e. batt and rigid) will require that either exterior or
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Image: Best locations in a building to add insulation.
1. Ceilings below an unheated area; 2. “Knee” walls of a
finished attic-level room; 3. Floor of a crawl attic; 4.
Sloping portion of the roof in a finished attic (leave air
space between insulation and roof); 5. Exterior walls; 6.
Floors above cold crawl spaces, floors above a porch or
unheated garage; 7. Walls of a heated basement
(Hanson & Hubby, 1983, p. 217)
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interior surface material be removed. In most cases, this will destroy the existing fabric and possibly
valuable character-defining architectural elements. If this is the case, alternative forms of insulation
should be explored, such as blown-in insulation. If the surface material is already missing or damaged
beyond repair, installing these types of material may be appropriate.
Initial Areas to Focus Thermal Efficiency
Most free-standing buildings lose about 20-30% of their heated or cooled interior air through walls
and foundations, with the remainder of heat lost through windows, doors and roofs. Given the
problems associated with installing insulation in existing walls and the relatively minor increase in
thermal efficiency often achieved, it is usually best to concentrate energy efficiency measures on the
attic, windows and doors if possible.
Attic Insulation
Heat rises, and therefore the best, most cost effective place to consider putting insulation in a
heritage building is the attic to limit the espcape of rising heat. Batt, rigid and blown-in insulation can
usually be installed easily between attic rafters, often without professional assistance. You must have
proper ventilation in your attic to avoid condensation, so be sure not to place insulation over the soffit
vents.
A great deal of heat loss occurs through ceilings located immediately below roofs, which can lead to
damaging ice dams forming at the cold projecting eaves. Ice dams can force water from thawing
rooftop snow up under the roof covering above to spill down through the eaves or into the interior.
Avoiding problems like this is another reason to increase the thermal performance of your structure’s
roof.
Vents
Small, round micro vents, easily found at most hardware stores, are helpful to incorporate into the
soffit of your heritage building to allow air to flow into and out of the attic. These vents can be painted
to blend into the wodden soffit and installed using a circle cutting saw on the end of a drill. The vents
should be added to the soffits between the roof rafters and roof joists at each bay around the house.
This will allow for balanced ventilation and aesthetics around the building.
Windows and Doors
When seeking to upgrade the thermal efficiency of your building, consider installing weatherstripping
and caulking around doors and windows to reduce infiltration through cracks and joints. If the existing
weatherstripping is deteriortated, it should be replaced in-kind. If it is missing, or never existed, new
weatherstripping can usually be added without altering the existing character of the door or window.
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The same can be said for the addition of synthetic caulking when sealing the joints between window
and door frames. Care should be taken when selecting caulking to ensure it is chemically compatible
with the surrounding materials and is the right colour to blend with the existing walls, windows and
doors.
Storm windows and doors can also be installed to decrease thermal conductivity through the glass.
Storm windows may be the most visible features in an insulating program and should be designed
with care. It is recommended that storm windows and doors be selected to match as closely as
possible to the size, shape, profile, colour and other character-defining features of the existing
elements and that clear glass, rather than reflective or tinted glass, be used. The same consideration
should be given to interior storm windows, however, because they are installed inside, a single pane
of glass can be used rather than matching the panes of the existing window. Care should be taken to
ensure that the window is properly vented to avoid condensation.
Mixing building components made for sealed building envelopes (such as modern plastic and
aluminium replacement windows) with traditional building envelopes should be avoided. The effects
on moisture movement between incompatible materials could encourage moisture accumulation
leading to rot and decay of some parts of the building envelope. For information on repairing older
windows, please refer to the Practical Guide: Windows, Shutters & Doors.
Considerations for Insulating Brick Walls
Due to a current lack of information and the potential for damage, there is still a great deal of debate
within the building design and construction community related to the addition of insulation to
buildings with solid masonry walls in cold climates. The main challenge with insulating solid masonry
walls is finding a way to improve performance while not comprising durability. In some cases the risks
of adding insulation to solid walls will outweigh the benefits. If this is the case, alternative ways of
improving energy effiency may be appropriate.
The following sections discuss the current thinking on the addition of insulation to the interior and
exterior of older brick buildings. Much of this advice similarly applies when insulating traditionally
constructed wood frame structures.
“Breathing” Buildings
Most heritage buildings are constructed of permeable materials and do not include barriers to
moisture movement commonly found on newer buildings. These barriers include air cavities, rainscreens, damp-proof courses, vapour barriers and membranes. As a result, the permeable materials
that compose historic buildings tend to absorb more moisture that is ultimately released by internal
and external evaporation. When older buildings are performing as they were designed to, evaporation
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will keep dampness to a manageble level, preventing decay. For this reasons, older structures are
often referred to as “breathing” buildings.
Impermeable Materials
Adding materials and systems that do not allow a building to breathe can exacerbate existing
problems or create new ones. Incompatible materials and systems that should be avoided include:
 Closed cell and extruded plastic insulation
 Plastic vapour barriers
 Cement or acrylic based renders
 Cement pointing
 Plastic based external wall paints
 Vinyl wallpaper and emulsion paint
The use of any of these materials on an outside wall will trap moisture within the wall, leading to
damp and decay, as well as making the walls feel cold and clammy. Installed on the inside, they may
do less damage, but will also reduce the ability to manage moisture levels in the internal air. Both of
these occurences can reduce the comfort of the building’s residents, who may compensate by turning
the heat up, leading to wasted energy.
Thermal Mass
Masonry buildings, especially those with thicker walls, have high thermal capacities. This means that
they can absorb heat over time and release it slowly as the outside temperature cools. In the summer,
when strong sun can cause very high temperatures, the thermal mass of a brick building’s walls cool
the interior by absorbing the excess heat during the day and releasing it slowly during the night as the
outside air cools. This phenomenon helps to reduce the need for air conditioning.
Environmental Influences
The location, orientation and exposure of your heritage building’s elevations to direct sunlight, wind
and rain have important influences on a building’s condition and performance. Different parts of a
building are affected by different micro-climates. For example, north and south facing elevations are
exposed to varying degrees of sunlight, shadow and exposure to precipitation and wind. Such
variations in microclimate need to be considered before determining an approach to insulation.
Damp
vapour
generated
a building.
do not
intointerstitial
consideration
how insulation
Most types
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arewithin
designed
to limit They
heat loss
andtake
avoid
condensation
from water
vapour generated within a building. They do not take into consideration how insulation can affect the
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movement of water and salts already present in an older brick wall. For insulation applied both
externally and internally, it is advised that it should not be applied to damp walls. As well, adding
vapour barriers and materials that resist the passage of water vapour are not generally appropriate
for use on older buildings as they will trap moisture, increasing the risk of decay.
Insulation can:
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Make existing moisture problems worse
Create new problems, such as the displacement of damp and salts and the decay of timbers
in contact with walls
Create health risks for residents (i.e. mould growth)
Be impacted by moisture that can reduce its performance
Walls that have been damp for a long time can take years to dry out completely. The selection of
insulation and the method chosen to install it should take into account the drying-out process, both
before and after installation, and the presence of remaining damp and salts.
Thermal Bridges
Thermal bridges occur where there are gaps in insulation due to the presence of other building
mateirals. When insulation is added externally these weak points are typically around windows and
doors, and with internal insulation they may occur where floors meet external walls. These areas
with reduced or no insulation will be colder and will attract relatively more condensation. This can
result in local decay, especially to wood members and finishes.
Care should be taken to avoid thermal bridges around window and door openings by installing
additional insulation in the gaps between building materials. However, this can increase the cost of
both the design and installation. In some cases it may be impossible to add the level of insulation
necessary, so depending on the potential severity of the consequences, it may be wiser not to install
insulation at all.
Solid Brick Wall Insulation
External Insulation of Solid Brick Walls
Structures built pre-1900 were often constructed with solid, load-bearing, clay-fired exterior brick
walls that were not insulated. This type of construction can be difficult and costly to insulate. Walls
from this era may have ‘beadboard’ insulation (i.e. expanded polystyrene [EPS]) between the
interior concrete block and drywall, batt insulation between studs inboard of the block backup,
and/or beadboard in the air space between the exterior brick and block backup. The insulation value
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provided is usually not at today’s performance
levels, but some of these structures are good
candidates to be over-clad with external
insulation so long as the heritage character of the
building will not be affected.
Generally, external insultation systems are
composed of an insulation layer fixed to an
existing wall with a protective render or cladding
installed on top to shelter the insulation from the
weather, impact or abrasion. These over-clad
approaches provide better energy performance,
more airtightness, and improved water
resistance. This method is suitable for buildings
without heritage designation and when changes
to exterior appearance are acceptable or desired.
Image: Illustration of the addition of a permeable insulating
solution with batts fixed to the masonry and finished with a
‘breathable’ lime render (English Heritage, 2012, p.14)
Physical Adaptation of the Building
The addition of external insulation will significantly alter the appearance of your building. It will
require an increase in the depth of walls along with changes made to the roof and wall junctions,
around window and door openings, and to the positioning of rainwater downpipes. While undertaking
these alterations, scaffolding access and possibly a temporary roof will be needed to reduce the risk
of water penetration.
For listed or designated heritage buildings, a heritage permit application may need to be submitted to
your municipality’s planning department or Municipal Heritage Committee before you undertake any
work to ensure that your plans respect the integrity of the structure. Please refer to the Region’s
Heritage Conservation Toolbox for a list of municipal heritage contacts.
Changes in the Movement of Moisture
It should be noted that the addition of vapour barriers to the outside or cold side of the wall should
be avoided as this will form a vapour trap, encouraging condensation and deterioration of the building
fabric. It is important that the insulation and protective finish installed externally have low vapour
resistance in order to retain the wall’s ‘breathability,’ and allow moisture to evaporate away without
causing any harm. A useful rule of thumb is that all layers of an insulated solid wall should become
increasingly more permeable from the interior to the exterior.
Materials
In order to prevent unwanted impermeable layers within the external insulation, the use of modern
closed-cell foam, other plastic-based insulations and protective finishes that limit the movement of
moisture should be avoided. A protective layer will also be needed to shelter the insulation from rain
and damage. External insulation should normally be considered as a two-component system where all
the layers need to work together.
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Useful materials for external insulation include:
 Hemp-lime composites
 Mineral wool
 Wood fibre panels
Effective moisture-permeable finishes include:
 Lime renders
 Rain-screen cladding (tile hanging, etc.) with lapped joints
Interior Insulation for Solid Brick Walls
In the case of heritage buildings where the
unique architectural features of the facades
are to be conserved, the addition of new
insulation is best placed on the interior side of
the building. This is often thought of as a
retrofit option to increase energy efficiency
and resident comfort. However, this method
does have some pitfalls. Brick that was
previously kept warm and dry by heat losses
will be colder following the placement of
interior insulation, which can lead to problems
such as condensation and freeze-thaw cycles
that can damage the bricks and supporting
framework.
Image: Illustration of rigid non-permeable insulation. A vapour
control layer is added to the interior room side face before
plastering (English Heritage, 2012, p. 16)
To allow the addition of a significant thickness
of insulation, it is usually placed between
timber studs or battens inside the wall, with a new internal finish applied to the timber structure.
Incorporating a vented airspace is one technique to keep bricks below the critical moisture content
level during the freezing and thawing cycles.
It is important to carefully consider the control of vapour from the warm internal air entering and
condensing within the insulation, or within vulnerable parts of the original solid wall.
Physical Adaptation of the Building
Similarly to external insulation, the design and installation of internal insulation should be undertaken
with care to avoid thermal bridging, especially surrounding windows and doors and wall and floor
junctions. It may also be necessary to relocate radiators, pipes, electric power outlets, light switches,
baseboards, plaster cornices, picture rails, window and door surrounds, built in furniture, etc. These
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features will likely be concealed or
disturbed by the addition of internal
insulation. Although it is possible to
replicate these details, the room
proportions will have changed as the side
walls of an insulated room will be shorter.
Careful attention should be paid when
designing this work to ensure that the
intervention does not significantly change
the character of the room.
Changes in the Movement of Moisture
The same rule of thumb as noted in the
section above applies to internal insulation: Image: Illustration depicting how to avoid a thermal break at the floor
all layers of an insulated solid wall should junction. Insulation should be added within the perimeter of the floor
zone and sealed to maintain air-tightness (English Heritage, 2012, p. 17)
become increasingly more permeable from
the interior to the exterior. To protect internal insulation from collecting condensation it is useful to
separate it from the warm, moisture-rich air of your building’s interior. To do this you will need either
the use of impermeable closed-cell foam insulation or an effective vapour control layer. A vapour
permeable system, like wood fibre, can also be used. That being said, effective vapour control is
difficult to achieve.
Air and vapour control layers are easily damaged by building users nailing through walls or through
the construction process itself. Any hole made will allow moisture vapour through in large quantites,
which will condense either within or adjacent to the insulation, leading to rot and decay. However,
many of these problems can be overcome by using insulation systems that are hygroscopic and
vapour permeable (i.e. wood-fibre).
Materials
Most insulation materials available can be used internally, taking into account the proper control of
vapour and avoidance of sources of dampness. All internal finishes can also be used, either to copy
the original or to introduce a new design.
New insulation products are always being developed, especially types with minimal thickness (10mm).
It is important to keep in mind that these products may only slightly reduce energy consumption and
can be expensive. However, they will help to make a room feel more comfortable by rising the surface
temperature of the walls and possibly reducing the occurrence of condensation. It is important to
understand the possible effects of your interventions at the design stage in order to avoid damage to
both the original and new historic building fabric.
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Brick Cavity Wall Insulation
This section provides guidance on how to improve the thermal performance of buildings constructed
with early forms of masonry cavity walls dating from before World War II.
Cavity or ‘hollow’ walls consist of two masonry leaves tied together but seperated by a continuous
airspace. The outer leaf acts as protection against the elements and the inner leaf serves as a dry
construction to support the interior walls. The two leaves are tied together to provide structural
stability. The cavity between the two leaves prevents moisture from passing from the outside to the
inside of the wall. This prevents damage from damp and decay to any woodwork or other decorative
elements in contact with the inner leaf. The cavity also allows for the evaporation of any
condensation or rainwater that penetrates the outer leaf and ensures a more even temperature
inside the building.
Many early cavity walls were tied together
with bricks bonded into both leaves making
them hard to distringuish from a
continuous cavity. Measurement of the
wall thickness and a careful assessment of
the construction should be carried out to
determine if the wall has a continuous
cavity.
A cavity will not be continuous if bricks are
used as ties. They create direct contact by
bridging the two leaves. This contact allows
moisture to transfer across the cavity and
results in the wall being similar to solid wall
construction rather then modern cavity
wall construction where metal or plastic
ties are used to prevent capillary transfer
of moisture across the cavity. Just like solid
masonry walls, early cavity walled buildings
are also ‘breathing’ structures, exchanging
moisture between the indoor and outdoor
environment.
Image: Illustration shows an early cavity with two brick leaves and a
bonding brick crossing the cavity. Often bonding bricks would be
disguised on the face-work with a snapped header matching the rest of
the brick cladding. The existence of a cavity can only be determined by
looking at the overall depth of the wall (English Heritage, 2012, p. 6)
Adding Insulation to Brick Cavity Walls
There are three ways to insulate an early cavity wall. The first two were discussed in the previous
section, Solid Brick Wall Insulation, and include external and internal insulation. But in some cases it
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may be useful to incorporate a combination of these methods:



External insulation
Internal insulation
Insulation within the cavity
Similarly to insulating solid masonry walls, a heritage permit application may need to be submitted to
your municipality’s Planning department or Municipal Heritage Committee before you undertake any
work to ensure that your plans respect the integrity of the structure if it is listed or designated. Please
refer to the Region’s Heritage Conservation Toolbox for a list of municipal heritage contacts.
Insulating the Cavity
Insulating the cavity of a wall can improve its thermal performance without impacting its appearance
or character. For this reason it is the preferred alternative when the technical risks can be overcome.
Currently the techniques used for insulating
existing cavity walls involve injecting or
blowing an insulating material into the
cavity. There are three general types of
cavity wall insulation that can be injected or
blown in:
 Mineral wool
 Beads or granules
 Foamed insulation
At present, there are no natural or
recyclable materials available that are
suitable for use as cavity fill insulation. The
products available now are not generally
very high performance insulators, especially
Image: Illustration of an early cavity wall with insulation
(English Heritage, 2012, p.15)
in narrow cavities. For this reason it is not
normally cost effective to install insulation in
cavities with a width of less than 50mm. Plus, with such narrow cavities there is an increased risk that
the insulation itself will allow water to cross the cavity to the inner-leaf.
Cavity wall insulation can be cost effective in some situations, but there are certain technical risks that
should be addressed before using this method. The suitability depends mainly on the exposure to rain
and the condition of the existing construction. The condition of the wall is critical as the addition of
insulation to a wall in poor condition will make the situation worse and could complicate later repairs.
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If there are any cracks spotted on the wall, they should be investigated. If the cracks are due to wall
tie corrosion, this should be repaired first as the addition of cavity insulation will make the situation
worse. Cavity walls with spalling on the brick faces should not be filled. Mortar joints should be full
and the pointing in good condition. Where bricks or stones have been used for tying between leaves
or where debris or mortar is blocking the cavity, problems may arise making cavity fill unwise.
It is recommded that cavity wall insulation be carried out by a certified installer who is required to
conduct a thorough survey of the cavity with a boroscope before any work is undertaken. There are a
number of potential problems that can make pre-1930s houses unsuitable for insulation and an
inspection can help to proactively identify these.
Although this method is the least visually intrusive of the three approaches to adding insulation,
retrofitting cavity insulation still requires drilling a number of relatively large holes in the brick or
stone façade. This can require skill to do well, and not all installers will be adequately trained. An
alternative approach involves removing bricks or stone and then replacing them on completion.
Physical Adaptation of the Building
Cavity insulation will require the services, ventilation ducts and flues to be sleeved where they pass
through walls. Electrical wiring within the cavity also needs to be relocated to prevent overheating.
Effects of Insulation on Dampness in Cavity Walls
Many heritage practioners report concerns that adding insulation to a cavity can reduce the
temperature of the outer leaf to the point where freeze-thaw cycles can damage the masonry. This
will accelerate damage to bricks, stones and mortar, notably where soft masonry walls have been repointed using inappropriately hard mortars. However, it is challenging to accurately determine the
likelihood that this will happen.
Masonry Deterioration
Masonry will be more resistant to deterioration if it absorbs less water. The more water within brick
pores typically means a greater risk for deterioration after exposure to freezing cycles. The wall may
experience more time at temperature levels supporting freeze-thaw deterioration of the brick after
insulating than it did in the past, so minimizing moisture is essential.
Moisture in brick masonry walls can come from different sources:



Water from rain will generally only dampen the exterior of the wall, which will dry out when
the rain stops if it is in good condition
Rising ground moisture can affect masonry walls if a damp proof course is not in place
Resident use internally, through breathing, cooking and washing
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A visual examination of parapets and chimneys, the wall components typically exposed to water and
freezing, can provide initial indications of how other wall areas might perform once they are made
colder by interior insulation. If parapets or chimneys are deteriorated, this might indicate the brick is
porous and susceptible to degradation. Establishing your brick’s water absorption potential through
material testing, regardless of its visual condition, should be considered early in the process.
Note: Avoid using vapour proof type insulations in direct contact with old masonry walls. Always leave
an air space between vapour-proof insulations and the masonry.
Financial Implications and Payback
The addition of external and internal insulation to older buildings can be expensive, and the time
associated with financial payback can be lengthy. It is key not to underestimate the costs associated
with the level of care that should be taken to avoid thermal bridges. Full payback periods can be 30+
years, but they can vary greatly between individual buildings.
As a result, in many cases it would not be worth considering the insulation of external walls until the
full range of easier and more immediate upgrades to older buildings have been done. These might
include repairing and draught-stripping windows and doors or insulating roofs and suspended ground
floors. Most of these types of upgrades will also have significantly fewer detrimental effects on the
character and cultural heritage value of historic buildings.
Summary
The base of knowledge surrounding the insulation of heritage buildings is progressing, enabling
practitioners to avoid problems associated with insulating solid and cavity masonry walls along with
wood frame buildings. This knowledge is furthering the effectiveness of retrofit strategies and is
continually being advanced as new lessons are learned from observing past retrofit projects.
References
If you would like to learn more about properly insulating your heritage building, please refer to the
following primary sources:
District of Columbia, Historic Preservation Office. (2010). “District of Columbia Historic
Preservation Guidelines: Energy conservation for historic buildings.”
http://dc.gov/DC/Planning/Historic+Preservation/Maps+and+Information/Policies+and+
Procedures/Design+Guidelines/Energy+Conservation+for+Historic+Buildings
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English Heritage. (2012). “Energy efficiency and historic buildings: Early cavity walls.”
www.english-heritage.org.uk/publications/eehb-early-cavity-walls/eehb-early-cavity-walls.pdf
English Heritage. (2012). “Energy efficiency and historic buildings: Insulating solid walls.”
www.english-heritage.org.uk/publications/eehb-insulating-solid-walls/eehb-insulating-solidwalls.pdf
R.E.E.P. Green Solutions (2013). “Green home planner.”
www.reepwaterlooregion.ca/info_green_home_planner.php
Additional sources:
Conrad, E. A. (1998, September/October). “Expert advice: Insulation.” Old-House Journal.
www.oldhouseonline.com/expert-advice-insulation/
Cooper, C. (2008/2009). “Attic insulation.” Edifice Old Home Magazine. Number 19, Winter, pp.38-39.
De Rose, D., et al. (2013, April). “Insulating older masonry buildings: Practical approaches for interior
insulation.” Construction Canada. http://www.constructioncanada.net/older-masonry-buildingsbenefits-risks-and-design-approaches-for-adding-interior-insulation/
De Rose, D., et al. (2013, March). “Insulating older masonry buildings: Insulation primer.” Construction
Canada.
District of Columbia, Historic Preservation Office. (2010). District of Columbia Historic
Preservation Guidelines: Walls and foundations of historic buildings.
http://planning.dc.gov/DC/Planning/Historic+Preservation/Maps+and+
Information/Policies+and+Procedures/Design+Guidelines/Walls+and+Foundations+of+Historic
+Buildings
Goncalves, M. D. (2002). “Insulating solid masonry walls.” Building envelope forum.
www.cebq.org/documents/Insulatingsolidmasonrywalls-BEF_000.pdf
Hanson, S. & Hubby, N. (1983). “Preserving and maintaining the older home”. New York: McGraw-Hill.
Kalman, H. (1979). “The sensible rehabilitation of older houses.” Prepared for Canada
Mortgage and Housing Corporation, Ottawa.
Linzey, R. (2008, Spring). “Heritage goes green: Upgrading your heritage home – Tips for conserving
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energy.” Heritage BC Quarterly. http://www.heritagebc.ca/resources/guides-tips1/upgrading-heritage-homes
O’Reilly, D. (2012, December 19). “Canadian heritage buildings – Both beauties and
beasts.” Daily Commercial News. http://www.dcnonl.com/article/id53295
R.E.E.P. Green Solutions (2013). “Energy profiles of houses by decades.”
http://www.reepwaterlooregion.ca/info_house_issues_by_decade.php
Stokes, P. J. (1977, Fall). “Insulation: Just a few words of caution.” Acorn, II(3).
Union Gas. (2013). “Energy conservation: Air sealing.”
www.uniongas.com/residential/energy-conservation/energy-savings/air-sealing
Alternate formats of this document are available upon request. Please contact Lindsay Benjamin
at [email protected], 519-575-4757 ext. 3210, TTY 519-575-4608 to request an
alternate format.
Disclaimer
This practical guide contains useful information on restoring and preserving heritage buildings, but it is
intended as a general resource only. Content from third parties with specific expertise has been heavily relied
upon and their original works have been acknowledged in the list of references included at the end of this
document. The Region of Waterloo has taken all reasonable steps to ensure the accuracy of the information
in this publication. However, it is recommended that building owners consult with trained specialists, such as
contractors, builders, plumbers, heating and air professionals and electricians, before undertaking any
renovations, repairs or construction on their properties. The Region does not assume responsibility for any
loss or damage resulting from adherence to the information in this practical guide.
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