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Insulating Your House
While previous
generations may have been content to live in drafty houses, most people now want
comfortable warm houses. A healthy house today is well-sealed, well-insulated
and properly ventilated.
A well-insulated
house is a bit like dressing for the weather.A wool sweater will keep you warm
if the wind is not blowing and it is not raining. On a windy, rainy day, wearing
a nylon shell over your wool sweater helps keep you reasonably dry and warm. A
house is similar. On the outside, underneath the brick or siding, there is an
air barrier that does the same thing as the nylon—it keeps the wind from
blowing through.Then there is the insulation (like your sweater) and then a
vapour barrier, which helps keep moisture away from the house structure where it
can do damage.
Signs of insulation problems
In the
winter
 | walls cold to touch
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| cold floors
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| high heating costs
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| uneven heating levels within building
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| mold growing on walls
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In the summer
| uncomfortably hot inside air
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| high cooling costs
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| ineffectiveness of air conditioning system
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| mold growing in basement
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Insulation effectiveness
R-values—and
their metric equivalent, RSI-values—are a way of labeling the effectiveness of
insulating materials.The higher the R-value or RSI-value the more resistance the
material has to the movement of heat. Insulation products sold in
Canada
are labeled with R
and RSI-values. Provincial building codes specify minimum R (or RSI) values for
new construction, with different values for different applications. It is
important to know what your local building code requires when planning new
construction.
Note that the
way the insulation is installed plays a large role in its effectiveness.
Compressing the insulation, leaving air spaces around the insulation and
allowing air movement in the insulation all reduce the actual R-value of the
insulation.
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Insulation
material
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R/in.
(RSI/m)
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Appearance
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Advantages-
Disadvantages
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Batt
type
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Fibreglass
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3.0-3.7
(21-26)
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All batts come in plastic wrapped bales.The
products are like fibrous blankets, about 1.2 m
(48 in.) long and wide enough to fit snugly
between wall studs.
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Readily available
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Mineral wool
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2.8-3.7
(19-26)
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Same as fibreglass
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Somewhat better fire resistance and
soundproofing qualities than fibreglass
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Cotton
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3.0-3.7
(21-26)
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Not readily available
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Loose
fill
(All loose fill typically requires a professional installer.)
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Fibreglass
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3.0-3.7
(21-26)
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A very light fibrous fill, usually pink or yellow
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Can be affected by air movement in attics
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Mineral fibre
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2.8-3.7
(19-26)
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A very light fibrous fill, usually brown
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Cellulose fibre
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3.0-3.7
(21-26)
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Fine particles usually grey in colour, more dense
than glass or mineral fibre
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Provides more resistance to air movement than
other loose fill insulations. Can have settlement
problems if not installed properly.
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Board
stock
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Type I and II
(expanded)
polystyrene or EPS
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3.6-4.4
(25-31)
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White board of small (about 8 mm—0.3 in. -diameter) foam beads
pressed together
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Typically no HCFCs used in production.
Must be covered.
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Type III and IV
(extruded)
polystyrene or XPS
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5.0
(35)
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Commonly blue or pink homogeneous foam board
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Works well in wet conditions, can act as a vapour retarder.
HCFC (an ozone depleter and greenhouse gas) usually
used in production. Must be covered.
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Rigid fibreglass
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4.2-4.5
(29-31)
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A dense mat of fibres, typically less rigid than
the polystyrene
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Drains water away. Sometimes hard to find.
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Rigid mineral fibre
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4.2-4.5
(29-31)
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See rigid fibreglass above
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Drains water away
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Polyisocyanurate
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5.6-7.7
(39-53)
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Foil-faced rigid foam
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HCFC usually used in production
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Spray
applied
All spray-applied insulations fill cavities very well .They must be
applied by specialized contractor.
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Wet spray cellulose
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3.0-3.7
(21-26)
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Fine particles held in place by a binder
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Polyicynene
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3.6
(25)
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A soft, spray foam that expands into the cavity
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Can act as the air barrier.
Must be covered.
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Polyurethane
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5.8-6.8
(40-47)
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A foam that expands into the cavity and sets
up fairly rigid
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Can act as the air barrier and vapour retarder HFC used in
production must be covered.
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Effective insulation systems
Effective
insulation systems slow the movement of heat and deal with the movement of
moisture at a reasonable cost.To do this they have:
| An air barrier which prevents the movement of
interior or exterior air through the system.
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| Carefully filled cavities which leave no gaps in
or around the insulation and which do not compress the insulation.
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| A minimum of thermal bridges.These are parts of
the wall that, with a lower R-value, extend from the warm side to the cold
side of the insulation, giving heat an easy escape.The structural members in
the wall will often be thermal bridges.
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| A vapour retarder, such as polyethylene sheeting,
which prevents moisture from moving from warm interior spaces into a colder
building envelope where it could condense.
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| Drying potential, which is the ability of the
insulated assembly to release any moisture that gets into the system.
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Wall insulation for new construction
Typically this
is a wood-frame wall with the potential for insulation in the stud cavity (batts
or spray-applied) and on the exterior face of the studs (rigid insulation). See
the attached sketch of an example. During planning and installation note that:
| The vapour retarder should be at or near the
inside surface of the insulation and would most commonly be 6 mil
polyethylene sheeting at the inside face of the studs or vapour retardant
paint on the finished drywall.
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| The air barrier can be provided by the
polyethylene vapour retarder, by the interior drywall or by air barrier
sheeting on the exterior face of the studs. In all cases, the air barrier
must be carefully detailed to be continuous at all penetrations.
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| Adding rigid (board stock) insulation to the
outside face of the studs minimizes thermal bridging as does spacing the
studs at 610 mm (24") rather than 406 mm (16") where possible.
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Wall insulation for existing construction
The two most
common wall types are wood-frame and solid brick. In a woodframe wall,
insulation (loose fill and some foams) is typically blown into the cavities
through holes that have been drilled through the drywall or siding. In solid
brick the largest cavity is usually 25 mm (1 in.) wide, which is not enough for
any significant increase in R-value.The builder must create a cavity. Usually, a
new cavity wall is built inside and insulated as a new wall, or board stock and
new siding are applied to the exterior.When planning a cavity wall retrofit
remember that:
| The cost of getting at and repairing the walls is
a significant part of the work and cost of the project.
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| Both air and vapour barriers are required.The
interior painted drywall can be both an air and vapour barrier, but details
at windows, electrical outlets, floors and other penetrations must be done
carefully to reduce air movement through the wall as much as possible. Air
movement can lead to mold growth and decay of the walls as well as loss of
insulation efficiency.
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| An insulation must be selected that will
completely fill the cavity and not settle. Some insulations, such as foams,
can provide reasonable air barriers themselves.
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Attic insulation
The attic is
often the most cost-effective place to add insulation. Usually, a contractor
blows loose fill into and over top of the ceiling joists. For the
do-it-yourselfer, batts laid sideways on existing insulation are an easy
alternative.
| The air barrier at the ceiling line must be tight
to ensure warm moist air from the house does not get into the cold attic and
condense in the winter. Check ceiling light fixtures, the tops of interior
walls and penetrations such as plumbing stacks for air leakage.
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| Ensure that soffit venting is not blocked by
added insulation; baffles may have to be installed.
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Basement insulation
Basement walls
are unique because they must handle significant flows of moisture flows from
both inside and outside the house.The preferred method, from a building science
perspective, is to insulate the wall on the outside with rigid insulation
suitable for below-grade installations—such as extruded polystyrene or rigid
fibreglass. The advantages are:
| Insulating the outside of the basement works well
with dampproofing and foundation drainage. Rigid fibreglass or mineral wool
acts as a drainage layer, keeping surface and ground water away from the
foundation.
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| The basement walls are kept at room temperature
protecting the structure, reducing the risk of interior condensation and
increasing comfort.
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The
disadvantages are the disturbance of landscaping, the need to cover the
insulation above grade, and the relatively high cost.
Interior
insulation can be used.This can be done when finishing the basement by using
batt insulation in the stud cavities or by installing extruded polystyrene and
strapping on the face of the perimeter walls. If the basement won't be finished,
install rolls of polyethylene-encapsulated fibreglass over the wall.The
advantages of interior installation are cost and ease of construction.The
disadvantages of interior installations are:
| The basement walls are now at the temperature of
the soil or the outside.Any moist air moving through the wall from the
inside will condense on the wall.
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| Usually there is a moisture barrier against the
foundation wall and a vapour retarder on the room side of the insulation. As
a result, the wall has poor drying potential.
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Never apply
interior insulation to a basement with moisture problems. Fix the moisture entry
problems before insulating.
Is it cost-effective to insulate?
The right
insulation system can save you money, reduce the amount of energy you use and
make your home more comfortable. Keep in mind that installation costs (including
changes to the framing, cladding, and finishes) are usually the most expensive
part of an insulation project. The local climate has an impact on the
cost-effectiveness of any insulating project.
Check the cost,
heat loss and heat gain of all the available options. Review all details to
ensure that moisture movement is handled correctly.You can then select the right
insulating system.When in doubt, consult a professional.
The final analysis
If your home is
poorly insulated, it usually pays to upgrade the insulation. If you are building
a new home, it makes sense to insulate well now so you don't need to retrofit
later.
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