Windows are an
important component of a home. In addition to enhancing the aesthetic beauty of
the house, windows can provide fresh air and ventilation to the home, allow day
lighting to brighten interior spaces and keep out harsh outdoor elements (wind,
rain, snow).
Buying new windows
can be a daunting task, especially for the uninitiated. Knowing the type of
window best suited for your home and geographic location can help you choose a
window that reduces direct drafts from air leakage and the potential for damage
from water leaks. It’s important to understand how windows perform with respect
to these factors. Equally important, knowing what to look for in a window can
help you avoid buying something you don’t need.
The performance of
windows sold in Canada is defined in a Canadian Standards Association standard
called CSA A440 (Windows). This standard sets the type of materials that are to
be used in the manufacture of windows and some minimum material properties,
such as thickness, hardness and durability. The A440 Standard also defines
minimum performance levels for windows evaluated under a standardized set of
conditions. The characteristics defined in the A440 Standard include:
All windows sold in
Canada must be evaluated for their performance level in air-tightness,
water-tightness and wind load resistance—the characteristics marked with an
asterisk (*) in the list. This About Your House focuses primarily on these
characteristics. Evaluating windows for the other characteristics is voluntary,
so not all windows are evaluated for their ability to resist, for example,
forced entry.
Why is an air
leakage standard so important? The uncontrolled movement of air into or out of
the house is a cost to the homeowner. For example, any cold outdoor air that
leaks into (air infiltration) the home must be heated to room temperature to
maintain the comfort of the occupants, so air infiltration is a heating cost.
The same problem occurs in air-conditioned homes in summer, when warm outdoor
air infiltrates, resulting in an additional cooling load.
When interior-conditioned
air (either heated for winter or cooled for summer) leaks to the outside, the
homeowner also pays the energy costs associated with the air leakage.
Windows are tested
for air leakage by applying a standardized air pressure (roughly equivalent to
a 40 km/h — 25 mph — wind) across a window of a standard size. The amount of
air that leaks through the window at that pressure difference is measured.
Windows are given
one of the following air-tightness performance ratings:
depending on the test result.
In general, fixed
windows tend to have higher air-tightness performance ratings because they
allow less air to pass through the unit than windows that open and shut. Slider
windows tend to be more leaky than casement windows. All windows sold in Canada
must at least meet the A1 performance level to comply with local
building codes.
A higher A
rating is a desirable attribute for a window if your home is located in a
region known to have frequent high winds or gusty winds.
The rated
performance only indicates the window’s leakiness relative to other products
evaluated. Installation procedures, manufacturing tolerances and other factors
also contribute to performance of an installed window.
Window units are
not evaluated when installed in a wall, so a window rated at a specific
performance level may not perform at that level when installed.
Window rating
programs are intended to allow consumers to compare similar products, not to
predict, for example, air leakage rates. The thinking is that, if one window
has a better air-tightness rating than another, it will have less air leakage
when installed.
Windows may also
allow water to leak into the house during rainstorms, leading to water damage
of interior finishes and potential mould growth. Because of this, all windows
sold in Canada are evaluated for their ability to resist water leakage and for
resistance to wind-driven rain. Water is continuously sprayed onto the outside
of a standard-sized window under standard temperature and air pressure
conditions.
The window is rated
in accordance with the highest air-pressure level for which no water leakage
occurs.
A B1 rating
is assigned to a window that exhibits no water leakage at a relatively low
air-pressure difference across the window. It is the lowest permissible result.
All windows sold in
Canada must meet at least the B1 rating to comply with local building
codes.
Every rating number
above B1 represents the highest air-pressure condition for which no
water leakage occurs. For example, a window rated B4 that shows no water
leakage at a test pressure of 400 Pascals (Pa), the metric unit of pressure,
presumably leaks at higher pressures.
The highest
possible rating in the A440 Standard for resistance to wind-driven rain is B7,
equivalent to a window resisting water leakage at wind speeds greater than 120
km/h (75 mph.) — a high-performance product.
As noted for air
leakage, the B rating does not necessarily indicate the performance of
the product as installed. It should only be used to compare products. The B
rating is a very important performance index in coastal climates, where
wind-driven rain is relatively common. A window rated B2 would be the
minimum advisable for low-rise houses in most of Canada, except for the areas
in the following table.
|
Table 1 — Suggested minimum ratings
for wind-driven rain resistance |
|
|
For most of Canada |
B2 |
|
Haida Gwaii/Queen Charlotte Islands |
B5 |
|
Western Vancouver Island |
B4 |
|
Eastern Vancouver Island and north
coast of B.C. |
B3 |
|
South-eastern Alberta, southern
Saskatchewan |
B3 |
|
St. Lawrence Valley, east Baffin
Island, east New Brunswick, Nova Scotia, central Newfoundland |
B3 |
|
Gaspé, Prince Edward Island, Gulf of
St. Lawrence, coastal Labrador, coastal Newfoundland |
B4 |
|
The above B-ratings are appropriate
for low-rise residences in relatively sheltered areas, and are only a
suggested minimum. Building height, shape and location, such as on hilltops,
promontories or bluffs, can increase the effect of wind-driven rain, so that
higher B ratings are advised. In new construction or replacement of existing
windows, it is advisable to discuss and choose the window rating levels with
a design professional. |
|
Windows are also
tested for their ability to resist wind pressures without deforming too much
and without blowing out of their frames. Test windows are subjected to a large
air-pressure difference to simulate hurricane-force winds (120 km/h and
higher). The resulting deformation of the framing components is measured, with
the window receiving a rating from: C1 — deflection or blow out of the
window at gale-force winds (62–74 km/h — 39–46 mph.) to C5 (resistance
to extremely high wind pressures without blow out or permanent deformation.
Windows rated C5 are appropriate for some high-rise buildings, or for
low-rise buildings in very windy climates.
A window rated C2
is the minimum advisable for low-rise houses in most of Canada, except for the
areas in the following table.
|
Table 2 — Suggested minimum ratings
for wind resistance |
|
|
For most of Canada |
C2 |
|
Haida Gwaii/Queen Charlotte Islands,
western Vancouver Island |
C3 |
|
Alberta south of High River |
C3 |
|
Except: Cardston
area of Alberta |
C4 |
|
Lower St. Lawrence Valley
(Baie-Comeau, Sept-Îles, Matane), western Prince Edward Island, western Cape
Breton Island, east Baffin Island, Labrador, Newfoundland |
C3 |
|
Except: Cape
Race, Gaspé region, Gulf of St. Lawrence, Resolution Island, Coral Harbour |
C4 |
|
The above C Ratings are suggested for
low-rise houses in relatively sheltered areas. They are typical values for
the regions listed. Building height, shape and location, such as on hilltops,
promontories or bluffs, increase the effects of wind pressures, so higher C
ratings are advised. Higher ratings are also suggested if local wind
conditions are higher than the average values for the regions listed. Typical
wind-pressure levels for the regions listed (upon which the suggested C
ratings are based) are taken from meteorological data valid for the location
of the meteorological station. There may be, for example, regions in the
Gaspé or in southern Alberta for which C5 ratings would be advisable. |
|
Manufacturers may,
but are not required, to have their windows tested for ease of operation,
resistance to forced entry, condensation and screen strength.
Ease of operation
Many operable
windows are tested to ensure that their operation is relatively smooth, with no
jamming of operator mechanisms. The amount of force required to turn operator
cranks or slide windows open and closed is measured in the test and cannot
exceed set levels.
As is always the
case with standardized testing, however, the performance of the product sold
may vary slightly from the rated value. The CSA Standard only indicates whether
a window model meets or does not meet the requirements of this (voluntary)
portion of the test. Consumers are encouraged to test window operation for
themselves, noting that showroom models may have been opened and closed many
times, and that dealers are unlikely to display products that do not operate
properly.
Over time, gaskets
and seals will tend to wear, so that window operation will become easier, but
the window will also tend to leak more air and water.
Resistance to
forced entry
The CSA Window Standard
includes a test method to determine a window’s resistance to forced entry, but
consumers are advised not to rely entirely on this rating for security of their
person and property. A consumer-rating index is no substitute for normal
precautions against unwanted or unlawful entry.
Condensation
resistance
The CSA procedure
contains standardized test methods to evaluate a window’s tendency to allow
condensation to form on the glazing or framing members under winter conditions.
Condensation, due to air leakage or heat loss through the unit itself, can
damage adjacent building materials or cause fungal growth.
The warning that
rated performance is different from actual performance of products sold is
never more important than with this index. A wide range of variables can
influence the formation of condensation, including:
Condensation
resistance of windows has an index called the Temperature Factor (TF). The TF
can be thought of as an indication of whether the interior surface temperatures
are more like the interior or the exterior. If the interior surface
temperatures of the window were the same as the outdoor temperature, the TF
would be 0; if the interior surfaces of the window were as warm as the room
air, the TF would be 100.
If a window is
tested for condensation resistance, the minimum level required to meet the A440
performance standard is TF 40. This is approximately equivalent to a double-glazed
window with a thermally broken metal frame.
Higher ratings are
suggested for humid climates, for example, near lakeshores, oceans or in river
valleys. Higher ratings may also be necessary in homes where interior relative
humidity levels are higher than average — for example, where frequent showers
are taken, or an unusually large number of plants are maintained, or food
preparation involves large quantities of boiling water. In situations where
high indoor humidity levels are expected, however, it may be more appropriate
to address that issue directly (for example, by installing a dehumidifier or
exhaust fan) rather than buying condensation-resistant windows.
Screen strength
Operable windows
usually feature a screen over the open portion of the window to keep insects
outside. Depending on the force that can be applied without separating the
screen from the frame, the screen is rated as either “Standard” or “Heavy
Duty.” It is important to note that the screen strength test is only designed
to determine the ability of the screen to resist nominal loads. An insect
screen is neither a fallprevention device nor an anti-theft feature: it is only
intended to keep insects out.
Windows must be
carefully selected to meet your needs. They must be suitable for resisting
certain environmental exposures (such as rain and wind) and be within your
budget. It takes care for the average homeowner and many professionals to make
the best selection.
All windows sold in
Canada must be evaluated for three key performance criteria, commonly referred
to as the A-B-C window ratings.
A — air-tightness (levels A1 to A3)
B — water resistance (levels B1 to B7)
C — wind resistance (levels C1 to C5)
Generally speaking,
the higher the numbers, the better the window performance. Choose a rating
level that satisfies the environmental conditions of your home. Determine if
any of the voluntary performance criteria are required for your window(s) and
if they meet the required standards.
For further
assistance, speak with a qualified window specialist. Many window manufacturers
may choose to have their products evaluated by an independent authority. In
Canada, it is either The Canadian Construction Materials Centre (CCMC) or the
Canadian Standards Association (CSA). An updated list of window products
evaluated by these organizations is given on their Web sites:
CCMC — http://irc.nrc-cnrc.gc.ca/ccmc/
CSA — http://directories.csa-international.org/help.asp