Windows and Doors in Northern Housing
Windows and doors used in northern housing are built in the south and are usually not designed for the severe northern climatic conditions. This factsheet examines common problems and some of the solutions that have been developed in recent years.
Windows are important not only for viewing the outside world, but also as a means of ventilation and emergency escape. Ideally, windows should have minimal air infiltration, high thermal resistance, a twenty-year lifespan under conditions of hard usage, low life-cycle costs and widespread consumer acceptance.
However, windows in the North typically exhibit a short lifespan. This, combined with relatively poor thermal resistance, affects other major building systems, leading to a reduced lifespan for the entire building. Major problems include poor performance, lack of durability and difficulties in maintenance.
Some causes of these problems are described below.
How Windows Fail
Weatherstripping - Weatherstripping is a primary area of failure for northern windows. It typically lasts only one or two seasons. Very low temperatures and rapid temperature changes cause it to age quickly. Extreme cold may cause weatherstripping to become brittle and fail.
Ice-bonding - Ice-bonding occurs when warm humid air from the house interior escapes and freezes at the weatherstripping. This bonds the frame and weatherstripping together making windows difficult to open. Attempts to open the window will damage the weatherstripping, increasing exfiltration and resulting in additional ice build-up. Once windows are opened, they may be impossible to close due to the build-up of ice and snow around the opening.
Hardware failure - When occupants try to open or close a window that has ice-bonding or snow accumulated around it, the hardware often fails from stress. Rotary operators are the most susceptible, with lever or scissor types running a close second. People interviewed who preferred sliding or double-hung windows did so because of their minimal operating hardware.
Glass breakage - Another problem is broken glass, caused by stresses in glazing created by high temperature differentials, movement of the building, or by vandalism. Breakage of glazing does not mean replacing the whole window unit, but replacements may not be available until the next summer or until the next aircraft delivery.
Advantages/Disadvantages of Different Window Types
Sliding windows - The high air leakage characteristics of sliding windows makes them less suited to northern applications than other types. Energy conservation is poor and cold drafts can cause discomfort for the occupants. It is difficult to weatherstrip this type of window properly without constraining the sliding motion. Because of the greater exfiltration rate, these windows are more likely to freeze shut. However, an advantage is that these windows do not rely on mechanical working parts to open or close. For this reason, they are a popular choice in the North.
Casement, awning and hopper windows - These windows close against weatherstripping for a tighter seal. The weatherstripping at the hinge point is subject to the greatest stress, and the frame, pane and hardware are under considerable stress when opening and closing.
Outward opening casements and awnings have operating hardware which by-passes the screen and penetrates the frame. The difficulty in providing good weatherstripping at this point increases the probability of air leakage.
In winter, inward opening hopper windows may be difficult to close due to the build-up of frost or ice at the head of the window.
Fixed windows - These windows have the fewest problems. Combinations of fixed windows and special ventilators have been tried in the past and new varieties offer potential for effective solutions; however, occupants dislike these windows because they cannot be opened.
The types of materials used will affect window performance.
Wood - Wood is a traditional, easily available and standard window material. It has a relatively high thermal resistance while being relatively inexpensive. Minor damage during transport and installation will not greatly influence performance.
The dimensional stability of wood is affected by humidity changes. Excessive shrinkage can occur with very cold, dry Arctic air. Therefore, wood needs to be sealed regularly with sealer or paint. Metal or vinyl-clad wood windows are also available. They cost more, but do not require regular maintenance.
Poly-vinyl chloride (PVC) - This material shows considerable promise for the northern climate, but good-quality PVC is expensive. It functions as well as wood and requires less maintenance. Several northerners have complained that PVC is too brittle in cold conditions and breaks easily; however, these complaints may be attributed to installation rather than use during cold weather. PVC is not as stiff as wood, requiring a careful approach to design. It is recommended that within PVC frames, metal reinforcement be provided at all the pressure points. PVC can also experience significant dimensional changes under temperature differentials.
Glass fibre - Advantages of glass fibre include high tensile and compressive strength, high thermal resistance, light weight and the same coefficient of expansion as glass. However, this material has been used infrequently because it is easily damaged by ultraviolet radiation. Durable and attractive protective coatings have been difficult to develop. The development of new production technologies and stable coatings may make this material competitive with PVC and wood windows in the near future.
Aluminum - It is unsuitable for the North because of its low thermal resistance.
There are very few standards for weatherstripping performance. It is a complex area due to the multitude of materials, configurations and installation conditions.
Spring-loaded compression weatherstripping has mechanical parts that can fail under the severe winter conditions.
Compression weatherstripping is the best at reducing air infiltration or exfiltration. Low infiltration rates are important in reducing energy costs and maintaining comfort, and low exfiltration reduces the outward flow of moist air that can cause ice build-up, which damages weatherstripping.
One type of weatherstripping that functions well at extremely low temperatures is a triple-row configuration of high-quality thermoplastic elastomer (e.g., Santoprene) or thinly extruded EPDM. Silicone-based neoprene rubber weatherstripping is available and functions at extremely low temperatures. All weatherstripping should be silicone-based or treated to limit moisture absorption, freeze-up and friction against contact surfaces.
Standard sealed double glazing is widely used in the North but this is rapidly giving way to triple glazing or double glazing with gas-fill and low-emissivity (Low-E) coatings. Depending on the number of layers, gas fillings, coatings, etc., thermal performance levels of RSI 0.7 (R4) to RSI 1.8 (R10) can be achieved. Besides providing space heating energy savings from 9 to 18% above standard glazing, these advanced windows will allow higher indoor relative humidities without causing condensation on the glass and reduce swings in room air temperature, thereby improving comfort.
Some "unbreakable" glazing materials, such as Lexan, have been tried, but a window that cannot be broken may be a problem in an emergency situation.
Spacers can affect the overall performance of windows, especially when high-performance glazings are used. Glazings and spacers work in tandem to enhance performance. Aluminum is the traditional material used but the extreme northern temperatures can cause stress fractures. Butyl-metal or "swiggle-strip" spacers are becoming more popular as they tolerate the temperature differences better than aluminum. Silicone foam is also being tested because of its high insulation factor.
As previously mentioned, hardware is one of the weakest features in northern windows. That is why sliding windows, which do not rely on mechanical hardware, are so popular in the North.
Conventional North American hardware systems are not adequate for Arctic conditions; however, many European designs function well and are more durable. European hardware is available through distributors in Canada.
Improved through-the-wall ventilation systems reduce the need for opening windows. One attractive example is the Swedish Fresh Air Ventilator. This system, which is easy to operate, provides fresh air to individual rooms. Another ventilation device is a non-glazed ventilator with a cylinder that rotates to provide ventilation.
Design and Location
Several well-known, simple design and construction techniques can improve the performance of even mediocre window units.
Many of the problems with exterior doors in the North appear to stem from both poor design and materials. Problems with doors include:
Solutions to some of these problems include the following.
Builders can take a low- or high-tech approach to solving problems in the North. The low-tech route uses simple, robust materials that require minimal maintenance. Technical advances have improved window performance so much that they cannot be ignored. However, high-tech products often cannot withstand the severe climate, hard use, vandalism and poor maintenance common in the North.
For further information on window technology, refer to Technical Series 90-250: New Window Technology for Northern Housing.
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