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WINDOWS & DOORS
This article describes the types of windows used in residential buildings, their features, how they work, and the advantages or disadvantages of each window type, including single hung windows, double hung windows, sliders, casement windows, awning type windows, hopper windows, and tilt-turn windows.
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In this article series we discuss the selection and installation of windows and doors, following best construction and design practices for building lighting and ventilation, with attention to the impact on building heating and cooling costs, indoor air quality, and comfort of occupants.
We review the proper installation details for windows and doors, and we compare the durability of different window and door materials and types. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
Windows have a bigger impact on the quality of life in a home than almost any other building component. They affect heating and cooling costs, natural lighting levels, ventilation quality, and the comfort of occupants year-round.
Subjected to high ultraviolet (UV) exposure, extremes of weather, and hundreds of operations over their service lives, windows must be well-engineered from durable materials if they are to provide satisfactory service.
It is well worth investing the time and money to select the right windows for the job and to install them properly.
The most common types of operable windows are double-hung, casement, and sliding.
Awning-style windows are commonly used either near grade to let light into basements or high on a wall for privacy. Tilt-turn windows, European imports that swing inward like a door on hinges, are often used in large sizes as emergency exits.
Windows with compression-type seals are the tightest, and windows that swing open provide the best ventilation (see Figure 3-1 above-left).
Common window types and their characteristics are summarized in Table 3-1 below.
[Click any photo, table or illustration for an enlarged, detailed version.]
The most common windows in the United States, doublehungs have upper and lower sash offset so both can slide up and down. Only the lower sash moves in the less common single-hung window. In older homes, the operable sash were connected by rope to heavy iron counterweights to hold the upper sash in place and to assist with raising the lower sash.
Modern double-hung windows ride up and down in metal or plastic tracks called jamb liners and use hidden springs in place of sash weights.
On many of the newer models, the sash are designed to tilt in for easy cleaning.
At left the sketch, courtesy of Carson Dunlop Associates illustrates the difference between a single-hung window sash and a double-hung window. As you can see, only the lower sash is movable in a single-hung window sash.
Because the top sash overhangs the bottom, and both are recessed in the frame, double-hung windows shed rain well and can be left open at the bottom in a light rain. They use exterior screens that are out of the way and inconspicuous. However, ventilation is limited to half the area of the frame, and visibility is somewhat hampered by the meeting rails, which often sit near eye level.
Also, because they rely on slide-by rather than compression-type weather-seals, many double-hungs have air leakage rates nearly twice that of casements. With improvements in materials and designs in high quality units, however, the performance gap has narrowed, at least when the windows are tested (with brand-new weather seals).
Although probably not the tightest windows in a high wind location, in general, double-hungs offer a versatile, moderately priced, and trouble-free option.
Sliders can offer large horizontal expanses of glass and operable sash that do not interfere with interior or exterior space. They are more common in western states, while double-hungs and casements prevail on the East Coast.
Our photo (left) shows Andeson gliding windows (photo-right) and casement windows (photo-left) that we [DJF] recently installed during a log cabin renovation in Two Harbors, MN.
Designing a window that slides sideways presents a few challenges.
First, the lower track must rely on weep holes to drain away water, and second, any grit that collects in the lower track tends to impair the sliding action.
If the weeps clog up, water may find its way into the sill or framing over time. Also, pushing a stuck window sideways is an awkward motion that tends to strain the back. (Also see STORM WINDOW WEEP HOLES).
As with double-hung windows, ventilation is limited to rougly 50% of the framed opening, and slide-by weather-seals are less effective than compression seals. And if the slider is large enough it can also qualify as an egress window.
List of Glider / Slider Window Defects
To avoid problems with slider windows, look for high-quality windows that slide freely. Also, consider alternatives such as a picture window with a casement along one side for ventilation.
For a list of common installation or maintenance defects that cause problems at gliding or sliding windows, see SLIDING GLIDING WINDOW DEFECTS This article describes windows with lost seal, clogged slider track drainage openings, out of square installation and other window defects that should be easy to spot during a visual inspection.
Casement windows provide a more contemporary look than traditional double-hungs and can provide large uninterrupted views. If oriented to open into the prevailing winds, the sash acts like a big wind scoop, directing breezes into the house.
When closed, the compression seals create a tight fit that only gets tighter with oncoming winds.
Casement windows are not without problems, however. The outward swinging sash is vulnerable to water damage if the top is not fully clad, and the sash can clash with screen doors or encroach on deck spaces.
Or worse. Our casement window photo at left (DF) shows spectacularly poor planning: these windows cannot open more than a few inches without jamming against the soffit overhang!
Also, hardware problems such as stripped crank handles or broken linkages are not uncommon, particularly on lower-end units or large units with heavy sash. An occasional squirt of lubricant on the crank mechanism and hinges can go a long way toward preventing problems.
Large, heavy sash can also rack slightly out of square over time, requiring a push from the outside to fully close. Sometimes this can be fixed by tweaking the hardware, but a new sash may be required.
For best results with casement windows, choose units with sturdy sash construction, heavy-duty hardware, and sash that are protected on top from the elements.
Awning windows swing outward from top hinges, and hopper windows swing inward from bottom hinges. Awning windows s are useful for privacy windows and other high-up locations like clerestories, while hoppers are often used in basements.
A principal advantage of awning windows is that they can be left open for ventilation with less risk of water entry should a rain shower occur. Our photo (left) shows a modern awning-style window in a newly-renovated building in Buenos Aires, Argentina (-DF).
Both awnings and hoppers can be combined with fixed glazing to add ventilation below a picture window.
Because they rely on cranking mechanisms, these windows have some of the same problems as casements.
But without the heavy vertical sash, they are less prone to malfunction.
For hard-to-reach locations, a pole, pull-chain, or motorized operators can be used to open and close awning or hopper style windows.Developed in Europe, tilt turn windows rely on intricate hardware controlled by a single lever that allows the windows to either swing in like a door or tilt in at the top like a hopper.
In tilt mode, the sash are open only a few inches, allowing the windows to provide ventilation in a locked house (see Figure 3-2 at left).
When closed, the lever locks the window tightly in four to six locations, providing the tightest fitting windows available as well as excellent security against would-be thieves.
And with their easy-to-operate in-swinging mode, large-sized tilt-turn windows often do double duty as emergency exits.
While tilt-turn windows offer several useful features, they are not commonly seen in the United States, perhaps because of the in-swinging sash and relatively high cost.
Also, they do not typically come with screens, making them problematic in areas with summer pests. While not heavily marketed in the United States, they can be found here in wood, aluminum, aluminum-clad, and solid vinyl frames, the least expensive option.
-- Adapted and paraphrased, edited, and supplemented, with permission from Best Practices Guide to Residential Construction.
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