Ottawa Citizen

Framed for success

- BY AVI FRIEDMAN

Picking the right windows, for a new home or when renovating an older place, will dramatical­ly improve your comfort and the look of your home. They will also slash your energy bills.

Heat losses through the building envelope can occur via conduction, convection, and radiation. In all three cases, windows are the weakest link and, as such, they represent the most important investment in the constructi­on or renovation of any dwelling.

Coupled with edge losses from the glazing unit, conductive heat losses through the window frame can account for up to 20 per cent of the total heat losses from the window.

The selection of an appropriat­e framing material, is therefore, not simply a question of appearance. Wood, for instance, is a good insulator, but it is easily damaged and requires higher maintenanc­e. Metal (aluminum) requires much less maintenanc­e, but is a good conductor. Plastic (vinyl) frames are maintenanc­e free, but like metal frames, are susceptibl­e to temperatur­e changes.

Combining these materials takes advantage of the thermal qualities of wood, while protecting it with either vinyl or aluminum and reducing maintenanc­e requiremen­ts.

Infiltrati­on losses between the frame and the moving part depend on the number and type of operable components and on the gasket.

Several windows can be categorize­d by the type of operation: fixed, awning, hopper, casement, sliding, single-hung, doublehung, pivoted (vertical), and multiple (for cleaning and ventilatio­n). It’s also possible to manufactur­e window units with combinatio­ns of these.

Generally, windows with fewer operable parts are more energy-efficient. The more linear feet of joint, the more heat loss occurs. Fixed windows are the best in this regard. As far as the type of operation is concerned, pivotal components (as in awnings and casements) are more energy-efficient, since they make use of compressio­n seals. Sliding parts are least effective in terms of air leakage.

Size, type, location, and orientatio­n of windows all affect the energy performanc­e of the home, and thus their careful selection and installati­on is critical in reducing the energy and costs required for heating, cooling, and lighting.

High-performanc­e windows with tight and water-absorbing seals between frames, sashes, and layers of glass increase thermal resistance, but also increase costs. Finally, proper installati­on of windows will also affect energy consumptio­n.

Unlike the past, homeowners have a wide selection of windows to choose from. A wise choice will not only improve the house’s appearance, but significan­tly reduce the energy bill. Avi Friedman teaches architectu­re at McGill University.

 ?? AVI FRIEDMAN, CANWEST NEWS SERVICE ??
AVI FRIEDMAN, CANWEST NEWS SERVICE
 ??  ?? Proper installati­on of windows is critical in reducing energy loss. The selection of an appropriat­e framing material is not simply cosmetic, since heat loss through the window frame can account for up to 20 per cent of the total heat losses from the...
Proper installati­on of windows is critical in reducing energy loss. The selection of an appropriat­e framing material is not simply cosmetic, since heat loss through the window frame can account for up to 20 per cent of the total heat losses from the...

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