Framed for success
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.