If your sash windows are sweating, letting in draughts, frosting during cold winter days, and developing mould, chances are your weather-stripping needs replacement. Instead of replacing wooden-framed windows with vinyl, renewing the window weather-stripping is an affordable solution to a typical Canadian problem.
How can you tell if your weather-stripping is causing you problems? With the window closed, check to see if there are any gaps between the glass frame and the box frame. Aging weather-stripping will shrink and develop gaps that allow airflow through the window. Next, open the window and inspect the inner and outer weather-stripping. If they are painted over, cracked, non-pliable, or broken, they’re ruined. If they are missing altogether, soon your window will be ruined and replacing it will be your only option.
Heat exchange results from the transfer of air between the inside and outside of the house. Some air exchange is needed, primarily to feed the furnace oxygen and to reduce indoor humidity, which can produce harmful bacteria and mould growth. Too much air exchange, however, can lead to draughts and wasted energy, resulting in higher bills and needless emissions of air pollutants.
According to the National Research Council of Canada, 30% of the total heat loss from a well-insulated bungalow comes from loose-fitting windows and doors. This drops to 5% with tight-fitting weather-stripping. In other words, poor-fitting weather-stripping can result in a 33% higher heating bill!
Sash windows should all have two independent sets of weather-stripping. The inner sash frame (the immovable frame of the window attached to the house) should have a “silicone bulb” type stripping around the perimeter of the opening. The sash window itself will have a “v-strip” molding around the outer edges of the glass frame. These two styles of weather-stripping create a sealed core of space, which is called “the thermal jump”.
The wider the thermal jump, the less likely heat transfer will occur. The thermal jump-gap, when unsealed (‘cracked’), creates both heat transfer (loss in winter, gain in summer) and unwanted air exchange. Broken seals between the glass panes, which cause windows to “sweat”, occur when the inner sash frame weather seal ceases to function, and allows the high-pressure outdoor air to work against the low-pressure indoor air (winter conditions).
Homeowners, when confronted with draughty wooden windows peeling with years of painterly neglect, may throw up their arms and give in to the ‘replace with vinyl’ argument. And guess what? After another 15-20 years, when the weather-stripping on these windows cracks and dries up, they’ll need replacement too.
If, rather than taking the big leap to replacement, homeowners apply “peel and stick-on” weather-stripping, they will be frustrated after a few months of humidity causes the glue to detach from the window frames. All good weather-stripping fits into a narrow slot in the sash, secured by a press fit. This prevents moisture from seeping into the inner window area.
When properly painted and caulked, and with fresh weather-stripping, wooden sash windows will offer all the benefits of vinyl windows, with two added bonuses – your house will have the natural beauty of wood, and you will be able to change the exterior colour scheme to suit your style.
A further benefit is, of course, the ecological one. One less vinyl window manufactured leads to our making a smaller ‘footprint’ on the planet. By not needlessly replacing your wooden windows you’ll save money, save on your heating and air-conditioning costs, and reduce greenhouse gas and smog emissions from unnecessary consumption of fossil fuels and electricity.
For more information on replacing your weather-stripping, contact Jeff Hladun atjeff.hladun@sympatico.ca or 905 880-9851.
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Dr. Richard Ehrlich