Winter Moisture Issues

‘Tis the season to stay inside and stay warm. Our homes are wonderful and in the depths of winter we really enjoy the protection they offer from the elements. Winter time is however the time our home works the hardest with the largest temperature (and sometimes humidity) difference between the indoor and outdoor environments. It is in this climate that otherwise unknown issues with the building envelope may come to light, most particularly with the attic and roof systems.

Basic physics tells us that hot air rises. In your home, in the winter, pressure builds up at the ceiling of the upper floor as the warm interior air rises. If there are any issues with the sealing of the air and vapour barrier between the interior space and the attic this warm moist air can escape.  When it cools as it enters the attic any moisture within it will condense, which can be the beginning of significant issues.

Despite best efforts during construction or renovations it is known that there is still a possibility of some moisture getting into the attic due to discontinuities in the air and vapour barrier (most often poly sheet). Ventilation is provided to dissipate any moisture due to these small discontinuities before it results in damage. When designed, installed, and sealed properly, the attic ventilation system serves to prevent moisture build-up in your attic due to condensation and you can live for many years with no issues.

Issues come however when installers have done a very poor job in installing and sealing the poly air and vapour barrier around penetrations, particularly recessed lighting, speakers, and bath fans. This is compounded when adequate attic ventilation is not provided.

In climates such as Calgary, a poorly sealed and ventilated attic typically only presents issues during winter warm spells. This is because moisture within the air will condense and freeze on the underside of the roof sheathing at the top of the attic. During long cold spells this condensation can build up into a significant layer of ice. As soon as the weather warms up during a chinook and sometimes during cold weather,when the the sun warms up the surface of the roof, this layer of ice will melt and the water will drip down through the insulation and run through seams and discontinuities in the poly air and vapour barrier. The result is often moisture staining on your upper ceiling. Sometimes this moisture may also run down wall cavities.

So how do you know if you are experiencing attic condensation issues?

The key is when you only notice moisture issues during warm and/or sunny spells in the winter.

How can you tell if your home is more likely to have issues like this before they occur?

A blower door test combined with an infrared thermography camera can pinpoint any discontinuities in the air and vapour barrier. The key to having a test like this successful is to have it completed when there is a moderate difference in temperature between your attic and lining space, either during the winter in any home or during a sunny summer day in an air conditioned home.

Areas most likely to have sealing issues as mentioned above are recessed lighting, speakers, and bath fans.

The other issue is when poor ventilation is provided to dissipate any attic moisture. Venting needs to be split evenly between the base and top of the attic space. Inadequate or unevenly distributed ventilation is most common on homes with cathedral ceilings, very complex roof systems with lots of ridges and valleys, and low slope or flat roofs.

If you think your home may be subject to winter condensation issues or you just want to make sure you won’t have to worry about it reach out to us. We would love to help you locate and resolve any current or potential sealing or ventilation issues so you can enjoy your winters without having to worry about attic condensation.

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