Winter Climate Roof Venting


Hi there. I’m having a house built right now and I have a question about the best (not just the adequate or min code) way to properly vent a standard roof on a single family home.

I live in Northern Canada. Temps can get below -40 and are often at -20 for prolonged periods. We do however get the occasional thaw cycle for a few days to a week where temps can shoot into the positive range.

The house I’m in right now actually has “attic rain”, frost building up in the attic space and thawing back. The roof looks to have just the regular old plastic square roof vents, no turbine or turbo. Front and back are perforated soffats, sides are solid. Minimum code appears to be met from what I read.

So, the house I’m having built has the same kind of set up. Plastic roof vents at the bottom and top of roof. Passive airflow, no whirlybirds etc.

These will inevitably be covered with snow and or ice, and I see a mix of this with turbos/turbines etc throughout the neighborhood.

So I guess my long winder question is: Regardless of cost, aesthetics or anything else, what is the most effective roof vent combination to exchange air in a very cold climate with lots of snow?

I’m researching myself but getting mixed reviews on it, so looking for help from this community, thanks!

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You need to have functioning intake vents for any system to work.

The most effective way would be to use power vents or gable end fans to move the air.

The best passive system is ridgevents along the entire length of the ridges.

A friend of mine used fans in the gable ends and he gets no ice build up at all, he says that he can sometimes hear the fan running though.

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Hi there. Thanks for the post. I am one of the owners at Safe Roofing located in Edmonton, Alberta, and we have a similar temperature in the winter time. We have helped several homeowners experiencing problems with condensation and ice damming.

The first step is to comply with the Canadian Building Code for attic ventilation.

You need 1 square foot of attic venting area for every 300 square feet of ceiling area (1/300). For low slope roofs or cathedral ceilings, use 1/150. Also, aim for a 50/50 balance between intake and exhaust vents.

Existing house

Consider having a specialist perform an attic inspection to insure those intake vents are not blocked by either a wall or too much insulation, as they will prevent air intake. The perforated soffits are a good sign, but you cannot assume that they are venting just because they are perforated. You also want to verify your insulation efficiency (R-value), all the vent stacks, fans and light fixtures for any unsealed gap that would let moist air into the attic, thus causing ‘attic rain’. You might want to consider upgrading your box vents to some higher end roof vents, wich will not be covered in snow. We will talk about them shortly.

New house

For newer houses, we would recommend vented soffits all around if it does not interfere with your regional firecoding. You want to install attic baffles to prevent any sort of blockages to air intake. For exhaust vents we recommend Maximum ventilation. They stand very tall, making them free of snow and capturing the full effect of the wind for as little as 6km/hr. What makes the Maximum vents more effective is that they have a much powerful drawing power compared to the other vents. For example, a 2000 sq. ft. ceiling area only requires 2 Maximum #301. They also offer roof intake vents alternatives if vented soffits is not an option.

Thank you and I hope this has been helpful.

Benoit Gosselin
Operating manager



Thanks very much for the replies. Very helpful!



I’m glad I found this threat. We bought a 4 level split house with a very shallow roof line three years ago. Our first winter in the house we had terrible attic rain. Ruined ceilings, seepage around light fixtures and switches, even dripping inside the inner walls and dripping through the bathroom fan on the lower level! It was a nightmare. We had the roof removed and the attic floor spray foamed because we were told blown in insulation was too bulky given the very small amount of clearance in the attic. Moreover, the spray foam should be impermeable to moisture in the future. But this year during the first winter warm up, our upstairs bathroom ceiling started leaking again. The paint is buckling and peeling and those ominous brown spots are appearing. Furthermore, as soon as temps warm up I can hear ice falling from the bottom of the roof onto the spray foam and breaking or skittering across it. WHAT DO WE DO??? there’s clearly still a venting problem but also warm air seems to be getting up there despite the spray foam. We love this house and couldn’t sell it without solving the problem in good conscience anyway but we’ve already spent many thousands of dollars trying to solve this problem. Suggestions???



good ridge vents with posive air flow from soffit to ridge or north or install gable vents at each end in sure grace ice and water 6 .feet instead of the 3 feet



take it all off if you can grace ice and water sdield if cos 140.00 per roll