Roof ventilation is a tricky subject but it is very important to consider when doing a roof replacement.
What is Roof Ventilation?
In a nutshell, roofing ventilation means allowing air to flow into and out of your attic area. The ultimate goal is to have the temperature of your attic to be as close to the temperature outside as possible.
Some people get the idea that you should insulate your attic and keep it sealed up. This is incorrect. You want your home to be sealed and insulated, but your attic should have nice open airflow at all times.
This allows hot air to escape in the summer, keeping the attic cooler. And in the winter it keeps the roof surface cold.
The reason you want the roof cold in the winter is that if the roof is warm, when it snows, the snow on the roof melts, and then freezes again when it gets to the edges, causing “Ice Dams” which can send water backwards, up through the shingles.
Older Homes Need Roof Ventilation
Most modern homes are built with roof ventilation in mind so it is not a concern. Where it becomes a very major concern is when you convert an older home from a cedar roof to an asphalt roof. There is a lot of this type of roof replacement done in Vancouver and the Lower Mainland so this comes up a lot.
A cedar roof doesn’t require ventilation because the cedar can breathe on its own.
When you take off the cedar and put on plywood and asphalt shingles you have very tightly sealed that roof so there will be no air flow. You have to put in intake ventilation at the bottom and exhaust ventilation at the top. There are numerous ways of doing this and many products available, but what is important is that your roofer is aware of the need to ventilate and discusses your options with you.
Some Roofers Will Not Tell You About Ventilation
You see, technically ventilation falls under the responsibility of the architect and not the roofer, so many roofers just ignore it and do not provide ventilation. But (and this is very important) a lack of ventilation will void your warranty. That’s right, on the majority of warranty calls for shingle failure the representative of the manufacturer will not even have to get out of his car to tell you that you have a lack of ventilation and therefore no warranty. That’s it. Done. That is the end of your warranty.
A Cautionary Tale
I have seen a home next door to a house we were working on with almost-new, triple-thick top of the line shingles. But I could see from fifty feet away that his shingles were wearing out fast and that the cause was lack of ventilation. His costly investment in top-tier shingles with the long term warranty was being wasted for a lack of maybe $100 worth of ventilation.
I don’t know if his installer never told him he needed to ventilate or if he was told and didn’t want to worry about it, but there is no way the manufacturer would honour the warranty with the ventilation as it was.
Converting From Cedar Roof to Asphalt Shingle Roof
Ventilation is a tricky thing to work out and many roofers will just skip it and not bring it up. If you are converting from cedar to asphalt then make sure you take this subject up with your roofer. A little extra money spent will go far towards making the roof last.
As a renovator Doug did many rot repairs which gave him a good understanding of where and why buildings leak, and how to prevent it. He realized the need for a different approach to roofing; one that educated the customer enough to make good decisions. With better trained installers and a quality inspection process Absolute Roof Solutions was born…” Read more.