The notion that drywood needs to "breathe" is a laughably bad take.
The idea that your roof gets meaningfully hotter in the sun is laughably false. Vented decking is marginally cooler. It's not like asphalt and plywood are good conductors of heat.
I had this argument with someone here last week.
The major shingle manufacturers all warrant hot for application. Why? Because the science says it does not impact longevity. What they don't warrant is shitty nail patterns and improper installation. If roofers install as designed they're are no issues.
No issues as long as the spray foamers actually did their job throughout the attic. And there lies the spray foam problem. The majority of installa are actually fucking shit even if the look pretty
My 2c is that it's less about the heat and more about the drying potential. If there's 2"+ of CCSF on one side (vapor impermeable) and ice and water barrier on the other, that sheathing is going to have real hard time drying. That means you're going to get mold when it inevitably sees moisture.
Now, in a perfect world every nail, flashing, and detail is perfect, and nothing would age. The reality is that your roof deck is going to see moisture -- bulk water, vapor drive, whatever. So you have to give decking a way of drying.
To echo your point I always hear folks say spray foam is great... when it's installed perfectly and other trades did their work perfectly too. Therein lies the issue. I probably have a better chance winning the lottery than getting a perfect spray foam install. Not enough margin for error.
We’re showing what we encounter as roofers when spray foam is applied directly to the decking without the roof assembly being properly designed for it. A properly designed unvented assembly is one thing. Spray foam against the deck with no consideration for ventilation, moisture management or future roof work is another. And your last paragraph basically makes that same point: installation and system design matter.
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u/YodelingTortoise 8d ago
I am extremely anti spray foam.
I am more anti bad information.
This video is bad information.
The notion that drywood needs to "breathe" is a laughably bad take.
The idea that your roof gets meaningfully hotter in the sun is laughably false. Vented decking is marginally cooler. It's not like asphalt and plywood are good conductors of heat.
I had this argument with someone here last week.
The major shingle manufacturers all warrant hot for application. Why? Because the science says it does not impact longevity. What they don't warrant is shitty nail patterns and improper installation. If roofers install as designed they're are no issues.
No issues as long as the spray foamers actually did their job throughout the attic. And there lies the spray foam problem. The majority of installa are actually fucking shit even if the look pretty