Venting using site-built ventilation baffles
tsloss
| Posted in General Questions on
When making self-built vents using foam board, how big of a vent channel do I need? I was thinking of just using 1 1/2″ thick by about 1″ wide nailed to roof joists along the underside of the roof deck, with the foam board on top, sealed and closed cell foam on top. Does the 1 1/2 deep vent seem adequate? Zone 5
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Replies
Code minimum is 1”. Joe Lstiburek recommends 2”. Many people compromise at 1-1/2”. 1-1/2” is a very convenient dimension when working with framing lumber or engineered joists.
I expect 1-1/2” will work just fine unless you have an especially shallow pitch roof.
Bill
Tom,
Here is a link to a relevant article: "Site-Built Ventilation Baffles for Roofs."
I have built baffles out of 1/2" foam attached as you are planning, and corrugated plastic like you see used for real estate signs. The corrugated comes in 4x8 sheets and can be cut with tabs that are bent down. You can staple those to give you whatever void you want. Very inexpensive, rigid enough for the purpose, and easy to install.
Hi Tom -
I am currently testing soffit-to-ridge venting for cathedral roof assemblies.
https://www.greenbuildingadvisor.com/article/wingnut-testing-soffit-ridge-roof-venting
So far I have been testing 1-inch depth vents because that is the minimum the code requires but I am in the middle of testing from 3/8-inch to 2 inch vent depth to see what impact the vent depth has on air flow.
Stay tuned. I hope to have more info soon.
Peter