Venting an attic in a mixed-humid climate
I’ve watched a bunch of Joe Lstiburek’s lectures on attics and roofs and he always had said that a traditionally vented attic with an air tight ceiling plane and insulation on the attic floor was a safe method that works in every climate zone. Now I’m reading his moisture control handbook where he has an entire section on how venting an attic can actually do more harm than good if the air coming in is more humid than the air in your attic, especially in heating season why the roof deck is cool. He also references that the roof deck can be about 10 degrees colder in the winter as it looses heat to the night sky and then the air entering the soffits can condense on the decking. I always thought that ventilated decking was critical in a cold climate for preventing ice cams. I’m in a climate zone 4A in NJ so hot humid summers and cold winters. I was going to try for a vented over roof but didn’t know if my 100 year old 2×4 rafters could withstand 2 layers of roof decking and didn’t want to bring in a structural engineer (plus it was over double the price) so we decided to stick with traditional soffit and ridge. But after reading what he wrote, I’m second guessing myself, any thoughts on this? Almost everyone in my areas has vented attics.
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I saw someone reply to this and now I don't see it, could it have possibly been deleted?
It seems like some posts are awaiting moderation today for some reason, so you may have seen a post reply notification email but no post. Not sure if that's a weekend thing, or there's extra security enabled because of a bot attack or something. I had a post reply like that earlier today; it took a while to actually show.
Usually deleted posts will have a blank post and say "deleted", and I can't see anything like that.
Just my observations as a fellow site user.
Thanks!
cathg,
As I understand it the cautions about vented roofs in humid climates refer to climate zones 1, 2 and 3. The conditions there are also why codes only allow some alternate roof assemblies like vapor-diffusion ports to be used in those regions. Vented roofs are the norm in lots of similar climates to yours with humid summers and cold winters, and they do fine. I would bet that almost every house around you relies on them.
Thanks for the reply Malcolm and yes almost all roofs around me are vented in some capacity!