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redpine17 06-20-2013 05:16 PM

Re: Unvented cathedral ceilings
I live in the Pacific NW. We have a 3:12 pitch roof with archies, installed about 9 years ago. The roof has been a headache ever since with numerous leaks. The roofing company seems ready to replace the roof and install an I&W membrane over all the sheathing before putting down the shingles. The issue is that several roofs have cathedral ceilings and no venting. They will not offer us a warranty on the new roof without the vents.

The older cathedral ceilings (1928 house) have an insulation-filled cavity (no room for airflow) between the sheathing and the ceiling (2x4 joists). The other cathedral ceiling is newer (1970's addition) and the joists are 2x6 or 2x8, also filled with insulation and no room for airflow. Almost everyone I talk to says that we have to find a way to vent these ceilings, though I have run across some evidence to the counter (on this site, for example). After all, there are many older homes, still standing, that have never been vented.

Solutions presented to me range from raising the roof 1" to 2" inches, to lowering the ceilings, to compressing the insulation an inch, to installing baffles. We have not, to my knowledge, had issues with condensation, but will only know after the sheathing comes up.

Curious what sort of feedback I might get here?

joecaption 06-20-2013 05:24 PM

Consider SIP roofing panels.
Google it.

redpine17 07-24-2013 01:54 PM


Failed to get back to you on SIP roofing panels. Very cool idea. Amazing R values! Unfortunately, for me personally, way too expensive right now.

Gary in WA 07-26-2013 10:51 PM

Find your Zone;

Then add the rigid to prevent condensation;

Good read;


redpine17 07-29-2013 12:27 PM

Re: Conditioned Attics

This was a great reply. I did not know about the option of a "hot roof" or an unvented attic assembly. I was just assuming that vents would absolutely be necessary.

The zone I'm in is 4C. I haven't had a chance to look into it yet, but one of my cathedral ceilings is only 3.5" between drywall and roof sheathing, i.e., a 2x4"

Nevertheless it might be the way to go even if I have to sacrifice some R-value.

Thanks again for posting!

shazapple 07-29-2013 12:38 PM

I'd consider a ventilated nail base, such as
These can also be made onsite with board insulation, strapping, and OSB. You could probably skip the OSB if you want to install metal roofing.

Personally I think ventilation is a best practice kind of thing, and hot roofs are favoured because they are a simpler (aka cheaper) fix. I think they are better on paper than in the real world, as a system with ventilation can deal with moisture/heat issues much better.

redpine17 07-29-2013 12:55 PM

Thanks for posting. So this option would also necessitate soffit and ridge/roof vents, no?

What do you think of this:

“For the most part, the focus of codes, researchers, designers, and builders on roof ventilation is misplaced. Instead, the focus should be on building an airtight ceiling, which is far more important than roof ventilation in all climates and all seasons. ... Once this is accomplished, roof ventilation becomes pretty much a nonissue.” ~building scientist Bill Rose

A related article by him:

Gary in WA 08-05-2013 11:50 AM

There are hundreds of unvented roofs here, locally, still standing, lol. I have used that link here before, it depends on local weather, air-sealing the attic, interior RH, diffusion (slightly), insulation, etc. Other links; (up-dated version)

Good for moisture;


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