Roofing roofing ventilation with cathedral ceilings, rigid foam insulation, open beam ceiling

Roofing roofing ventilation with cathedral ceilings, rigid foam insulation, open beam ceiling

Roofing /roofing ventilation with cathedral ceilings

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Expert: Stan Skarbek — 8/31/2006

Question

Thanks for your prompt reply. Do you think I should add more than the 1″ rigid insulation I already have along with the layer of plywood? I live in RI and it gets cold here in the winter. I did explain the open beam ceiling to Certainteed and they agreed it sounded like I didn’t need a ridge vent but they would need to contact their warranty «people» and would get back to me. That was about a month ago! And no replies from my e-mails. So I’ll check out GAF. Thanks again, Mary

Followup To

Question -

Hi Stan I’m in need of a new roof and wonder what you think about the need for any kind of ventilation needed for an open-beamed cathedral ceiling (no attic). I wanted to go with Certainteed archetectural shingles (30 yr) but the company states thwy cannot give me any more than a 5 yr warranty unless I have a ridge vent. This doesn’t make sense to me as I would be able to «see» light right through this from inside my house. I also think I see air coming into my house as it is (tassles on the wall move about in winter). I wonder if I need more insulation on top of my roof. My heating bills are very high. I presently have a layer of tar paper, followed by 1″ rigid foam insulation, then the shingles which are only 16 yrs and in bad shape. (My ceiling is leaking badly). Thank you for your advise, Mary Peterson

Answer -

Hi Mary,

Certainteed didn’t realize that you have an open beam ceiling. They are thinking that you have an 8″ space between a sheetrock ceiling and the actual sheathing boards for the roof. That 8″ space is the distance used by the rafters in most cathedral style ceilings. It’s that air space between the rafters and between the ceiling and the sheetrock that needs to be ventilated.

In your situation, there is no air space. Talk to Certainteed again and make that clear to them. The only air space under the roofing is the living area. Tell him that you’ll gladly open a window on humid days :o) Tell him about the rigid insulation that you currently have in place. Then say, «given my situation, the warranty would be in full effect, right? Or do we need to use a different Manufacturer?» If Certainteed tells you that the warranty will be in full effect, ask them to send you a letter that says that, for your house files.

By your description, it sounds like the current shinlges are attached to the rigid insulation but that the rigid insulation doesn’t have a layer of wood (plywood or OSB) on top of it, for a better nailing base. If the current roof is nailed to the rigid insulation with no wood directly under the shingle system, then Certainteed will probably require that. That’s reasonable.

I hope that helps. If Certainteed remains steadfast, ask your contractor to look around for another manufacturer with a more reasonable view of life.

I hope that helps. Definitely don’t install ridge vents over your roof. That would be a significant mistake to make. Feel free to follow up in the future as the drama unfolds.

Your roofer with a keyboard,

Stan Skarbek

Answer

Hi Mary,

The issue is the R value of your insulation. Ask the local building department how much R value you should have on an open beam ceiling for your area, there in RI. Different weather conditions would call for different amounts of R value. Your local building department will know what’s best for your area. Ask him how much R value there is in the 1″ rigid insulation you already have, if you don’t already know. There may be different R values, depending on exact what kind of insulation you have.

I hope that helps. I hope GAF treats you with a little more respect and gets back to you within a day.

Your roofer with a keyboard,


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