I need to replace my roof as the shingles have cupped and are falling apart
gjf1973
| Posted in Energy Efficiency and Durability on
I need to replace my roof as the shingles have cupped and are falling apart. I understand this to be a insulation/ventilation issue. I live in New Hampshire and have a cathedral ceiling over a large portion of the house. I have exposed 6×8 trusses with 1×3″ .
I plan to eliminate the vented drip edge with metal roofing.
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Greg. Is your ceiling uninsulated? If so, do you want to address that issue?
Others will chime in. In the meantime, I think you would benefit from reading the following article:
https://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling
Thanks Steve. I had read that article. For some reason some of my question did not get posted. I have 4" of foil faced foam, same is in the picture of the article you posted. If I recall correctly had a R 14.4 which only gives me R29. Above the foam is 2x4s spaced every 2' OC that anchor the foam and create an air space below the sheathing, paper and shingles. We have vented drip edge. There are small gaps in the 2x4s to allow some air flow to move towards the ridge vent. I am considering filling the 1.5" space with some sort of insulation, foam or cellulose. I am also considering adding insulation on the inside of the house. I would have to cut out all the ceiling boards or cover them with foam and drywall or wood, I'm just concerned about moisture rotting the existing ceiling.
Greg. It sounds like you have a well-ventilated roof assembly. How old were the shingles? What was their rated service life?
I'm not sure what means "...exposed 6x8 trusses with 1x3". Can you post a picture?
Using 2x4 furring to hold down exterior rigid foam, with a vented nailer deck for the new roofing is fine. The furring has to be through-screwed to the rafter/truss elements to have sufficient resilience to wind, but it will work.
New Hampshire ranges from zone 5 in the southern portion of the state (all of Cheshire, Hillsborough, Rockinham and Strafford counties) to zone 6 (the rest of the state.)
In zone 5 at least 40% of the total R needs to be above the structural roof deck for dew point control without using interior vapor retarders (other than standard latex paint on sheet rock.)
In zone 6 it needs to be at least 50%.
How much room do you have for fiber insulation below the roof deck?
Greg,
I'm not sure whether the 2x4s that were installed above the rigid foam are parallel to the ridge or perpendicular to the ridge.
If they are perpendicular to the ridge, the venting is more effective than if they are parallel to the ridge.
In either case, however, I would leave the gap as is and not try to fill it with more rigid foam. Just install new roofing, leaving the existing vents at the soffit and ridge.
If you want to add more interior insulation, the best material would be continuous rigid foam, installed in an airtight manner, followed by a new finish ceiling.
Martin,
The 2x4s are parallel the ridge, unfortunately. If I am to add foam over the existing wood ceiling it should be foil faced polysio? Cut shy of the trusses so that I can spray foam for a good seal and cover with drywall for best results? Thanks!
Greg,
We still don't have a clear description of the layers of your roof -- for example, from the interior to the exterior -- something like this (I'm making this up):
1. Tongue-and-groove boards
2. 4 inches of foil-faced polyiso
3. 2x4 purlins, 24 inches on center, parallel to the ridge
4. 7/16 inch OSB
5. Asphalt felt roofing underlayment
6. Asphalt shingles.
Give us information like this, and we will be better able to help you.
Right now, your roof has an R-value in the range of R-24 or R-29. You should be aiming for at least R-49. If you are about to install new roofing, it makes the most sense to install more insulation from above, not from below.
If you like the idea of a cold roof (with ventilation channels above the insulation), you can still create that above your last layer of foam. But you need to add more foam first. To do that, it may make sense to remove the existing 2x4 purlins, so that the next rigid foam layer is continuous.
For more information, see this article: How to Install Rigid Foam On Top of Roof Sheathing.
This is exactly what the roof system is! 1. Tongue-and-groove boards
2. 4 inches of foil-faced polyiso
3. 2x4 purlins, 24 inches on center, parallel to the ridge
4. 7/16 inch OSB
5. Asphalt felt roofing underlayment
6. Asphalt shingles.
I'm concerned about the amount of work/money it would take to rip the current sheathing off so that we can add foam above the existing foam. I thought about drilling holes so that it could be filled with cellulose though I realize the R value is not that great. What are your thoughts on filling that 1.5"space with cellulose, 2" of new polysio on top of the sheathing, purlins and metal roofing?
Greg,
You have a poorly insulated roof, and it's going to cost money (and it's going to be a hassle) to bring it up to modern standards. You have to decide whether it's easier (a) to add insulation on the exterior side as part of a re-roofing project, (b) to add insulation on the interior side (which means a new ceiling), or (c) to do nothing and live with higher energy bills.
If you do the work from the exterior, I advise you to remove the top layer of roof sheathing and the 2x4 purlins before you add more rigid foam. But you're right -- that's a hassle.