Foam over T&G?
Does anyone have advice to offer regarding the pros/cons of installing foam over an existing tar and gravel roof? I would especially like to hear from someone who has lived with this type of installation for the last 5 years or so.
Does it hurt the longevity of the roof to install this way? We have rigid foam insulation under the existing tar and gravel, so it seems we would benefit from the extra insulating this provides.
Thanks for your input.
Randy from Dura-Foam is my expert on roofing, but here's some info till he posts.
Mine is a ditto to yours. Bought the worst one on the block and in the process of rebuilding it.
It has the OEM with some sort of insulation and one more on top of that. That second had rigid insulation too.
Had 5 firms quote and they all said one more roof is allowed by code. Had three foam roofers and Dura-Foam came out the "best". Not price (two were very close), but in the information and "trust" of the company. I call all providers of this type and ask questions of their staff. I'm a pain, know that, but tough, it's my money and I'll spend it why I chose to or not to.
Only one issue is that the over all roof is too high for the curbs along the perimeter, so on the pitched section....water falls. I fixed that myself with aluminum angle lengths that divert the water flow to the flat section gutter holes.
My house is typically 10*F-15*F cooler than it was before in summer and warmer than before in winter.
It's all in the code for your city governing roofing. IT will state how many roofs can be underneath the new roof and hope/guess it has metrics for type of house construction/roof structure/etc.
A cleaned and stapled tar or single-ply roof makes a great base for a foam roof. A good foam roof is the waterproofer, and is not compromised by thousands of staples (and staple holes) securing the existing membranes.
If you decided to remove the old roof (for emotional reasons ?) you would incur large disposal and labor fees. Then, new replacement materials must be installed over the wood decking. This is also certainly expensive. When you get done, the job is probably not as waterproof, or as attractive as it would be over the old roof.
To some people, installing a foam roof over the well prepared existing membranes sounds like putting new carpet over the dirty old pad. This is not the case here at all. The old membranes work perfectly, and are already installed and paid for.
On commercial buildings, we remove a lot of tar roofs to solve roof load problems. We seldom see this situation on Eichlers.
