What are the disadvantages in having my roof spray foamed. I have heard that it's not good for your shingles.
Having done many restoration projects in the past, the only caution I would have is that should you ever get a leak and a need for remedial work on your roof, the spray in insulation would be a time consuming and expensive hurdle to deal with.
I suspect it would not conform to code either, as you have to have good air flow around a roof, with foam troughs called Baffels , that are placed at the top of the wall where the roof trusses are set to promote a good air flow.
If you do not have this, mold is often a problem .
If you don't have a cathedrial ceiling, then there is no problem with spray foam. It creates a continous vapour barrier and as long as you have proper attic ventilation then mold and your shingles will be fine. However to cost will be high and you won't get any payback from the investment (blown in insulation is much cheaper and will pay for itself).
If you have a cathedrial ceiling and spray foam directly to the back of the plywood, like structurally insulated panels. They say you won't have problems with the shingles. However I'm of the opinion that the air flow provided by air baffles would greatly extend the life of the shingles.
I am a big supporter of spray foaming the underside of a roof for many reasons and research as shown it to be a better method of insulating. However, before doing so there are two things you must do first: 1) make sure your local building authority is comfortable with a non-ventilated roof system 2) verify with your shingle manufacture that a spray foam, non-ventilated attic does not void their product warranty.
Kingsway Construction Inc
Hi Marc, I am assuming that this is just one of the many ways to insulate your attic that you are considering. If you want some up to date, science based findings on this, search for "building science corporation" and look in the info section under high R-value roofs.
Sorry I can't just put the link here for you but they always mysteriously disappear :)
Good Luck with it!
Kettleby Handyman Services
In my opinion blow-in insulation is good enough and not as expenssive but a really good thing to do before hand if you would spend the bit of xtra money is to insulate with batt insulation before you do the blow insulation... if you dont already have drywall on the ceiling it much easyer... also if you want to foam you can foam on the ceiling from inside the attick once the drywall is done.
The only disadvantage is if you need to repair wires of leaks like someone mention before it will be a pain in the *** :) but if you want foam i recommend faom on ceiling not roof! roof must be ventilated well to last many years and to foam the roof will cost you a hell of a lot more then to foam the ceiling.
Any questions feel free to call
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