Guest User
4/13/2017
I'm getting ready to metal roof my home and I plan to go directly over the old shingles but I hear that putting down foam board insulation is a great idea? I would like to know what type of foam board I should use and how thick the foam board should be? will it be ok to lay the foam board directly on top of the shingles? Thank you for your time
Todd Miller
Classic Products, Inc.
4/14/2017
There are times this can work though generally I am not a fan of it. With normal construction, the place for insulation is down on top of the ceilings. Then you have a well vented attic about that, followed by a reflective metal roof -- great system. The insulation board, aside from not being at its most effective on top of the roof, can interfere with the installation of some metal roofs.
Guest User
5/9/2017
Hi, We have just done a room addition, enclosing the patio, and replacing the old flat roof with a high gable. That gable is now covered with plywood and peel and stick. The rest of the roof is 30 yr old shingles (single layer). We are putting on a new metal roof (galvalume). My roofer insists that it is fine to put the metal over the shingles, that it adds a layer of protection etc. We are putting foam insulation between the shingle and metal. I am concerned that leaving the shingles on will add to the thermal heat load in the attic, reducing the energy efficiency of the roof, defeating one of the main purposes of having a metal roof. Am I right to fight for this or not? The roofer is putting in 4 off-ridge vents and of course the ceilings will have new insulation. Any advice greatly appreciated!
Info @windowsonwashington.net
An informed customer is our best customer.
5/9/2017
Depending on where you are located and your current roof venting, you may be right. I am not a fan of leaving shingles on roofs in climates that have a predominantly large cooling season.
Guest User
5/9/2017
We are in central Florida and currently passively venting through one off-ridge vent. Thank you for your thoughts, Janb9CY39
Info @windowsonwashington.net
An informed customer is our best customer.
5/10/2017
Being in Florida, my default response would be to get that thermal mass off of the home and off the roof.
Guest User
5/10/2017
Thank you Eric. Do you have an opinion on the merits of on or off ridge vents. The roofer I am working with is not a fan of ridge vents with Cobra inserted. Many thanks, Jan
Info @windowsonwashington.net
An informed customer is our best customer.
5/10/2017
Cobra vents? Do you mean the Cobra Vent mesh drop in or do you mean like a box vent.
Guest User
5/10/2017
Cobra vent mesh drop in. Our roofer prefers off ridge vents (4 are planned), says the Cobra mesh gets clogged with dirt quickly and becomes ineffective at allowing air to flow well. Intuitively I think your advice is correct, get that thermal mass off the roof! However I have now had a long conversation with someone at the Florida Solar Energy Centre/ UCF who says that while we are correct, strictly speaking, the actual increase in attic temps is very small. Such that perhaps the shingle does provide another layer of insulation and if one wants to be green, leaving them on keeps them out of the landfill for a very very small energy cost. Which doesn't warrant the significant expense of tearing them off and putting more peel and stick down. Sigh........ Also....we have opted for foil-backed Styrofoam insulation between the shingle and the metal. (maybe it is foil on both sides) Solar man is in favour of radiant barriers but says they must have an air space under them to be effective. I have had other roofers tell me the air space should be above them, between foam and metal. Some use a bubble wrap type barrier under the 1x4's...........help! I value your opinion, thank you Jan
Info @windowsonwashington.net
An informed customer is our best customer.
5/11/2017
You will forgive me if I tell that person at the Florida Solar center that they are flat out wrong. Insulation at the roof level serves you no purpose in this case (i.e. vented attic). If the roof plane was the air barrier, they might have a point but you wouldn't insulate with asphalt shingles in this case. Again...can you do it, sure. Will foam mitigate the impact of the thermal mass, yes. I would still tear them off and put them in the dump. I prefer to not have the additional weight across my roof, inspect and address the sheathing in totality, and have a nice and level substrate. If you are going to install the foam, ask the roofer about some cross battens for some above deck ventilation in that case.
Guest User
5/11/2017
For better or for worse, the roof is going on over the shingles with foam between, foil side up. Not how I would have liked it but I am only one vote. Hopefully it will work out. Thank you for your prompt replies, Best regards, Jan

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