apply closed cell foam directly to underside of metal roof

Cathy Tallman
6/8/2016
Hi, We are building a pole barn home and will have catheral ceiling with a metal roof. We are thinking of using closed cell insulation and not venting the roof. Can we apply the foam directly to the back side of the metal roof?? Should we vent the roof or nave it non vented?? Should we have anything under the metal when applying the roof or will the closed cell foam adhere better to the metal directly??
Info @windowsonwashington.net
An informed customer is our best customer.
6/8/2016
The answer is yes that you can spray foam the roof. The next question would be, is that the best application for this roof. Are you doing an exposed rafter type home? I would apply sufficient rigid foam to the outside of the roof deck and create an "insulated" roof deck with a combination of rigid foam and some above deck venting. That would be the best of both worlds.
Lynn Noesser
6/8/2016
If you continue with the option to spray the foam insulation you will want to limit the thickness on the first pass. Reducing the thickness to a few inches and allowing to dry will reduce the amount of moisture directly against the metal roofing but, more importantly, it will reduce the amount of heat generated on the panel during the application. Unless this is a different type of material, these typically create a significant amount of heat during the expansion phase. Regarding venting, most metal roofing suppliers will recommend venting through the ridge cap.
Cathy Tallman
6/9/2016
Thanks for the quick response. We are using scissor trusses and using tongue and groove pine for the ceiling and walls. This area will be a tack room/lounge area. Original plan was to use typical fiberglass bat insulation, but when reading on line about the closed cell spray it sounded like it would be more efficient. We just want to insulate it the best way. When reading about closed foam, it says do not use any type of venting, no sofit vents or ridge vents. That you use the closed foam to make an airtight seal. I do not have experience with the foam insulation for any help you can give as the best way to insulate the barn/tack room would be very helpful.
Info @windowsonwashington.net
An informed customer is our best customer.
6/10/2016
If it is vaulted application, you are correct that fiberglass isn't as effective an application as SPF is here. Lynn is correct that you need to have controlled lifts of foam, especially Closed Cell, to negate the heat build up for the sake of the roof, but more importantly to prevent a fire. I would still incorporate a couple of inches of right foam to the exterior and you could reduce or eliminate the use of foam in the interior space at that point or at least just have to use a thin "skinning" of foam for the purposes of air seal.

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