Metal Roof Over Wood Truss Sheathing With Continuous Insulation

I am planning a new home construction. Naturally, I am looking to make it as energy efficient as possible and worry free. I plan to use the closed-cell spray foam insulation on 3/4 inch sheathing. Will I be looking at any problem with going to a metal roof?		Guest User 8/19/2011
No, in fact metal is very well suited to hot roof applications like this.		Todd Miller Isaiah Industries, Inc. 8/19/2011
Not at all. Best of both worlds in both insulation and and roof choices. Rigid foam to the exterior surface can be a bit more cost effective as compared to applying the insulation depth to the underside of the sheathing in the total R-Value depth required and create a true thermal break between the roof and the structure below. A polyisocyanurate foam and system of battens can give you the overdeck venting and 100% thermal break that is ideal.		Eric Novotny An informed customer is the Best Customer! 8/19/2011
hey todd' i dont unnerstand. when i asked you the same question u said that not all metal roofs were compatible with foam. the guys at two foam spray companies got a laugh out of that cus they couldnt figger what metal roof would be incompatible with foam. metal is metal and foam is foam and never the twain shall conflict. as for bsbs approval your response to guest seems to have been remarkably free of this. btw if u need someone to defend your status as a tech expert and not a salesman for a company the website is already in trouble. dont worry about any more offensive posts from me. im outa here. ray t		ray tartakoff energy saver in the catskills 8/22/2011
Thanks Ray. Feel free to call me anytime at 1-800-543-8938 ext 201 and I will be happy to talk it through. My reference to not all systems being compatible with foam was referencing situations when the foam is installed on top of the roof deck. I am not at all a fan of that application unless battens are involved. I will not allow my company's products to be installed that way. This particular forum posting, however, is referencing foam sprayed to the bottom side of the roof deck. That is a different situation entirely and all metal roof systems can be compatible with that. I do apologize for any confusion I may have created but I saw this post and yours as two very different situations, hence my different answers.		Todd Miller Isaiah Industries, Inc. 8/22/2011
I should give a little extra clarification here ... the issue with foam on top of the deck is that many panels can "walk" into the foam, causing deformation of the panels. Additionally, the foam can allow fasteners to be over-driven which also can have damaging results. On metal panels that can be installed over battens, though -- that can work well with foam on top of the roof deck. The battens provide the support for walkability and for fasteners that does not exist if only foam is there. I hope this helps. And, again, to reiterate -- "hot roof" or "hot attic" assemblies where the foam is beneath the roof deck, are okay.		Todd Miller Isaiah Industries, Inc. 8/22/2011
Gotta agree with Todd - most panels directly over foam are a bad idea. Insulation between battens, or sandwiched between two layers of plywood/OSB is a better options.		Nate Libbey 8/23/2011
+1 Todd's advice is spot on.		Eric Novotny An informed customer is the Best Customer! 8/25/2011
I am hearing that spray foam under the plywood deck and peel and stick membrane on top of the plywood deck and then metal roofing, is causing the plywood to deteriorate. Comments?		Guest User 7/22/2013
This is not true in my observations if the foam on the underside of the deck is closed cell or treated with a vapor retarder paint. If, however, you spray the underside of the roof with what is a vapor open foam (open cell) and you have enough moisture in the air, it can collect on the cold underside of the sheathing, condense, and rot the roof deck from the bottom up. The peal and stick on the top surface does not really decrease the permeability of the plywood though as it is not tremendously permeable anyway. If you didn't spray the right foam or application, the roof deck can rot out regardless of peal and stick vs felt.		Eric Novotny An informed customer is the Best Customer! 7/24/2013
I have an older single wide mobile home in Arizona where the heat is. Several friends I know had new roofs installed by a contractor by putting 4 inches of hard foam than wrapping it with metal across the whole thing. They all state how energy efficient this makes the mobile plus it's a good roof for weather as there's no nail or screws except on the very outside edge. However I seem to be the only one with the following problem. instead of being efficient my electric bill increased once the roof was installed. The air conditioner was checked and is working fine but it runs a lot trying to cool the mobile. I feel it runs more than it did before and I think the new roof is trapping the hot air in the house. There never were any vents anywhere on these units but I'm wondering if it would be beneficial to open both ends and let the air flow through between the roofs and even putting a small fan in there if needed to remove the heat between the old and new roof. There isn't much space maybe 8 to 10 inches at the highest point but anything is better than nothing. I might add that the mobile only has a 7 foot height inside and I have insulated the outside over the years put new windows and siding on this unit to upgrade it. I don't think all my efforts made that much difference.		Bill Boulrice 10/22/2013
I agree that some ventilatuon would be a good thing. Also, do you have high humidity levels inside the home for some reason? Are there any unusual large sources of moisture inside the home? Those could be contributing to a feeling that it is warmer because now that moisture is not escaping perhaps.		Todd Miller Isaiah Industries, Inc. 10/22/2013
It seems to have been a while since you posted, Bill boulrice. I am wondering if you found any remedy to your problem? It sounds like they may have used some setup similar to the Madden Industry with double the foam. Foam can be expensive. When you installed did you do any research on the EPS? I'm going to go out on a limb and say that the white stuff that they sell at Lowe's as a 4x8 sheet @2" thickness is awful. It's not as well made as the EPS that some consumer electronics are packed with and may not provide the desired r value.		Guest User 4/28/2014
There should be a space between the metal wrap and another layer collecting heat, shingles or metal		Guest User 8/5/2014
I am installing a metal roof over synthetic felt on 5/8 OSB, MS Gulf Coast. Plan to go with closed cell foam on the underside of the OSB to include the roof as it extends over three porches. My contractor said I have two options. 1. Leave the roof over the porches uninsulated and insulate only the roof line in line with the conditioned living space below. Or 2. Insulate the entire envelope to include the porch ceiling. Which is best. Would number 1. Leave a super heated dead space on 3 sides of house since no soffit vents due to potential high wind entry leading to roof failure.		Guest User 2/5/2015
If you don't insulate the underside of the porch roof, you will need to allow for a bit of convection to happen in there by providing some vents on the gable ends or otherwise to the exterior. I would probably incorporate some rigid foam to the roof deck to help that SPF work that much better.		Eric Novotny An informed customer is the Best Customer! 2/9/2015
This site seems difficult to enter questions, if one is not currently a contractor or provider of materials. It's kinda mind-blowing that foam insulation and metal roofing has been around so long, yet so many roofers are still not doing it?! Can only think there might be reasons why most roofers are not yet including foam insulation under the metal? We want to increase insulation any good way we can; our roof, as-is, generates tremendous heat-gain in summer, and loads of heat loss in winter. The roof trusses are bottom-grade [read: smallest possible wood parts possible]. Climate: SW WA State. Two old layers of old comp. roofing must come off. Only one contractor so far, could address placing 2" solid foam insulation panels Between Roof Underlayment and a new Standing Seam Metal roof; says he's installed numerous; some's been in place for over 20 years, no problem, applied like this. He didn't mention purlins. A few of our concerns/questions have yet to be answered by any source: ---How well do 2" foam insulation panels withstand heating/cooling cycles .over time., in this application? ---Do some types of foam insulation panels work better than others [i.e., open vs. closed-cell]? ---This type of application: good or bad idea? [if it's bad idea, why?] ---Is it necessary to place Purlins on top of the foam, to give an air-space between the insulation and the metal? ---Is a Stick-down, or Non-Stick-down, Synthetic Underlayment the best choice, for this application? ---Is there a better way to do plumbing roof vents, than putting holes through metal roofing? [We're trying to minimize roof penetrations!] ---Does anyone usually install permanent eye-bolts at the roof ridge, to hook on safety equipment? ---The contractor who says this is a good idea, also said he'd have to remove the gutters, replace those and raise gutters higher on new facia boards...yes or no necessary to change location of gutters? Or replace them at all [they seem to be working OK] ? I really appreciate advice! Thanks!		Guest User 7/25/2015
Chi, Tell me about your home currently. Questions (some already answered but in list format): Location of the home: SW WA Attic Type: Vented or non-Vented Roof construction: Trusses or Rafters		Eric Novotny An informed customer is the Best Customer! 7/26/2015
It's about 2600 s.f of roof on a '79 housing-boom, single-story, "flipper-special-lipstick-on-a-pig-bank-repo-special" house; "... roof generates... heat-gain in summer, and... heat loss in winter.... "roof trusses... bottom-grade [read: smallest possible wood parts possible], average-pitch... " "Two old layers of old comp. roofing must come off." Add: Olympia area; A few frank leaks, a few threatening leaks; shingles age-worn. We want to get rid of existing plastic roof vents, to use Ridge-venting. An unknown number of roof-deck pieces need replaced, per some contractors, but last one said decking seems fine. Modest gable-end vents x 3, and eave/soffit vents about every-other truss. Chimney is at edge of roof, w/leaking flashing and spalling bricks. Unsure what else? We're thinking, condensation on underside of decking [in attic] will be largely Reduced, if foam boards are placed between metal and underlayment on roof deck. That is, doing that reduces the temperature-changes thru the large roof surfaces, so that should nicely reduce incidence and severity of condensate under the decking [in the attic]? As well as taking a bite out of our indoor air tempering costs until we can do more. [[Our roof needs fixed this summer; insulation in ceiling/walls must wait, due to budget constraints. We're looking for viable ways to keep things "spackled together" for a generous several years until we can afford to do things right. ]] Thanks!		Guest User 7/27/2015
Chi, If the roof is vented, insulating the roof deck won't impact condensation formation at the end of the day. The attic needs to be air sealed and insulated and you need to up the venting. If there isn't any HVAC in the attic, going with a lighter color (while it will keep some of the radiant heat out of the attic) is entirely inconsequential. You have to stop the moisture from migrating into the attic and if/when it does, the roof/attic needs to be properly ventilated to remove it. If you were putting foam on the roof deck and then spray foaming the underside of the roof (i.e. making he attic a conditioned space), that is all fine and good but we aren't doing that here. http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/ba_airsealing_report.pdf		Eric Novotny An informed customer is the Best Customer! 7/27/2015

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Source: https://www.metalroofing.com/spirit/topic/4918/metal-roofing-on-sheathing-and-closed-cell-foam-in/

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