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TOPIC: Energy Efficiency

Metal roofing on sheathing and closed cell foam insulation

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I am looking at installing a new metal roof on new trusses (closed attic/sealed Attica). Roof will be 35'x70'. I would like to not have to sheath the entire roof just to put the metal roof on. I plan to have runner every 2 foot and the truss company said we could go in on a 4 foot center for trusses. I would like to spay foam to the underside of the metal roof. What will I need to do to do this? Vapor barrier on top of the trusses under the metal? Can you spay the metal directly with out a vapor barrier?
Guest User

1/3/2016
If you use a closed cell foam you do not need an additional vapor barrier. However, should the roof ever need replaced, having the vapor barrier will be very helpful so I would suggest it.
Todd Miller
Isaiah Industries, Inc.

1/3/2016
How can I tell if the contractor is using open or closed cell foam?
Guest User

1/3/2016
They will be able to tell you. They are two very different products.
Todd Miller
Isaiah Industries, Inc.

1/3/2016
Old Farmhouse Restore.. 1850 build, Upstate NY climate. A recent reno to the upstairs of my old farmhouse has left us with bigger problems. Our roof is tin over osb and clap boards with MINIMAL air circulation . We installed 8" of batten insul. to the bottom of the roof deck & a knotty pine the ceiling. now that the house is more air tight condensation has developed b/w the underside of the roof deck and batten insulation thus saturating the insulation. The obvious start is to pull down the pine (which breaks my heart to do) & insulation to expose the underside of the roof deck. Question 1.) will 4" to 5" of closed cell spray foam applied to underside of roof deck be enough of a moisture barrier to prevent further condensation from forming on the bottom of the roof deck? (would that create the thermal break we need to stop the dew point from being reached?) Question 2.) If i spray foam will that just isolate condensation b/w the bottom of tin and closed cell foam and rot out the roof deck faster. Im trying to come up with solutions that dont involve complete reconstruction of the roof.
Guest User

1/9/2016
4-5" would be enough and would give you sufficient R-Value as well. Opt for the 5" range and code may require that you put R-38/R-49 (whatever that equates to). https://energycode.pnl.gov/EnergyCodeReqs/?state=New%20York The moisture is coming from the home. You will fix that via the spray foam. I would stick some rigid foam inside the joists and then spray the backside of the rigid board.
Eric Novotny
An informed customer is the Best Customer!

1/9/2016
not enough space to get r 49 in there 5-1/2" is ALL i can get in there. the ceiling is nailed onto 2x6 nailers i added. original "rafters" if one can call them that are 3" x 4" roughcut @ 3-4 feet on center!! I dont know how these old houses stood for so long with the snow loads we get here! May i ask what the rigid-foam will accomplish that the spray foam wont?
Guest User

1/9/2016
Poly-Iso has a higher R-value per inch and will also allow the room to to serviced at a later date without destroying the foam. The framing will still be the weak point in the thermal system but plenty of roofs have been converted to insulated and do quite well. You will need to condition that space when you are done though. It is now part of the interior space and envelope.
Eric Novotny
An informed customer is the Best Customer!

1/9/2016
I'm hoping someone can give guidance. We are building a new smaller (about 750sf on main floor) home in mid-Missouri, so zone 5. We want it very energy efficient , at least as much as practical and we can afford. But we can sacrifice surface stuff to get the structure right. No attic- the whole space is a loft open to below. There is a big front porch that extends over the front room's roof about 6' in, and there is a dormer in the front also. Otherwise pretty simple with a 8/12 pitch. We plan on doing a red metal roof, over I think 3/4" OSB and roof is site built with16" on center spacing. The house faces south/east but there are some trees that might shade a little. The north west side is uninterrupted except for a vent pipe. We aren't planning on VHAC on the loft unless we find we need it, But are doing a ductless minisplit system downstairs . It does dehumidify, which is needed here. Will also have a wood stove. The bath, stove and shower are vented outside. It has a concete floor but we did put R 5 insulation blankets under the slab and will insulate the outside of the slab edges. Only 2 of us, so may not generate a lot of internal moisture, but we do keep our windows open a lot on spring and fall and we have humidity here. The house has a fairly open floor plan. We were going to install wood "car siding" as the ceiling rather than drywall. Worried about best way to insulate, protecting the roof structure from moisture, and possible leaks and how that might be to repair , though the metal guy says it won't. So, what is the best way to insulate this? -Closed cell at least 2" under roof deck? If so, is it ok to leave the rest of the cavity empty? Is it best to fill the cavity with open cell or rock wool or combination? -Or Maybe put 2" rigid foam boards between the cavity and spray either open or closed after that( thicker and could do the board part ourselves and so if there was ever a leak, could access that easier???) -Could look at foam board on top of the roof deck/ vapor barrier but not built for that now and not sure how to modify it and if our metal roof would be ok with that method. -One foam installer recommended about 3 1/2 " of open cell but recommended closed cell for the walls so would probably have both equipment if we want to combine it( most of his work was Florida- no cold issues like here-but R factor of that not up to code). -Would open cell be ok if we dry walled and painted the ceiling with a bathroom paint ( not my favorite idea)? Any better ideas? Is it needed to still caulk everything (air seal) if doing any of these methods?- does that mean every crack? This is a one shot deal for us, so any help would be greatly appreciated.
Guest User

3/6/2016
Best bet here is going to be to incorporate right foam to the outside layer (i.e. sheathing side). This will help uncouple the framing from the thermal boundary and make the entire assembly more resistant to condensation formation.
Eric Novotny
An informed customer is the Best Customer!

3/6/2016
I have enclosed a pole barn with metal skin all the around. The dimensions are 32 x 48. I plan on spraying foam insulation directly to underside of metal roof and to the inside of the metal walls. Do I need open or closed cell? I have been told use open it will allow moisture to escape and also use closed because it will create moisture barrier. Rusty
Guest User

4/12/2016
Rusty, Depends on where the barn is, but the prescriptive recommendation on roofs is usually Close Cell (CC SPF). We have done open cell before and it works quite well as long as the application is left exposed and uncovered. If you aren't covering the foam (FYI...it will need to be covered with an intumescent barrier of some sort), it is best being closed cell.
Eric Novotny
An informed customer is the Best Customer!

4/12/2016
Hi Guys,Ok we bought a home in May 2015,we live in southwest Louisiana.Well here is the cold weather about 35 degrees and we start to see wet spots on our ceiling,we are all confused about what's going on so that's when I went to do research,here I am trying to figure out what is condensation.....sweat in my attic.....we still not really understanding so we call a roofer and he says we need more air flow in our attic so we get 3 turbines hoping this would help our situation but it didn't.....We had a cold day today an guess what my metal roof is still sweating..... please tell me what I can do.We don't have any sheathing on the underside of our metal roof and we would really like to get this situation solved.....In our area I need help!!!
Guest User

11/21/2016
It does sound like you need ventilation in the attic. The turbines you added are to act as exhaust vents. Do you have adequate intake vents, usually in the eave soffits / overhangs to feed air to the turbines? A great source of venting information is www.airvent.com Also, look for ways to reduce moisture levels in the living space of the home. Also, are things like dryer vents, bathroom and kitchen fans, plumbing stacks all vented to the outside rather than just into the attic? Additionally, if your home has a furnace with a fan, try keeping the fan running all the time, not just when the furnace is on. Call me if you'd like to talk this through further. Todd Miller. 1-800-543-8938 ext 201
Todd Miller
Isaiah Industries, Inc.

11/22/2016
Jerry T I have been reading your forum. I am an an HVAC contractor but am looking to do battens over existing comp my house and interested in the best way to do insulation or if best not to? some open attic and some cathedral ceiling The cathedral ceilings has a lot of heat loss and I would like to insulate if possible?
Guest User

2/18/2017
I am having a hard time deciding about this insulation issue. I am about to install a metal roof over a layer of comp with purlins..I am trying to figure out which insulation is best for the space and should I use 2x4 or 1x4 ....some of the forum appears to be leaning towards solid closed cell and some seem to lean towards spray foam The ceiling is open with gable vents and truss vents...blown in insulation . Open attic in 50% of the house and the other cathedral ceiling all has 1/2 in omb lid
Guest User

2/18/2017
This can be difficult and to some degree depends upon where you live and what the risks are there. You basically have thermal break, vapor barrier, insulation and ventilation to play with and all can be necessary in some cases. Ideally I like from the bottom up, ceiling, vapor barrier, insulation, vented air space, decking, underlayment, roofing. I'd be happy to talk to you sometime if you would like to call me at my office at 1-800-543-8938 ext 201.
Todd Miller
Isaiah Industries, Inc.

2/19/2017
Jerry, How do the vaulted sections tie in with the vented sections? How about some pictures?
Eric Novotny
An informed customer is the Best Customer!

2/19/2017
Question I have a barn / shop that gets hot in the summer and cold in the winter. The walls are insulated to R20 but I have this metal roof that seems to radiate heat into the the space. The metal roof is of a "mini v " used on MD horse Barns. If I were to use Expanded Polystyrene Foam Board Insulation either attached to the metal roof or suspended below the roof would this help. Second what direction should I point the metal side of the Expanded Polystyrene Foam Board Insulation? Thanks you in advance
Guest User

5/3/2017
Adding insulation and/or an enclosed ventilated airspace would help dramatically at creating a situation that helps block heat. Radiant barriers need to face an air space ... no major different whether they face in or out.
Todd Miller
Isaiah Industries, Inc.

5/3/2017

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