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Insulating a steel building used as a home

Dwayne Cormier | Posted in Energy Efficiency and Durability on

I recently erected a red iron framed steel building with 26 gauge steel panels on the exterior walls. During the planning stages, I was going to apply closed cell foam. Unfortunately, I am no longer able to afford this option. I am now looking at using fiberglass batts. My plans are to stick frame the interior walls with standard wood 2×4 studs. This will create a 12″ deep wall cavity in which to insulate. My thought is to install batts of EcoTouch R30 in the steel wall cavity and R13 in the 2×4 stud interior walls. This will yield R43 in my walls.

Can anyone offer any their thoughts on this and should I use Kraft faced R13 on the stud walls or unfaced for both layers? It was suggested by a couple of people to install a plastic vapor wrap on the stud walls before covering with sheetrock. The building is located about 60 miles form the coast in South Louisiana. My concern is any kind of condensation from improper vapor barriers and finding information on insulating steel buildings is hard to come by,

Thanks in advance.

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Replies

  1. John Klingel | | #1

    Dwayne: I am just a diy guy who reads here a lot, and asks more questions than I answer. As no one has spoken yet, I'll pose this. "...batts of EcoTouch R30 in the steel wall cavity and R13 in the 2x4 stud interior walls. This will yield R43 in my walls...." I believe that is inflated by the industry. FG batts will have conductive loops to deteriorate the suggested R value; they are not real dense. Do you need that high an R in your area? They'll be OK, but the worst insulation on the market. I would think that an inner vapor barrier would be destructive, as the steel is likely to get wet, and the vb on the inside may, too. Don't people who use VBs in your area generally put them on the outside, to keep the high humidity out? A steel building vendor and an insulator up here said that spray foam is the only way to properly insulate steel buildings. Dunno if that applies to you. It will be informative to see what the pros here say about this.

  2. GBA Editor
    Martin Holladay | | #2

    Dwayne,
    You have several problems you need to address:

    1. Your wall needs an air barrier. Since it sounds like your building has no OSB or plywood sheathing, that's going to be tricky.

    2. I don't know how frequent your steel posts or studs are, but it makes little sense to insulate between steel studs. The steel framing members are such serious thermal bridges that the presence of insulation between steel studs or posts is basically useless.

    3. All of your wall insulation needs to be either on the interior side of the steel framing or on the exterior side of the steel framing -- not between the steel posts. Ideally, you will use some type of insulation that isn't air-permeable. That means spray foam or rigid foam sheets.

    4. You definitely don't want to install poly sheeting on the interior side of your wall.

  3. Stuart Fearn | | #3

    IMO you want open cell Icynene foam. Cheaper than closed cell and it is flexible and will move with the steel & not buckle the sheets or become disconnected. Icynene is a certified air barrier.

    If you can't afford it now can you afford to re-do it later when it is moldy? Metl buildings are fantastic air leakers and you will have issues for sure.

  4. Dwayne Cormier | | #4

    Thanks so much for the replies. It looks like the use of spray foam is simply out of the question due to the high costs and unexpected loss of funds. That is why I am on to plan B unfortunately. I do realize that I will not get the full effect of R43 and I really do not require or need that much. We do have a lot of steel buildings around here in the commercial market.

    Generally they install batt insulation on the outside of the red iron framing and then install the sheet metal siding over that. The batts they use are lined with a white plastic film facing the interior side. Then they apply traditional stick framing for the interior walls to create office space.

    I understand that the red iron beams and girts will act a huge thermal bridges. What if I was to add sheets of rigid foam to the back side of the interior wood framed walls? It will be foaming all the edges of the metal siding and corners so air infiltration should be minimal.

    So what I would have would be this. Exterior sheets of metal siding, 9" of unfaced FB, sheet of rigid foam, 3.5 inches of FB then sheetrock. Again, I know foam would be the best option. I am looking for input on a second option. I have attached a pic of what I am dealing with.

    Jumping back to the foam and thermal bridges, the two companies that quoted me spray foam will either spray 3 inches of closed cell or five inches of open cell. My steel girts are 9 inches wide and in theory would not be covered with foam. How would thermal bridging with a spray foam be dealy with?

  5. GBA Editor
    Martin Holladay | | #5

    Dwayne,
    It sounds like you are going to install rigid foam sheets between the 2x4 framing and the steel framing. How are you going to do that if the 2x4 framing is already up?

    If I were you, I would skip the 9 inches of unfaced fiberglass and put all my insulation on the interior side of your steel frame. Rigid foam on one side of your stick framing is a good idea, as long as you seal the seams with a compatible tape.

    But you have another problem: a huge thermal bridge at the slab. The only way to address that is to install rigid foam on top of the slab, and then new flooring or concrete on top of the rigid foam.

    Whatever you do, remember to have continuity between your wall air barrier and your ceiling air barrier. You also need continuity between the wall's thermal barrier and the thermal barrier at the ceiling.

  6. TJ Elder | | #6

    Dwayne,

    Something you want to avoid here is having air permeable insulation next to that cold metal skin, because there will be condensation at the inner face of the metal. Any wetting at that surface would need to dry toward the interior because the metal is not vapor permeable. I think it would make sense to have rigid foam at the outer face of 2x framing, if you can install it that way. Basically you'd frame the walls on the floor, sheathe with rigid foam and then tip them up. Forget adding batts into that 9" space behind the metal, because you can't control moisture or airflow in there. You'll end up with a cold shell and a warm inner lining. It looks like that door has a steel header--as Martin said you want to insulate the floor, so any openings will need retrofitting several inches higher.

  7. Jim Merrithew | | #7

    Dwayne,
    I live near Ottawa, Canada, so our climatic concerns are quite different.
    A few years ago, I worked on a construction crew which built a chain of restaurants. Most of the structures were wood framed. However, one project was red steel with steel studs. The construction took place between December and March, so winter temperatures and record snowfalls created other issues.
    We insulated between the studs with fiberglass batts. The exterior sheathing was Densglas. On the inside, we added Poly Vapour barrier and drywall.
    To provide heat and melt the frozen ground before we poured the slab, we ran propane and natural gas heaters. The vapour moisture from the heaters and the melting ground condensed on the drywall wherever there was a steel structural member. This moisture ran down the walls. I remember thinking that the owner was paying almost a million dollars for his new building and there might be mould in the walls before he took possession.
    Based on these observations, I concluded that the best way to insulate steel framing is to use rigid board insulation and install it outside of the framing. This would keep the steel warm and reduce thermal bridging.

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