How do I insulate my steel panel house?
Hi there, we’re building our home in southwest MI (5a) and am unsure of how to properly insulate our home to avoid condensation issues.
Exterior we’ve got 2×4 girts (on laminated 6xcolumns)>osb>stapled housewrap>stapled sill gasket for rainscreen>steel panels.
I see now that we should’ve insulated exterior under the panels but we’re past that and need to now figure how to best insulate interior walls.
It’s looking like spray foaming the entire interior wall is out of the budget but I’m under the impression I’m still going to need some type of vapor barrier?
My concern is that if the osb does get wet and we use an interior vapor barrier up against it, that it won’t be able to dry in or out either way.
So I’m unsure of where it should actually go inside of the wall? Especially with us using both heating and cooling. (radiant heating/cooling concrete floors and a ductless mini split for 80-90f summers and below freezing winters)
The roof (hidden fastener steel panels>high heat synthetic underlayment>osb) will have 2”ventilation through soffit and ridge so I’m not as concerned about condensation issues up there.
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In your climate you need roughly 8" of insulation on the walls and 12" in the ceiling. If your roof is trusses the ceiling should be easy, just drywall the ceiling and pile the insulation up over the drywall.
For your walls, they either need to be able to dry to the outside, or the cold side has to have enough impermeable insulation to prevent moisture from condensing during the winter. I don't see how to do that.
If you could figure out a way to make the outer wall vapor permeable, you could build a 2x4 wall in front of the posts and fill the whole cavity with blown insulation. That would be pretty inexpensive and would give you good insulation. I know you said spray foam is out but spray foaming before stuffing would solve your condensation problem.
Another solution would be just to build another whole wall on the front of the posts -- girts, sheathing, 2" of foam and then a 2x6 wall filled with either blown insulation or batts, then drywall. But that would take 10" on each wall; your windows would look funny.
What would be a good way to make the exterior vapor permeable in your opinion? Do you mean something like taking off the house wrap? I’m unsure of whether the house wrap will allow any drying. We taped the top and bottom of it as well.
But just to clarify, you’re saying if we did maybe an inch or two of spray foam onto interior osb/framing and then the rest blown in on top of the foam/before drywall, we should be safe from condensation? Does that include the osb as well? Not sure if condensation can get through the wrap into the osb, but we did use staples for the wrap so might be possible wetting from that I suppose
House wrap is vapor permeable.
The condensation concern in a cold climate is that in the winter, the air inside the house is warm and humid compared to the outside air -- the dew point typically is around 50F. If that air comes into contact with anything colder than the dew point the moisture will condense out. If there isn't a way for that condensation to dry it accumulates and causes problems.
In a cold climate heat will flow from inside to outside in the winter. That heat tends to drive moisture in the same direction, so if a wall has the ability to dry to the exterior the heat will drive any moisture that gets into the wall out. So the usual recipe for cold climates is to have some sort of vapor block on the interior side of a wall -- paper facing on batt insulation is the most common -- along with air sealing of the interior wall, to keep the interior air out of contact with the cold part of the wall. The sheathing and housewrap will allow vapor to exit to the exterior, and you either use a siding that is also vapor permeable -- wood -- or you leave a gap between the siding and the sheathing so vapor can escape.
If the siding is impermeable you have to do things a little differently. Instead of letting the wall dry to the outside, you have to use impermeable insulation so that moist air never comes into a surface that is cool enough to cause condensation. That could be foam board, but looking at your pictures the inside of the walls looks so busy that it would be hard to create a layer of foam board that would be continuous. (That said one possibility would be to do three layers of 1.5" foam board -- one layer between the girts, one layer over the girts and between the diagonal braces, and one layer over the diagonal braces. We can talk more about that idea if you find it interesting.) The other impermeable insulation is closed cell spray foam, its main attraction is that it's easy to create a continuous airtight layer, the downside is it's expensive.
Inside the impervious layer you can put fluffy insulation -- batts or blow-in-- which is where you get the most insulation for the money.
I'm assuming the steel siding is impermeable. If it weren't you could use fluffy insulation throughout which would be the most cost-effective. There's two ways that the siding could allow the wall to dry. The first would be if there were a gap between the housewrap and the siding that allowed air to flow between them. The second would be if there was a gap between the insulation and the sheathing that similarly allowed for airflow. In either case there'd have to be a way for air to get in at the bottom and out at the top. Roofs are frequently constructed with a gap between the insulation and the sheathing, in a roof 1" is considered the minimum acceptable gap. I don't really know what you'd need in a wall but probably the same would do.