Yeti cooler like lid details for my 48′ tall multigenerational ICF home
I wanted to get some feedback on my roof details that are kind of a take off of the article that Martin did a few years back about “Installing Rigid Foam above Roof Sheathing. Except in my case the sheathing and the foam are one and the same because I am using a product that embeds metal studs into the 5.5″ of EPS foam. One metal stud on both sides so they are thermally broken. Basically it is a skip sheathing method with Sharkskin Ultra SA on top of the foam panels and then a mechanically seamed standing seam metal roof that is at a .5″/12” pitch on a mono slope roof.
So couple of questions. I plan on treating the bottom steel stud in the foam panel like the bottom sheathing in Martin’s article which means in my climate I can only have 49% of the insulation of the 5.5″ of EPS foam below that point to avoid condensation issues. Part of that insulation will be 3″ EPS foam panels that go in the opposite direction as the 5.5″ foam panels. These will be sitting on top of the I-Joists. Both the 3″EPS and the I-joists are inside my ICF walls and the 5.5″ EPS will be on top of the ICF walls and will overhang the ICF walls. Hence the Yeti cooler like lid. So my question is does this make sense to treat the bottom metal stud as if it was wood sheathing?
Also I will have either rock wool or fiberglass batts in the cavity of the i-joists to make up the rest of the insulation to almost match the EPS foam in the 5.5″ panels. And I will be using the Intelo smart vapor barrier to hopefully control the humidity in that cavity because I will have a serious stack effect going on given the fact that I have 5 levels in this 48′ tall multigenerational home.
I will also strap the ceiling under the I-joists so that I have no penetrations from lights. And one other detail is I will have zero penetrations through my roof.
Any thoughts on what I might be missing.
One thing I learned today is that when I am connecting my metal roof panels that before I seam them I need to use a butyl sealant.
Any other thoughts for me to consider as I try and make this roof/lid as airtight/watertight and manage the vapor in a way to decrease issues for my posterity over the next 500 years?
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Not to be pedantic, but I want to be clear what we're talking about. A stud is a vertical framing member. A joist is a horizontal framing member that supports a ceiling or floor. A rafter is a diagonal framing member that supports a roof. A framing member that runs horizontally between rafters to support the roof is a purlin.
I'm trying to picture what you're describing. I don't think your roof foam is going to have studs in it. It sounds like they might be purlins. If you're sloping the i-joists they're rafters, though I can't tell from the description if your plan is to slope them.
Since the roof is only 0.5:12 it sounds like it's supported by the joists. I would say the easiest way to do this would be to run joists that are strong enough for your snow load, horizontally. Put a layer of subfloor over them. Then put as much foam as you want, with the top layer made from tapered foam. Commercial roofs are often done this way and the roofer will be familiar with it. I don't know if your heart is set on monoslope but if you do it this way it's easy to do the roof as gabled or even hipped, which solves a lot of problems.
Then fill the cavity with batt and put intello below.
I would verify that the standing seam works with a slope that low, they usually want more slope.
Seems like you are talking about a product like from Thermasteel or Greenstone's ICE panel?
excerpt:
"ThermaSteel’s patented composite joining technology bonds light gauge steel structural members together with EPS, delivering a stronger, lighter wall system which installs faster, and performing as structural framing, insulation, sheathing and vapor barrier — all in one."
I have been looking at both of these too, but I am pretty sure you are going to have to put sheathing on your roof joists BEFORE installing the EPS panel.
I think in the excerpt above from Thermasteel (about "all in one"), might just refer to a wall but not the roof...
https://thermasteelinc.com/about/panels/
https://gsbp.ca/what-are-ice-panels/
Yeah, when OP talked about "studs" I suspected it was a material meant for walls. Engineered steel is meant to be used in a specific orientation.
Five stories sounds like a lot for ICF. Have you had it engineered?
Three stories is as high as you can go with conventional framing under the prescriptive IRC. Around here what's popular for 5-story buildings is to build a 2-story "pedestal" out of concrete and then stick-frame three stories above that.
I think you're not going to see a lot of love here for ICF.