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How to fasten exterior foam on metal stud walls?

Xiao House | Posted in General Questions on

My wife and i are building a tiny home on 10ftx24ft gooseneck trailer with metal framing. It’s a 1/12″ shed pitched roof. We live in Northern Colorado, so winters can get quite cold and windy(more like Wyoming, so I want to build to that code as much as possible).
We want to put the insulation on the outside of the framing in the perfect wall and roof method. This should also allow us to put plumbing in the exterior walls without risk of freezing, and also remove all thermal bridging and condensation problems that can occur with metal studs.
Im thinking at least 3″ polyiso on the walls, planing on 4″, and about 8-9″ on the roof. will fulfill all insulation requirements.
The questions arise in my mind when thinking about how to secure it to the framing, and how many fasteners. Normally people seem to use long lag screws through 1×4 nailers into the framing, and that is my plan for siding, and 2x4s for the roof. We are using metal studs though, so there isn’t the deep stud material to bite into.
With our wind and especially the roof’s thick insulation, are standard practices of using lag screws enough? Will the sheathing and metal stud be enough for the lag screws, or would using long bolts with washers and locknuts be a more secure method to secure the foam? How many screws/bolts would be necessary on a nailer? i was hoping just 3-4 bolts for the walls(about every 30″) might work, to minimize the only metal through connections,
For the roof. I am basically thinking building a SIP and then putting the metal roof on top of the second sheathing layer over the 2×4 nailers, and the same question of securing foam applies, but through ticker foam.
One last question I had is a need for ventilation under that sheathing, since it will be on the cold side of the envelope, over 8-9″ of foam?

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    This looks like an interesting system for attaching foam to metal studs. https://www.youtube.com/watch?v=tzEFku03YtY

    Has anyone Grip-Deck ci? How did it perform?

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