Moisture control in a tiny house trailer
I am preparing to insulate and sub-floor my 10′ x 28′ tiny house trailer. The trailer was built specifically for tiny house construction and arrived with a seamless steel belly pan that is welded solid to the trailer frame, joists and runners. I plan to use rigid foam insulation, topped with rockwool, then advantech subflooring, then hardwood. My concern is moisture control. Should I drill holes in the belly pan to allow moisture to escape? Is there some material that I could cover holes with that allows moisture OUT but not IN?
Help. I’m stumped!!
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There is little value to insulation put between steel framing (even more so with a steel pan attached to the underside). So build everything above the frame.
Here is some info about exterior perms (if you don't ventilate the pan) and how it effects a design. But trapped moisture (eg, between floor and pan) isn't good for wood or steel.
If you want to apply rigid foam directly to a steel frame, you may be able to use round squash blocks to avoid foam compression without adding much thermal bridging.
From recent experience: the time to take additional action against a trailer frame rusting is when it is new and open.
You don't need to drill holes in the steel pan. Adding a continuous layer of rigid foam above the steel pan is a good idea. Skip the mineral wool, however -- just add whatever thickness of rigid foam you need to achieve your R-value goal, followed by a layer of OSB subflooring. You can attach the OSB to the steel pan with long screws.
Thanks to you both. Jon, that info about exterior perms is invaluable!
I'll go with the rigid foam. Martin...why OSB instead of Advantech?
As Tim explains below, Advantech is a brand of OSB -- so the OSB was your suggestion, not mine. Many builders (including me) might prefer to use plywood. Either will work.
Advantech is a brand name OSB