Hey folks,

We are building a cabin/tiny house on wheels in zone 6a.  It won’t be moved often.  The trailer has the deck over the wheels, with the steel cross-members flush to the top of the frame, 16″ on center, that way we can attach the subfloor directly to the trailer.  There is metal flashing (to minimize road spray) under the joists the majority of the trailer, but the flashing is over the joists in the wheel area, to allow clearance for the wheels.  Our floor assembly is currently planned as outlined below, but before we do the final install, we have a couple questions.

From bottom to top…
-Flashing
-Steel joists – then some flashing just above the wheel area
-Construction adhesive
-OSB 3/4″ T&G – 100 day exposure

We’ll build the walls on that, then once it’s dried in, between the walls it will go…
-2″ EPS
-2″ Polyiso
-OSB/Plywood
-Underlayment if necessary
-Finished floor (TBD)

1a. I’ve read that some folks put sill sealer/gasket between the steel joists and OSB subfloor, what benefits might that provide?

1b. If sill sealer recommended, would construction adhesive be applied to both sides of the sill sealer (between metal and sill sealer, then between sill sealer and OSB)?

2. Would it be prudent to paint the bottom of the OSB subfloor with a waterproofing primer of some sort?  I’ve heard conflicting views on the subject, and am dubious of the those sources’ credibility…

Thanks for your input,
Mat