Insulating metal holddowns and bearing plates in wall assembly- Condensation Concerns? – GreenBuildingAdvisor

Hi Folks,

I’m curious if people provide any special attention to insulation around metal components in the wall assembly, particularly holddowns (i.e. simpson HDU4) and bearing plates, considering these are typically bolted into a relatively cold concrete foundation, or in my case a very cold steel trailer which my tiny house is built on.  The general recommendation for intake air ducts seems to be to wrap them with a vapor impermeable insulation. Wouldn’t these structural components also represent a similar condensing surface, or am i missing something?

I can’t seem to find any real info on the vapor permeability of the one part foam, and parts of the holddowns are within 1/4″ to 1/2″ of the interior wall surface anyway, so it would have to have a very low permeance. If we operated on the assumption that it would be best to have a vapor barrier insulation on these, i could spray foam a large blob around them, and then wrap that all in an impermeable tape like Siga Rissan. As for the all -thread run through some of the holddowns (which travels up to the top plate), i could pretty easily wrap those in a pipe insulation like Armaflex if it was thought to be safer than just spray foam alone.

For some project specifics:

-2×4 wall, plywood sheathed, rainscreen gap. Exterior joints all well-taped for an air barrier.

-installing cut and cobble polyiso foam board, with one part spray foam (Osi quad foam) at the perimeters in the stud bays.

– interior cladding will be tongue and groove boards with two coats water based poly.

– climate zone 4 marine, but may move to zone 5 at some point.

As always, many thanks for everyone’s time and expertise!