Foil-faced polyiso in 2″x6″ stud bays – with shower wet wall
So I’m not entirely sure which Category this should be posted, but here’s my question:
For the first time in all my years remodeling, the Design for the Master Bath “requires” that the shower valves/head be located on an exterior wall. I won’t go into the details of why/how this came to be designed (not by me), but given the sunken costs and logistical challenges of alternative layout options, I’m left to make this work.
First, I’m in Zone 5 (Front Range – Colorado). Second, the walls are 2″x6″. Third, we will vertically stack the shower valve, head, and diverter for a supplemental hand-held.
And so now, what I’m trying to determine is whether I can get away with filling the 16″ o.c./96″ tall stud bay(s) behind the plumbing with 2 layers of foiled faced poly-iso (and foaming all seams), getting me +/- R-20 of rigid, plus additional radiant (R3?) for the void between the rigid board and the back of the tile backer board. And so if we set the valve and water lines inside the void between the poly-iso and the tile backerboard, could/should/would I feel “comfortable” the water lines wouldn’t freeze?
Alternatively, I could forego the void, and add some batts to fill out the full 5.5″ depth.
Or, as initially planned, I could first add some 2″x furring strips to the face of the studs and attach the valves to the furring, and run the pipes through that outside 1.5″ – and then still adding layers of foil-faced polyiso to the bay(s) behind the plumbing. Clearly, that would add additional R-value to the bay behind the plumbing. (But it would also add some detail challenges to the wall that continues on to the adjacent double vanity).
So I guess what I’m wondering is whether I really need to add the furring? And in either case, if I am going with rigid board insulation in the bays behind the plumbing (with the intent to just use batts in all the other adjacent exterior wall bays), is foil faced polyiso the way to go, or would I better off with non foil faced XPS?
And the reason I listed this question in this category, is that, aside from the insulation logistics to consider, I’m not entirely sure what code requirments/violations might be involved in this plan.
A long questions with many variables, I know. But I surely appreciate your insights.
FullerHouse Construction, LLC
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