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Old 03-11-2012, 10:30 AM   #32
Join Date: Oct 2010
Location: Florida
Posts: 97
A) I could not agree more from a building sciences perspective that an exterior wall system needs to allow vapor transmission and where appropriate, have proper drainage planes. One look at a mold infested tear out would convince anyone that attention to design and installation detail here is important.

This is why foil faced rigid foam board has given way to unfaced foam and Fi Foil came out with a hi perm version (with slits in it) and lo perm elastomeric exterior paint is now discouraged for new construction. I guess one could argue that these are still not hi perm enough but they account for virtually all new construction here. I considered aerated concrete block to avoid additional insulation and pick up additional soundproofing but I could not find a collection subs willing to work with it.

All exterior walls are the same: 8" block-1.5" furring strips/air gap-Fi Foil, including the shower areas. Drywall hanging starts this week and I have a few choices: 1) tile backer against the fi foil like every other wall, 2) cut additional slits in the fi foil in areas with tile backer, 3) remove the Fi Foil in tile backer areas.

B) Point taken on interior plumbing elsewhere but it seems that the wall containing the shower head and mixing valves might be at higher risk. More mechanical action and solder joints as well as direct penetrations from a high water area.

C) Many comments here about the "speed bump" issue at board joints being a reason to prefer a backer board such as Permabase with tapered reinforced edges but if it is prefered to just let the joints get handled at the Kerdi step then it should not matter. A more pressing issue appears to be hydration during thinset/Kerdi hence plain white drywall being prefered and Hardi backer being cautioned. Does rough vs smooth on cement board matter here?

GeorgeG is offline   Reply With Quote