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New bath addition with tile walls inside: What is most foolproof wall assembly?

Will use rain screen approach outside. Will use a layer of 3/4" plywood behind Durock or similar on inside of wall to attach grab bars anywhere in future. Plywood behind wall finish is suggested by various websites for handicap bathroom. Closed-cell spray foam is in budget. Using all pressure-treated lumber. Will use sealants in all appropriate locations to prevent air leaks.

Will install bathroom fan with humidistat.

My concern is the limited drying potential of this wall. I will allow all wood to dry before completing wall finishes using a dehumidifier if necessary. The choices seem to be stud wall with closed cell foam sprayed from inside or 2" EPS outside of sheathing and some cavity insulation. it seems to me that the simple stud wall with rain screen approach might provide some limited drying to the outside through the wood frame. The outside foam might impede the little drying potential that exists.

Floor is suspended concrete slab on an ICF foundation. Roof will be vented, conventional rafters with adequate amount of closed-cell spray foam,

Asked by Guy Wachtel
Posted Jun 23, 2014 6:13 AM ET
Edited Jun 23, 2014 8:08 AM ET


2 Answers

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First of all, if the tile is part of a shower enclosure, I assume that your tile contractor will include a waterproof layer (for example, a liquid-applied membrane such as Laticrete Hydro Ban or Mapei Mapelastic AquaDefense) -- products that are installed on the interior side of the backerboard.

Your wall will be able to dry adequately to the exterior, especially if it includes a ventilated rainscreen gap between the OSB or plywood wall sheathing and the siding.

Answered by Martin Holladay, GBA Advisor
Posted Jun 23, 2014 8:30 AM ET


Thanks, Martin. Probably using a Kerdi membrane. If that was not optimal i could ask the tile contractor to use one of the liquid membranes that you suggest. Walls that are not part of shower enclosure will have tile to about 36" off floor. Absolutely using a rain screen gap under siding. Guy W.

Answered by Guy Wachtel
Posted Jun 23, 2014 2:30 PM ET

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