Waterproofing a Shower With OSB Walls
I’m about half-way through building our tiny house on wheels, and am trying to decide how to waterproof our shower/tub walls. The back wall and one side are OSB, the inside skin of the SIPS we used to construct our walls. The second side is currently bare wood framing, our only framed interior wall. The tub measures 48″ L x 32 in wide, so standard 1-piece plastic shower wall kits don’t fit (plus they are ugly!). The photo I have is older, and doesn’t show the framed wall. We have an acrylic tub, so no need to waterproof the floor, but I’m trying to figure out the best way to keep the OSB dry. I’m planning to use corrugated metal as the inside shower wall surface, since tile walls are heavy, stiff, and likely to crack with the amount of vibrations that a trailer will make on the road. I want a solid waterproof layer behind that metal. I’ve looked at liquid-applied waterproofing like Red Guard or Proflex Hydraseal; membranes like Shluter Kerdi, and waterproof xps backer board like kerdi board and wedi board, which are all designed for hanging tile. The option I like the most currently is shingling 12-in wide butyl window flashing (Grace Vycor Pro) to the OSB to seal everything completely, including any fastener penetrations from attaching the corrugated metal. I’ll have to use a hefty amount of silicone caulk at the wall-ceiling transition, but should be able to flash over the edge of the tub. The ceiling in the bathroom will be 2×6 T$G eastern red cedar- the bottom of our loft floor. Our loft beams (4×4 doug fir) will be stained on all 4 sides with Rubio monocoat. I’m installing a bathroom exhaust fan that is selectable from 50-100 cfm with a humidity-controlled auto switch to keep the humidity at 30% or less. I’m happy to layer the walls a bit in order to make a good waterproof layer, but not sure what would be best. My priorities are 1) waterproof (no rotting OSB), 2) low cost and 3) green! Code is not a concern. Thank you!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part