Design a Fully Contained Wet Zone
In an attic ensuite, moisture loads are concentrated and close to the roof deck. Build the shower as a tank: slope the pan (1/4″ per foot) to a linear drain, wrap floors and walls with a bonded waterproofing membrane, and flood-test before tile. Use cement board (not green board) in the shower and carry the membrane 12–18″ beyond the wet area to catch overspray.
Vapor, Venting, and Seams
Seal every seam with manufacturer tapes; treat niches and benches as penetrations with preformed corners. Specify a low-sone exhaust fan (≤1.0 sone) sized per code, ducted outdoors with insulated, smooth pipe and a backdraft damper—never into soffits or the attic cavity. Add a humidity timer so the fan runs 20–30 minutes post-shower.
Thermal Breaks and Condensation Control
Insulate and air-seal skylight shafts near the bath, use insulated access hatches with compression gaskets, and maintain the attic’s air barrier around light fixtures (IC/AT) so warm, moist air cannot reach cold surfaces. Target 40–50% RH and monitor with a smart sensor.
Grab a step-by-step waterproofing checklist tailored to sloped ceilings on our attic remodeling moisture control in NYC page.