Plan Short, Insulated Runs
Additions above the roofline can support a quiet, efficient bath if you plan for gravity, venting, and temperature swings. Stack the new bath over existing wet walls to minimize run lengths, fittings, and roof penetrations. Use insulated PEX home runs to control heat loss and add shutoffs in an accessible knee-wall panel. Vent properly with a dedicated line sized per fixture units; if slope or distance is an issue, coordinate an engineered venting solution with the design professional.
Waterproofing and Exhaust
Specify a bonded waterproofing membrane for the shower and a sloped pan (linear drain works well at low headroom). Run a quiet (<1.0 sone) exhaust fan directly outdoors—never into soffits—to clear steam and protect assemblies. Add humidity sensing or timer controls so ventilation runs long enough after showers.
Power, Lighting, and Protection
Bathrooms need GFCI protection at receptacles and, in many cases, AFCI for circuits serving the room. Provide dedicated circuits for heat (radiant or towel warmers) and consider low-glare, high-CRI LED lighting with layered scenes (ceiling ambient, niche/task, mirror lighting). Seal penetrations at the air barrier and choose IC/AT-rated fixtures where they contact insulation.
Serviceability and Noise
Photograph rough-in locations before close-up and label shutoffs behind knee-wall doors. Use sound-damping for the shower wall and toilet zone (mineral wool, sound-rated backer) so the suite remains peaceful. For checklists and fixture planning matrices, see our Attic Remodeling Service bathroom integration in NYC resource.