Continuous Air Barrier + Correct Vapor Control
Mold feeds on moisture and air leaks. Begin with a continuous air barrier across ceilings, knee walls, and skylight shafts; seal penetrations with tapes/mastics and gasketed boxes. Choose vapor-smart membranes on the warm side of unvented roofs so assemblies can dry seasonally.
Insulation Ratios and Thermal Bridges
In unvented assemblies, keep roof sheathing above dew point with the right ratio of exterior/interior insulation; in vented roofs, maintain unobstructed soffit-to-ridge pathways with rigid baffles. Break thermal bridges at rafters, knee-wall caps, and skylight returns with continuous insulation.
Ventilate Wet Zones and Condition the Space
Run quiet, exterior-ducted bath exhausts on timers or humidity sensors, and consider a small ERV for steady fresh air. Right-size HVAC (often a variable-speed heat pump) and target 40–50% RH; monitor with a smart sensor to spot issues early.
See detailing diagrams and checklists in our attic remodeling waterproofing & moisture control in NYC guide.