Start at the Roof Edge
Moisture control begins outside: healthy shingles or membrane, solid sheathing, and meticulous flashing at valleys, dormers, and penetrations. At eaves, continuous ice-and-water shield plus correct drip edge sequencing helps stop wind-driven rain and ice dam back-ups. Clean gutters and direct downspouts away from the foundation so bulk water cycles don’t telegraph into the attic.
Air Barrier & Vapor Control
Inside the assembly, continuity is king. Maintain an unbroken air barrier across ceilings, knee walls, and skylight shafts; seal penetrations with compatible tapes and mastic, not just foam. Choose vapor-smart membranes on the warm side of unvented roofs where appropriate, and verify the insulation ratio for dew-point safety at the sheathing.
Wet-Area Detailing & Venting
Bathrooms need bonded waterproofing membranes, sloped pans (linear drains excel under low headroom), and quiet exhausts ducted outdoors—not into soffits. Insulate and air-seal skylight shafts, use manufacturer pan flashing kits, and confirm minimum slopes per cut sheet.
For a step-by-step checklist, use our NYC Attic Remodeling Service waterproofing guide to coordinate roof work, air sealing, and interior membranes.