Start at the Roof, Then Work Inward
The best attic is dry from the outside in. Verify roof health before finishes: intact shingles or membrane, sound sheathing, and flawless flashing at penetrations, dormers, valleys, and chimneys. In snow-prone seasons, proper insulation and air sealing at the roofline reduce ice dams, while a continuous ice-and-water shield at eaves and valleys buys insurance against wind-driven rain.
Interior Moisture Defense
Within the assembly, continuity is everything: maintain an unbroken air barrier, select vapor control appropriate to your vented or unvented roof (vapor-smart membranes inboard of insulation are common), and seal all penetrations with compatible tapes and mastic rather than only foam. In wet areas (ensuite bath), use a bonded waterproofing membrane on floors and walls, slope the shower pan to a linear drain, and include a flood test before tile. All exhausts must terminate outdoors to prevent interstitial condensation.
Details That Prevent Hidden Damage
Insulate and air-seal around skylights and roof windows, specify pan flashing kits, and use insulated attic hatches with compression gaskets. Add drip-edge extensions where needed, keep gutters clean, and direct downspouts away from the foundation to limit bulk water cycles that telegraph upward. Post-occupancy, monitor RH with a sensor and set dehumidification to hold 40–50%.
Documentation & Assurance
Photograph each layer—flashing, membranes, insulation—before they are covered, and keep a material submittal log for warranties. A blower-door test after air sealing verifies performance. For a step-by-step waterproofing checklist, visit our attic remodeling service moisture control resource.