An attic must operate as a "cold roof" system during the winter and a massive heat-exhaust engine during the summer. When this balance fails, moisture accumulates, eventually turning your plywood roof deck into a spongy, rotting biohazard.
The Formula for Rot
- 1. The Vapor Source: Cooking, showering, and natural human respiration generate massive amounts of humidity inside the home. Leaky ceilings allow this warm, wet air to naturally rise into the cold attic space during winter.
- 2. The Condensation Plane: When the warm, wet air hits the freezing cold underside of the wood roof deck, the water vapor instantly condenses back into liquid water droplets. The roof literally "sweats" on the inside.
- 3. The Ventilation Failure: If the soffit intake vents are clogged, or the ridge vent is absent, the attic cannot flush the moisture out with fresh air. The water soaks into the wood, delaminating the plywood and feeding black mold.
The 1/150 Code Requirement
Building code dictates you must have 1 square foot of Net Free Ventilating Area (NFVA) for every 150 square feet of attic space, balanced perfectly 50/50 between intake (soffits) and exhaust (ridge/turbines). Only professional balancing stops the rot.