Short Answer
Common contributors include warm moist air entering the attic, inadequate ventilation, poor air sealing, bathroom exhaust terminating in the attic, and temperature differences.
Detailed Explanation
Attic condensation occurs when warm, moisture-laden air from the living space enters the attic and contacts cold surfaces (roof decking, rafters, nails). The moisture in the air condenses into liquid water on these cold surfaces, just like water droplets form on the outside of a cold glass on a humid day. The main contributors are: warm air leaking through gaps in the ceiling (around light fixtures, attic hatches, plumbing penetrations), bathroom or kitchen exhaust vented into the attic rather than to the exterior, inadequate attic ventilation that traps moist air, and inadequate insulation that allows heat to reach the attic and warm the roof deck. The solution depends on the cause: air sealing, proper exhaust venting, ventilation improvement, or insulation upgrades.
Why It Matters
Attic condensation can cause mold, wood rot, and insulation damage. Identifying and correcting the moisture source is essential — adding ventilation alone won't help if the source is air leakage or improper exhaust.
Common Mistakes
- ✕Adding ventilation without addressing air leakage
- ✕Not correcting improperly vented bathroom exhaust
- ✕Assuming condensation is a roof leak
Questions to Ask Your Contractor
- ?Is warm air leaking from the living space into the attic?
- ?Are all exhaust fans vented to the exterior?
- ?Is ventilation adequate?
- ?Is insulation adequate and properly installed?