For unvented roofs with spray foam in heavy-snow climates, how do you control condensation without over-insulating above the deck?
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Use the right amount of closed-cell spray foam, keep inside moisture under control, and have a continuous air/vapor barrier. This stops condensation, but don’t overdo the insulation.
Vapor Permeable Membranes: Using vapor-permeable underlayment membranes can allow for drying towards the exterior, reducing the risk of condensation.
Adequate Insulation: Ensuring sufficient insulation while avoiding over-insulation is crucial. This balance helps maintain a stable temperature and reduces the risk of condensation.
Air-Tight Construction: A well-sealed roof assembly is essential to prevent warm, moist air from entering the roof cavity and condensing on the deck.
Use enough closed-cell foam for dew-point control, keep interior airtight, add vapor control, and allow outward drying.
For unvented spray foam roofs in heavy snow: seal air leaks, use closed-cell foam, avoid over-insulating above sheathing, and control indoor humidity; a small vented gap can help if allowed.
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Use closed-cell spray foam under the deck, control interior humidity, and limit foam thickness to meet R‑value without trapping moisture.
Use closed-cell spray foam at the roof deck for sufficient warm-side R-value per code ratio, seal all air leaks, and manage indoor humidity so you meet condensation control without excess above-deck insulation.
It is controlled by maintaining a warm roof deck temperature, which can be achieved by limiting the amount of insulation above the deck and ensuring proper air sealing and ventilation in the conditioned space below. Over-insulating above the deck can lower the deck temperature, increasing the risk of condensation