RDH Technical Bulletin No. 010: Mold in Vented Wood-Frame Roofs in the Coastal Pacific Northwest


This RDH Technical Bulletin covers the causes of vented wood-frame roof moisture problems, suggests possible solutions, and provides additional resources for further information.

A sloped roof over a ventilated attic is one of the most common, if not the most common, roof configuration in the United States and Canada. This type of roof assembly is typically associated with single-family houses, but they are also commonly used on townhouse complexes and large, architecturally complex multi-unit residential buildings. Unfortunately, in coastal areas of the Pacific Northwest, moisture problems—including mold growth on roof sheathing—are common in vented wood-frame roofs. Often this type of damage is attributed to rainwater ingress through the roof assembly, inadequate ventilation of the attic space, and condensation associated with airborne moisture from air leakage, duct leakage, or re-entrainment of humid exhaust air into the attic space. However, despite recent improvements in ceiling airtightness, reduced duct leakage, and code-compliant attic ventilation rates, issues of fungal growth and mold on roof sheathing are still common throughout coastal areas of the Pacific Northwest.

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How to reference this bulletin:

Mold in Vented Wood-Frame Roofs in the Coastal Pacific Northwest, RDH Technical Bulletin No. 010. RDH Building Science Inc., September 2015. https://learnbuildingscience.com/products/rdh-bulletin-mold-in-vented-wood-frame-roofs-in-the-coastal-pacific-northwest.