Buckling plywood under the shingles can be unsightly, but what causes it to happen? Most attics generate heat from the living space below. It naturally rises through the insulation, or maybe a dryer vent dumping hot air into the attic and not exiting out the roof vents. If the attic does not have enough ventilation this heat causes condensation when it meets cold surfaces like the bottom of the sheathing that has a load of snow on the roof. When the roof sheathing gets damp from condensation it swells or what we call expands and if the edges are not spaced correctly has no other option but to buckle upwards or downwards.

The American Plywood Association, (APA) primary functions are to provide product certification and testing, applied research, and market support and development of wood products like OSB, (oriented strand board) and plywood. They say by “using a #10 penny box nail as a spacer is a way to gap the 1/8 inch needed for panel expansion.”

Since the expansion is a result of moisture getting to the wood, then that attic must not be ventilated properly. The recommended amount of ventilation without a vapor barrier is 1sq. foot for 150 sq. feet of attic space. This also must be a balanced system. The goal is 50% intake and 50% exhaust. There are many ways to ventilate an attic. Seek a certified roofing contractor like Dependable Construction to provide this service and design a balanced ventilation system for your attic to avoid future buckling of OSB or plywood.


For any ventilation system for your attic, or roofing needs, call Dependable Construction at (937) 318.9572 to speak to a roofing professional. You can also visit Dependable Construction online to learn more.


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