Remedies for Roof Plywood and Rough Lumber Problems

When you see bulges, humps and bumps on your roof after just a few months of moving in, your builder could tell you a lot of reasons.

Among the most common causes of roof plywood bulges and bumps are expansion or contraction of the roof plywood or the rough lumber supporting the system, inadequate spacing between the plywood boards, moisture accumulation and inadequate attic ventilation.

Wood Expansion and Contraction

Rough lumber products naturally expand and contract as temperature and humidity change their moisture content. Their cellular structure makes them so. The biggest wood movement occurs across the grain of the wood. Plywood, which has larger expanses of grain across its width and length, is therefore more susceptible to the effects of contraction and expansion.

Plywood makers, builders and skilled carpenters know these characteristics and problems. And they have standard procedures to prevent these problems from occurring. One of these is allowing at least 1/8 in gap around the edges of adjoining plywood.

Attic Ventilation

Air circulation in the attic should be adequate. During the summer, air in the attic could get hot. This heat buildup enables the air to keep moisture. As moisture accumulates in the attic, wood in the attic, roof plywood and rough lumber pieces easily absorbs moisture. The moisture can either cause the roof plywood to expand more than its natural expansion movement or cause the start of wood rot in the rough lumber.

Roof Ventilation

Good roof ventilation can prevent the heat buildup also associated with attics. If roofs are properly ventilated, air in the roof spaces is allowed to circulate and exchange with air outside the attic spaces. As air in the roof spaces circulate and participates in the air exchange with outside air continuously, balance in air temperature and humidity is attained. This prevents moisture from building up.

Roof Ventilation Solutions

You and your builder can choose from several ways to ventilate your roof spaces. Your roof ventilation and attic ventilation should complement each other. Some of the more common ventilation systems are stationary roof vents, continuous roof vents, power attic vents and turbine vents. These vents should work with your soffit ventilation system.