Correct Roof Deck Construction

A well-constructed roof deck is comprised of plywood that is at least a half-inch thick.  This plywood must be clean, dry and properly secured to the rafters.  Older homes used a material called roof board, whereas most homes that were built in the last 50 years used plywood.  It is a dimensionally stable wood that does very little expanding and contracting, which is why it is an ideal material for roof decks.  However, if exposed to moisture, it can easily warp, rot and delaminate.

How Does a Roof Deck Rot?

A rotting roof deck can be attributed to one of three circumstances:

  • Moisture has leaked in from the outside ( leak )
  • Warm, moist air has migrated from your interior home into the attic
  • Moisture is trapped inside, which formed as a result of summer or fall weather conditions

During the winter, warm air naturally makes its way into the attic and all the way up to the cold, plywood surface of your roof deck.  This warm air then releases its moisture, forming condensation, which can rot the wood.  If you notice condensation on your windows, chances are a similar situation exists in your attic.

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