Rotting Roof Deck
‘Roof deck’ is the name for part of the structure that supports your roof surface materials. This deck is what your shingles are attached to. It is the foundation for all the surface materials.
The ideal roof deck is dry, clean and secured to the rafters, made from plywood at least 1/2" thick.
Did you know?
If the wood deck the shingles are installed onto doesn’t meet the manufacturer’s requirements or is inadequate, this will void your shingle warranty.
Your roof deck can begin to rot for three reasons:
- from moisture leaking in through the outside
- from warm moist air escaping from the interior living space into your attic
- trapped moisture lingering from the summer or fall
During the winter, warm moist air finds its way into the attic. It is attracted to the cold surface of the plywood and then releases its moisture and condensation forms, causing the wood to rot or delaminate.
(NOTE: If you see condensation on your windows, it is a sign you might have a similar problem in your attic.)
Two of the most common materials used in our market for roof decks are:
- plywood (on newer homes constructed from 1960 and up)
- 1x8, 1x10 1x12 roof board (used prior to the 1960s.)
Plywood (when installed correctly) is dimensionally stable; that is, it doesn’t allow a lot of expansion and contraction. This makes plywood an acceptable material for shingles to be installed onto. However, when exposed to moisture, plywood is vulnerable to warping, delaminating and rotting.
Shingles installed on 1” roof boards or planks wider than 6” are susceptible to shingle buckling. Roofing manufacturers do not approve shingles installed on roof boards that are larger than 6”, because when the moisture goes in and out of the wood, the wood expands and contracts, causing the shingles to buckle. This in turn damages the shingles and leaves the roof vulnerable to water penetration. (This can happen on an old roof or a new one.)