Why can't a contractor simply install shingles over rotten plywood?
Short Answer
Because the new roof would be installed over a compromised substrate. Potential problems include inadequate fastening, structural weakness, movement, poor installation surface, and continuing moisture problems.
Detailed Explanation
Shingles are held in place by fasteners driven into the decking. If the decking is rotten, the fasteners won't hold — they'll pull out under wind uplift, and shingles will blow off. Ice and water shield and underlayment need a solid surface to adhere to; on rotten wood, they'll peel or bubble. Rotten decking may also be structurally inadequate, meaning it could sag or fail under the weight of snow, ice, or even the roofing materials themselves. And rotten decking means moisture has been present — if that moisture source isn't identified and corrected, the new roof will experience the same problem. Installing over rotten decking is like painting over rust — it looks better temporarily but the underlying problem continues to worsen.
Why It Matters
A roof installed over compromised decking will fail prematurely, potentially causing more damage than if the decking had been properly replaced.
Common Mistakes
- ✕Allowing a contractor to install over damaged decking to save money
- ✕Not asking about decking replacement before the project starts
- ✕Assuming decking damage is always minimal
Questions to Ask Your Contractor
- ?What happens if you find rotten decking during the project?
- ?How is decking replacement priced?
- ?What's the per-sheet cost for decking replacement?