Why can't you tell exactly how much decking needs replacement before removing the roof?
Short Answer
Because some deterioration is concealed beneath the existing roof covering. A responsible estimate should explain that concealed conditions can affect final quantities.
Detailed Explanation
Before tear-off, the decking is covered by existing roofing materials — shingles, underlayment, and possibly multiple layers. Some decking damage is visible from the attic side (water stains, soft spots visible from below), but much of it is hidden between the attic and the roof surface. Water can enter through a small roof leak, run along the top of the deck, and cause rot on the top surface that's not visible from the attic below. Only after the old roofing is removed can the full extent of deck damage be evaluated. This is why decking replacement is typically priced per sheet as an allowance — the contractor estimates based on visible conditions but the actual quantity is determined during the project. A responsible contractor explains this in the estimate.
Why It Matters
Understanding that decking quantities can't be fully determined until tear-off helps homeowners budget appropriately and avoid surprises.
Questions to Ask Your Contractor
- ?How do you price decking replacement?
- ?What's the per-sheet cost?
- ?Can you estimate how much decking might need replacement based on what you can see?
- ?How will you communicate decking findings during the project?