Plywood Underlay
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April 13, 2026 at 6:32 p.m.
HannahFord7
Rachel from California asks: I am currently having my roof replaced. After they tore off the original roofing, it was found that the entire roof would need plywood installed prior to the asphalt shingles (no plywood was previously present, only would planks). My question is whether the roofing company should have been able to observe the absence of plywood underlay during their initial assessment in order to provide an accurate estimate. They are now adding $6500 to the original estimate.
April 13, 2026 at 6:32 p.m.
HannahFord7
Hello Rachel,
Below is what our roofing expert John Kenney of Cotney Consulting has to say:
Rachel, this is a very common situation—especially in older homes—and I’ll give it to you straight.
Without seeing your contract or knowing exactly how the contractor presented the scope, I can only speak based on typical industry practice.
In many cases, a contractor cannot fully confirm what’s under the roof until it’s torn off. If your home had spaced wood planks instead of solid decking, that’s often not visible during a standard inspection from the exterior—and sometimes not even from the attic, depending on access.
That said, an experienced contractor should recognize the possibility, especially with older homes, and communicate that upfront. Most professional proposals include language stating that decking repairs or upgrades may be required once the roof is opened up.
The reason for the added plywood is legitimate. Modern asphalt shingles require a solid, continuous nailing surface to perform properly and meet code. Installing over-spaced planks without proper sheathing can lead to performance issues and void the manufacturer's warranty.
As for the additional $6,500—that’s not out of line depending on:
- Roof size
- Material thickness and pricing
- Labor involved
Bottom line
- It’s normal that this condition wasn’t fully confirmed until tear-off
- It should have been anticipated and communicated as a possibility
- Adding plywood is the correct and necessary step, not an upsell
Questions I would ask your contractor
- Was potential decking replacement noted in the original proposal?
- What thickness and type of plywood are being installed?
- Are they installing it to meet current code and manufacturer requirements?
- Is this a full redeck or partial, and how was that determined?
If this wasn’t discussed at all beforehand, you’re justified in asking questions. But based on what you’ve described, the work itself is valid and important to get right.
Thank you for using AskARoofer! Find more resources to answer your roofing questions here: podcasts, articles, previously answered questions and more!
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