A.Bryan Readling, a senior engineer with APA/Engineered Wood Association, responds: If the deck footings, framing, and house connections are adequate for the anticipated loads, and the existing decking is sound and reasonably flat, you don’t necessarily have to remove it before laying down a new OSB subfloor and framing the addition. However, there are some advantages to doing so anyway.

For one, removing the decking would allow you to thoroughly inspect the framing and easily make any needed repairs or upgrades. You’ll also avoid squeaky floors, bumps in the floor sheathing, and other problems caused by loose, warped, or misaligned deck boards, or by wet joists drying out and causing decking fasteners to lose their grip. If you...

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