Replacing Old Decking

Hello John,  

 

Below is what our roofing expert Jose Castellanos with Bumble Roofinghad to say in response to your question:

Below is what our roofing expert John Kenney with Cotney Consulting Group had to say in response to your question:

John, although the 11-inch plank decking may still have some structural integrity, it doesn’t always meet today’s manufacturers' standards for shingle application. Installing a layer of 4x8 OSB or plywood over the existing deck is a smart upgrade that solves those concerns and helps ensure the roof system performs as it should in the long term.

You can install OSB over the existing plank decking, assuming the planks are in good condition, meaning they’re flat, secure, and rot-free. Doing so gives you a clean, consistent nailing surface and reduces the chances of shingles telegraphing board movement underneath. This is a common and accepted approach when reroofing older homes. Just make sure to use the proper fasteners that secure the OSB to the planks and penetrate into the rafters below. That’s key for maintaining structural integrity.

Now, if any of the existing plank decking is soft, warped, or shows signs of decay, it needs to be replaced before proceeding. Laying OSB over bad wood doesn’t solve the problem; it just covers it up. That said, if the planks are solid, this method brings the roof up to modern standards cost-effectively. I’d also recommend checking with your local building department, but this method is acceptable in most areas as long as structural load requirements are met.

Below is what our roofing expert Donavan Morgan with The Roof Gallery had to say in response to your question:

Yes, you can overlay old 11” plank decking with OSB instead of tearing it all out. Ideally it should have space less than 1/4 of an inch. 

 Rule of thumb If planks are mostly solid and less than 1/4 inch gap → overlay with OSB. If they’re shot → tear out and replace with full OSB decking.