DIY Network

Why would decking nails back out on a three year old roof? The attic is vented properly with ridge vents and vented soffit. No bathroom vents are vented to the attic.

Even with venting, there is still expansion/contraction movement in the roof decking. While the movement distance is small, over time it will have the ability to pull a nail completely out. A ring shank or spiral nail will have a better chance of staying in place, but even those types of nails can pop over time.

The swelling and shrinking of the wood moves hails out and doesn't pull them back in. Sometimes longer nails are used to get ahead of this. Actually using the shortest nail that will work reduces the amount of nail movement. ringshanks were developed for this problem. They won't work that well either. Generally the nail should go into the wood underneath just a bit farther than it goes through the wood on top. When nailing 1/2" sheathing a 6d nail works better than an 8d nail. Screws work better because the threads are more agressive in holding the wood. Screws that are too long will move a bit too.

The previous posts are right on. However, if you went low bid on the decking, thinner material but still meets code, this will flex more than thicker material, causing the prying action that pulls nails out. Also, is there a lot of unplanned load on your roof? Such as people walking around up there or has there been a few very strong wind storms that would cause the decking to flex. Are you up north where you might have to deal with a larger than normal snow load last winter? These could all be reasons why your decking nails are pulling out.

Even something as simple as the wood being to wet when it was used can cause this. As the wood drys out it shrinks.