OSB (Oriented Strand Board) is a popular and cost-effective building material. It works great for wall sheeting and general construction, and it's often a little less expensive than plywood. But when it comes to roofs with metal roofing, OSB is not the best choice.

Here's why: metal roofing screws don't grip OSB well, and over time they loosen, causing leaks. Once water gets in, OSB starts to disintegrate, making the problem worse. The screws come out faster, and the roof deteriorates.

Plywood is a slightly better option, but not by much when used alone with metal roofing. Even thicker plywood, like 5/8", can give you a bit more durability, but it's not a complete solution.

What We've Seen

We've seen roofs where OSB was used directly under metal (as shown in the photo), and after less than 10 years, the screws were loose, the OSB was deteriorating, and leaks were already a problem. Fixing it required removing the metal, installing strapping, and reapplying the roof—an avoidable and costly repair.

Taking the extra step to install strapping or choosing thicker materials upfront can save you time, money, and headaches down the road.

How to Do It Right

The best solution is to add strapping. Install 1x4 or 2x4 strapping on top of the OSB or plywood. This gives the screws something solid to bite into, solving the looseness problem.

If you're set on using plywood, choose a thicker grade (like 5/8") to improve performance, but still consider adding strapping for long-term durability.

Strapping used to reinforce roof structure