What happens to OSB when it is exposed to moisture?

When oriented strand board (OSB) is exposed to moisture, it absorbs that moisture quickly and begins to swell. This happens because OSB is manufactured from wood strands bonded together with adhesives, and the wood fibers are hygroscopic, meaning they can absorb water from the surrounding environment.

As moisture enters the board, it disrupts the bond between the strands and causes the individual strands to expand, leading to swelling. This swelling can result in Warping, buckling, and a loss of structural integrity over time.

In contrast, other materials may remain stable in moisture or repel it, but OSB is particularly vulnerable to the effects of water exposure. This is an important consideration for builders and inspectors, as prolonged exposure to moisture can significantly decrease the performance and longevity of OSB used in construction.