Direct Answer
Both OSB (oriented strand board) and plywood are approved roof decking and perform well when kept dry. Plywood is slightly more moisture-resistant and holds fasteners a bit better; OSB is less expensive and more widely used in modern construction. The difference matters less than keeping the decking dry with good flashing and ventilation — moisture ruins both.
OSB and plywood are the two common decking materials. Both are structural wood panels rated for roof use. The choice usually comes down to cost and availability, with a slight edge to plywood for moisture performance.
OSB (Oriented Strand Board)
- Made of compressed wood strands with adhesive
- Less expensive and most common in newer homes
- Swells more at the edges when wet (but recovers when dried)
- Performs well when kept dry with proper ventilation
Plywood
- Made of thin wood veneers layered and glued
- Slightly more expensive
- More moisture-resistant and holds fasteners a bit better
- Less prone to edge swelling
The Real Deciding Factor
Neither material survives ongoing moisture. The key to long-lasting decking — OSB or plywood — is keeping it dry: proper flashing, no leaks, and balanced attic ventilation. Rot comes from moisture, not from choosing the "wrong" panel.
Signs & Symptoms
- Soft or spongy spots (rot, regardless of material)
- Edge swelling visible at panel joints (more common with OSB)
- Sagging between rafters
- Dark stains on the underside in the attic
Repair Options
- Replace rotten sheets with matching OSB or plywood
- Fix the moisture source (leak or ventilation) so the new panels last
- Full replacement if rot is widespread
When to Call a Roofer
If you're replacing your roof or have soft spots, have the decking inspected. We assess every sheet during tear-off and replace only what's bad.
How Beyond the Ladder Handles It
We replace rotten decking with quality OSB or plywood and — most importantly — fix the moisture source so the new panels don't rot again.
Related Questions
Does OSB rot faster than plywood?
Both rot when wet. OSB swells more at the edges when exposed to moisture, but when kept dry with good ventilation and flashing, both last the life of the roof. Moisture — not the material — is the enemy.
Should I upgrade to plywood when replacing my deck?
It's an option if you want slightly better moisture tolerance, but it's not necessary. Keeping the decking dry matters far more than the panel type. We recommend based on your roof and budget.