Which Sheet Material Would We Use for a Shed Roof?
For most shed roofs, we would use OSB3. It is a structural board suitable for humid conditions and is normally a more economical choice than plywood for a roof that will be fully covered.
The main thing is choosing the right thickness for the roof frame: around 400mm support centres = 11mm OSB3; around 600mm centres = 18mm OSB3 from our stocked range.
Support spacing matters more than shed size
A larger shed does not automatically need thicker OSB. What matters more is how far the board has to span between rafters or supports.
| Roof build | What we would normally use |
|---|---|
| Small shed with supports around 400mm centres | 11mm OSB3 |
| Supports around 600mm centres | 18mm OSB3 from our stocked range |
| Heavier-duty or specifically designed roof | Follow the specified board thickness |
Make sure sheet edges and joints are properly supported. Add noggins where needed rather than leaving important joints floating. With square-edge OSB3, leave around 2–3mm expansion space between boards and fix them securely with suitable corrosion-resistant fixings.
OSB3 still needs a waterproof roof covering
OSB3 can cope with humid conditions, but it is not a finished waterproof roof surface. Once the deck is fitted, cover it with a suitable system such as mineral shed felt or EPDM rubber roofing.
If the OSB gets wet during construction, allow it to dry properly before covering it.
If the old roof is sagging, check the structure first
New felt or EPDM will not repair a weak roof deck. If the existing OSB or plywood is soft, swollen, rotten or badly bowed, replace it. If the roof has sagged because the supports are too far apart, strengthen the structure before fitting the new covering.
Can you use plywood instead?
Yes. Suitable plywood sheets can also be used for roof decking where the grade, thickness and roof construction are suitable. If your plans specify plywood, use the required grade and thickness.
For a straightforward garden shed that will be completely covered, however, we would normally start with OSB3.
What would we buy?
Supports around 400mm centres → 11mm OSB3 → felt or EPDM.
Supports around 600mm centres → 18mm OSB3 → felt or EPDM.
Support the joints, leave the expansion gap, keep the deck dry and install the weatherproof roof covering correctly.
Choose your OSB3 thickness
Shop 9mm, 11mm and 18mm OSB3 sheets for shed roofs, roofing, flooring and structural sheet work.
Shop OSB3 Board →General guidance for typical shed and outbuilding roof decks. Support spacing, loading, fixing pattern, roof pitch and the chosen covering can change the required specification. Follow any structural design and the installation instructions for the roofing system you use.
