SolidBuild®️Staff Answer
Jun 03, 2026 - 08:01 AM
Most SolidBuild customers insulate between the floor joists (or beams) using foam board or similar material. If you’re adding a subfloor like OSB or plywood, the usual order is: foundation, floor joists, insulation between joists, subfloor (OSB/plywood), then the shed’s floorboards on top. This gives you a solid, insulated base and protects the insulation during assembly.
If your insulation has a foil backing, you may not need a separate vapor barrier, but if not, it’s smart to add a vapor barrier under the insulation layer to prevent moisture issues. OSB or plywood in the 19/32" to 3/4" range is commonly used for subfloors, depending on how heavy-duty you want it to feel.
If you prefer to insulate your platform and cover it with OSB, then omit the floor joists that come with the kit, and build the shed directly on your wood foundation. It will eliminate the gap.
On your side note: if your platform is 1' larger on each side than the shed, that’s not a problem structurally, but you’ll have an exposed ledge around the shed. Some people add skirting or trim to cover this for looks and seal it to keep water out. Just make sure the shed itself is centered and fully supported on the platform.
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