How to build a wooden floor base for a 6m x 3m shed?

vangem

After working out that a steel shed on a slab was going to get to expensive to get a steel shed company to do, given a moderate slope and cement pump hiring etc., I thought I go back to building a wooden shed myself. I want to build a bae of 6m x 3.2m, and use yellow tongue flooring for the base. The shed will be timber base with a pitched roof (15deg), colorbond roof and probably HardiePlank siding, a window, and double doors. The floor will all be h3 treated pine (190x45), with 150mm or more ground clearance with bearers on posts with stirrups cemented in. The bearings and joists will be all one level.

So after pouring over the span tables I could get, I've come up with the design below. Will this be strong enough? Have I over or under designed it? Do I need the double beams around the edges? It's only going to be used for storage of tools and garden equipment, with shelving running up the sides.

MitchellMc

Welcome to the Bunnings Workshop community @vangem. It's brilliant to have you join us, and many thanks for your question about building a structure base.

That sounds like a well-thought-out plan, and your specifications seem to line up with what’s recommended in the span tables. Using 190x45mm H3-treated pine joists spanning 3.2m is within the typical limits, and the rest of the structure sounds well designed for its intended use. For a storage shed with shelving, it should more than handle the load.

That said, the first thing I’d recommend is checking in with your local council before going too far ahead. Given the size and construction, this could fall into a category that requires a building permit. Many councils have square metre exemptions for small garden sheds, but once you start building on stumps, adding a pitched roof and HardiePlank cladding, it often shifts into permit territory.

And if a permit is required, you’ll likely need to have engineer-certified drawings. While your current design appears sound, getting formal sign-off from an engineer might be necessary to meet council requirements.

As for the double bearers on the perimeter, I think that’s a good call. While a single bearer might be enough structurally, doubling up will definitely strengthen the base—particularly helpful for resisting any flex or racking over time, especially with the size of the structure and the shelving loads.

Please let me know if you have any questions.

Mitchell