A small garden shed can sit on a level paved or well compacted base. A workshop, a shed that will hold heavy stored items, or anything that catches a lot of wind needs a concrete slab with footings sized for the job. The shed is only as level, dry and secure as whatever is under it, and a kit shed from a hardware store does not include the base in the box.
When does a shed need a concrete slab?
The deciding factors are weight, size and use.
- Garden shed, light storage. A level base of compacted gravel, pavers or a timber frame sitting on blocks is enough for a small steel or plastic shed, as long as the base is flat and drains.
- Workshop or a shed with benches, machinery or heavy stock. The floor takes concentrated loads and has to stay flat. A slab is the standard answer.
- Anything with a roller door or a wide opening. A door that has to seal and run smoothly needs a floor that has not moved, so the slab is worth doing properly.
- A carport. The posts need footings regardless, and a slab under the whole structure is the usual base, as covered in the carport cost guide.
If you are not sure which group a shed falls into, size it by what will live in it. Weight and wind decide the base more than the footprint does.
How does a sloping block change the base?
Plenty of Illawarra blocks fall away, and a shed cannot be set on the dirt and left to find its own level. There are three usual ways to get a level floor on a slope:
- Cut into the hill to make a flat pad.
- Build the low side up with fill and edging.
- Pour a stepped slab that follows the fall.
Each one changes where water goes. A cut pad needs drainage behind it so water does not collect against the back wall, and a built-up pad needs the edges held so they do not wash out. The same slope problems apply to garages, and the garage building guide goes through them for a bigger structure.
What happens with drainage around a shed?
A slab or base should fall slightly away from the shed so water runs off it rather than under the wall. Older fibro and brick houses around the area often have poor drainage already, and a new shed placed in a low spot can end up with water pooling at the door. Looking at where water goes during rain, before the base is built, avoids that. Before any digging for footings, check for buried services with Before You Dig Australia.
How is a shed tied down?
Flat-pack sheds are often anchored with little more than the fixings in the booklet, and a shed that is light and tall has a lot of surface for the wind to push. The escarpment funnels wind and the coast adds gusts on top, so anchoring is worth doing properly.
On a slab, the frame is bolted down with dynabolts into the concrete, with heavier brackets where the site is exposed. A carport or a timber structure has posts set in concrete rather than pushed into clay. A shed sitting on soft ground with nothing holding it down is the one most likely to move in a strong southerly.
Do you need approval for a shed?
Often not. The NSW Planning Portal lists garden sheds among the works that can be exempt development, provided the shed meets the standards in the State Policy. Those standards cover size, height and distance from the boundary, and flood, bushfire and heritage mapping can change the answer for a particular block. Anything over the limits goes through a complying development certificate or a development application with the council. The sheds and carports page covers how we check a site before starting.
What does a slab add to the price?
The slab, footings and anchoring are separate from the shed itself, and a quote for a kit does not include them. When comparing quotes, check whether the base is in the number. A supplied-and-built shed quote should say what it sits on and how it is fixed down.
To have a base and a shed priced together, or to have a kit you already own put up and anchored properly, call Dave on 0414 007 351 or use the contact form.
Want a hand with this at your place? Get a free quote or call 0414 007 351.
