Thread: Pre-Shed Build Questions

The base that the slab sits on is super important so consider spending more than the recommend minimum on the base first. Like 200m of well compacted base course for example.
The earth moves. Your base isolates that movement from the slab which can't flex.

No stress from weight on top of the slab can compare to the forces involved when the earth moves under it. Which it does.

After that a 150mm slab would be advantageous if reinforced properly. If your budget allows.
Concrete cracks but it is a lot harder to crack a 150mm reinforced slab than a 100mm slab. The thing about vehicles is that all that weight is transferred to the slab at only 4 points. Woodworking machines perhaps not such a big deal.
All depends how much the slab is going to expand and contract through the years. (refer back to first point).

Sent from my SM-G935F using Tapatalk

P.S. I'm not a civil Engineer I just work with them a lot and have them in my family.
P.P.S. 200mm slab seems over the top for a workshop that has a good base IMHO. but what would I know?

Sent from my SM-G935F using Tapatalk

Do it once and do it well is my motto - you can't redo the slab (well not easily)!

On my shed the specifications called for 400mm deep foundations, and I went for 1200mm deep. The slab specification was 100mm and I went for 125mm thick with heavier reinforcement.

The rationale was if I want to put heavy machinery such as a metal lathe in it, I was covered. If I recall correctly, a car hoist requires a 150mm thick slab as a minimum.

A 125mm slab is usually ample and all that is used in factory complexes with thickenings and edge beams where required to support the structure.
If the structure is going through council they will require a structural engineers design so there is little need to deviate too much from that apart from placebo effect that you are doing a bettter job.

A 300mm thick slab will crack the same as a 100mm one will if it is poorly designed or laid.

if you can stop a slab from cracking you are going to be a very rich man.

When I got quotes for my shed built the shed people asked me what I was going to do in there and they all specified a 75mm floor and were quite surprised when I asked for 100mm because there were no vehicles going to be stored/moved in it. I also said I would prepare the base. I had to back fill with about 350 mm of builders yellow sand anyway which I watered and compacted to within an inch of its life. It depends what size of machine you are going to be installing. My heaviest machine is 230kg for which a 100 mm floor is more than adequate. It's a different kettle of fish if you start installing ton+ machinery and things like vehicle hoists.

Originally Posted by Beardy

A 125mm slab is usually ample and all that is used in factory complexes with thickenings and edge beams where required to support the structure.
If the structure is going through council they will require a structural engineers design so there is little need to deviate too much from that apart from placebo effect that you are doing a bettter job.

A 300mm thick slab will crack the same as a 100mm one will if it is poorly designed or laid.

Not necessarily. If the slab is poured inside an existing shed there is no need for engineer details. It goes through council as an earth floor.

The only advantage in a thicker floor is for unperceived use. Who knows what you may wish to use the shed for at a later date. If it could possibly involve the use of heavy vehicles, like high weight forklifts, a thicker slab would be the way to go. Normally, a 100mm slab is sufficient for a general workshop.

Originally Posted by Christos

... we been given the development approval on the location of the shed. We are now talking to builders to provide quotes for the construction of the shed.

You know the rule Christos - do it once do it right. Go a bit thicker if you can afford it - say 125mm. You never can tell what future use it might get. Also may make life easier for the next owner down the track (i.e. increases sell-ability)

Originally Posted by rustynail

Not necessarily. If the slab is poured inside an existing shed there is no need for engineer details. It goes through council as an earth floor.

Doesnt really make sense to pay an engineer to design the footings without giving the infill detail as well.
It is usually more cost effective and practical to pour the whole slab in one go as well but yes technically you are correct

Christos, get the slab at 125mm, then cover it with yellow tongue flooring, your back will appreciate it, especially in the colder months.

I found that offering the boss of the concretors, a case of beer, everything went smoothly, pun intended

Originally Posted by Pat

Christos, get the slab at 125mm, then cover it with yellow tongue flooring, your back will appreciate it, especially in the colder months.

That's very interesting. Did you build a false floor to lay the yellow tongue on or did you just put it directly on the slab?


Sent from my SM-G935F using Tapatalk

Dave, a double layer of concrete plastic, Aircell insulation then the flooring.

This was done several months after the concrete was poured and the shed was constructed, to allow the concrete to cure.

Originally Posted by mature one

if you can stop a slab from cracking you are going to be a very rich man.

does controlling where the slab cracks count?