Notes

A Slab for a Workshop or an Addition

We pour the footings and the floor. We do not put up what goes on them. That boundary is the most useful thing to establish early, and it shapes how the whole project should be sequenced.

Updated October 2026 · Oak Creek Concrete

This is the enquiry where expectations most often diverge from what we actually do, so it is worth being direct at the top. Somebody planning a detached workshop or an addition needs several trades, and we are one of them. Knowing which one, and where the handovers fall, makes the project go considerably better than discovering it in week three.

Where our part starts and stops

Flatwork and footings. That covers the excavation, the base preparation, the formwork, the reinforcement, the concrete itself, the finish and the jointing.

It does not cover erecting the building, framing it, roofing it, wiring it, or running the addition as main contractor. None of that is a gap we are apologising for. It is a deliberate limit, and its purpose is that the concrete is placed by people who place concrete and nothing else.

What it means for you practically is that somebody has to own the sequence, and on a project with a structure on it that person is usually the builder rather than us. We fit into their programme, and the more clearly that is established at the start, the fewer arguments there are about who was waiting for whom.

The distinction that decides the job

There are two quite different pieces of concrete on a project like this, and they follow different rules.

A slab on grade is a floor. It rests on compacted material, it is not tied down to anything, and a small amount of seasonal shifting is something it accommodates rather than fights. Driveways are slabs on grade. So are patios, and so is the floor inside many light outbuildings.

Footings carry a structure into the ground and are meant to stay put. The state sets that depth in two parts, and both have to be satisfied:

Test	Requirement
Frost	Beneath the depth to which the ground freezes
Minimum	At least 48 inches down from the grade beside it
Which applies	Whichever of the two is deeper

That third row is the one general writing on the subject tends to lose, and it is the reason a mild winter does not licence a shallower footing.

Which of those your project needs is a question about what is going on top, and it is not always obvious from the size of the building. It is also not a question to settle by assumption, because getting it wrong in either direction is expensive: founding a light structure unnecessarily wastes money, and floating something that needed founding produces a building that moves away from itself.

What must be settled before anybody pours

• Everything that runs underneath. Drainage, conduit, any plumbing. Once there is a slab over it, changing your mind means breaking concrete.
• The finished level. How the floor relates to the ground outside, to a threshold, and to whatever you will be wheeling in and out.
• Where the door goes. It sounds like a building decision and it is a concrete one, because thresholds, falls and any thickening under a wall all follow from it.
• How water leaves. Both surface water outside and anything that arrives inside on a vehicle or a wet day.
• What the floor will carry. A workshop with a vehicle lift or heavy machinery is not the same specification as a garden studio, and that conversation belongs before the design rather than after it.

None of those are difficult. All of them are effectively permanent, and they are the items that get deferred because they feel like details.

Sequencing, which is where projects actually go wrong

The usual failure is not technical. It is that the concrete gets booked as though it were an independent job, when it sits between two other trades who both have views about it.

Groundworks and services come before. The structure comes after, and it has to wait for the concrete to be ready rather than merely finished, which is a real interval rather than a formality. Where a slab has to take a wall, the timing of that handover is worth agreeing explicitly rather than assuming.

Our practical advice is to have whoever is building the structure talk to us before the dates are fixed. Ten minutes at that stage saves a fortnight of everybody waiting.

Access, which decides more than the design does

Worth raising early on any project behind a house, because it can change what is buildable.

Concrete has to reach the site. Where a truck can get within chute range, a pour is a morning. Where it cannot, the same volume arrives by barrow or by pump, and those are different jobs with different prices and different crew sizes. A narrow side passage, a gate, a mature tree or a slope between the road and the plot all matter more to the cost of a rear workshop slab than the square footage does.

It is also worth checking before the building itself is designed, because an oversized structure in a spot nothing can reach is a more expensive discovery than a slightly smaller one positioned where a pour is straightforward. Ten minutes walking the route with whoever is quoting settles it.

Permits, and who owns them

A building means a building permit conversation with the City, and that sits with the project overall rather than with the flatwork inside it. A detached workshop, an addition and a replacement floor in an existing structure are three different situations.

We will say plainly what we think falls where, and we would rather you confirm it directly with Oak Creek than treat our reading as the last word. Where work also touches the driveway or reaches the street, that is separately permitted and covered in the Oak Creek driveway approach permit.

Costs for slabs by use case, with the assumptions written out, are in what a concrete slab costs. To have the concrete part of a project quoted, start at concrete patio, which is where our flatwork enquiries begin whatever the eventual shape of them.