Machinery store buildings
The building most farms put up first, and the one they regret sizing smallest. The frame is the easy part to price. What catches people out is the floor it stands on — and that is a separate job, on a separate bill.
- Typical slab
- 200 mm
- Sub-base
- 150 mm
- Concrete, 12 × 20 m
- 52 m³
- Planning route
- Prior approval
With mesh. 150 mm can do if it only ever sees light tractors.
Compacted Type 1, spread around 190 mm loose.
Slab only, waste allowed. Pads are extra and engineer-designed.
On qualifying agricultural holdings, not a full application.
What the frame quote covers
Steel, purlins, side rails, cladding, roof lights, doors and erection. That is the number you get quoted, and for what it covers it is usually a fair one. It assumes a level, prepared base is waiting when the erectors arrive.
It does not include getting that base there. Site strip, cut and fill, hardcore, the slab, the drainage and the access track are groundworks, priced by a different trade at a different time.
Why the floor works harder here
A machinery store floor takes moving loads. A loaded trailer turning on the spot puts far more through a slab than the same weight standing still, and it does it in the same few places every day — inside the door, wherever you always swing round.
That is why 200mm with mesh is the usual starting point rather than the 150mm that would do for a hay barn. If you are running a combine, a loaded grain trailer or a telehandler with a full bucket, say so when you spec it. Those are the loads that decide it, not the size of the building.
Get the falls right while you are at it. A machinery store floor collects diesel, oil and whatever comes in on the tyres. A floor that drains towards a door is easier to keep than one that puddles in the middle, and it matters far more once the building is full.
The slope is the variable
Two identical buildings on two different fields are two different jobs. On a level site you strip the topsoil, level, stone up and pour. On a field with half a metre of fall across the footprint you are cutting into one end, filling the other, and deciding whether the surplus goes on a heap or into a lorry.
88 m³
Topsoil shifted before you touch the level, stripping 250mm off a 350m² working platform. If it leaves site, that is ten lorry loads — and it is the figure most people guess.
Dig a trial hole and measure the topsoil rather than estimating from the top of the field. It moves more material than the slope does on most sites.
Where you stand on planning
A machinery store on a working farm is usually agricultural development rather than a full planning application. Part 6 of the General Permitted Development Order gives rights on agricultural units of five hectares or more under Class A, and narrower rights on units between 0.4 and five hectares under Class B.
Two things have to be true. The unit has to qualify on size, and the building has to be reasonably necessary for agriculture on that unit — a shed for a contracting business, or for storing something unrelated to the holding, is not covered however agricultural it looks.
Where it applies you do not apply for planning permission. You apply to the council for a determination on whether prior approval is needed for the siting, design and external appearance, and they have 28 days to come back. That is a quicker and cheaper route than a full application, which is why it is worth establishing early whether you qualify.
There is a floor area limit, and it has moved. It was 465 square metres until 2018, when it rose to 1,000, and the rules were amended again in May 2024. If you are reading an older guide, check it against the current position before relying on it.
The exclusions matter more in Cornwall than in most places. Rights are restricted on protected land, which covers a substantial part of the county, and removed altogether for livestock accommodation within 400 metres of a protected building. Scheduled monuments were added to the exclusions in 2024. None of that is a reason not to build. It is a reason to establish your position before committing to a frame.
A summary, not planning advice. The legislation is Part 6 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended. Talk to Cornwall Council or a planning consultant about your own site.
What nobody can tell you from a web page
The pad foundations. The concrete bases the stanchions sit on are sized by a structural engineer against your span, your eaves height, the wind loading where you are and what your ground will bear. There is no formula for it, and anyone giving you a pad size without a design has guessed.
Everything else below is geometry, worked out from the dimensions of the building.
Work out the base for your machinery store
Already set to a machinery store specification. Change the span and length to your building, and tell it what the ground is doing.
What this does not work out: the pad foundations
The concrete pads the stanchions sit on are sized by a structural engineer, not by a formula. They change with the span, the eaves height, the wind loading on your particular site and what the ground will bear. Anyone quoting you a pad size without a design has guessed it.
Want this priced properly?
Send us the job and we'll get you engineered drawings and a quote for the frame — with the pad sizes this tool can't work out. The figures above go with your enquiry, so you don't have to type them again.
Every enquiry gets a reply the same day, and your figures are sent with it. We are not a steel building manufacturer — we pass your details to a steel building supplier so they can price the job and contact you. How we handle your details.
Common questions
- What slab thickness does a machinery store need?
- A 200mm slab with mesh is the usual starting point for a machinery store, and it is the band UK suppliers quote for agricultural and commercial floors. If the building will only ever see light tractors, 150mm can be enough. What decides it is the heaviest thing that will regularly stand or turn on it, so spec it against your own machinery rather than the building size, and confirm it with your groundworker.
- Is the concrete base included in a steel building quote?
- No. A steel frame quote covers the frame, cladding, doors and erection. The site strip, cut and fill, sub-base, slab, drainage and any access track are a separate trade billed separately, and on a sloping site they are frequently a third or more of the total spend.
- How much concrete does a 12m by 20m machinery store need?
- A 12m by 20m building with a 200mm slab and a 100mm oversail works out at roughly 52 cubic metres of concrete once a waste allowance is added, plus around 78 tonnes of Type 1 for a 150mm compacted sub-base. Change the dimensions in the calculator to get the figures for your own building.
- Do I need planning permission for a machinery store?
- Often not, if it is a genuine agricultural building. Part 6 of the GPDO gives permitted development rights on agricultural units of five hectares or more under Class A, and more limited rights on units between 0.4 and five hectares under Class B. The building must be reasonably necessary for agriculture on that unit, and a floor area limit applies. Instead of a full planning application you apply to the council for a prior approval determination on siting, design and external appearance, which they have 28 days to decide. Rights are restricted in protected landscapes and removed entirely for livestock accommodation within 400 metres of a protected building.