Grain store buildings
The one farm building where the walls are doing structural work, because the crop leans on them. Tell us roughly what you need to hold and you get engineered drawings and a price for the building — plus an honest figure for the floor, and the sum that tells you whether it is big enough.
- Capacity, roughly
- 0.75 t/m³
- Wall panels
- 150–280 mm
- Typical slab
- 200 mm
- Planning route
- Prior approval
Wheat, as a working figure. Floor area × depth × that, for a level bulk.
The range precast suppliers commonly offer. Deeper bulks want the thicker end.
Loader traffic, not the grain, is what decides it.
A genuine grain store on a qualifying holding is agricultural development.
What you are actually buying
A flat store is the one building here that is structurally different from a shed with things in it. Everything else on this site stores something that sits still and stays where it is put. A bulk of grain leans on the walls, and it does it hard enough that the frame and the walling have to be designed for it. That is the whole game with a grain store: the frame, the walls and the floor are one system rather than a building with a floor in it.
Span and length are tonnage
Work out the tonnage you need to hold, decide the depth you can safely fill to, and the footprint falls out of the arithmetic. Do it in that order rather than picking a shed size and hoping it takes the harvest.
Wall height is the depth of the bulk
The retaining walls decide how deep you can go, and depth is worth far more than floor area — every extra metre of wall is tonnage across the whole footprint. It is also the number that has to be designed rather than guessed.
Eaves height is filling and emptying
Enough clearance above the wall for a loader bucket at full lift, or for the conveyor and the spout if it is being filled mechanically. Too tight at the eaves and you cannot fill the corners of your own store.
What you get asked to decide
- Precast panel walls or a poured retaining wall, and how high they go
- A drying floor with ducts, or laterals laid on the slab, or neither
- Which end you tip at, and whether the doors are big enough for a loaded lorry
- Bird and vermin proofing at the eaves, the ridge and the doors
- Supplied for your own team to erect, or supplied and erected
There is one more choice underneath all of those: whether the frame iscold rolled or hot rolled. It changes the price, the lead time, whether you can put it up yourself, and what goes in the ground.
How it goes from here
Five steps, in this order. The fourth is the one nobody prices for you up front, which is why there is a calculator further down this page.
Step 1
Tell us roughly what you need
Span, length and what it is for. Approximate is fine — nobody expects you to have decided, and it means the first reply can be useful rather than a list of questions.
Step 2
Drawings and a price for the frame
South West Steel Buildings prepare engineered drawings and quote the building. That includes the pad foundation sizes, which no calculator can work out for you.
Step 3
Settle the planning position
Prior approval on a qualifying agricultural holding, or a full application. Worth establishing before steel is ordered rather than after.
Step 4
Get the base in
Site strip, level, stone and slab, ready and cured before the erectors arrive. This is the part you can price on this page today.
Step 5
Delivery and erection
Delivered for your own team to put up, or supplied and erected. Both are normal; the difference is worth asking about at quote stage, not later.
Rough dimensions are enough to start. You get a reply the same day.
The walls are holding the crop back
Everything else on this site stores something that stays where it is put. Grain does not. A bulk leans on whatever is retaining it, and it leans hard — that is why a purpose-built flat store has proper retaining walls rather than sheeting down to the floor, and why the walls, the frame and the floor are one system rather than three separate decisions.
Precast panel systems are the common answer, and suppliers offer them from around 150mm thick for ordinary grain loads up to 280mm where the bulk is deeper or heaped. Which one you need is a design output, not a shopping choice. The reference for loads from stored bulk solids is Eurocode 1 Part 4, which covers silos and tanks — the point being that somebody with the standard open should be sizing this.
Pushed from inside
A shed built to keep rain off machinery was never designed to be shoved outward from within. Tipping grain against the side of one is the mistake that bends side rails and pulls stanchion bases.
If you are thinking of putting grain into a building you already have, that is a question for an engineer before it is a question for a haulier. Either the frame gets checked, or you build a retaining wall inside it that stands up on its own.
Working out what it holds
This is arithmetic and it is worth doing before anybody prices a frame. Floor area, multiplied by the depth you can fill to, multiplied by the bulk density of what you are storing. Wheat is commonly worked at around 0.75 tonnes per cubic metre — it varies with crop, variety and moisture, so it is a working figure rather than a promise.
A 15 by 30 metre store filled level to three metres is 450 square metres, times three metres, times 0.75 — about 1,000 tonnes. Change the wall height to four metres and the same footprint is holding a third more. That is why depth is worth more than floor area, and why the wall height is the number to get designed properly rather than the one to economise on.
Work in that order: the tonnage you need, then the depth you can safely go to, then the footprint. Picking a shed size first and hoping it takes the harvest is how farms end up with a heap outside under a sheet in October.
The loader decides the floor
Grain itself is an easy load — spread out, sitting still, no worse than bales. What decides the slab is the telehandler working in it: full bucket, turning on the spot, in the same few places all week. That is why a grain store floor sits with the machinery stores at 200mm with mesh rather than down with the hay barns.
If a drying floor is going in, that changes the job rather than the thickness. Ducts have to be designed and formed as part of the pour, laid out against how the store will actually be filled rather than spaced evenly for the look of it. Cutting ducts into a finished slab afterwards is a much worse job than forming them on the day, and you only get one day.
The roof that rains on the crop
A big uninsulated steel roof over a cool bulk of grain is a condensing surface. Warm moist air off the crop rises into the headspace, meets cold sheeting, condenses and drips back down onto the top of the heap. That is not a comfort problem — that is a rejection at the weighbridge.
It is a specification decision, made when the cladding is chosen: an anti-condensation lining or an insulated sheet, and ventilation that lets the headspace air out rather than trapping it. Both are cheap at the point of ordering and awkward to retrofit over a store with a thousand tonnes in it.
The same thinking applies to birds and vermin. Where the sheeting meets the eaves, how the ridge is closed and how the doors seal are the difference between a store that holds a crop to assurance standards and one that quietly does not.
Where you stand on planning
A genuine grain store on a working holding is agricultural development, so the prior approval route usually applies rather than a full planning application — provided the holding qualifies on size and the building is reasonably necessary for agriculture on it.
Storing somebody else's grain commercially is where it gets less straightforward, because the test attaches to agriculture on that unit. Worth being straight about at the prior approval stage rather than later.
Part 6 of the General Permitted Development Order splits at five hectares, and the two halves are not the same right with different numbers on them.
On a unit of five hectares or more, Class A permits the erection, extension or alteration of a building that is reasonably necessary for agriculture on that unit. The ground area of the building cannot exceed 1,500 square metres. That figure rose on 21 May 2024 — it was 1,000 square metres before then and 465 square metres before April 2018, so an older guide will understate it. A separate cap of 1,000 square metres applies to structures for accommodating livestock and to plant arising from engineering operations.
On a unit of at least 0.4 but under five hectares, Class B does not let you put up a new building at all. This is the part most often got wrong. Class B permits the extension or alteration of an agricultural building you already have — along with plant and machinery, private ways, hard surfaces and services — but there is no erection right anywhere in it. The extension is capped at 1,250 square metres of ground area and at a 25 per cent increase in the original building's cubic content, with no increase in height. If you have four hectares and no building to extend, a new shed is a full planning application.
Where Class A or B does apply, you are not applying for planning permission. You apply to the local planning authority for a determination as to whether prior approval is required for the siting, design and external appearance — currently £249 — and they have 28 days. If they do not respond inside 28 days you may proceed, provided the work genuinely is permitted development in the first place.
Two exclusions catch people. No building or structure for accommodating livestock or storing slurry or sewage sludge is permitted within 400 metres of the curtilage of a protected building — broadly a dwelling that is not on your own unit. And since 21 May 2024, nothing can be built under Class A or B on land that is, or is within the curtilage of, a scheduled monument.
On protected land the rights are not usually removed, which is a common misunderstanding. What changes inside a National Park is that the prior approval procedure applies more widely — to every extension or alteration rather than only to significant ones. In Cornwall and Devon that means Dartmoor and Exmoor. Cornwall's National Landscape is a different designation and does not take Class A or B away, though an Article 4 direction or a condition on an earlier permission can, and both are worth checking on your own holding.
A summary, not planning advice, and England only. The legislation is Part 6 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended — most recently on 21 May 2024. Figures checked against legislation.gov.uk in September 2026. Confirm your own position with the authority that covers your site.
Work out the base for your grain store
Set to a grain store specification at 200mm. It prices the slab, the stone and the earthworks under the building. The retaining walls and any drying floor are separate items, and both want designing rather than estimating.
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 go with it. The building itself is designed and priced by South West Steel Buildings, who we work with — so your details go to them too, and they will be in touch. How we handle your details.
Common questions
- How much grain will my store hold?
- Floor area multiplied by the depth you can fill to, multiplied by the bulk density. Wheat is commonly worked at around 0.75 tonnes per cubic metre, though it varies with crop, variety and moisture, so treat it as a working figure rather than a guarantee. A 15 by 30 metre store filled level to 3 metres is 450 square metres by 3 metres by 0.75, which is roughly 1,000 tonnes. Work the sum in that order — tonnage first, then depth, then footprint — rather than picking a shed size and hoping it takes the harvest.
- Can I store grain in an existing machinery shed?
- Not against the walls, unless someone has checked them. This is the mistake that costs money. A bulk of grain pushes outward hard, and a building put up to keep rain off machinery was never designed to be shoved from the inside — the side rails, the cladding and the stanchion bases are not doing that job. Either build a retaining wall inside it that stands on its own, or get the frame checked by an engineer before you tip anything against it. The relevant design reference for loads from bulk solids is Eurocode 1 Part 4, which covers silos and tanks.
- How high can grain store walls be?
- As high as the walling system is designed for, and that is an engineering question rather than a preference. Precast panel suppliers commonly offer thicknesses from around 150mm for standard grain loads up to 280mm for deeper or heaped bulks, with systems available well above head height. Depth is worth more than floor area — every extra metre of wall height is tonnage across the whole footprint — which is exactly why it is the number to have designed rather than guessed.
- Why does my grain store roof drip?
- Because a large uninsulated roof over a cool bulk of grain is a condensing surface. Warm moist air in the headspace meets cold steel, condenses and runs back down onto the crop, which is a rejection risk rather than a nuisance. It is dealt with at the specification stage — an anti-condensation lining or an insulated sheet, plus ventilation of the headspace — and it is far cheaper to specify than to retrofit over a full store.
- What does the floor of a grain store need to be?
- What decides the floor is the loader, not the grain. Grain is a distributed load and an easy one; a telehandler turning on a full bucket in the same spot every day is not. A 200mm slab with mesh is the usual starting point for that reason. If a drying floor with ducts is going in, the duct layout has to be designed and formed as part of the pour — cutting ducts into a finished slab afterwards is a different and much worse job.
- Do I need planning permission for a farm building?
- It depends on the size of the holding, and the answer is not the same for both classes. On an agricultural unit of five hectares or more, Class A of Part 6 of the GPDO permits the erection, extension or alteration of a building reasonably necessary for agriculture on that unit, up to a ground area of 1,500 square metres — raised from 1,000 on 21 May 2024, and 465 before April 2018. On a unit of at least 0.4 but under five hectares, Class B does not permit a new building at all. It allows only the extension or alteration of a building you already have, capped at 1,250 square metres and at a 25 per cent increase in the original cubic content with no increase in height. A new building on a holding that size needs full planning permission. Where Class A or B does apply you make a prior approval application to the local planning authority, currently £249, and they have 28 days to tell you whether prior approval is required.
- Will putting this building up affect a barn conversion later?
- It can, and it is worth knowing before you commit. Erecting or extending an agricultural building under Class A or Class B blocks a Class Q conversion of a building on that established agricultural unit for ten years, and the reverse also applies — if a Class Q conversion has been carried out on the unit in the previous ten years, you cannot use Class A or B to put up or extend an agricultural building. If a barn conversion is anywhere in your thinking, sequence the two rather than discovering the conflict afterwards.
Other buildings we cover
Same approach on each: what the building is, how it gets sized, where you stand on planning, and what the base underneath it comes to.
Machinery store buildings
Clear span, no posts in the way, and a floor that works harder than most. What it costs to put up and what it costs underneath.
Livestock building buildings
Housing that has to ventilate, drain and be scraped out. Falls, channels and the slurry rules — plus the 400 metre planning trap.
Farm workshop buildings
Room to get a machine in and work all round it, with a floor specced for the jack rather than the tractor.
Hay barn buildings
Open sides, air through it, and the lightest slab on the farm — if it needs one at all.
General purpose building buildings
The shed that ends up doing everything. How to spec a building for a use you have not decided yet.
Stables and arenas buildings
Stable blocks, American barns and indoor arenas. The same steel frame as a farm building — and a completely different planning position.
Industrial unit buildings
Workshops, warehousing, trade counters and light manufacturing. Full planning, full Building Regs, and a yard that often costs more than the shed.
Get a price for your grain store
Tell us the tonnage you need to hold and how deep you want to fill, and the footprint can be worked back from it. You get engineered drawings and a price, including the pad foundation sizes.