Picking the wrong size is one of the most common mistakes people make when ordering a temporary structure. Too small and you are back on the phone before the project is halfway done. Too big and you are paying for space that sits empty. Get it right first time and everything else falls into place.
Here is how to work out what you actually need.
The Three Dimensions That Matter
Width is the span from one eave to the other. Our standard range runs from 3m up to 30m and beyond for clearspan builds. The wider you go, the more usable floor space you get without internal columns getting in the way. That matters a lot if you are running forklift trucks or moving large equipment around inside.
Length is the most flexible dimension. Most structures extend in 3m or 5m bays, so if you are not sure how much you need, rounding up by one extra bay is always the sensible move. It adds less to the cost than you would think.
Eave height is the measurement from the ground to where the wall meets the roof. Our warehouse and storage structures start at 2.3m and go up to 7.2m. For welfare units and temporary classrooms, 2.4m to 3m is usually plenty. For forklift operations you need to think much more carefully about this one.
Working Out Your Floor Area
Before you call us, spend ten minutes doing this calculation. It makes the whole conversation faster and more useful.
For storage and warehousing, start with the floor footprint of everything you need to cover. Add at least 20% on top for access aisles and turning space. If you are running racking, the height of the top shelf determines the eave height you need, not just the floor area. A lot of people only realise this partway through the conversation.
For site welfare, the HSE guidance sets out minimum floor areas per person. Roughly speaking, allow 1 to 1.5 square metres per person for rest and seating, then add space for toilets, changing rooms and somewhere to dry wet clothing. A site with 50 workers typically needs at least 60 to 80 square metres in total.
For temporary classrooms, UK school building guidance recommends a minimum of 2.3 square metres of net teaching space per pupil. A class of 30 children needs roughly 70 square metres to work in comfortably. Our classroom structures generally run between 60 and 90 square metres per unit.
For events and exhibitions, map out your layout before you call anyone. Allow at least 1 metre of clearance around the perimeter for visitor movement, and factor in where people will queue, gather and exit. Our exhibition structures can be built around a floor plan you bring to us.
The Sizes We Build Most Often
For storage and light industrial work, the sizes that come up most are 10m x 15m, 12m x 18m and 15m x 24m. All are available in PVC, insulated and solid wall depending on what the job requires.
For site welfare, the standard range runs from 6m x 9m up to 9m x 12m, which covers most sites with 20 to 50 workers with room for canteen, toilets, changing and drying facilities.
For classrooms, a single unit is typically 6mx12m. You can read about how those work in practice in our Surrey primary school case study, where we installed two units during a school building programme.
What Might Change the Size You Can Install
Leave at least 1 metre of clear space around the full perimeter of the structure. Our installation team needs room to work on all four sides and anything tighter than that causes problems on the day.
If the ground is uneven, you may need a sub-frame levelling system before the structure goes up. We installed exactly that for Mid Kent Golf Club where the site had a significant slope. It is not a problem, but it needs to be flagged early.
If the structure will be in place for more than 28 days, planning permission may be needed. Our planning permission guide covers the rules in plain language.
Go Bigger If You Are Not Sure
An extra bay costs far less than bringing us back to extend a structure that turned out to be too small. If you are genuinely unsure whether you need 18m or 21m of length, go with 21m. You will not regret it.
Book a free site visit and we will come to you, walk the space and tell you exactly what we think you need. No cost, no obligation. Or call 0203 758 3315 if you want to talk it through first.