Construction Site Accommodation: Sizing a Camp for a Moving Headcount

A construction site does not hold the same number of people for two years. It starts with a mobilisation crew, climbs to a peak the programme fixes months in advance, then sheds labour as commissioning takes over. Ordering construction site accommodation against a single headcount, whatever that number is, means most of the camp is either short or empty at some point. This article works through the alternative: derive a monthly bed requirement from the programme, split it into batches, and put the batch structure into the purchase terms so the tail of the project does not become dead stock.

The Straight Line Nobody Actually Builds On

Two numbers get used to size a camp, and both fail on a project lasting more than a year. The peak is the easy one to defend in a budget meeting, and the one a supplier quotes against. It is also true for only part of the programme: on a 24-month build the peak may hold four or five months, leaving a camp whose occupancy falls away for the remaining two-thirds, with the same maintenance, security and insurance obligations.

The average looks efficient on paper and fails in the field, because beds are not consumed evenly: short at the peak, over at both ends. Averaging also hides the rotation effect - on a 28-on, 28-off roster the camp houses the crew physically on site plus handover overlap, not the payroll headcount.

Neither is the number to order against. What you order against is the curve between them.

Draw the Curve From the Programme, Not From the Organogram

The organisation chart says how many people the contract employs. The programme says how many are on site in a given month, which is the only figure that sets bed count. Build the curve from four points:

• Mobilisation. Site management, setting-out, plant and early trades, plus the crew installing the camp.
• Peak construction. The month in which the most trades overlap - the month, not the total, because it sets when the last batch must be standing and connected.
• Commissioning. Trade labour drops as commissioning specialists, client representatives and inspectors arrive. Numbers fall, but the mix changes and the room standard sometimes rises.
• Demobilisation. The number still on site while the camp is struck and shipped out. This sets the floor you cannot go below, and is routinely forgotten.

Two adjustments sit on top. Subcontractor labour often sits outside your own headcount and can be a material share of the peak, so the figure has to come from the package contractors rather than from HR. Rotation then converts payroll into bodies in beds, where a 28-on, 28-off roster produces a peak well above a simple division by two.

The wider sequence around the curve, from building mix to layout and utilities, is in the modular workforce accommodation camp planning guide. What follows is narrower: what the curve does to unit count, freight and contract terms.

Peak and Tail Answer Different Questions

Treating the camp as one purchase hides that peak and tail are two problems with two solutions. The peak sets the permanent system: dormitory units, but also canteen throughput, ablution ratio, water storage, generator capacity and sewage load. Those systems do not scale down gracefully - a canteen built for 400 still has to be staffed, cleaned and powered when 120 remain. That is why a camp sized on average occupancy fails exactly when the client is watching.

The tail sets the size of the write-off. Every unit still standing in month 20 with no occupant carries transport cost already spent, storage or hire cost still running, and a dismantling cost not yet incurred. The tail is where the money quietly goes, and the part of the curve nobody puts in the budget submission.

So density and unit type belong to different stages. Room sharing changes how many containers the peak requires. Unit type changes what you can do with those containers once the peak is over.

Three Ways to Cover the Tail

Three structural answers exist, differing in who carries the residual risk.

Buy-or-hire for construction site accommodation generally is covered in the construction site cabins guide. The point specific to a moving headcount is narrower: hiring tends to win when the peak is short and the site is near a hire market, buying when the tail can be moved rather than stored.

That third option only works if the unit was chosen for it. Not every modular unit takes a second and third installation equally well, and the difference shows up in container slots per move and site hours per rebuild. The guide to relocating a container camp compares the four types on those numbers, and it is worth reading before the peak order, not after.

What Batch Size Does to Freight

Batched arrivals mean batched freight. Cost per unit is the wrong comparator; containers per shipment is the right one.

Loading density varies by type, and by a lot. In the published ranges for the current lines, a foldable container house loads at roughly ten units per 40HQ, a stackable quick-assembly unit at roughly six, and a knock-down quick-assembly unit at approximately fourteen; a 20 ft dual-wing expandable loads two per 40HC and a 40 ft expandable loads one. Those figures drive the freight estimate, and mean two suppliers quoting the same number of rooms can produce very different container counts.

Batching adds a fixed cost that does not shrink with volume: each shipment carries its own booking, export clearance, documentation and inland haulage, and each arrival its own receiving and lifting mobilisation. Two batches cost more in fixed charges than one, and the question is whether not paying for units four months early exceeds that gap.

Site area can override the cash-flow answer. If the footprint cannot hold the peak at the required spacing, one large delivery produces units with nowhere to stand, and the batch structure ends up set by site area rather than by money.

A Worked Example: 24 Months, Peak 400

The arithmetic below uses one hypothetical programme. Headcounts, months and room-sharing figures are assumptions chosen to make the calculation visible; they are not industry standards and not product specifications.

At two per room the peak needs 200 rooms. Taking the ten units per 40HQ published for the foldable type, that is 20 containers; at four per room it is 100 rooms and 10 containers. Halving the room count roughly halves the containers, which is why density gets argued about so hard in the early weeks.

The part density does not fix is the tail. At two per room, commissioning needs 75 of the 200, so 125 stand empty for six months; demobilisation needs 30, so 170 stand empty for the last three. At four per room the absolute numbers shrink but the proportion is identical - roughly 62 per cent and 85 per cent of the peak camp sits unused. Sharing rooms reduces the size of the problem. It does not change its shape.

That is why unit type follows density rather than competing with it. If the peak camp has to be 200 rooms and the tail needs 30, the useful question is not how to make rooms smaller but whether the 170 rooms coming off line can leave the site, and what that move costs in containers.

One more lever sits on the peak side. Stacking halves the footprint for the same bed count, which matters when site area rather than budget is the constraint; see the two-story modular dormitory guide.

What Changes the Answer

The method assumes a fixed programme and labour that is yours. Four conditions break that.

A long rotation. Where crews fly in for 28 days and out for 28, the camp is half-populated by definition, which flattens the curve and weakens the case for density: you are already at half occupancy per bed. Short rotation with long handover overlap does the opposite.

Subcontractors with their own accommodation. On many sites the mechanical, electrical and piping packages arrive with their own temporary site accommodation. That removes a large block from your curve but leaves you responsible for the shared facilities they use, so canteen and ablution sizing must be agreed with them in writing rather than assumed from your own headcount.

A programme that is not firm. Early works contracts often have a target duration and no fixed end date, so the curve cannot be drawn with confidence. Batching then becomes an option worth paying for: fewer units now with a right to call off more at an agreed price usually beats the discount for buying the whole camp at once.

A female workforce. Separate sanitary provision changes the block count independently of beds and lands as a fixed addition rather than something that scales with the tail. It belongs in the mobilisation batch, not the peak batch.

Terms to Fix Before the First Batch Ships

A batch plan that exists only in your own spreadsheet is not a batch plan. Five terms carry the risk.

• Call-off quantities and dates. Which units, how many, by which month. Without a dated call-off schedule, later batches are new orders at whatever the price then is.
• Price validity on later batches. Steel and panel costs move. A quotation valid for 30 days does not cover a batch ordered in month eight, and the second batch is where budgets usually break.
• Model continuity. If the model is revised or discontinued between batches, the second may not match the first - which matters most for stacked or linked configurations where structural interfaces must align.
• Who stores what, and where. Early delivery to secure a price creates a storage obligation. Agree whether unshipped units stay at the factory, at the port or on site, and who insures them in each case.
• Reuse expectations in writing. If the tail plan depends on moving units to the next project, say so at inquiry stage. The published documentation does not state a maximum number of relocation cycles for these modular types, so the realistic position is a condition inspection at each teardown rather than a promised number of moves.

None of this asks the supplier to carry project risk. It asks for the batch structure to be visible on both sides before the first container is booked - a far smaller request, and a much more useful one.

Frequently Asked Questions

Should construction site accommodation be sized to peak or average headcount?

Neither alone. Size permanent systems to the peak, because canteen, ablution, water and power capacity cannot be expanded cheaply later; size dormitory units to the curve, covering the gap by batching or relocatable units rather than by buying the peak outright.

How far in advance should the accommodation be ordered?

There is no single figure: production time depends on confirmed model, quantity, customisation and order timing, and sits separately from sea freight and inland transport. Fix the model and first batch early, then hold later batches on a dated call-off schedule.

Is it cheaper to share rooms more densely or to buy fewer units?

Density cuts the peak requirement and the container count, but not the proportion of the camp empty in the tail. Whether the saving is real depends on the client's accommodation standard and local labour practice, either of which can rule out higher occupancy regardless of cost.

Can the camp be dismantled and used on the next project?

Often yes, and the unit type decides how practical it is, measured in containers per move and site hours per rebuild. No maximum number of relocation cycles is published, so inspect frame, panels and flooring at each teardown.

What information is needed to quote a phased camp?

The stage-by-stage headcount, room sharing, building types and quantities per batch, target date for each batch, project country, site access conditions, and whether tail units will move on.