Guides / Modular Buildings
A published average cost per square metre for modular buildings is close to useless in a quotation, and the reason is not that the market hides its prices. Four different build systems are sold under the same two words, each priced on a different base, and the area the figure is divided by is not the same area from one supplier to the next. This page sets out what each system actually prices, works the denominator arithmetic on one 100 m² building, and lists the scope lines that have to be inside or outside the figure before two quotes mean anything.
There is no average cost per square metre for a modular building, because the figure is a scope divided by an area and both halves change with the system you choose. A container module is quoted per unit on a fixed envelope. A light-gauge steel frame villa is quoted against wall and roof area. A panelised house is quoted as a panel set. Divide any of those by a floor area and you have three numbers with three different meanings.
The useful question is therefore not “what is the average” but “what is inside this figure, and what was it divided by”. Get those two answers and two offers compare in an afternoon. Leave them out and the numbers are not on speaking terms.
The range we build runs across four families, and they are not variations on one product. Each has its own manufacturing logic, its own transport form and its own natural unit of price. The light-steel villa and prefab house page lists the sub-models; the table below says what the square metre is made of in each of them.
| System | What arrives on site | Natural unit of price | What the m² is mostly made of |
|---|---|---|---|
| Container module (detachable) | A finished box, lifted and bolted to the next one | Per unit, on a fixed external envelope | Corner posts and frames, insulated wall panels, floor deck, doors and windows |
| Flat-pack container module | Folded panels and frame parts, assembled on site | Per unit, plus the assembly labour you carry | The same panel build-up, with the labour moved from the factory to the site |
| Light-gauge steel frame villa | Frame, panels, roof and finishes as a kit | Against wall and roof area, and the section schedule | Galvanised C and Z sections, cement board, insulation, exterior cladding |
| Panelised / integrated house | Wall and roof panels made to the drawing | Per panel set, by area and opening count | Insulated panels with the openings cut at the factory |
That table is the first reason an average misleads. A container module carries its own structural frame, its own floor and its own corner castings for lifting, so part of what you pay for is a certified handling system you may never use again. A light-gauge villa carries a frame designed to the building's own loads, with no lifting castings and no corner posts, and the steel it contains is decided by the structural calculation rather than by a standard box. Same category, different bill of materials.
Before any rate is compared, the area underneath it has to be agreed. Three denominators are in common use and they give three different answers for the same building.
Take one 100 m² building at a 3.0 m storey height and put it on the ground as a single storey, then as two storeys of 5.0 × 10.0 m. The floor area does not change. Everything the envelope is made of does.
| Measure | Single storey, 10.0 × 10.0 m | Two storeys, 5.0 × 10.0 m | Change |
|---|---|---|---|
| Footprint | 100.0 m² | 50.0 m² | −50% |
| Gross floor area | 100.0 m² | 100.0 m² | none |
| Roof area | 100.0 m² | 50.0 m² | −50% |
| Perimeter per storey | 40.0 m | 30.0 m | −25% |
| Wall area (perimeter × 3.0 m, all storeys) | 120.0 m² | 180.0 m² | +50% |
| Wall area per m² of floor | 1.20 | 1.80 | +50% |
The second building has half the roof and half the foundation, and half again as much wall. A system that is expensive in walls — glazed facades, heavy cladding, many openings — gets dearer per square metre when the same floor area is stacked. A system that is expensive in roof and slab gets cheaper. Neither supplier has changed a rate; the denominator moved.
The shape of a single storey moves the same way. At a constant 100 m²:
| Plan | Perimeter | Wall area | Wall per m² of floor |
|---|---|---|---|
| 10.0 × 10.0 m | 40.0 m | 120.0 m² | 1.20 |
| 8.0 × 12.5 m | 41.0 m | 123.0 m² | 1.23 |
| 4.0 × 25.0 m | 58.0 m | 174.0 m² | 1.74 |
The 4.0 × 25.0 m plan is 45 per cent more envelope than the square plan for identical floor area. On a panelised or framed system that difference lands directly in the price; on a container module it lands in how many modules the plan needs.
The same arithmetic explains the oldest observation in this trade: a 40 ft module does not cost twice a 20 ft one. Part of that is fixed cost — end walls, doors, lifting points, the electrical board — being spread over more floor. The part that can be computed is the envelope ratio.
| Module | External size | Floor area | Perimeter | Envelope per m² of floor |
|---|---|---|---|---|
| 20 ft | 6,058 × 2,438 mm | 14.77 m² | 16.99 m | 1.15 m/m² |
| 40 ft | 12,192 × 2,438 mm | 29.72 m² | 29.26 m | 0.98 m/m² |
The 40 ft module carries about 14 per cent less external wall per square metre of floor than the 20 ft. Both are bolted the same way and both arrive finished, so the unit price rises by less than the floor area does. That is a geometric result, not a discount, and it holds whether the modules come from us or from anyone else. When someone quotes you a per-square-metre figure for container modules without saying whether it was built on 20 ft or 40 ft units, that is the number you cannot compare.
Most of the gap between two quotes for the same building is scope, not price. These six lines are the ones that move in and out of a quotation without being announced.
| Line | What it covers | Question that settles it |
|---|---|---|
| Foundation and ground works | Slab, strip footing, piers, levelling, drainage falls | Is the slab in the figure, and to whose drawing? |
| Transport | Inland haulage, sea freight, port charges, unloading | Which leg, to which port, and who pays the destination charges? |
| Lifting and placing | Crane or telehandler time, rigging, set-down tolerance | Is plant hire in scope, or does the buyer supply it? |
| Assembly labour | Bolting modules, closing joints, fitting trims, sealing | Factory-finished or site-assembled, and who supplies the crew? |
| Services connection | Water, power and drainage from the boundary to the unit | Internal wiring only, or the connection as well? |
| Approvals and inspections | Local permits, structural sign-off, utility applications | Which documents are supplied, and who files them? |
A quotation that includes foundation, freight and lifting can be twice the number of one that stops at the factory gate, on the same building. That is why the comparison has to be made line by line before any rate is discussed, and it is the same discipline set out in the container house cost guide for the container side of the range.
Frame weight is quoted as kilograms per square metre by most suppliers and almost never shown as arithmetic. It can be, because steel density is fixed. Under EN 1993-1-1 the density of steel is 7,850 kg/m³, so the mass of a light-gauge section per metre is its developed strip width multiplied by the gauge multiplied by that density.
| Developed strip width | Gauge | Mass per metre |
|---|---|---|
| 300 mm | 0.8 mm | 1.88 kg/m |
| 300 mm | 1.2 mm | 2.83 kg/m |
| 200 mm | 1.2 mm | 1.88 kg/m |
Read the first and last rows together. A 1.2 mm section rolled from a 200 mm strip weighs the same per metre as a 0.8 mm section from a 300 mm strip, and it is a different member doing a different job. So “1.2 mm frame” on its own says nothing about how much steel is in the building. Ask for the section schedule and the frame weight per square metre of floor, then check the second against the first.
The same conversion works for the envelope. Aluminium sheet is 2,700 kg/m³ under EN 1999-1-1, so a 0.9 mm cladding sheet is about 2.43 kg per square metre of face, and a specification that moves from 0.9 to 1.2 mm has added 0.81 kg per square metre of wall to handle, fix and freight. Small numbers per square metre become real numbers across a building, and they land in different scope lines.
Eight lines, all of them knowable before a price is asked for. Put both offers onto these and the difference usually explains itself.
| Line | Why it changes the number |
|---|---|
| System and sub-model | Container module, flat-pack, steel frame or panel set — different bill of materials, different transport form |
| Denominator | Footprint, gross floor area or envelope, and the measurement rule used |
| Storeys and plan shape | Roof, foundation and wall each scale differently against floor area |
| Wall and roof build-up | Board, insulation type and thickness, cladding, and the fire classification the panels are tested to under EN 13501-1 |
| Openings and glazing | Count, size, frame material and glass specification — the line that most often separates two similar totals |
| Fit-out standard | Wet areas, partitions, cabinetry, and what the buyer supplies |
| Design loads | Imposed floor load to EN 1991-1-1 and wind action to EN 1991-1-4 for the site, which set the frame |
| Scope boundary | The six lines in the table above, marked in or out, per offer |
Two of those lines are worth insisting on. The design loads decide the frame, and no supplier can price a frame honestly without knowing the site: a villa specified for a coastal wind zone and one specified for an inland site are not the same villa. The fire classification of the wall and roof panels decides both the material and the documentation, and it is a stated class rather than an opinion.
If you want one number to compare across offers, use cost per square metre of envelope rather than floor. The envelope is what the frame, the panels, the cladding and the openings are all priced against, so it recovers most of the differences the floor-area figure conceals.
This page is about the denominator and the scope line. The container side is worked through in the container house cost guide, which takes the same question on a fixed envelope and shows why a 40 ft unit is not twice a 20 ft one. The comparison against a conventional build, including lifespan, is in the light steel villa or concrete house piece, and the calendar side — how long each stage takes from drawing to handover — is in the lead time guide.
On the product side, the light-steel villa and prefab house page carries the four sub-models and the specification lines that the quotation is built from; flat-pack and expandable covers the folded and slide-out modules, and detachable container buildings covers the bolt-together box. Documents a project can ask for before dispatch are on the certifications page, and how they are checked is described under inspection.
Send the floor plan, the site, the number of storeys and the standard you want to build to, and the reply comes back as a scope with the area it was divided by. Send drawings and the destination, or use the contact page.
There is no average that carries across the category, because four different build systems are sold under the same name and each is priced on a different base. A container module is priced per unit on a fixed envelope; a flat-pack module per unit that has to be assembled on site; a light-gauge steel frame villa against wall and roof area; a panelised house as a panel set. On top of that, the area the price is divided by can be the footprint, the gross floor area or the envelope, and those three differ for the same building. A figure is usable only when the system, the scope and the denominator are stated together.
Most of the difference sits in four places: whether foundation, transport, lifting and on-site assembly are inside the figure; whether the wall and roof build-up and the glazing are the same specification; whether the denominator is footprint or gross floor area; and how many storeys the same floor area is spread over. A two-storey 100 m² building has half the roof of a single-storey one and one and a half times the wall, so roof-heavy and wall-heavy systems move in opposite directions on the same plan.
Usually yes, and the reason is arithmetic rather than discounting. Envelope and roof scale with the perimeter and the footprint, not with the floor area. A 40 ft module carries about 0.98 m of external wall per square metre of floor while a 20 ft module carries about 1.15 m, so the longer module spreads the same end walls, doors and lifting points over twice the floor. The same effect appears when a building goes from one storey to two: roof and foundation per square metre halve, while wall area per square metre rises.
Not on its own. The mass of a light-gauge section follows the strip width it was rolled from as well as the gauge, because steel density is fixed at 7,850 kg/m³ under EN 1993-1-1. A 300 mm strip at 0.8 mm weighs about 1.88 kg per metre and a 200 mm strip at 1.2 mm weighs about the same, so thickening the gauge while narrowing the profile brings the frame weight back to where it started. Ask for the frame weight per square metre and the section schedule rather than a gauge figure on its own.
Every figure on this page is either a standard dimension and a physical constant, or arithmetic from the dimensions printed beside it, and each one can be recomputed from the table. No price rate is published, because prices in this category follow steel and aluminium material cost and are quoted per project against a specification.