1. The three families of offsite construction
- Panelised prefabrication: wall panels, floors and roof structures pre-assembled in a factory. The most widespread and least transformative; most of the assembly still happens on site. The saving is mainly on the duration of the structural works.
- Volumetric construction: whole volumes, hotel rooms, complete dwellings, are manufactured, fitted out and finished in a factory, then transported and assembled on site. The most complete approach, and the most constrained by transport and site access.
- Offsite timber and cross-laminated timber: panels or timber frame prefabricated in a workshop. Particularly suited to roof extensions and to programmes with a controlled carbon footprint.
The key distinction: partial or integral offsite
Most projects described as offsite in France are in reality partially prefabricated: the structure is made in a factory, but the finishing trades, the finishes and the services are carried out on site. The time saving is real but smaller than manufacturers' marketing suggests.
Fully volumetric construction, a module delivered finished and ready to connect, is still marginal in France, essentially limited to budget hotels and student residences with high repetition. It represents a complete change of paradigm for economists and design teams.
2. Overall economic comparison
| Criterion | Conventional | Modular offsite | Advantage |
|---|---|---|---|
| Construction cost excl. VAT | The reference, 100 % | 95 – 115 % according to programme | Conventional, unless over 120 repeated units |
| Site duration | 14 – 24 months, excluding design | 6 – 12 months, excluding design | Offsite, by 40 to 60 % |
| Weather risk | Exposed, stoppages possible | Manufactured indoors | Offsite |
| Quality and control | Variable with the site teams | Industrial, continuous control | Offsite |
| Architectural flexibility | Very high, complete freedom | Constrained by standard modules | Conventional |
| Adaptability to the site | Optimal, suits any form | Limited, needs a regular plan | Conventional |
| Transport and logistics | Materials to site | Finished modules by road, 60–80 km maximum | Conventional, if the site is remote |
| Carbon footprint | Variable with materials | Often timber, favourable carbon balance | Offsite, where timber is used |
| Reversibility and dismantling | Standard demolition | Removal and reuse possible | Offsite |
| Structural warranties | Standard, well established | Developing; insurance still adapting | Conventional |
3. The real cost structure of offsite
One of the most frequent confusions is believing factory manufacture is systematically cheaper than site trades. That is partly true for economies of scale on long runs, but offsite generates costs conventional building does not have: transport, craneage of the modules, coordination between factory and site.
| Item | Conventional, share | Offsite, share | Comment |
|---|---|---|---|
| Manufacture and structure | 35 – 45 % | 55 – 65 % | Higher: skilled factory labour, tooling |
| Transport and placing of modules | 0 % | 8 – 15 % | An item specific to offsite, expensive over distance |
| Finishing trades on site | 30 – 40 % | 10 – 20 % | Reduced, since finishing happens in the factory; only interfaces and connections remain |
| Foundations and external works | 8 – 12 % | 10 – 15 % | Slightly higher: foundations designed for the point loads of the modules |
| Coordination and interfaces | 5 – 8 % | 8 – 12 % | More complex: factory, site and structural engineer must align |
| Site contingency | 5 – 8 % | 3 – 5 % | Reduced: manufacture in a controlled environment |
| INDICATIVE TOTAL | 100 % | 100 – 115 % | The offsite advantage is in time, not necessarily in cost |
The conclusion is structuring: offsite is not a lever for reducing construction cost, it is a lever for reducing duration and controlling site risk. Its economics stand up where the value of time is high, rental income not earned during construction, variable-rate loans, an inflationary context, and where repetition is sufficient to absorb the transport premium.
4. Where it fits, programme by programme
The economic relevance of offsite depends strongly on the type of programme. The table rates each use and states the condition for it to pay.
| Programme | Suitability | Time saving | Cost saving | Condition for it to pay |
|---|---|---|---|---|
| Social housing | ★★★★★ | − 40 % | − 5 to 10 % | More than 30 dwellings, simple forms |
| Student residence | ★★★★★ | − 45 % | − 8 to 12 % | Maximum repetition, urban site with lorry access |
| Modular offices | ★★★★ | − 35 % | − 3 to 8 % | A repeated typical floor, more than 3,000 m² |
| Two- or three-star hotel | ★★★★ | − 40 % | − 5 to 10 % | A repeated room type, more than 60 rooms |
| School | ★★★ | − 30 % | − 2 to 8 % | Public procurement; the statutory timescales are not reduced |
| Individual house | ★★ | − 20 % | 0 to + 5 % | Package builders only, little financial advantage |
| Complex public buildings such as hospitals | ★ | Limited gain | Frequently a premium | Poorly suited; architectural complexity outweighs economies of scale |
| Extensions and roof extensions | ★★★ | − 30 to 40 % | − 5 to 15 % | An excellent use case, minimal disruption to occupants |
Transport distance: the decisive parameter
Beyond 80 to 120 km between factory and site, the cost of moving the modules, abnormal loads, escorts, timing restrictions, significantly erodes the economic benefit. The map of modular factories in France is still thin, so this parameter is often decisive against projects in rural or isolated areas.
A 35 m² module transported 200 km costs 1,500 to 4,000 € in transport, that is 45 to 120 €/m², not negligible against a construction ratio of 1,840 €/m².
5. Social housing and student residences: the most convincing cases
Social housing offsite
Social housing is the programme where offsite shows the most favourable economics. Three reasons converge: the repetition of dwelling types across levels, the pressure on delivery dates given structurally unmet demand, and the labour constraints on conventional sites.
Social landlords who have tried offsite on programmes of 40 to 120 dwellings report time savings of 35 to 50 % against conventional building, that is six to nine months of earlier delivery. On an 80-dwelling programme generating 800,000 € of annual rent, each month gained represents 67,000 € of additional income, which makes any construction premium very easy to absorb.
The student residence: the optimal case
The student residence is the optimal offsite programme: a room type of 18 to 22 m² perfectly identical across five to ten levels, standardised technical requirements, and an imperative to deliver for the start of the academic year. Specialist modular builders have developed turnkey offers for this segment with site durations of four to eight months for programmes of 100 to 200 rooms, impossible conventionally.
6. The economist's role on an offsite project
Offsite construction profoundly changes the economist's assignment. On a conventional project the economist measures and prices works defined by the drawings. On an offsite project the modules come from a manufacturer at a catalogue price; the economist's role is to validate that price, assess the complementary works on site, foundations, external works, residual finishing, connections, and compare the whole cost against a conventional alternative.
The economist must also anticipate the risks specific to offsite: an incompressible manufacturing lead time, since modules are ordered six to nine months before delivery; rigidity of the brief, since any change after ordering is expensive; and questions of structural warranty insurance on construction systems still lightly standardised in France.
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In summary
Offsite construction is a lever on time, not systematically on cost. Its principal advantage is cutting site duration by 40 to 60 %, which carries real economic value when rental income depends on the construction period. The best-suited programmes are repetitive social housing above 30 dwellings and student residences above 60 rooms, where repetition offsets the transport premium. Distance from factory to site is the decisive parameter: beyond 100 km the benefits erode. The economist's role is to compare the whole cost, construction plus the value of the time gained, rigorously between the two approaches before any decision.
Reference basis of the figures
These bands are orders of magnitude for framing, and their reference market is the Paris region. They serve to place a budget at the earliest stages and to compare building types with one another. They replace neither a tender exercise nor an estimate prepared on drawings, and they are not a record of prices actually charged.
The ratios per square metre and per item on this page are stated in January 2026 values. They were updated from January 2025 values, the basis adopted for the whole cocoon, using the BT01 all-trades index published monthly by INSEE on its 2010 base: 132.0 in January 2025, 134.7 in January 2026, a rise of about 2 %.
The global amounts quoted as examples, and any rents, charges or receipts expressed per year or per night, remain on their own basis: a building cost index does not apply to them.
To bring the ratios forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7). The index has kept rising since: it stood at 138,3 in June 2026, the last value published when this page was checked, that is 2,7 % above the reference base. BT01 measures contractors' input costs, wages and social charges, materials, plant and energy, not the prices actually tendered.
Sources: the BT construction cost indices published monthly by INSEE on its 2010 base, used to update the figures · construction cost statistics from SDES, the statistical service of the ministry responsible for construction · regulatory texts published in the Journal officiel and consolidated on Légifrance for the requirements cited.