What a ratio actually covers
A construction cost ratio expresses the works cost excluding VAT per square metre of floor area. That apparently simple definition hides several subtleties which must be understood before a ratio can be used correctly.
| Regulated floor area | The definition in force since 2012: the sum of enclosed and covered areas with a ceiling height above 1.80 m, after deducting the area taken by walls, partitions, stairs, stairwells and lift shafts. The thickness of insulated external walls is excluded. |
|---|---|
| The former definition | Used before 2012, it included the thickness of external walls and excluded spaces the current definition includes. Ratios predating 2012 are expressed on that former basis and should be used with care. |
| Usable and habitable area | Accounting or letting definitions, distinct from the regulated floor area. Not to be confused when applying a ratio. |
| What the works cost covers | A standard ratio includes structure, internal finishing trades, partitions, finishes and ceilings, façades, external joinery and the technical packages, mechanical, electrical and plumbing. It excludes external works, landscaping, fees and insurance. |
Reference bands by building type
The bands below are indicative, in euros excluding VAT per square metre of floor area, for projects in mainland France in average market conditions. They must be brought forward to the date of the study using the BT01 all-trades index published monthly by INSEE.
Housing
| House, standard | 1,430 – 1,940 €/m² |
|---|---|
| House, high-end | 2,040 – 3,060 €/m² |
| House, very high-end | 3,060 – 5,100 €/m² |
| Apartments, ordinary location | 1,630 – 2,140 €/m² |
| Apartments, dense location, Paris region and major cities | 2,040 – 2,860 €/m² |
| Apartments, inner Paris | 2,450 – 3,570 €/m² |
| Social housing | 1,630 – 2,240 €/m², constrained by rent ceilings |
| Senior living and care homes | 2,240 – 3,270 €/m² |
Offices and commercial
| Offices, standard fit-out | 1,530 – 2,240 €/m² |
|---|---|
| Offices, intermediate quality, low-energy or certified | 2,040 – 2,860 €/m² |
| Offices, high-end, BREEAM or HQE certified | 2,550 – 3,880 €/m² |
| Light industrial and simple warehousing | 610 – 1,120 €/m² |
| Retail units, standard shell | 1,220 – 1,840 €/m² |
Public buildings
| Nursery and primary school | 2,040 – 2,860 €/m² |
|---|---|
| Secondary school | 2,240 – 3,060 €/m² |
| Day nursery | 2,550 – 3,570 €/m² |
| Simple sports hall | 1,840 – 2,550 €/m² |
| Multi-purpose hall | 2,040 – 3,060 €/m² |
| Library and media centre | 2,550 – 3,570 €/m² |
| Town hall and standard administrative building | 2,240 – 3,270 €/m² |
| Hospital and clinic | 3,570 – 6,100 €/m², highly variable with the brief |
Refurbishment
| Light refurbishment, finishing trades only | 610 – 1,220 €/m² |
|---|---|
| Intermediate refurbishment, façades and finishes | 1,220 – 1,840 €/m² |
| Heavy refurbishment, structure and finishes | 1,840 – 3,060 €/m² |
| Refurbishment with substantial asbestos removal | Additional cost of 200 to 610 €/m² depending on density |
| Thermal refurbishment, insulation, services and joinery | 310 – 820 €/m², before grants |
The correction factors to apply
A raw reference ratio is only a starting point. It must be corrected for the specifics of the project if the estimate is to be credible.
| Location | Paris and its region: 20 to 40 % above the national average. Major cities such as Lyon, Bordeaux and Nantes: 10 to 20 % above. Rural areas and medium-sized towns: 5 to 10 % below. |
|---|---|
| Specification level | Standard, intermediate and high-end differ by 30 to 50 % on the same programme. The brief must state which is intended. |
| Environmental certification | An additional 3 to 8 % depending on the level sought and the technical systems chosen. |
| Site constraints | Steep slope, high water table, shrinkable clay, complex party walls, difficult access: an additional 5 to 20 % according to the constraint. |
| Market conditions | In periods of strong demand or material inflation, tender prices can exceed historic ratios by 15 to 25 %. Updating through the index is indispensable. |
| Size of the operation | Large operations gain economies of scale on the technical packages. Very small operations, below 500 m², are often dearer per square metre because the fixed costs cannot be spread. |
The BT01 index: the instrument for updating
The BT01 index, covering all building trades and published monthly by INSEE, measures the movement of construction costs in France. It is the reference for bringing a ratio forward or revising a contract price.
The formula: updated price = reference price × (BT01 at the date of updating / BT01 at the reference date).
Between January 2020 and January 2023 the BT01 moved from 111.8 to 128.4, a rise of 14.8 %. Over the longer span from January 2020 to January 2026 it reaches 134.7, a cumulative rise of 20.5 %, which means a ratio established in 2020 under-states today's real cost by that much. Updating reference data systematically is a professional obligation of the construction economist.
What Quostra takes on
Maintaining a database of ratios by building type, by region and by specification level is permanent work. It is what allows Quostra to produce reliable orders of magnitude from the concept stage, without the architect having to invest in market intelligence.
ℹ Quostra, the construction economist on demand Cost estimates, pricing schedules, developer appraisals, summary notes. The deliverables that take you days today, taken on by a dedicated economist. You have better things to do. Submit your project and an economist takes over. → quostra.com
Sources: Yves Widloecher and David Cusant, Manuel de l'étude de prix, 4th ed., Eyrolles, 2018 · INSEE, BT01 index · Professional practice.
Reference basis of the figures
The bands on this page are stated in January 2026 values. They were updated from January 2025 values 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 coefficient of 1.0205.
To bring them forward, apply the usual revision formula: updated value = page value × (BT01 for the month in question / 134.7).
The BT01 measures contractors' input costs, labour at 44.9 % and materials at 36.5 %, not the prices actually tendered. The two series diverge as soon as margins move: over 2024 the BT01 rose by 0.9 % while the construction cost observed by the SDES survey rose by 2.1 %. These bands remain orders of magnitude, to be set against an estimate specific to the project.