The BT47 index appears in construction and renovation contracts whenever an electrical lot is involved. Published by Insee, this index measures the evolution of costs related to electrical work in buildings. Knowing how to read it allows you to verify whether the price you sign today will be revised tomorrow, and to what extent.
Composition of BT47: what the index actually measures
BT47 is not just a simple thermometer for domestic electricity prices. It aggregates several cost items specific to electrical companies in the building sector: labor (wages and charges), materials (cables, equipment, panels), energy, and transportation costs.
See also : Touching Poem to Honor a Deceased Mother in Family
Since April 2023, Insee has revised the weights and inputs of BT47. The new structure, aligned with the NAF rev. 2 classification, has modified the respective share of wages and charges in the calculation, without changing the reference base (still base 2010). Values prior to April 2023 have not been revised: there is therefore a slight methodological discontinuity at this point in the series.
To understand the BT47 index with Le Comptoir de l’Immobilier, it is important to keep in mind that each component weighs differently depending on the economic situation: a surge in copper prices drives the index up even if wages stagnate, and vice versa.
Related reading : Can you really drop off a Chronopost package at La Poste? What you need to know
Price revision clause: reading a contract that mentions BT47
A construction or renovation contract can set the price of the electrical lot in two ways: fixed price or adjustable price. The difference has a direct impact on the final bill.
| Price Type | Role of BT47 | Consequence for the signer |
|---|---|---|
| Fixed Price | No contractual revision clause | The signed amount does not change, even if costs increase |
| Adjustable Fixed Price | BT47 is used to update the price between the signing date and the start of work | The price can be adjusted before the start of the project |
| Revisable Price | BT47 is applied periodically during execution | Each work situation can be recalculated according to the evolution of the index |
The revision formula follows a standard pattern: the initial price is multiplied by the ratio between the value of BT47 at the revision date and its value at the contract reference date (often referred to as “month zero”).
Check the reference date before signing
The most common trap is an old reference date. If the contract mentions a reference month that is several quarters old, the first revision may result in a significant adjustment from the very first progress bill. Before signing, locate this date in the specific conditions and compare the value of BT47 for that month with the most recent value published by Insee.
Private contracts without a revision clause: how BT47 is still useful
In private contracts with fixed prices, no clause provides for automatic adjustment. However, the French Building Federation notes, in its recent sector analyses, that electrical companies are increasingly using BT47 to justify amendments during renegotiations of private contracts.
Their method: document the rise in costs based on the historical series from Insee, then propose a quantified amendment to the project owner. This practice is not based on any contractual obligation, but the existence of a public and verifiable index provides a factual framework for discussion.
Discrepancy between national BT47 and local prices
Specialized quoting platforms (Batichiffrage, regional scales from CAPEB) show, in their recent updates, that unit electricity prices in Île-de-France and PACA are rising faster than the national BT47 curve. This discrepancy is explained by local factors (pressure on labor, land costs for companies, urban logistics).
In other words, a contract revised based on the national BT47 may underestimate the actual increase in certain metropolitan areas. For an individual signing renovation work in these areas, the revision clause offers less protection than elsewhere.
Consulting and using the value of BT47: practical steps
Insee publishes the BT47 every month under the series identifying 001710979, freely accessible. The value is generally available with a delay of two to three months compared to the reference period.
- Locate the exact mention of the index (BT47) in your contract and the reference month, often noted as “month zero” or “M0”.
- Consult the chronological series on the Insee website to find the value of BT47 for the reference month and the most recent value.
- Apply the ratio between these two values to the initial amount of the electrical lot to estimate the price adjustment.
If the contract cites another index (BT01, for example, which covers the entire building), the measured evolution will be different. BT47 is specific to the electrical lot and reflects cost dynamics distinct from those of structural work or plumbing.
When the index is not mentioned in the contract
Some work contracts do not mention any index. In this case, the price is deemed fixed. If the work spans several months and the economic context is unstable, the absence of a revision clause transfers the entire risk of increase to the company, or to the client if the company refuses to start without an amendment.
- Check for the presence or absence of a revision clause before signing.
- Request the explicit mention of BT47 for the electrical lot if the contract does not specify any index.
- Keep the index values at the time of signing to be able to verify the revision bills.
The BT47 index remains a tool for transparency in the contractual relationship between the project owner and the company. Its reading requires no accounting expertise, but a methodical verification of three elements: the cited index, the reference month, and the revision formula. These three points are sufficient to know what the signed price will become once the work begins.