Methodology

How Sous Zinc estimates the summer heat risk of every residential building in Paris with 2 dwellings or more. Method version 2027.3.

Every rating is an estimate, not a measurement: it replaces neither a temperature reading nor your dwelling’s own energy certificate.

What the estimate measures

The energy performance certificate (DPE, diagnostic de performance énergétique) states, for every dwelling it covers, whether its summer comfort is good, average or insufficient. Sous Zinc estimates the share of a building’s dwellings whose DPE would say “insufficient”, for the upper floors and for the top floor.

Sous Zinc rates the Paris buildings with 2 dwellings or more in the national building database (BDNB).

The building’s own DPE

A DPE belongs to the building the BDNB links it to most reliably. A DPE newer than the BDNB belongs to the building of its address. A DPE replaced by a newer one is ignored.

A DPE issued before July 1, 2024 that gives a floor of 1 or more, or before November 1, 2024 that gives no floor, is not counted: ADEME often publishes its summer comfort with “good” and “insufficient” exchanged. Such a DPE is set aside before any series vote, as a replaced DPE is. The building page still shows the DPE the estimate does not count.

A DPE that gives floor 0 (often a field left blank) or a floor below ground counts, whatever its date and whatever position it declares.

Apartment DPE generated from the same building DPE count as one, with their most frequent value on their latest issue date. A tie goes to the less severe value.

n is the number of the building’s counted independent DPE (a series of DPE generated from one building DPE counts as one), and p_own the share of “insufficient” among them.

Similar buildings

For each group of buildings sharing a construction period (before 1948, 1948–1974, 1975–2000, 2001–2012, since 2013) and a roof group (zinc, other, unknown), Sous Zinc computes the share of “insufficient” among all their counted DPE in Paris: that is p_prior.

A group with fewer than 200 DPE falls back to its period alone, then to all of Paris.

The blend

The building’s counted DPE and those of similar buildings are combined. The more counted DPE a building has, the more its own weigh.

p = (n × p_own + k × p_prior) / (n + k), with k = 5

The top floor

The top floor is the highest level of the BDNB building group. A DPE is on the top floor when it says so. A DPE that declares the ground floor or an intermediate floor is on a known lower floor. Otherwise, in a building of more than one level, a floor of 1 or more is the top floor from the number of levels minus one up, and a known lower floor below. The number of levels comes from the DPE or else from the BDNB. Any other DPE has an unknown floor, floor 0 without a declared position included.

A series generated from a building DPE never has a floor.

The top-floor uplift, u, is the share of “insufficient” among top-floor DPE minus that among the other known floors. It can be negative. A group only gets its own uplift with at least 30 top-floor DPE and 30 DPE on other known floors; otherwise the period’s uplift is used under the same rule, then that of all of Paris. The uplift of all of Paris is used whatever its number of DPE, and it is 0 when all of Paris lacks DPE on either side.

The uplift pools the DPE placed on a floor, nearly all issued since July 2024. In the smallest groups it is uncertain by about ±12 to ±18 points. That range is a 95% interval.

p_top = (m × p_own_top + k × t) / (m + k), with t = p + u, clamped between 0 and 1

m is the number of the building’s counted independent top-floor DPE, and p_own_top the share of “insufficient” among them. With none (m = 0), p_top = t: the top floor is estimated from the building’s upper-floor estimate, p, plus the uplift, u, measured on comparable buildings.

The categories

The estimated share gives the category: Low below 25%, Moderate from 25%, High from 50% and Very high from 75%.

The building page says it the way people count: “7 dwellings out of 10” for a share of 70%. It never says 10 out of 10: from 95% it says “more than 9 dwellings out of 10”, and below 5% “fewer than 1 dwelling out of 10”.

Confidence

The upper floors and the top floor each have their own confidence. The upper floors’ comes from the building’s counted independent DPE, the top floor’s from those on its top floor: high with 5 or more, medium with 1 to 4, low with none.

With no counted DPE and no construction year, the building is “Not enough data” and drawn grey.

The explanation

Each rating keeps the factors that explain it, and the building page writes them in your language, in this order: the building’s counted independent DPE, those of its top floor, similar buildings, then the top-floor uplift and where it comes from (comparable buildings, the same period or all of Paris).

Shown beside, never mixed in

The building page always shows the building’s official DPE beside the estimate, those the estimate does not count included.

It also shows the building’s surroundings, from the Cerema local climate zones: dense and mineral, open, or green. The surroundings do not change the estimate until observations show how much they should weigh.

From afar, the map colours each IRIS neighbourhood by the median category of its rated buildings. With an even number of buildings, the lower of the two middle categories is used.

Limits

• The DPE summer-comfort indicator is computed by the assessor from the building’s features. It does not measure the temperature people live with.
• The DPE published by ADEME do not represent every dwelling: they mostly cover dwellings sold or let since July 2021.
• About 93% of buildings have no top-floor DPE that the estimate counts (about 89% have none at all, counted or not): their top floor is estimated from the building’s upper-floor estimate plus the uplift measured on comparable buildings, with low confidence. A building marked “Not enough data” has no estimate.
• After summer 2027, residents’ answers will be used to check the method and adjust it in a new version.

Versions and changes

Any change to an output changes the version number. Every computation records the version it applies, and each building page cites it.

Version 2027.3

Two kinds of DPE, whose summer comfort ADEME often publishes with “good” and “insufficient” exchanged, no longer count. They stay on the building page, marked as not counted.

An investigation in Paris found the exchange in more than half of the DPE issued before July 2024 that give a floor of 1 or more, and in about a quarter of those issued before November 2024 that give no floor. A check across France confirmed it.

Version 2027.2

The first Paris run placed only 513 DPE on a top floor, most of them the member that a tie-break on the certificate number kept from a series generated from a building DPE, so each group’s uplift rested on 1 to 93 DPE. Every output change against 2027.1:

• A group’s top-floor uplift is used only when the group holds at least 30 top-floor DPE and 30 DPE on other known floors; otherwise the period’s uplift is used under the same rule, then that of all of Paris. The rating records where it comes from.
• The height a floor is placed against is the DPE’s own level count, else the floor count of the BDNB building group.
• A declared “intermediate floor” counts as a known floor even without a floor number, as a declared “ground floor” already did, and it stays a lower floor even when its number would make it the top floor.
• A DPE level count of 0 or 1, or no level count from the DPE or the BDNB, leaves the floor unknown instead of making it another known floor.
• DPE generated from one building DPE count once, with the value held by most members issued on the series’ latest issue date; a tie goes to the less severe value, the building DPE votes in its own series, and a series is never placed on a floor.
• The upper floors and the top floor each have their own confidence, and the explanation lists the building’s own top-floor DPE.

Version 2027.1

The first version, used for the first Paris run.

Sources

All the data used is open and public. See each source, its licence and its date