Could this building become homes?

How this check works

It is a desk check from public records — no site visit, no drawings. It reads what the radar knows about a building (or measures an OpenStreetMap outline in your browser), then runs three layers. Rules version 2026-10-10.1.

1 · Fit

Five parts, each scored 0–10 and weighted: floor plate 30%, daylight 30%, height and storeys 20%, services and structure 10% and location 10%. 70 and up is band A, 50 and up band B. The method follows the published office-conversion screens — Gensler's five categories (whose own scorecards weigh windows and daylight twice their brochure weight) and the TU Delft Transformation Meter's veto and gradual criteria — adapted to what public records hold in Europe.

• Floor plate. Depth façade to façade of 10–16 m is ideal, still workable to 20 m and worth nothing at 30 m (Basel study: up to 16 m good, from 20 m special concepts; Brussels Task Force Bureaux: 17 m takes dual-aspect flats, 20 m and more does not; Banque des Territoires' 2026 guide: under 15 m; BBSR Redevelopment: post-war offices are 12–17 m). A plate of about 750 m² is best.
• Daylight. The share of each floor within 7.5 m of a façade, measured on the outline. On this page the outline is measured again on the base map: walls shared with a neighbour are not façades, and the daylit band shrinks to 2.5 × the clear height where that is less (BDA Bayern, Office to Housing).
• Height. Floor-to-floor height (official height ÷ storeys) on a scale, with 0.4 m of slab and services (BDA): below the country's minimum clear room height it is a warning, below the 2.6 m clear the market expects it is capped (the Transformation Meter), 3.3–4 m earns a bonus and taller floors none. Homes above 4 storeys need a lift, which buildings not built as offices often lack.
• Services and structure. What the building was built for, and its age where a record has it: asbestos is likely from 1930 to 1993, slabs of the 1950s–70s often fail today's fire and sound rules, from 1985 they are sound (BDA; BBSR).
• Location. Steps at 300 / 500 / 800 / 1,200 / 1,700 m to rail or metro (BDA); road noise costs points from 55 dB (the Transformation Meter wants under 50); an industrial estate counts against it.
• Flags. A listed building goes to the challenging cost tier (heritage conversions cost the most); a co-ownership has every owner to win over (Brussels); the year built, listing and land use come from the record or OpenStreetMap.

2 · Programme

It starts from the economic model's site default — shared rooms, ground-floor businesses, furnished mid-term flats — and lets the floor plate move it: a dark core becomes the building co-op's shared rooms (up to 25% of the floor), the ground floor of a building of 3 storeys and up stays commercial, what is still dark is let as storage and workspace or cut out as a light well, and the band 7.5–10 m from a façade suits small furnished flats (up to 50% of the homes) — for awkward plates the Basel study recommends small flats and serviced shared flats run by an operator. The 3D model stacks the layers from the ground up — businesses, the shared rooms both groups use, furnished flats, long-term homes — on the building's own outline; only a dark core breaks the stack. A rough check of floor areas, not a design.

3 · Money

EHC's economic model — its own engine — runs the building on today's site default for Strasbourg: its floor area and mix, a conversion cost and a purchase price. The conversion cost starts from the country's factor and the building's fit band (the model's good / typical / challenging tiers); a replaced façade adds 20 points of new-build cost (BDA: conversions cost 60–120% of new build, the façade being the biggest item; BBSR: 22–42% of works) and a light well 5. “Works” means the bank lends and the deal balances at the site default's own money, and the homes' fee for the same flat starts at or below the market. The most the building's co-op could pay is the highest price at which it still works. Public pages show it in bands so that a named building's ceiling is not printed for everyone; signed-in members see the figure. A ground lease is modelled as a yearly ground rent on the value, with nothing paid up front. The carbon line compares the materials of a new building (about 505 kg CO₂e per m²) with the conversion's ( ULI 2025, 24 US conversions; materials only), as a range.

Timber storeys on top

Where a building stands lower than its street — measured on satellite heights of it and its neighbours — the check offers to build the missing storeys on top in serial timber, at most 3 and never past a 25 m roof or 8 storeys. It is off until you switch it on: it needs the city's consent and a structural survey, which no desk check knows. The new floor (90% of the footprint a storey, the rest set back) joins the building's: the shared rooms keep their share of all of it, and the homes go up top. It adds no land. It costs 110% of new build a m² (95–130% in the sources: the TU Darmstadt Deutschlandstudie, a Dutch top-up business case and ARGE Kiel: about what new build costs, a little more for small projects), blended with the conversion's cost by floor area; storeys that take the homes above 4 storeys need a lift, a new one about €150,000. The timber's own carbon, 200–400 kg CO₂e a m² of materials, is counted apart from what the conversion saves, the carbon the wood stores not subtracted (timber against concrete, SBUF 2018, on the new-build figure above). The price stays per m² of the building as it stands.

Tested on buildings that were converted

Does the check turn down buildings that real projects did convert? We ran the fit layer on 294 buildings in Paris that received a permit to turn them into homes (Ville de Paris — autorisations d’urbanisme with a change of use to housing (person export, 6 Oct 2026); outlines IGN BD TOPO): 65% scored A, 33% B and 2% C; their median depth is 12 m. Location, services and use are not on the permits, so those parts sat at the middle. It cannot show the reverse — that a low band is right — because nobody publishes the conversions that failed. A C is not a no; it is where cost and compromise pile up.

The rules in France

• Minimum clear room height for homes: 2.2 m — Décence standard for rented homes (décret 2002-120 art. 4): at least one main room with 9 m² floor area AND ceiling height of 2.20 m or more, OR a habitable volume of at least 20 m³. The 2023 public-health rules (décret 2023-695, CSP R.1331-20: 2.20 m 'sufficient') were annulled by the Conseil d'État on 29 Aug 2024 for arts. R.1331-17 to R.1331-23 [page, ANIL]. I found no national new-build ceiling minimum in force (the old 2.50 m rule in CCH R.111-2 is no longer cited as current) [snippet; treat as unverified]. Typical offices are 2.70 m clear, homes 2.30–2.50 m. (Décret n° 2002-120 du 30 janvier 2002 (logement décent), art. 4 (Légifrance))
• Daylight: No national window-to-floor ratio found. Décence: main rooms must have 'sufficient natural lighting' and an opening to the open air (décret 2002-120 art. 2).
• A second escape route or stair from about 50 m — Housing fire rules (arrêté du 31 janvier 1986) work by 'family' using the floor level of the highest dwelling: 3rd family up to 28 m; 4th family 28–50 m (protected stair mandatory, 1-hour compartments, sealed lobby); above 50 m the building is an IGH (high-rise), which needs at least two stairs and firefighter lift arrangements. A single protected stair is normal in 3rd and 4th family housing. So 28 m is the main design threshold for conversions, and 50 m the two-stair threshold.
• Smallest flat: 9 m² — No flat minimum as such; the décence decree requires one main room of at least 9 m² (with 2.20 m height) or 20 m³.
• Affordable-housing quota: Paris PLU bioclimatique (approved 20 Nov 2024): in the 'hyper-deficit' zone (centre and west), 50% of each housing project must be social housing; office restructurings over 5,000 m² in office-dominated areas must give 10% of floor area to housing. Exact floor-area thresholds and how they apply to pure office-to-housing conversions were not shown on the page (unknown).
• Loi n° 2025-541 (loi Daubié): derogation from PLU use rules (CU L.152-6-5, L.152-6-6): The authority issuing the permit may allow a non-residential building to change to mainly residential use even where the local plan's use rules forbid it, in all zones covered by a plan. Binding opinion (avis conforme) from the PLU authority. May be refused for nuisance to occupants, poor transport access, school-capacity impact, or social/functional mix. Agricultural/natural zones need departmental commission approval; agricultural buildings must have been unused for 20+ years. (source)
• Permis à destinations successives (CU L.431-5): One building permit can authorise several successive uses (e.g. offices, then housing) in any order. Valid 20 years from issue; later PLU changes do not affect it; owner must tell the mayor within 3 months of each change of use. Implementing decree was pending at the time of ANIL's analysis (status not re-checked). (source)
• Co-ownership vote and primary-residence servitude (loi 2025-541): Converting non-residential lots (excluding commercial premises) to housing in a co-owned building needs only a simple-majority vote (art. 24, loi 1965); the PLU may restrict converted homes to primary residences (CU L.151-14-1); student residences get the +50% density bonus (CU L.151-28). As stated in the law. (source)

What it cannot tell you

The façade, the structure, pollutants, heritage listing, whether the owner would sell, and what a planning office will accept. It is a first sort, to decide which buildings deserve a feasibility study — not the study.