Pre-1930 terraced houses in London conservation areas

London units (GLA stock model, local authority code E09*). For each address (UPRN) with a lodged domestic certificate (RdSAP/SAP), take its most recently lodged certificate. Keep it where that certificate records property type 'House', built form Mid-Terrace, End-Terrace, Enclosed Mid-Terrace or Enclosed End-Terrace, and construction age band 'before 1900', 'Pre-1900', '1900-1929' or a single year before 1930, and where the unit's centroid falls inside a GLA conservation-area polygon. The comparison group is the same houses outside conservation areas.

249,376 domestic units in London conservation areas, of which 178,575 (71.6%) have a lodged certificate. Archetype-level coverage cannot be computed because age, form and type come from the certificate itself.

1. 82.5% of the 55,344 certified pre-1930 terraced houses in London conservation areas are rated D or worse, against 49.6% of all certified London homes; 3.7% are F or G.
2. 94.4% have walls lodged as uninsulated solid brick, and 92.2% of certificates recommend internal or external wall insulation (most common cost text '£4,000 - £14,000'). In a conservation area the external option needs planning permission, so internal insulation is the realistic default.
3. 21.8% are still single glazed, against 6.1% of the same houses outside conservation areas. Double glazing is recommended on 47.7% of certificates inside conservation areas and 16.4% outside.
4. 83.3% of the below-C houses show a potential rating of C or better. That potential assumes every recommended measure is installed, including wall insulation (92.2%) and PV (96.3%).
5. Of the 10,203 houses lodged as privately rented, 8,259 (80.9%) are below the 2030 band C standard (confirmed policy, not yet law) and 123 (1.2%) are below the E floor that applies in law today.

Consents

General planning position in England, not legal advice; check the borough's Article 4 directions. Cladding or rendering the outside of a house on conservation-area (article 2(3)) land is not permitted development, so external wall insulation needs planning permission, and BuildGrade's screening rules never offer it for a unit in a conservation area or a listed building. Internal wall insulation, floor insulation, draught-proofing, controls and boiler work need no planning permission on an unlisted house. Replacement windows on a house fall within permitted development only if they look similar, and Article 4 directions in many conservation areas remove even that. Roof-mounted solar is generally permitted development on a house in a conservation area, but wall-mounted panels fronting a highway are not, and an Article 4 direction can remove the right. The 7.4% of houses that are also listed need listed building consent for most fabric, window and roof work.

Sequencing

1. Check the borough's Article 4 directions, and whether the house is also listed (7.4% are), before choosing measures.
2. Plan first the work that needs no planning permission on an unlisted house: suspended floor insulation, draught-proofing, heating controls and boiler work.
3. Treat wall insulation as internal by default: 94.4% of walls are lodged as uninsulated solid brick, and the external option needs planning permission here. Confirm the wall construction by survey before specifying.
4. Take windows and solar separately: replacement windows and roof-mounted PV can fall within permitted development, but an Article 4 direction can remove the right, so check before relying on it.

Planning statements are general context for England, not legal advice. Article 4 directions vary by borough and were not checked for these figures.

• MHCLG Energy Performance of Buildings register, domestic certificates and recommendations, lodgements to 2026-09-09 (non-address fields OGL v3; 'Energy Performance of Buildings Data England and Wales (c) Crown copyright.')
• GLA London Datastore Conservation Areas, 1,089 areas, OGL v3, imported 2026-09-12
• Historic England National Heritage List for England listed-building polygons, OGL v3, pulled 2026-09-12
• GLA London Building Stock Model (units, borough), OGL v3, imported 2026-09-12
• BuildGrade retrofit screening rules, version 1 (external wall insulation excluded in conservation areas and listed buildings)
• BuildGrade policy glossary (MEES policy status)

Data month September 2026.

Building units (GLA London Building Stock Model): Contains public sector information licensed under the Open Government Licence v3.0 (Greater London Authority / UCL Bartlett Energy Institute and CASA). Contains OS data (c) Crown copyright and database right, published under the Ordnance Survey presumption to publish.

Energy performance certificates (MHCLG register): Energy Performance of Buildings Data England and Wales (c) Crown copyright.

Listed buildings (Historic England): © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026. The Historic England GIS Data contained in this material was obtained on 12 September 2026. The most publicly available up to date Historic England GIS Data can be obtained from HistoricEngland.org.uk. Licensed under the Open Government Licence v.3.0.

Conservation areas (GLA London Datastore): Contains public sector information licensed under the Open Government Licence v3.0.

Every rating here is certified: the most recently lodged energy performance certificate for each address. Modelled ratings, the GLA’s 2017 estimates for buildings without a certificate, are never averaged in; where a population relies on them they are counted separately. Figures come from read-only queries run on 22 and 23 October 2026. Counts that could identify a building are merged or left out, and no addresses or owner names are published.

• The register's age bands are 1900-1929 and 1930-1949, so a 'pre-1919' archetype and a '1945-1980' archetype could not be isolated. Studies use pre-1930 and 1950-1982 instead, and the 1930-1949 semi study includes wartime and early post-war builds.
• Domestic archetype membership uses facts lodged on each address's latest certificate (property type, built form, age band), so domestic archetype counts are certified addresses by construction and unit-level certified coverage cannot be computed for them. Unit-level coverage is given for heritage-defined populations (conservation-area and listed domestic units) and for non-domestic units.
• Certified means a lodged register certificate (RdSAP/SAP or CEPC). GLA 2017 aggregate rows and modelled (rvEPC) ratings are excluded from every distribution. Modelled ratings appear only as separate counts of units that rely on them.
• The unit of analysis for ratings is the address (UPRN): its most recently lodged certificate, with ties broken as the product does (lodged date, then record order). A stock-model 'unit' can be a whole block, so unit counts and address counts differ. 29.5% of London's latest domestic certificates are past 10 years from lodgement and may predate works since done.
• Numeric domestic recommendation codes are labelled with the register's own summary text, taken from certificates BuildGrade holds with both code and text. This assumes a code means the same across register versions. Code 7's current register text reads '50 mm internal or external wall insulation', and older certificates phrase it differently. Hot-water-cylinder codes 2 and 3 were left out of the top-measure lists.
• Recommendation rows are loaded for 79-97% of the latest domestic certificates and 97-99% of the latest non-domestic certificates, depending on lodgement year (some certificates carry no recommendations), so recommendation shares are lower bounds.
• Cost text is reported exactly as lodged and varies with register version (PV, for example, carries '£3,500 - £5,500', '£5,000 - £8,000' and '£9,000 - £14,000'), so the most common text and its share of rows is given. The texts are not current prices. Lighting cost text varies per certificate (most common share under 15%). Non-domestic recommendations carry a payback category (SHORT, MEDIUM, LONG, OTHER), not a £ cost.
• Heritage flags are spatial matches applied to the whole stock-model unit: listed means the centroid is within 5 m of an NHLE polygon or the footprint overlaps one by at least half; conservation area means the centroid is inside a GLA polygon. Every flat in a flagged block inherits the flag, so listed counts can be over or under. Listed matches: 10,294 domestic units by centroid and 5,551 by footprint.
• Tenure is as recorded at lodgement and may have changed since. Certificates with unknown or blank tenure are excluded from tenure shares (tenure-known share given per study). The MEES counts are screening counts, not compliance findings, and exemptions are not modelled.
• MEES status. Domestic: the E floor is law for private lets (since April 2020); band C by 2030 is confirmed policy, not yet law (government response 21 January 2026; needs legislation, and compliance is to be judged on reformed EPC metrics). Non-domestic: the E floor is law (since April 2023); the 2027 C milestone is not being taken forward, and B by 2030 was revised on 18 June 2026 to B from 2031 for buildings over 1,000 m², where cost-effective, which is not yet law. These are BuildGrade's recorded policy positions; check the current government position before relying on them.
• Wall descriptions marked 'as built ... (assumed)' are RdSAP defaults where the assessor could not verify the construction (for example 79.4% of 1930-1949 semis lodged as solid brick). Treat them as lodged descriptions, not survey findings.
• The potential rating on a certificate assumes every recommended measure is installed, including measures that may need planning permission or listed building consent, so 'potential C or better' is an upper bound on what is consentable.
• Consent statements (permitted development, conservation-area cladding, listed building consent, flats lacking householder rights) are general planning context for England, not legal advice, and are not computed from the database. Article 4 directions vary by borough and were not queried.
• London only: units outside the 33 London local authorities were not used. Other UK cities are in preparation; the Bristol and Cardiff pilots are not yet live.

All six studies: method and caveats