Mansard Roof Extensions in Hounslow

Where in Hounslow does a mansard roof extension actually get determined?

Every Hounslow postcode district we draw in, the stock that dominates it and the authority that validates a mansard roof extension there. Hounslow fees below are the statutory England rates for 2026, not mansard roof extension estimates.

How does a mansard roof extension differ street by street across Hounslow?

Roof pitch, wall build-up and plot depth change every few Hounslow streets, and each one changes what a mansard roof extension can achieve at that address.

• Chiswick (W4) — a mansard roof extension in Chiswick starts from edwardian villas, victorian terraces, and Chiswick reads as Edwardian villas, conservation. A mansard on a Victorian terrace almost always needs full planning permission in W4. Hounslow Council assesses Chiswick mansard roof extensions against its own Chiswick character guidance, and the location plan we draw for Chiswick references Chiswick House.
• Brentford (TW8) — mansard roof extension work in Brentford means georgian fragments, victorian terraces, new-build. Brentford is Georgian fragments, riverside new-build. Mansards read as original on Georgian terraces throughout TW8. Hounslow Council decides the Brentford application, and Kew Bridge anchors the Brentford location plan.
• Isleworth (TW7) — a mansard roof extension in Isleworth starts from georgian and victorian terraces, and Isleworth reads as Georgian and Victorian terraces. Mansards read as original on Georgian terraces in TW7. Hounslow Council assesses Isleworth mansard roof extensions against its own Isleworth character guidance, and the location plan we draw for Isleworth references Old Isleworth.
• Hounslow (TW3) — mansard roof extension work in Hounslow means 1930s semi-detached, post-war flats. Hounslow is 1930s semi-detached, post-war flats. Mansards are rare on 1930s stock — the hipped roof form works against the geometry throughout TW3. Hounslow Council decides the Hounslow application, and Hounslow Central anchors the Hounslow location plan.
• Feltham (TW13) — a mansard roof extension in Feltham starts from 1930s semi-detached, post-war estates, and Feltham reads as 1930s semi-detached, post-war estates. Mansards are rare on 1930s stock — the hipped roof form works against the geometry in TW13. Hounslow Council assesses Feltham mansard roof extensions against its own Feltham character guidance, and the location plan we draw for Feltham references Feltham station.
• Hanworth (TW13) — a mansard roof extension in Hanworth starts from 1930s semi-detached, and Hanworth reads as 1930s semi-detached. Mansards are rare on 1930s stock — the hipped roof form works against the geometry in TW13. Hounslow Council assesses Hanworth mansard roof extensions against its own Hanworth character guidance, and the location plan we draw for Hanworth references Hanworth Park.
• Turnham Green (W4) — a mansard roof extension in Turnham Green starts from edwardian villas, and Turnham Green reads as Edwardian villas, conservation. Edwardian parapets give a mansard a clean base line in W4. Hounslow Council assesses Turnham Green mansard roof extensions against its own Turnham Green character guidance, and the location plan we draw for Turnham Green references Turnham Green.

What local planning policy applies to a mansard roof extension in Hounslow?

How designation changes a Hounslow mansard roof extension: Hounslow Council maintains 30 conservation areas, including Brentford, Chiswick, Bedford Park. Inside any of them a Hounslow mansard roof extension cannot rely on permitted development, and the route becomes a £548 householder application determined in 8 weeks rather than a £249 prior approval in 6 weeks. Chiswick sets the tone for Hounslow casework.

Hounslow permitted development status: there is no borough-wide direction from Hounslow Council, so a mansard roof extension at a W4 address is normally still permitted development. We certify that with a £274 Lawful Development Certificate rather than leaving a Hounslow sale to argue it later.

The building fabric around Hounslow: Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford. Chiswick is one of west London's most conservation-controlled areas; outer Hounslow is permissive suburban. A mansard roof extension in Hounslow is scoped against that stock first, because it decides whether the scheme runs as permitted development, a £274 Lawful Development Certificate, or a full £548 application to Hounslow Council.

Which neighbouring authorities border Hounslow?

• Hillingdon — the Hillingdon boundary runs against Hounslow, so a mansard roof extension a street from Hounslow is decided by Hillingdon Council instead. Hillingdon runs 29 conservation areas across HA4 and its neighbours, which is why mansard roof extensions priced for Hounslow are re-checked against Hillingdon policy whenever the Hounslow address sits on that edge.
• Ealing — adjoining Hounslow, with 30 conservation areas centred on W3. A mansard roof extension on the far side of the Hounslow line is determined by Ealing Council, so the Hounslow quote for mansard roof extensions is checked against Ealing guidance before it is issued.
• Hammersmith and Fulham — the Hammersmith and Fulham boundary runs against Hounslow, so a mansard roof extension a street from Hounslow is decided by Hammersmith & Fulham Council instead. Hammersmith and Fulham runs 45 conservation areas across W6 and its neighbours, which is why mansard roof extensions priced for Hounslow are re-checked against Hammersmith and Fulham policy whenever the Hounslow address sits on that edge.
• Richmond upon Thames — cross the Hounslow boundary and Richmond Council takes the mansard roof extension instead, applying 72 conservation areas of its own around SW13. We re-price mansard roof extensions at the Hounslow edge because Richmond upon Thames policy and Hounslow policy rarely align on mansard roof extension depth.

Sources for this Hounslow mansard roof extension page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.