House Extension Drawings in Harrow

Where in Harrow does a house extension actually get determined?

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

How does a house extension differ street by street across Harrow?

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

• South Harrow (HA2) — a house extension in South Harrow starts from 1930s semi-detached, and South Harrow reads as 1930s semi-detached. 1930s semis here have the deepest rear gardens in the area in HA2. Harrow Council assesses South Harrow house extensions against its own South Harrow character guidance, and the location plan we draw for South Harrow references South Harrow Tube.
• Harrow on the Hill (HA1) — house extension work in Harrow on the Hill means georgian and victorian houses, listed buildings. Harrow on the Hill is Georgian and Victorian conservation hilltop. Georgian rear elevations here are usually the listed or locally listed face of the building throughout HA1. Harrow Council decides the Harrow on the Hill application, and Harrow School anchors the Harrow on the Hill location plan.
• Pinner (HA5) — a house extension in Pinner starts from tudor fragments, edwardian villas, 1930s semi-detached, and Pinner reads as Tudor and 1930s village. Edwardian plots here are wider in HA5. Harrow Council assesses Pinner house extensions against its own Pinner character guidance, and the location plan we draw for Pinner references Pinner High Street.
• Stanmore (HA7) — 1930s semi-detached, Green Belt fringe defines Stanmore, where 1930s semi-detached, edwardian villas set what a house extension can do. Edwardian plots here are wider across HA7. Any Stanmore house extension is validated by Harrow Council, with Stanmore Tube the usual Stanmore reference point on the site plan.
• Harrow Weald (HA3) — house extension work in Harrow Weald means 1930s semi-detached. Harrow Weald is 1930s semi-detached, Green Belt. 1930s semis here have the deepest rear gardens in the area throughout HA3. Harrow Council decides the Harrow Weald application, and Harrow Weald Common anchors the Harrow Weald location plan.
• Kenton (HA3) — 1930s semi-detached defines Kenton, where 1930s semi-detached set what a house extension can do. 1930s semis here have the deepest rear gardens in the area across HA3. Any Kenton house extension is validated by Harrow Council, with Kenton station the usual Kenton reference point on the site plan.
• Wealdstone (HA3) — 1930s semi-detached, post-war defines Wealdstone, where 1930s semi-detached, post-war flats set what a house extension can do. 1930s semis here have the deepest rear gardens in the area across HA3. Any Wealdstone house extension is validated by Harrow Council, with Wealdstone High Street the usual Wealdstone reference point on the site plan.

Does Harrow planning policy restrict a house extension?

How designation changes a Harrow house extension: Harrow Council maintains 29 conservation areas, including Harrow on the Hill, Pinner Village, Stanmore. Inside any of them a Harrow house 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. Harrow Weald sets the tone for Harrow casework.

Harrow permitted development status: there is no borough-wide direction from Harrow Council, so a house extension at a HA1 address is normally still permitted development. We certify that with a £274 Lawful Development Certificate rather than leaving a Harrow sale to argue it later.

What Harrow is built from: 1930s semi-detached dominates; Edwardian villas in Harrow on the Hill and Pinner; Metropolitan Green Belt in Stanmore and Harrow Weald; post-war flats around Harrow Central. Outer north-west London suburban; Harrow on the Hill has exceptionally strict heritage controls; rest of borough permissive. That mix decides the house extension route in Harrow more than the postcode does, and it is what a Harrow Council case officer reads first. A householder application costs £548 paid to Harrow Council direct, with 8 weeks to a decision once validated.

What happens if a Harrow property sits on a boundary?

• Hillingdon — the Hillingdon boundary runs against Harrow, so a house extension a street from Harrow is decided by Hillingdon Council instead. Hillingdon runs 29 conservation areas across HA4 and its neighbours, which is why house extensions priced for Harrow are re-checked against Hillingdon policy whenever the Harrow address sits on that edge.
• Barnet — cross the Harrow boundary and Barnet Council takes the house extension instead, applying 20 conservation areas of its own around N2. We re-price house extensions at the Harrow edge because Barnet policy and Harrow policy rarely align on house extension depth.
• Brent — the Brent boundary runs against Harrow, so a house extension a street from Harrow is decided by Brent Council instead. Brent runs 22 conservation areas across NW2 and its neighbours, which is why house extensions priced for Harrow are re-checked against Brent policy whenever the Harrow address sits on that edge.

Sources for this Harrow house 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.