Rear extension drawings in Hounslow from £625
Chiswick, Isleworth, Feltham and Brentford: Hounslow caps a rear extension at 3.05, 3.65 or 4.25 metres by house type, and counts the roof overhang.
£625 £475 drawings + £150 survey (£625 total), no VAT to add
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The short answer
Hounslow’s Residential Extension Guidelines, adopted in December 2017, set the maximum depth of a single-storey rear extension from the original rear wall at 3.05 metres (10 ft) for a terrace, 3.65 metres (12 ft) for a semi and 4.25 metres (14 ft) for a detached house, with any roof overhang counted. These limits apply to first extensions; a second one normally gets refused. Our fee is £475 drawings + £150 survey (£625 total), no VAT to add; the council’s fee is separate.
Rear extension drawings
from £625
- Drawings
- £475
- Measured survey
- £150
- Total you pay
- £625
- VAT
- None to add
- A measured survey that finds the original rear wall and any extension already built
- The depth measured the Hounslow way, including any overhanging roof or eaves
- A check that no gutter or footing crosses the boundary, which the guidelines forbid
- A check of your address against Hounslow’s conservation areas and Article 4 directions
- Plans to the householder checklist, and the route that fits submitted for you
£475 drawings + £150 survey (£625 total). A starting fee: we confirm one fixed figure after checking your address. The council’s own fee, where there is one, is paid to the council.
Get my fixed feeHow a Hounslow rear extension runs
Original house check
We establish what is original and whether a first extension has already used the allowance.
Survey
We measure the original rear wall, the garden and the neighbours’ extensions.
Design
You choose depth and roof, with the overhang counted and the route written down.
Draw and submit
We prepare the pack and submit it, then answer the case officer.
Three depths, and the overhang trap
Section 4.3 of Hounslow’s guidelines says a single-storey rear extension should be secondary to the original house and not project so far that it causes enclosure or blocks light. The maximum depths, measured from the main rear wall of the original house, are 3.05 metres (10 ft) for a terraced house including an end terrace, 3.65 metres (12 ft) for a semi-detached house and 4.25 metres (14 ft) for a detached house.
The measurement must include any overhanging roof added to the rear wall of the extension. For example, a 3.5 metre box on a semi with a deep eaves overhang can pass 3.65 metres once the overhang is counted, so we draw the overhang as well as the wall.
First extensions only, and what else is controlled
The guidelines say these limits apply to first-time extensions. Second extensions, canopies or conservatories added to existing extensions, which exceed the limits, can severely overshadow neighbours and will normally be refused. No part of the extension, including guttering, may cross or overhang the boundary. Flat roofs are normally acceptable, a roof terrace on one is likely to be refused, and small gardens are tested against the amenity space standard.
Since 30 May 2013 permitted development has allowed larger single-storey extensions of up to 6 metres, or 8 on a detached house, through prior approval; Hounslow has 28 conservation areas, with Article 4(2) directions confirmed for Bedford Park and Gunnersbury Park in 2001. We check your address first.
What Hounslow asks for, and CIL
Hounslow’s validation requirements are its householder checklist, which asks for existing and proposed plans and elevations, and a design and access statement for 100 square metres or more of new floor space in a conservation area.
Hounslow adopted its CIL charging schedule on 24 July 2015 and indexes it each year, on 100 square metres or more of new floor space, so a typical extension is outside it. Mayoral CIL is in band 2.
Rear extensions in Hounslow in numbers
380 of 391
Householder decisions by Hounslow Council between July 2025 and June 2026 (prior approvals left out) that were made inside 8 weeks.
Source: MHCLG live table PS2, district planning application statistics, July 2025 to June 2026 (GOV.UK)
3.05 m
Maximum depth of a single-storey rear extension to a terraced house, including an end terrace, from the original rear wall.
3.65 m
Maximum depth of a single-storey rear extension to a semi-detached house.
4.25 m
Maximum depth of a single-storey rear extension to a detached house.
Overhang counts
The measurement must include any overhanging roof added to the rear wall of the extension.
20 Dec 2017
Date Hounslow adopted its Residential Extension Guidelines SPD.
6 m / 8 m
Deepest single-storey extension through prior approval since 30 May 2013, for non-detached and detached houses.
24 Jul 2001
Date the Bedford Park and Gunnersbury Park Article 4(2) directions were confirmed.
Source: Article 4(2) directions for Bedford Park and Gunnersbury Park conservation areas (Hounslow Council)
24 Jul 2015
Date Hounslow adopted its borough CIL charging schedule, indexed each year.
£72.73
Mayoral CIL per square metre for permissions granted in 2026 in Hounslow, which is in band 2 (£60 when set in 2019). It applies only where CIL is due at all.
Source: Mayoral CIL: Annual CIL Rate Summary 2026 (London.gov.uk)
Questions about rear extensions in Hounslow
How deep can I extend a Hounslow semi?
The guidelines say 3.65 metres from the original rear wall, counting the roof overhang. Permitted development with prior approval can allow more.
Does the limit include the roof overhang?
Yes. Measurements must include any overhanging roof added to the rear wall of the extension.
I already have an extension. Can I add a conservatory?
Second extensions that exceed the limits will normally be refused, so check before adding to an existing one.
Can I put a roof terrace on the flat roof?
The council will normally refuse a balcony, roof terrace or garden on the flat roof of an extension, because of overlooking.
See how far your Hounslow house can go
Send the address and a photo of the back. We reply with the route and a fixed fee, from £475 drawings + £150 survey (£625 total).