Double-storey extension drawings in Hounslow from £905
Chiswick, Isleworth, Feltham and Brentford: Hounslow’s guide calls an upper floor the most harmful kind of extension, and then sets three limits for it.
£905 £755 drawings + £150 survey (£905 total), no VAT to add
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The short answer
Hounslow’s Residential Extension Guidelines, adopted in December 2017, say a first-floor rear extension should be no wider than half the original house, project no more than 2.5 metres beyond the rear wall, and have eaves matching the house. It must be set at least 2 metres from a neighbour’s original side wall. On a mid-terrace house it will rarely be acceptable. Our fee is £755 drawings + £150 survey (£905 total), no VAT to add; the council’s fee is separate.
Double-storey extension drawings
from £905
- Drawings
- £755
- Measured survey
- £150
- Total you pay
- £905
- VAT
- None to add
- A measured survey of both floors at the back and the neighbours’ original side walls
- The half-width, 2.5 metre and 2 metre separation lines drawn on the first-floor plan
- An eaves line that matches the host house
- A check of your address against Hounslow’s 28 conservation areas and the Bedford Park direction
- Plans to the householder checklist, and the route that fits submitted for you
£755 drawings + £150 survey (£905 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 double-storey extension runs
House type check
We see whether you are mid-terrace, end of terrace, semi or detached, since it changes the odds.
Survey
We measure both floors, the eaves and the neighbours’ side walls.
Design
You choose the layout, with the three limits and the route written down.
Draw and submit
We prepare the pack to the checklist and submit it.
Three limits for the floor above
Section 4.6 says two-storey and first-floor rear extensions may cause severe enclosure and overshadowing, so one on a mid-terrace house will rarely be acceptable, while end-of-terrace, semi-detached and detached houses may be acceptable depending on the site. The ground floor follows the single-storey depths. For the first floor, the width should be no greater than half the original house, the depth no more than 2.5 metres beyond the rear wall, and the eaves should match those of the host house.
On position, the first floor should be set at least 2 metres from the original side wall of a neighbouring property, and as far off the shared boundary as possible while keeping 2 metres from the non-adjoining neighbour. For example, a Feltham semi with a neighbour’s flank wall near the boundary has to hold the bedroom a clear 2 metres from it.
Outriggers and conservation areas
Any application for another storey on top of an original two-storey outrigger will generally be refused, and the council will normally refuse a two-storey rear extension in a conservation area where it is clearly visible from the public realm or harms the area. Permitted development allows more than one storey only up to 3 metres and not within 7 metres of the rear boundary, so most of these are householder applications.
Hounslow has 28 conservation areas, with Article 4(2) directions confirmed for Bedford Park and Gunnersbury Park on 24 July 2001, and we check your address first.
Validation and CIL
For validation, Hounslow’s householder checklist 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 most double-storey extensions on a house are outside it. Mayoral CIL is in band 2.
Double-storey 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)
Half width
Widest a first-floor rear extension should be, relative to the original house.
2.5 m
Furthest a first-floor rear extension should project beyond the rear wall of the house.
2 m
Least distance a first-floor extension should be set from the original side wall of a neighbouring property.
Mid-terrace
A two-storey or first-floor rear extension on a mid-terrace property will rarely be acceptable.
Outrigger
An extra storey on top of an original two-storey outrigger will generally be refused.
20 Dec 2017
Date Hounslow adopted its Residential Extension Guidelines SPD.
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)
100 m²
New floor space in a conservation area from which Hounslow requires a design and access statement.
Source: Householder planning application checklist (Hounslow Council)
£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 double-storey extensions in Hounslow
How far out can the first floor go?
About 2.5 metres beyond the rear wall, no wider than half the original house, with the same eaves as the house.
Can I add a floor above my outrigger?
Generally not. The guidelines say an extra storey on an original two-storey outrigger will generally be refused.
Does the ground floor have limits too?
Yes. It follows the single-storey depths of 3.05, 3.65 or 4.25 metres by house type.
Do I pay CIL on a double-storey extension?
Not normally. CIL arises from 100 square metres of new floor space or a new dwelling.
See what your Hounslow house can take upstairs
Send the address and a photo of the back. We reply with the route and a fixed fee, from £755 drawings + £150 survey (£905 total).