Hounslow, London
Double-storey extension drawings in Hounslow
Hounslow's Residential Extension Guidelines are specific about upper floors: a width limit, a depth limit and a separation from the neighbour. Our double-storey extension drawings for Hounslow homes start at £1,295 including VAT and are built around those limits from the first sketch.
From £1,295 (VAT included)
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- £2m PI insured
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- Fixed fees, VAT included
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What Hounslow expects of a double-storey extension
The Residential Extension Guidelines SPD sets out two tests. For a side extension: 1 m set-back; less than half width; 0.5 m set-down. The figures are the first-floor set-back from the front wall, the maximum share of the house width and the distance the new roof must sit below the main roof.
For a rear extension the second test reads half width; 2.5 m deep; 2 m separation: the first-floor width as a share of the house, the greatest projection and the gap to a neighbour's side wall. The guidelines add that two-storey rear extensions are rarely acceptable on mid-terrace houses.
A third sentence matters where the house already has a back addition. An extra storey on top of an original two-storey outrigger will generally be refused. If your house already has a tall back addition, the realistic options are a single-storey scheme beside it or a side extension that meets the test above.
Local figures for Hounslow
| Measure | Value | Period | Source |
|---|---|---|---|
| Two-storey side extensions should be set back at least one metre from the front wall at first floor, be less than half the width of the house, and have a roof at least half a metre below the main roof. | 1 m set-back; less than half width; 0.5 m set-down | — | hounslow.gov.uk, Residential Extension Guidelines SPD 2017, p.22, section 4.5 |
| Two-storey rear extensions are rarely acceptable on mid-terrace houses; elsewhere the first floor should be no wider than half the house, project no more than 2.5 metres, and stay 2 metres from a neighbour's side wall. | half width; 2.5 m deep; 2 m separation | — | hounslow.gov.uk, Residential Extension Guidelines SPD 2017, p.24-25, section 4.6 |
| Conservation areas | 33 named conservation areas published by the council | — | planning.data.gov.uk |
| Article 4 directions | 3 Article 4 directions published by the council | — | planning.data.gov.uk |
| Listed building entries | 519 list entries (Historic England, within the LPA boundary) | — | planning.data.gov.uk |
| Households living in a house | 54 % of households living in a house or bungalow (detached, semi-detached or terraced) | Census 2021 | nomisweb.co.uk |
| Householder decisions | 689 decisions | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Householder applications granted | 78.5 % | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Householder applications decided in time | 97.8 % decided within 8 weeks or an agreed extended period | 1 July 2025 - 30 June 2026 | assets.publishing.service.gov.uk |
| Class A, para A.1(h) | Over one storey: max 3 m beyond the original rear wall and not within 7 m of the rear boundary | — | legislation.gov.uk |
| Class A, para A.2(c) | No rear extension of more than one storey under PD on article 2(3) land | — | legislation.gov.uk |
| Approved Document B Vol 1, 2019 ed. incl. 2026 amendments, para 2.10 | Escape window: unobstructed openable area at least 0.33 m², at least 450 mm high and 450 mm wide, bottom of opening no more than 1100 mm above floor | — | gov.uk |
A blank value means the figure has not been published, not that there are none. Check your own address with the council.
Householder applications by street in Hounslow
| Street | Applications | Approved |
|---|---|---|
| Firs Drive | 37 | 61% |
| Wood Lane | 32 | 59% |
| Park Drive | 31 | 69% |
| Parkwood Road | 28 | 59% |
| Worton Road | 27 | 58% |
| Arnold Crescent | 26 | 54% |
| Popes Lane | 24 | 83% |
| St Stephens Road | 24 | 77% |
| Whitton Dene | 24 | 50% |
| Harewood Road | 23 | 78% |
| Princes Avenue | 23 | 82% |
| Spring Grove Road | 23 | 55% |
| Fern Lane | 22 | 68% |
| Netheravon Road | 22 | 73% |
| North Hyde Lane | 22 | 55% |
The 45-degree test in plan
A line from the middle of the neighbour's nearest window: the extension should stay behind it.
- A · Test used in daylight assessments
- 45 degrees (plan and elevation)
Terraces, semis and where the tests bite
Only 54 per cent of Hounslow households live in a house or bungalow, and among those houses the terraced ones have the least room. A neighbour on both sides tightens the separation distance, because a mid-terrace plot has no room to step away from either boundary.
End-of-terrace and semi-detached houses have more latitude, and a side extension with a lowered roof is the form the guidelines spell out. We test the options on the model and show you the width and depth that the guidelines allow, not the ones we would like.
Conservation areas, listed buildings and the world heritage site
The borough has 33 conservation areas, 3 Article 4 directions and 519 listed building entries, plus 1 world heritage site within its boundary. Inside a conservation area: No rear extension of more than one storey under PD on article 2(3) land.
We check every address against these lists before quoting, because a protected address loses some permitted development rights, and a listed house needs listed building consent as well. The architectural drawings in Hounslow page explains the checks in more detail.
When a second storey can be permitted development
For houses outside protected land the national rule is: Over one storey: max 3 m beyond the original rear wall and not within 7 m of the rear boundary. Where a plot misses it, the route is a householder application judged against the guidelines.
If a scheme does qualify, the conditions still apply. Windows in a side wall: Upper-floor side windows obscure-glazed and non-opening below 1.7 m above floor. Roof pitch: Roof pitch of a 2+ storey enlargement to match the original house so far as practicable. A lawful development certificate in Hounslow can confirm the position in writing before building starts.
Fire escape and party structure notices
Any new first-floor bedroom needs an escape window. The Approved Document sets: Escape window: unobstructed openable area at least 0.33 m², at least 450 mm high and 450 mm wide, bottom of opening no more than 1100 mm above floor. On a narrow Hounslow flank the position of that window competes with the privacy rule above, so we resolve both on the elevation.
Terraced and semi-detached owners should also plan for the party wall process: Party structure notice at least 2 months before work.
How Hounslow decides householder applications
Hounslow decided 689 householder applications in its latest published year and granted 78.5 per cent, with 97.8 per cent decided on time. We check the guidelines line by line before submission.
Those numbers describe the whole borough and every kind of householder scheme, so they set expectations for timing rather than predict a decision.
Your drawing set, price and related services
The set includes floor plans for both storeys, the roof in section, four elevations and the site plans. It starts at £1,295 with VAT included, fixed before you commit, and we redraw free until approval if the council asks for amendments.
If the second storey is too much for your plot, see rear extension drawings in Hounslow or side return extension drawings in Hounslow. The same service in nearby boroughs is at Richmond upon Thames, and the full service is described at double-storey extension drawings.
What you receive
Related pages
Other services in Hounslow
Questions
Can I add a second storey to a mid-terrace house in Hounslow?
Hounslow's guidelines say two-storey rear extensions are rarely acceptable on mid-terrace houses. A mid-terrace house has no side to extend, so a single-storey scheme is usually the answer.
How wide can a first-floor side extension be in Hounslow?
The side extension measures are 1 m set-back; less than half width; 0.5 m set-down: the first-floor set-back, a width under half the house and a roof set below the main roof.
How deep can a two-storey rear extension be in Hounslow?
Where one is acceptable, the measures are half width; 2.5 m deep; 2 m separation: the first floor no wider than half the house, with the greatest projection and a gap to the neighbour's side wall.
How much do double-storey extension drawings cost in Hounslow?
From £1,295 including VAT, fixed up front. The council's application fee is paid separately.
Sources and dates
- hounslow.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- planning.data.gov.uk, retrieved
- nomisweb.co.uk, retrieved
- assets.publishing.service.gov.uk, retrieved
- legislation.gov.uk, retrieved
- gov.uk, retrieved
- planning.data.gov.uk, retrieved
- legislation.gov.uk, retrieved
- merton.gov.uk, retrieved
- Contains public sector information licensed under the Open Government Licence v3.0.
- Contains OS data © Crown copyright and database right 2026.
- Contains HM Land Registry data © Crown copyright and database right 2026. This data is licensed under the Open Government Licence v3.0.
- Contains Historic England data © Historic England 2026. Contains Ordnance Survey data © Crown copyright and database right 2026.
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