Double-storey extension drawings in Harrow from £905
Pinner, Stanmore, Kenton and Harrow on the Hill: an upper floor is tested against the 45 Degree Code, and a house south or west of its neighbour starts at a disadvantage.
£905 £755 drawings + £150 survey (£905 total), no VAT to add
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The short answer
Harrow’s Residential Design Guide SPD says there is generally no potential for a first-floor or two-storey rear extension on a mid-terrace house, and one against a side boundary risks bulk and loss of light. Any that needs permission must comply with the 45 Degree Code, and siting south or west of the neighbour would normally be unacceptable. 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’ rear corners and protected windows
- The 45 degree splay drawn on plan from the nearest first-floor or two-storey corner next door
- An orientation check, since a house south or west of its neighbour is normally refused
- Ground and first floor plans, elevations and section to Harrow’s checklist
- The route that fits submitted for you, and answers to the case officer
£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 Harrow double-storey extension runs
Orientation check
We work out which side the sun and the neighbour are on, since Harrow weighs it heavily.
Survey
We measure both floors, the corners next door and the protected windows.
Design
You choose the layout, with the 45 degree splay and the route written down.
Draw and submit
We prepare the pack to the 2024 checklist and submit it.
The 45 Degree Code and where the house sits
Paragraph 6.31 of the SPD says no part of a new first-floor or two-storey extension should interrupt a 45 degree splay drawn on plan from the nearest first-floor or two-storey rear corner of the house next door, or from a single-storey rear corner if that elevation has a protected window. Projecting eaves count, shallow fascias and gutters do not. Protected windows are the main windows of habitable rooms and of kitchens over 13 square metres.
Paragraph 6.65 adds site tests: the orientation of the houses, where siting south or west of the neighbour would normally be unacceptable, how far the extension relies on the neighbour’s garden for its setting, and the neighbour’s existing extensions and garden use. For example, the semi on the north side of a pair has a far better chance than the one to its south.
Terraces, boundaries and permitted development
In general there is no potential for a first-floor or two-storey rear extension on a mid-terrace house; end-of-terrace houses are tested as semis. Extensions that abut a side boundary have considerable potential for detrimental impact because of bulk and loss of light and must always comply with the Code.
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. Harrow has conservation areas with their own residential planning guide, and Article 4 directions can add controls, so we check your road before drawing.
Validation and CIL
For validation, Harrow’s checklist of 1 February 2024 gives 21 days to supply missing information or challenge the request before the application is disposed of.
Harrow CIL is £110 a square metre for residential, 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 Harrow in numbers
657 of 695
Householder decisions by Harrow 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)
45°
Splay, drawn on plan from the nearest next-door first-floor or two-storey rear corner, that a new extension must not interrupt.
South or west
Siting a two-storey extension south or west of the neighbour would normally be unacceptable.
Mid-terrace
In general there is no potential for first-floor or two-storey rear extensions on mid-terraced properties.
13 m²
Kitchen size above which a kitchen window counts as a protected window for the 45 Degree Code.
15 Dec 2010
Date Harrow adopted its Residential Design Guide SPD.
1 Feb 2024
Date of Harrow’s current National and Local Validation Checklist.
Source: National and Local Validation Checklist, 1 February 2024 (Harrow Council)
21 days
Time Harrow gives to supply missing information or challenge the request before the application is disposed of.
Source: National and Local Validation Checklist, 1 February 2024 (Harrow Council)
£110
Harrow CIL per square metre listed for residential development (Use Class C3).
£72.73
Mayoral CIL per square metre for permissions granted in 2026 in Harrow, 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 Harrow
Can a mid-terrace house in Harrow have a first-floor rear extension?
In general no. The SPD sees no potential for them on mid-terrace houses because of the effect on neighbours and gardens.
Why does the direction of the sun matter?
The SPD says siting south or west of the neighbour would normally be unacceptable, because of the shadow it casts.
What is a protected window?
The main window of a habitable room, or of a kitchen over 13 square metres, whose light the 45 Degree Code protects.
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 Harrow 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).