Double Storey Extension Drawings in Harrow on the Hill HA1
Fixed-fee, MCIAT-chartered double storey extension drawings for Harrow on the Hill (HA1) homeowners — London Borough of Harrow validation and local constraints handled from the start.
Harrow on the Hill (HA1) is built around a steep historic village on the ridge above the town, where the High Street, Church Hill and West Street keep their Georgian and early-Victorian character alongside the Harrow School buildings. Householder work here is dominated by careful rear and side extensions and internal reconfiguration rather than visible roofline changes.
The Harrow on the Hill Village Conservation Area was designated in 1968 and carries a revised Article 4 Direction, so window, door, roof and boundary changes that would be permitted development elsewhere need a planning application here. We check where a property sits relative to the village and Mount Park Estate boundaries before advising a route.
Planning in Harrow on the Hill (HA1): what to know before you apply
Because the village core is both a conservation area and covered by an Article 4 Direction, many HA1 houses on and near the hill have lost the permitted-development rights that similar homes elsewhere in Harrow retain. Rear extensions kept out of the protected street views, and interior remodelling, are usually the most deliverable projects; roofline and front-elevation changes attract close conservation scrutiny.
Typical Harrow on the Hill housing stock
The hilltop village around the High Street and Church Hill mixes Georgian and early-Victorian houses with the Harrow School estate, giving way to substantial Edwardian and inter-war villas on the Mount Park Estate and South Hill Avenue below.
Streets we regularly draw for in Harrow on the Hill
High Street · West Street · Church Hill · Grove Hill · Mount Park Road
What HA1 is actually built of
Measured from 126 classified residential buildings in HA1, not from a description of the area.
Harrow on the Hill HA1 housing mix
Residential building form across the HA1 postcode district, from 126 classified buildings.
| Attached on more than one side | 33% |
|---|---|
| Attached on one side | 53% |
| Detached | 14% |
| Median building footprint | 74 m² |
| Addresses per buildingAbove about 2 means flats and maisonettes dominate | 1.74 |
| Buildings classified | 126 |
Source: Ordnance Survey National Geographic Database (derived statistics). Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. Extracted 2026-08-17.
Double Storey Extension Drawings for Harrow on the Hill (HA1) homes: the package and the process
At first-floor level the drawings have to answer for daylight, privacy and massing. That means proposed elevations showing every new window with its position relative to the boundary, a section taken through the extension and the neighbouring building, and a roof form drawn to sit below the existing ridge rather than compete with it.
We draw the neighbouring property alongside your own, because the officer's assessment is comparative — the effect on their windows and outlook is the test. Setting the first floor in from the boundary, and showing that set-back as a dimension, resolves most objections before consultation begins.
At first floor the boundary relationship decides everything. A detached house has room to set the addition in on both sides; a semi has one shared wall and one clear flank; a mid-terrace can usually only go to the rear, where the effect on both neighbours has to be drawn.
Do I need planning permission for a double storey extension in London?
Almost always. Permitted development rights for two-storey extensions are far more restrictive than for single-storey work, particularly on how close the new structure can come to a boundary and how closely its roof pitch and eaves height must match the existing house, so most double storey projects are drawn and submitted as full householder planning applications rather than relying on permitted development.
Where the property sits in a conservation area or is subject to an Article 4 direction, any remaining permitted development allowance for a second storey is typically removed entirely, reinforcing the need for a full application. We check your property's status and your borough's design guidance before drawing.
How do councils control the impact of a double storey extension on neighbours?
Because a second storey introduces new windows and massing at first-floor level, London boroughs apply design guidance aimed specifically at protecting neighbouring light, privacy and outlook.
- The 45-degree rule, tested at neighbouring windows, to check the extension does not block an unreasonable amount of daylight
- A common design expectation that a two-storey side extension is set in roughly 1 metre from the shared boundary, rather than built hard against it
- A first floor commonly set back from the ground floor front elevation, so the upper storey reads as subordinate to the main house from the street
- Obscure or high-level glazing on flank walls facing directly into a neighbour's garden or windows, to limit overlooking
Matching the roofline and materials
Planning officers assess a double storey extension heavily on how convincingly it reads as part of the original house rather than an addition bolted onto the side. Our drawings match ridge height, roof pitch, eaves detail and brick or render finish to the existing building wherever the design brief allows, which is consistently one of the strongest factors in securing approval without delay or redesign. Where a subtly contrasting material is proposed instead — a different brick tone, or a zinc or slate roof against a tiled original — we set it out clearly on the elevations so the design intent reads as deliberate rather than a mismatch, which is how most London boroughs prefer a genuine design statement to be presented.
| Option | What it adds | Typical fee |
|---|---|---|
| Single-storey rear extension | A ground-floor kitchen-diner only, may qualify for permitted development | see Rear Extension Drawings, from £1,100 |
| Double storey side or rear extension | Two rooms across two floors, usually needs full planning | Full Planning pack ~£1,600–£2,400 |
| Double storey + Building Regulations (structural) | Combined pack including structural calculations for two-floor loads and foundations | Planning + Building Regs pack ~£2,200–£3,850 |
| Wraparound (rear + side return) | Combines two single-storey extensions into one L-shaped ground floor | see Wraparound Extension Drawings, from £2,200 |
Double Storey Extension Drawings in Harrow on the Hill HA1 — FAQs
How much does a double storey extension cost to design in London?+
Do I need planning permission to add a second storey?+
Will a double storey extension overlook my neighbour's garden?+
Do I need an architect for a double storey extension?+
How long does it take to get double storey extension drawings?+
Do I need planning permission for a loft conversion in Harrow?+
What does Harrow expect for a rear extension on a 1930s semi?+
Can I extend a home in Harrow on the Hill or Pinner?+
How long does Harrow Council take to decide?+
How much do planning drawings cost in Harrow?+
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