Back-of-house extension drawings for Denne homes — the glazed kitchen-diner across the rear, drawn to Horsham District Council's depth and daylight limits, delivered in days and revised free until your decision, with a free approval-odds check first.
Horsham District Council granted 97% of the householder planning decisions it made in its latest published year — 10 points above the 87% England-wide householder average. Denne contains Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area, Horsham Conservation Area conservation areas (Horsham (London Road) Conservation Area designated 1984), so materials, fenestration and roof form are assessed against the appraisal, which is where a policy-literate drawing pack earns its keep. Its dominant postwar (1945–1970) housing stock sets the design brief on most streets.
Under Class B, a rear dormer stays permitted development up to 40m³ of added roof volume on a terrace or 50m³ on a semi-detached or detached house, while Class A allows a single-storey rear extension of 3m beyond the original rear wall on a terrace and 4m on a detached house before a full application is needed. Denne carries at least one Article 4 direction, and conservation areas including Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area and Horsham Conservation Area remove those rights outright, so we confirm your exact address before a line is drawn. A validated householder application in Denne is determined against an 8-week statutory target.
Horsham (London Road) (conservation area designated in 1984), Horsham (Park Terrace Gardens) (conservation area designated in 2023) and Horsham (conservation area designated in 1974) — these are the Denne pockets our drawings cover most. Heritage designations here include Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area and Horsham Conservation Area. Horsham District Council weighs each proposal against Horsham District Council's adopted local plan and its householder design guidance, where the 4,910 homes here are 16% 1955-1964, 12% 1983-1992, 11% 2000-2008, which is what sets the realistic roof and rear-projection options. On roofs the borough is shallow gabled roofs typical of that period's building and trussed-rafter roofs typical of 1980s building, over late-1950s and early-1960s houses (16% of 4,910 homes), 1980s estate houses (12%) and 2000s houses and apartments (11%).
Denne's designated heritage is specific, and it is the first thing we check against your address: Horsham (London Road) (conservation area designated in 1984), Horsham (Park Terrace Gardens) (conservation area designated in 2023) and Horsham (conservation area designated in 1974). Inside those boundaries permitted development is curtailed and Horsham District Council assesses materials, window detail and roof form against the area's own appraisal, so a scheme that would be waved through two streets away can need a full application here.
Horsham District Council has 53 recorded Article 4 directions, removing permitted development for rear and side extensions and roof enlargements such as dormers — check the address before assuming PD applies in Denne.
On stock, Denne is late-1950s and early-1960s houses (16% of 4,910 homes), 1980s estate houses (12%) and 2000s houses and apartments (11%) — which is why shallow gabled roofs typical of that period's building and trussed-rafter roofs typical of 1980s building govern what a loft or rear projection can realistically be. Horsham District Council decided 679 householder applications in the latest published year and granted 97%, with 72% issued inside the eight-week target. Those are the numbers our drawings are prepared against.
The full build-period split for Denne runs pre-1900 6% (290 homes), 1900-1918 1% (30 homes), 1919-1929 1% (30 homes), 1930-1939 5% (240 homes), 1945-1954 4% (190 homes), 1955-1964 16% (770 homes), 1965-1972 4% (190 homes), 1973-1982 10% (500 homes), 1983-1992 12% (610 homes), 1993-1999 4% (220 homes) and 2000-2008 11% (520 homes). That distribution is why pre-1900 detailing dominates the drawings here, and it is measured from council-tax records rather than assumed from the street name.
Horsham District Council also decides for Billingshurst, Colgate & Rusper, Holbrook West and Steyning & Ashurst, so a decision in Denne sits inside a wider pattern of decisions we track across the same authority — useful when an officer cites a precedent from the next area over.
The Article 4 directions recorded for this council include ART4002 - LAND AT WOLVENS FARM BILLINGSHURST ROAD ASHINGTON, ART4003 - LAND AT CODMORE HILL PULBOROUGH, ART4020/1 and ART4040. Each removes a specific permitted-development right inside its own boundary, which is why the check is done on the address rather than on the town.
Published figures for Denne and Horsham District Council. These are the numbers that decide what is realistic on your street, so we work from them rather than from national averages.
| Measure | Denne |
|---|---|
| Dwellings recorded | 4,910 |
| Built pre-1900 | 290 (6%) |
| Built 1900-1918 | 30 (1%) |
| Built 1919-1929 | 30 (1%) |
| Built 1930-1939 | 240 (5%) |
| Built 1945-1954 | 190 (4%) |
| Built 1955-1964 | 770 (16%) |
| Built 1965-1972 | 190 (4%) |
| Built 1973-1982 | 500 (10%) |
| Built 1983-1992 | 610 (12%) |
| Built 1993-1999 | 220 (4%) |
| Built 2000-2008 | 520 (11%) |
| Built before 1919 | 7% |
| Built 1919–1939 | 5% |
| Built 1945–2008 | 61% |
| Conservation areas in Denne | 3 (Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area…) |
| Conservation areas district-wide | 40 |
| Article 4 directions recorded | 53 |
| Householder applications decided | 679 |
| Householder applications granted | 97% |
| Decided within 8 weeks | 72% |
Dwelling stock from VOA council-tax data at 31 March 2025; conservation-area and Article 4 counts from planning.data.gov.uk (MHCLG); decision figures are Horsham District Council's own, from MHCLG live table PS2 for the year to 31 March 2026.
The rear extension is the workhorse of Denne home improvement — it is how a dark back kitchen becomes an open family room facing the garden. Because the borough is built largely from late-1950s and early-1960s houses (16% of 4,910 homes), 1980s estate houses (12%) and 2000s houses and apartments (11%), most back walls sit close to a neighbour on at least one side, and that proximity, not the design, is what Horsham District Council scrutinises. The council reads the proposal against Horsham District Council's adopted local plan and its householder design guidance, and the first line an officer draws is the 45-degree splay from the neighbour's nearest window.
So the drawings live or die on geometry. We set the depth against the exact permitted-development figure, hold the eaves and the flat-roof or lantern build-up under the 4-metre height ceiling, and show the projection tested against both the 45-degree plan angle and the 25-degree section angle to the neighbouring windows. Denne contains Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area, Horsham Conservation Area conservation areas (Horsham (London Road) Conservation Area designated 1984), so materials, fenestration and roof form are assessed against the appraisal, so the rear elevation is composed around it rather than corrected after an objection.
Where the property sits in a conservation area — Horsham (London Road) Conservation Area, Horsham (Park Terrace Gardens) Conservation Area and Horsham Conservation Area among Denne's — the larger-home extension route is switched off and even a modest rear addition needs consent. Horsham District Council has 53 recorded Article 4 directions, removing permitted development for rear and side extensions and roof enlargements such as dormers — check the address before assuming PD applies in Denne. We confirm the designation before the survey.
Many single-storey rear extensions in Denne are permitted development and need no application. You will normally need to apply to Horsham District Council, or use the larger-home prior-approval route, if any of these apply:
We draw the depth, the roof build-up and the daylight splays to each neighbour on the page — the tests Horsham District Council's officers apply first — and submit a validation-complete pack, whether that is a lawful development certificate, a larger-home prior-approval notice or a full householder application.
Below is Horsham District Council's real householder decision record, taken from official planning statistics and refreshed as new data lands. Horsham District Council granted 97% of its householder applications in the year to 31 March 2026, and Horsham (London Road) Conservation Area shapes what is approved here. Rear extensions turn most often on neighbour daylight and depth, so a drawing pack that proves those tests upfront is decided faster and refused less often than a DIY submission.
Source: MHCLG planning application statistics (householder decisions, England, 1 April 2025 - 31 March 2026). Compare every borough on our London approval-rate league table.
Tell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
Across Horsham (London Road), Horsham (Park Terrace Gardens) and Horsham, the approved rear extension is typically a single-storey glazed box within the depth limit, roofed either flat with a lantern or in a shallow mono-pitch, and finished in brick or render to match the host wall. On the borough's late-1950s and early-1960s houses (16% of 4,910 homes), keeping the projection to the permitted-development figure often avoids an application entirely; where owners want the full 6 metres, the larger-home route succeeds when the neighbour-consultation period passes without a sustained objection.
The 4,910 homes here are 16% 1955-1964, 12% 1983-1992, 11% 2000-2008, which is what sets the realistic roof and rear-projection options. We keep the extension inside the daylight splays, set any glazed roof below the first-floor cill, and retain the garden depth Horsham District Council expects — so the back elevation answers the amenity case before a neighbour can lodge one. Two-storey rear extensions we draw with the 7-metre boundary gap and privacy screening resolved on the plan.
We draw rear extensions on every street in the borough. A few of the neighbourhoods where Denne back-of-house projects come up most often:
Rear extension drawings for Horsham (London Road)'s conservation area designated in 1984 — depth-checked, daylight-tested and drawn to Horsham District Council's guidance.
Rear extension drawings for Horsham (Park Terrace Gardens)'s conservation area designated in 2023 — depth-checked, daylight-tested and drawn to Horsham District Council's guidance.
Rear extension drawings for Horsham's conservation area designated in 1974 — depth-checked, daylight-tested and drawn to Horsham District Council's guidance.
How far you can extend at the back in Denne depends on your house type and the route you take. This is how the options compare.
| Route | Depth allowed | Consent needed | What Horsham District Council checks |
|---|---|---|---|
| Standard permitted development | 3m terrace/semi · 4m detached | Lawful development certificate (optional) | Depth, 4m height, materials |
| Larger-home prior approval | 6m terrace/semi · 8m detached | Prior-approval notice + neighbour consultation | Neighbour objections on amenity |
| Full householder application | Beyond the above, or two-storey | Full planning permission | Daylight (45°/25°), bulk, garden retained |
| Conservation area | Case by case | Full planning permission | Character, roof form, boundary treatment |
The larger-home route is switched off on designated land — conservation areas such as Horsham (London Road) Conservation Area and Horsham (Park Terrace Gardens) Conservation Area and Article 4 streets need a full application.
A fixed process built around how Horsham District Council validates and decides rear-extension applications — most drawings are submission-ready within seven days of survey.
Send us your Denne postcode and house type. We confirm your conservation and Article 4 status, how much rear-extension depth you have under permitted development, and score your odds against live Horsham District Council decisions.
We measure the original rear wall, floor and eaves levels, side and rear boundary distances and the neighbours' window positions — the numbers the depth limit and daylight splays depend on.
Chartered designers develop the single or two-storey rear extension to your brief, drawn inside the permitted-development limits or to Horsham District Council's extension design guidance, with the daylight angles shown.
We submit the certificate, prior-approval notice or application, handle validation and case-officer queries, and revise the drawings free until Horsham District Council issues its decision.
Often not. A single-storey rear extension up to 3 metres deep on a terrace or semi, or 4 metres on a detached house, and no higher than 4 metres, is usually permitted development in Denne. You will need to involve Horsham District Council for anything deeper via the larger-home route, for two-storey rear extensions, and for any rear extension in a conservation area such as Horsham (London Road) Conservation Area and Horsham (Park Terrace Gardens) Conservation Area, where those permitted-development rights fall away.
The larger-home extension scheme lets a single-storey rear extension reach 6 metres on a terrace or semi, or 8 metres on a detached house — double the standard allowance. It is not automatic: you submit a prior-approval notification to Horsham District Council, neighbours are consulted, and if one objects on amenity grounds the council rules on it. It also does not apply on designated land such as Denne's conservation areas.
It is the daylight test Horsham District Council applies to protect neighbours. Drawn on plan, a line at 45 degrees from the midpoint of the neighbour's nearest ground-floor window should not be crossed by your extension; a companion 25-degree line is checked in section. If the projection breaches it, the extension is likely to be shortened or refused, so we test and prove it on the drawings before submission. This applies to your Denne address specifically.
A two-storey rear extension almost always needs a full householder application to Horsham District Council, as it sits outside permitted development on most homes. The council checks that it stays at least 7 metres from the rear boundary, does not overbear the neighbours and avoids new overlooking. We resolve the boundary gap, privacy and daylight on the plans so the application is decided on its merits. This applies to your Denne address specifically.
Frequently, yes. If the rear extension involves work to a shared wall, building up to the boundary, or excavating foundations near a neighbour's structure, the Party Wall etc. Act applies and you must serve notice — this is separate from Horsham District Council's planning decision. We flag it early and can prepare the drawings a party-wall surveyor needs alongside the planning set. This applies to your Denne address specifically.
We price each Denne rear extension on its own footprint and send a fixed, no-obligation quote within one working day. It covers the full drawing pack with free revisions until Horsham District Council approves, and we confirm at the outset whether your extension is permitted development, needs prior approval, or a full application. Call 020 7864 7245 to begin.
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