Back-of-house extension drawings for Three Rivers homes — the glazed kitchen-diner across the rear, drawn to Three Rivers District Council's depth and daylight limits, delivered in days and revised free until your decision, with a free approval-odds check first.
Three Rivers District Council granted 93% of the householder planning decisions it made in its latest published year — 6 points above the 87% England-wide householder average. Metropolitan Green Belt covers roughly three-quarters of the district, so the plan pushes growth onto brownfield and town-centre sites rather than releasing countryside, which is where a policy-literate drawing pack earns its keep. Its dominant Victorian (1837–1901), Edwardian (1901–1910), interwar (1918–1939) and postwar (1945–1970) housing stock sets the design brief on most streets.
Class A and Class B set the thresholds — a rear dormer to 40m³ on a terrace or 50m³ on a semi or detached, and a single-storey rear extension to 3m on a terrace or 4m on a detached house — beyond which Three Rivers District Council needs a full application. Three Rivers carries at least one Article 4 direction, and conservation areas including Rickmansworth, Chorleywood Common and Moor Park remove those rights outright, so we confirm your exact address before a line is drawn. A validated householder application in Three Rivers is determined against an 8-week statutory target.
Rickmansworth (the historic market-town core with a Victorian and Edwardian centre and its own conservation area), Chorleywood (a Metro-land commuter village of Arts and Crafts and interwar houses around Chorleywood Common), Moor Park (a private gated estate of large interwar detached houses under an Article 4 direction), Croxley Green (mixed Victorian and interwar suburban housing gathered around the green), Abbots Langley (a village with a historic core and postwar suburban growth) and Sarratt (a rural green-belt village of historic vernacular cottages) — these are the Three Rivers pockets our drawings cover most. Heritage designations here include Rickmansworth, Chorleywood Common, Moor Park, Croxley Green, Sarratt and Abbots Langley. Three Rivers District Council weighs each proposal against the Three Rivers Core Strategy (adopted October 2011) and Development Management Policies LDD, where part of the district around Chorleywood and Rickmansworth falls within the Chilterns National Landscape (AONB), where landscape protection is at its highest. Converted flats are common through Rickmansworth and around the stations, and none of them hold householder permitted-development rights.. On roofs the borough is hipped roofs on the 1930s Metro-land semis and gabled and dual-pitch roofs on the older village cottages, over interwar and Edwardian Metro-land semi-detached and detached houses across Chorleywood, Croxley Green and Moor Park, Victorian and Edwardian terraces around Rickmansworth, postwar estate housing at Abbots Langley and South Oxhey and period vernacular cottages in the green-belt villages of Sarratt and Heronsgate.
The rear extension is the workhorse of Three Rivers home improvement — it is how a dark back kitchen becomes an open family room facing the garden. Because the borough is built largely from interwar and Edwardian Metro-land semi-detached and detached houses across Chorleywood, Croxley Green and Moor Park, Victorian and Edwardian terraces around Rickmansworth, postwar estate housing at Abbots Langley and South Oxhey and period vernacular cottages in the green-belt villages of Sarratt and Heronsgate, most back walls sit close to a neighbour on at least one side, and that proximity, not the design, is what Three Rivers District Council scrutinises. The council reads the proposal against the Three Rivers Core Strategy (adopted October 2011) and Development Management Policies LDD, 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. Metropolitan Green Belt covers roughly three-quarters of the district, so the plan pushes growth onto brownfield and town-centre sites rather than releasing countryside, so the rear elevation is composed around it rather than corrected after an objection.
Where the property sits in a conservation area — Rickmansworth, Chorleywood Common, Moor Park, Croxley Green, Sarratt and Abbots Langley among Three Rivers's — the larger-home extension route is switched off and even a modest rear addition needs consent. The Moor Park Article 4 direction covers the private Moor Park estate and conservation area, removing permitted-development rights so external alterations to these large interwar houses need consent, and further conservation areas such as Rickmansworth and Chorleywood Common layer additional controls. We confirm the designation before the survey.
Many single-storey rear extensions in Three Rivers are permitted development and need no application. You will normally need to apply to Three Rivers 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 Three Rivers 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 Three Rivers District Council's real householder decision record, taken from official planning statistics and refreshed as new data lands. Three Rivers grants a high share of decisions overall, with green-belt containment across most of the district and Chilterns AONB protection the recurring constraints on larger schemes. 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 Rickmansworth, Chorleywood and Moor Park, 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 interwar and edwardian metro-land semi-detached and detached houses across chorleywood, croxley green and moor park, 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.
Part of the district around Chorleywood and Rickmansworth falls within the Chilterns National Landscape (AONB), where landscape protection is at its highest. We keep the extension inside the daylight splays, set any glazed roof below the first-floor cill, and retain the garden depth Three Rivers 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 Three Rivers back-of-house projects come up most often:
Rear extension drawings for Rickmansworth's the historic market-town core with a Victorian and Edwardian centre and its own conservation area — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Rear extension drawings for Chorleywood's a Metro-land commuter village of Arts and Crafts and interwar houses around Chorleywood Common — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Rear extension drawings for Moor Park's a private gated estate of large interwar detached houses under an Article 4 direction — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Rear extension drawings for Croxley Green's mixed Victorian and interwar suburban housing gathered around the green — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Rear extension drawings for Abbots Langley's a village with a historic core and postwar suburban growth — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Rear extension drawings for Sarratt's a rural green-belt village of historic vernacular cottages — depth-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
How far you can extend at the back in Three Rivers depends on your house type and the route you take. This is how the options compare.
| Route | Depth allowed | Consent needed | What Three Rivers 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 Rickmansworth and Chorleywood Common and Article 4 streets need a full application.
A fixed process built around how Three Rivers District Council validates and decides rear-extension applications — most drawings are submission-ready within seven days of survey.
Send us your Three Rivers 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 Three Rivers 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 Three Rivers 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 Three Rivers 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 Three Rivers. You will need to involve Three Rivers 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 Rickmansworth and Chorleywood Common, 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 Three Rivers 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 Three Rivers's conservation areas.
It is the daylight test Three Rivers 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.
A two-storey rear extension almost always needs a full householder application to Three Rivers 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.
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 Three Rivers District Council's planning decision. We flag it early and can prepare the drawings a party-wall surveyor needs alongside the planning set.
We price each Three Rivers 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 Three Rivers 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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