Single-storey, double-storey, rear and side extension drawings for Three Rivers homes — measured to Three Rivers District Council's design guidance, delivered in days and revised free until your decision, with a free approval-odds check before you commit.
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.
Three Rivers homes come in a handful of recurring shapes, and each one points to a different extension. 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, so a Victorian terrace usually wants a rear or side-return infill, while an interwar semi has room for a wider single-storey wrap or a two-storey side addition. Three Rivers District Council judges every one of them against the Three Rivers Core Strategy (adopted October 2011) and Development Management Policies LDD, weighing footprint, height and the impact on the house next door before it looks at the elevations.
That is why the drawings decide the outcome. We set the extension depth against the permitted-development limits precisely, keep the eaves and ridge within the allowances, and plot the 45-degree daylight lines to the neighbours' windows so the case officer can see the amenity test is passed. 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 we design around it from the first sketch rather than discover it at validation.
Three Rivers also protects whole streets — Rickmansworth, Chorleywood Common, Moor Park, Croxley Green, Sarratt and Abbots Langley among them. 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. On designated land the larger-home extension route and most side extensions stop being permitted development, so we confirm your address against those layers before drawing a line.
Plenty of Three Rivers extensions are permitted development and need no planning application — a single-storey rear extension within the depth and height limits is the common case. You will normally need to apply to Three Rivers District Council if any of these apply:
We draw the footprint, the ridge and eaves heights and the neighbours' daylight on the page — the relationships Three Rivers District Council's officers weigh first — and submit a validation-complete pack, whether that is a lawful development certificate, a prior-approval notification or a full householder application.
Below is Three Rivers District Council's real householder decision record, drawn 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. A complete, policy-literate extension pack anticipates those pressure points before submission, which is why professionally drawn applications are decided faster and refused less often than DIY ones.
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 extension that lands most often is the single-storey rear addition — a glazed kitchen-diner across the back of the house, kept within the permitted-development depth or taken to a full application where the ground floor wants more. On the borough's interwar and edwardian metro-land semi-detached and detached houses across chorleywood, croxley green and moor park, a side-return infill frequently pairs with it to square off the plan; on wider period vernacular cottages in the green-belt villages of sarratt and heronsgate, a two-storey side or rear extension can add a bedroom above without swallowing the garden.
Part of the district around Chorleywood and Rickmansworth falls within the Chilterns National Landscape (AONB), where landscape protection is at its highest. We size the extension to the amenity and daylight tests, match the roof and materials to the host house, and keep enough garden to satisfy Three Rivers District Council's space standards — so the scheme answers the borough's questions before an objection can raise them. Where permitted-development rights are used up or removed, we prepare the householder application to the council's extension design guidance instead.
We draw extensions on every street in the borough. A few of the neighbourhoods where Three Rivers projects come up most often:
Extension drawings for Rickmansworth's the historic market-town core with a Victorian and Edwardian centre and its own conservation area — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Extension drawings for Chorleywood's a Metro-land commuter village of Arts and Crafts and interwar houses around Chorleywood Common — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Extension drawings for Moor Park's a private gated estate of large interwar detached houses under an Article 4 direction — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Extension drawings for Croxley Green's mixed Victorian and interwar suburban housing gathered around the green — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Extension drawings for Abbots Langley's a village with a historic core and postwar suburban growth — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
Extension drawings for Sarratt's a rural green-belt village of historic vernacular cottages — footprint-checked, daylight-tested and drawn to Three Rivers District Council's guidance.
The right extension in Three Rivers depends on your house type and how much garden you can give up. This is how the main options compare on planning route and what they add.
| Extension type | Permitted development? | What it adds | What Three Rivers District Council checks |
|---|---|---|---|
| Single-storey rear | Often, within 3m/4m depth (6m/8m via prior approval) | Bigger kitchen-diner across the back | Depth, height, neighbour daylight (45°) |
| Side-return infill | Sometimes, if within width and height limits | Squares off an L-shaped ground floor | Width vs the original house, glazing to boundary |
| Two-storey rear/side | No — full application | Extra bedroom or bathroom above | Bulk, overlooking, 7m rear-boundary gap |
| Wraparound (rear + side) | No — full application | Whole-width open-plan ground floor | Combined footprint and garden retained |
Route depends on your street — conservation areas such as Rickmansworth and Chorleywood Common and Article 4 directions can remove permitted-development rights.
A fixed process built around how Three Rivers District Council validates and decides householder extension applications — most drawings are submission-ready within seven days of survey.
Tell us your Three Rivers postcode and house type. We confirm your conservation and Article 4 status, how much permitted-development depth you have left, and score your odds against live Three Rivers District Council decisions.
We measure the existing footprint, floor and eaves levels, boundary distances and the neighbours' window positions — the numbers the depth limits and daylight tests depend on.
Chartered designers develop the single-storey, two-storey or side extension to your brief, drawn inside the permitted-development limits or to Three Rivers District Council's extension design guidance.
We submit the certificate, prior-approval notice or application, manage validation and case-officer queries, and revise the drawings free until Three Rivers District Council issues its decision.
Not always. 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 apply to Three Rivers District Council for two-storey extensions, side extensions wider than half the house, anything forward of the front wall, deeper rear extensions under the larger-home prior-approval route, and any extension in a conservation area such as Rickmansworth and Chorleywood Common.
Standard permitted development allows 3 metres on a terraced or semi-detached house and 4 metres on a detached one. The larger-home extension scheme can double that to 6 or 8 metres, but it needs a prior-approval notification to Three Rivers District Council and a neighbour-consultation period, and it does not apply on designated land such as Three Rivers's conservation areas. We confirm which route your property qualifies for before drawing.
Two-storey and double-storey extensions almost always need a full householder application to Three Rivers District Council, because they fall outside permitted development on most homes. The council looks closely at bulk, overlooking of neighbours and the 7-metre gap a two-storey rear extension must keep from the rear boundary. We design to those tests and show the daylight and privacy angles on the drawings.
A householder planning application in Three Rivers runs to a statutory eight-week target, a larger-home prior-approval notification to around six weeks including the neighbour-consultation period, and a lawful development certificate to eight weeks. Incomplete submissions stall at validation, so we submit a complete pack and manage officer queries to keep the decision on schedule. Three Rivers District Council is the decision-maker.
Yes — planning permission and building regulations are separate consents, and almost every extension needs both. Planning governs whether you can build it; building control governs how it is built, covering structure, insulation, drainage and fire safety. We prepare the building-regulations drawings alongside the planning set so Three Rivers District Council's building control or an approved inspector can sign the work off.
Every house and brief is different, so we price each Three Rivers extension individually and send a fixed, no-obligation quote back within one working day. It covers the full drawing pack with free revisions until Three Rivers District Council approves, and we tell you upfront whether your extension qualifies as permitted development. Call 020 7864 7245 to get started.
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Same fixed quotes, same fast drawings — wherever your project is.