Annexe and granny-flat drawings for Three Rivers homes — designed to stay ancillary to the main house rather than become a separate dwelling, drawn to Three Rivers District Council's policies, delivered in days and revised free until your decision.
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.
Councils do not decide annexes on square metres. They decide whether, once built, the accommodation forms part of one planning unit with the main house or a second one beside it. Three Rivers District Council looks at whether the garden is shared or divided, whether the annexe has its own street access and address, whether the occupier could live there entirely independently, and whether the two households would function as one. That is the whole case, and it is made or lost on the layout.
Three Rivers is largely 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, which shapes the realistic options: converting part of the existing house, extending it, or building a detached unit in the garden. A detached annexe can sometimes sit under Class E as an outbuilding incidental to the enjoyment of the dwellinghouse — but sleeping accommodation is generally not "incidental", so a garden annexe with a bedroom usually needs its own permission rather than relying on outbuilding rights.
In Three Rivers's conservation areas — including Rickmansworth and Chorleywood Common — a garden building is also judged on its effect on the character of the area, which limits height and footprint before the use question is reached. 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.
An annexe almost always needs an application to Three Rivers District Council. Expect one where any of these apply:
We plan the annexe so its relationship to the main house is visible on the page — shared garden, connected access, a layout that reads as one household — and set out the case Three Rivers District Council has to test, rather than leaving the officer to assume the worst.
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. Annexe applications are decided on use as much as design, so the supporting case matters as much as the elevations.
Source: MHCLG planning application statistics (householder decisions, England, 1 April 2025 - 31 March 2026). Compare every borough on our London approval-rate league table.
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Across Rickmansworth, Chorleywood and Moor Park, the annexes that succeed keep one shared garden, take access past the main house rather than from the street, and are modest against the host building — single storey where the plot is overlooked, and set back from boundaries. On interwar and edwardian metro-land semi-detached and detached houses across chorleywood, croxley green and moor park, converting an integral garage or a rear ground floor is often approved more readily than a detached garden unit, because the ancillary relationship is self-evident.
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. Where Three Rivers District Council grants permission, it commonly attaches a condition tying occupation of the annexe to the main dwelling. That condition is not a problem to be avoided — it is usually the mechanism that makes approval possible, and we draft the application on that basis rather than pretending the annexe is something it is not.
We draw annexes across Three Rivers. A few of the areas where multigenerational schemes come up most often:
Annexe and granny-flat drawings for Rickmansworth — the historic market-town core with a Victorian and Edwardian centre and its own conservation area — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Annexe and granny-flat drawings for Chorleywood — a Metro-land commuter village of Arts and Crafts and interwar houses around Chorleywood Common — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Annexe and granny-flat drawings for Moor Park — a private gated estate of large interwar detached houses under an Article 4 direction — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Annexe and granny-flat drawings for Croxley Green — mixed Victorian and interwar suburban housing gathered around the green — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Annexe and granny-flat drawings for Abbots Langley — a village with a historic core and postwar suburban growth — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Annexe and granny-flat drawings for Sarratt — a rural green-belt village of historic vernacular cottages — planned to stay ancillary and drawn to Three Rivers District Council's policies.
Three similar buildings, three different consents. This is what separates them.
| What you build | Planning status | Key test | What Three Rivers District Council checks |
|---|---|---|---|
| Garden room, no sleeping space | Often Class E permitted development | Incidental to the house | Height, footprint, boundary position |
| Annexe used by the household | Full application, usually with a tie condition | Ancillary use | Shared garden and access, layout |
| Self-contained unit, own access | New dwelling — full application | Separate planning unit | Policy on new homes, amenity, parking |
| Converted garage or ground floor | Often permitted, use still assessed | Whether use changes | Independence of the accommodation |
| Annexe on designated land | Full application | Designation | Character and appearance |
The ancillary/separate-dwelling distinction comes from section 55 of the Town and Country Planning Act 1990; outbuilding limits from the GPDO 2015, Schedule 2, Part 1, Class E.
A fixed process built around how Three Rivers District Council tests the use question as well as the design.
Tell us who the annexe is for and where it would sit on the plot. We confirm designation status and tell you honestly whether the scheme reads as ancillary or as a separate dwelling in Three Rivers.
We measure the plot, the existing house and the access route, so the shared-garden and shared-access case can be drawn rather than asserted.
Chartered designers develop the annexe to your brief, with the layout, access and garden relationship arranged to support the ancillary case under Three Rivers District Council's policies.
We submit the application with a supporting statement on use, manage validation and case-officer queries, and revise free until Three Rivers District Council decides.
Almost always. Sleeping accommodation is generally not "incidental" to the enjoyment of a house, so it falls outside the outbuilding permitted-development right, and any annexe that could function independently raises a change-of-use question under section 55. In Three Rivers we prepare a full application to Three Rivers District Council and make the ancillary case explicitly rather than hoping it is not asked.
A shared garden rather than a divided one, access through the main property rather than a separate street entrance, occupation by a member of the same household, and a physical and functional relationship with the main house. Three Rivers District Council weighs those together — no single feature decides it, but a separate front door and a fenced-off garden together usually settle it against you.
Yes, subject to permission. A detached garden annexe is assessed on its scale against the plot, its effect on neighbours and the character of the area, and then on the use question. Keeping it single storey, set in from boundaries and served off the shared garden gives it the best prospect in Three Rivers, particularly near designated areas such as Rickmansworth and Chorleywood Common. Three Rivers District Council is the decision-maker.
Commonly, yes — a condition tying occupation of the annexe to the main dwelling, so it cannot be sold or let separately. That is normally what makes approval possible, because it removes the concern that a new independent home is being created without going through housing policy. The condition runs with the land, so it matters at resale, and we explain the implications before you commit. This applies to your Three Rivers address specifically. Three Rivers District Council is the decision-maker.
Yes. A new annexe is new habitable accommodation, so structure, fire escape, insulation and ventilation all apply, and a detached annexe close to a boundary raises fire-spread requirements as well. Planning and building control are separate consents with separate submissions — we prepare both so the approved design is the one that can actually be built. This applies to your Three Rivers address specifically. Three Rivers District Council is the decision-maker.
A householder application runs to an eight-week statutory target; where the council treats the annexe as creating a new unit it becomes a minor application with a thirteen-week target instead. Which route applies depends on how the use is characterised, which is precisely why the ancillary case is worth making properly at the outset. This applies to your Three Rivers address specifically. Three Rivers District Council is the decision-maker.
We quote each Three Rivers annexe individually, because plot, access and whether you are converting or building new all change the work, and send a fixed, no-obligation quote within one working day. It covers the full drawing pack and supporting statement, with free revisions until Three Rivers District Council approves. Call 020 7864 7245 to start.
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