Annexe and granny-flat drawings for Hillingdon homes — designed to stay ancillary to the main house rather than become a separate dwelling, drawn to Hillingdon Council's policies, delivered in days and revised free until your decision.
Hillingdon Council granted 84% of the householder planning decisions it made in its latest published year — 3 points below the 87% England-wide householder average. A large slice of the borough sits in Green Belt to the west, where extensions face the openness test rather than ordinary householder policy, which is where a policy-literate drawing pack earns its keep. Its dominant 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 Hillingdon Council needs a full application. Hillingdon carries at least one Article 4 direction, and conservation areas including Old Uxbridge, Harefield Village and Ickenham Village remove those rights outright, so we confirm your exact address before a line is drawn. A validated householder application in Hillingdon is determined against an 8-week statutory target.
Uxbridge (the town centre with its Old Uxbridge conservation area and Edwardian terraces), Ruislip (Metro-land semis around the Ruislip Village conservation area), Ickenham (a village green surrounded by interwar suburban housing), Harefield (a rural Green Belt village of cottages and detached homes), Northwood (affluent detached and semi-detached houses on leafy plots) and Hayes (mixed interwar and postwar estates near the former industrial belt) — these are the Hillingdon pockets our drawings cover most. Heritage designations here include Old Uxbridge, Harefield Village, Ickenham Village, Ruislip Village and Eastcote. Hillingdon Council weighs each proposal against Hillingdon Local Plan and the HDAS: Residential Extensions SPD, where the design guidance polices the spacing and building line of Metro-land semis so paired houses keep their rhythm. On roofs the borough is hipped roofs on the 1930s semis and gabled roofs on the older village cottages, over interwar Metro-land semi-detached houses, Edwardian terraces around Uxbridge and West Drayton and detached houses and cottages in the rural western villages.
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. Hillingdon 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.
Hillingdon is largely interwar Metro-land semi-detached houses, Edwardian terraces around Uxbridge and West Drayton and detached houses and cottages in the rural western villages, 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 Hillingdon's conservation areas — including Old Uxbridge and Harefield Village — 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. Ruislip Village and the Harefield and Ickenham conservation areas carry tight controls, and Article 4 directions on some of these older village streets strip out the permitted-development rights suburban owners otherwise assume.
An annexe almost always needs an application to Hillingdon 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 Hillingdon Council has to test, rather than leaving the officer to assume the worst.
Below is Hillingdon Council's real householder decision record, drawn from official planning statistics and refreshed as new data lands. Hillingdon grants a fair share of householder applications, with Green Belt openness in the western villages and roof and spacing changes to interwar semis the recurring pinch points. 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, rolling year). Compare every borough on our London approval-rate league table.
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Across Uxbridge, Ruislip and Ickenham, 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 metro-land semi-detached houses, 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.
A large slice of the borough sits in Green Belt to the west, where extensions face the openness test rather than ordinary householder policy. Where Hillingdon 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 Hillingdon. A few of the areas where multigenerational schemes come up most often:
Annexe and granny-flat drawings for Uxbridge — the town centre with its Old Uxbridge conservation area and Edwardian terraces — planned to stay ancillary and drawn to Hillingdon Council's policies.
Annexe and granny-flat drawings for Ruislip — Metro-land semis around the Ruislip Village conservation area — planned to stay ancillary and drawn to Hillingdon Council's policies.
Annexe and granny-flat drawings for Ickenham — a village green surrounded by interwar suburban housing — planned to stay ancillary and drawn to Hillingdon Council's policies.
Annexe and granny-flat drawings for Harefield — a rural Green Belt village of cottages and detached homes — planned to stay ancillary and drawn to Hillingdon Council's policies.
Annexe and granny-flat drawings for Northwood — affluent detached and semi-detached houses on leafy plots — planned to stay ancillary and drawn to Hillingdon Council's policies.
Annexe and granny-flat drawings for Hayes — mixed interwar and postwar estates near the former industrial belt — planned to stay ancillary and drawn to Hillingdon Council's policies.
Three similar buildings, three different consents. This is what separates them.
| What you build | Planning status | Key test | What Hillingdon 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 Hillingdon 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 Hillingdon.
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 Hillingdon Council's policies.
We submit the application with a supporting statement on use, manage validation and case-officer queries, and revise free until Hillingdon 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 Hillingdon we prepare a full application to Hillingdon 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. Hillingdon 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 Hillingdon, particularly near designated areas such as Old Uxbridge and Harefield Village. Hillingdon 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 Hillingdon address specifically. Hillingdon 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 Hillingdon address specifically. Hillingdon 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 Hillingdon address specifically. Hillingdon Council is the decision-maker.
We quote each Hillingdon 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 Hillingdon Council approves. Call 020 7864 7245 to start.
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