Annexe & Granny Annexe Extensions

Ancillary accommodation, or a separate dwelling

This is the question the whole job turns on, and it has nothing to do with how the annexe is built.

Planning law has no tidy definition of the word annexe. What it has is a distinction between accommodation that is ancillary to an existing house, meaning part of the same single dwelling and the same household, and accommodation amounting to a separate dwelling, meaning a new planning unit that happens to be attached to yours.

An ancillary annexe is, in planning terms, an extension, assessed on scale, appearance and effect on neighbours. A separate dwelling is a different application entirely, judged as a new house against policies on density, garden land, parking, amenity space and access. On a suburban plot in Colchester that is a materially harder case, and on some plots it cannot be made at all.

The distinction runs forward through everything else on this page. It changes which parts of the Building Regulations apply, it affects council tax banding, and it can affect what happens when the house is sold. None of it is decided by the label on the drawing. Councils look at how the accommodation would function in practice, and so does the Planning Inspectorate on appeal. The test is blunt: if you handed the keys to a stranger, could they live there as an independent household without ever entering your house.

Permitted development, and why a full application is usual

Permitted development can build the box. It cannot create the household.

Permitted development rights allow certain extensions to be built without applying for planning permission, subject to limits on depth, height, materials, boundary position and garden coverage. An annexe built as an extension can in principle sit within those rights, because in planning terms it is an enlargement of the house rather than a new building.

The catch is that those rights apply to a single dwellinghouse and to work that keeps it one. They do not authorise the creation of a separate dwelling. The moment the accommodation is genuinely independent, permitted development stops helping.

There is a further trap in the outbuilding route. Detached garden buildings have their own rights, but those cover structures incidental to the enjoyment of the house, which is a narrower idea than ancillary. A gym or a store is incidental. Somewhere a person sleeps, cooks and lives is not, and a garden building used as living accommodation falls outside those rights even where the shell would have been fine.

All of which is why a full planning application is the normal route for an annexe with independent living facilities, even where a plain extension of the same size would not need one. It is slower and it costs a fee. It also produces a decision notice saying what you are allowed to have.

Part M, and designing for someone who becomes less mobile

The most useful section on this page, and the one most often skipped.

Part M covers access and use. For a new dwelling the baseline is modest: a level or gently sloping approach, an accessible threshold, a WC at entrance level, and clear door and corridor widths that let someone get through. Higher standards exist for accessible and adaptable dwellings and for wheelchair users, and those normally apply only where a planning condition imposes them.

Here is the part that matters. Nobody is required to build an annexe to the higher standards. On an annexe for an elderly parent, you should anyway.

The reason is arithmetic. If someone moves in at seventy-eight, the annexe has to work for them at eighty-eight. Mobility rarely collapses overnight; it declines, and it declines faster after a fall or an operation. A space designed for how someone is today will be wrong within a few years, and retrofitting is disruptive, expensive, and happens at the worst possible moment.

What we would build in whether or not anyone asked. A genuinely level threshold, not a small step. Doorways with an eight hundred and fifty to nine hundred millimetre clear opening, measured with the door open and the ironmongery on, which means ordering wider door sets. A clear turning space of about one and a half metres in the main rooms.

A wet room rather than a bath: level access, drained and tanked properly, floor falls set out before the screed goes down. A bath is the hardest thing on the list to change later. Noggins in the walls beside the WC, in the shower and along the hall, so grab rails can go into solid timber in future rather than into plasterboard.

Sockets raised to around four hundred and fifty millimetres and switches lowered to around eleven hundred, which costs nothing at first fix and matters enormously to someone who cannot bend. Lever handles rather than knobs. Even lighting with no dark patches, because failing eyesight and a poorly lit hallway is how people fall. And if a hoist may ever be needed, the structure to carry it decided now.

Heating, services and metering

Run it off the house or run it separately, and the answer is not the same for everyone.

Extending the existing heating system into the annexe is usually cheaper and simpler. The catch is control. An older person is likely to want the heating on longer and warmer than the rest of the household, and one thermostat means one of you is uncomfortable. If the annexe runs off the house boiler it needs its own zone, thermostat and timer, and the boiler needs checking against the larger load rather than assumed to cope.

A separate heat source gives complete independence and puts the running cost where the occupant can see it. That might be its own boiler, or an air source heat pump, which suits an annexe reasonably well because it is a small well insulated space built to current standards and can take low temperature underfloor heating without compromise. Underfloor heating is worth considering either way: the floor is new anyway, and it frees the walls in a space where every wall is needed. Decided before the slab, not after.

Metering carries a planning shadow as well as a practical one. Separate electricity and gas supplies with their own meters make the annexe independent to run and easy to bill. They also add to the picture of a separate household, which is precisely the evidence a council weighs. If the annexe is being presented as ancillary, running services off the main house is the more consistent position. Decide that with your eyes open rather than leaving it to the electrician. Either way the annexe needs its own consumer unit, alarms interlinked appropriately, and drainage designed rather than teed into the nearest pipe.

How long it takes

Longer at the front end than an ordinary extension, and about the same on site.

The paperwork is the part that stretches. A householder planning application has a statutory determination period of eight weeks from validation, and an annexe is more likely than most extensions to attract questions, a request for further information, or a condition that needs discussing. Where the proposal is assessed as a new dwelling it is a different application with a heavier evidence burden. Building Regulations full plans approval runs alongside, and party wall notices have fixed statutory periods that cannot be shortened except where the adjoining owner consents in writing, which is the only thing that shortens them.

Realistically, allow two to three months from first drawing to a decision, run what you can in parallel, and order nothing before the decision notice is in your hand.

On site, an attached annexe is commonly twelve to twenty weeks from breaking ground to completion, longer than a plain extension of the same size because of the second kitchen, the second bathroom and the additional drainage and electrical work. Deep foundations add time and weather affects groundworks. If someone is moving in from another property, do not exchange or give notice against a programme date. Build in a margin. Every experienced builder has watched a family arrive at a house that is a fortnight from finished.

How we work

One contract, one contact, and the awkward questions answered before you spend money.

Our team has 25+ years in the trade and comes out. The first visit is a survey rather than a sales call. We look at the plot, the access, the ground, the drains, the planning history on the address and what the annexe has to do for the person who will live in it. That last part takes longest, and it should.

Most people who call us already have drawings and permission and want a builder to price the work and build it. That is the ordinary job here, and we are glad to work to somebody else’s plans. Where the drawings do not exist yet, we bring in the technician who draws it and the structural engineer who calculates it, we manage the planning route and set out the ancillary case properly, we notify Colchester City Council Building Control, and we run the trades as main contractor through to the completion certificate. Where a question belongs to the council, a solicitor or an accountant, we point you at them rather than guess.

Probuild Extensions Colchester is the extensions arm of Essex Probuild Ltd, company number 15979928. We carry £2m public liability cover, we are based in West Bergholt about three miles north west of Colchester, and we work across the city and roughly thirty miles around. The survey and the quotation cost nothing and there is no pressure afterwards.