The Royal Borough's 3.3 by 7 metre rule
In April 2026 the council's Cabinet adopted a new Parking SPD for the whole borough. Until then its parking guidance dated from 2004. One line in it says a lot about garages. On new developments, a domestic garage smaller than 3.3m by 7.0m inside no longer counts towards the parking standard.
Get a tape measure into your own garage. If it falls short, the council has now said in writing that on a new estate a box that size isn't really a parking space. The rule looks forward, though. The SPD states it can't be applied retrospectively to homes already permitted and built, so it doesn't reclassify yours.
What it does give you is a sensible check on the drive. The SPD's standard bay is 2.5m by 5.0m, with an extra 0.3m of width for each side hemmed in by a wall or fence, and no part of the car may hang over the boundary. Once the garage door becomes a wall and a window, that bay is where the car lives. If the drive falls short, a part conversion that keeps storage at the front might suit you better.
Where the integral garages are
The Victorian terraces of Ray Street and Boyn Hill went up long before anyone needed a garage, so this page will rarely apply there. The garages are out on the edges. Cox Green's own history notes that the Larchfield estate was started after the Second World War, and that the second half of the century brought an explosion of building which joined Cox Green up with Woodlands Park, Altwood and Maidenhead itself.
Houses of that sort are where integral and attached garages turn up, and where a planning condition is most likely to be hiding. The Planning Portal warns that permitted development rights are sometimes removed, and names new housing developments as the place to check first. Ask the council for the original decision notice for your estate before anyone starts work. The same goes for the new homes going up in South West Maidenhead.
Integral garage. Common on the later estates, and the one where a condition on the original permission is likeliest. The wall you share with the hall or kitchen becomes an internal wall, so expect building control to ask how the whole room, that wall included, is insulated to habitable standards.
Planning and building control. Planning permission usually isn't needed for internal work that doesn't enlarge the house. Building Regulations approval normally is, from the Royal Borough's own building control service or a private approver.
Single garage. Makes one modest room. The new wall under the old door opening may need its own foundation, which on river gravels over chalk is worth digging and inspecting rather than guessing.
Read our full guide: Single Garage Conversion: What Is Involved and What to Budget For →
Bedroom. Plan the escape window and smoke alarm from day one. On a low plot near the Thames, a bedroom at garage level is the room you would least want water in, so check the flood map before you commit.
Home office. For your own desk work this stays a domestic room. If clients start calling or staff turn up, the Planning Portal says a business run from a garage needs permission in most cases.
Utility or playroom. A back half conversion keeps a store for bikes at the front. The new SPD accepts a covered garage as cycle storage, which suits families who don't want bikes through the house.
Double garage. Where a house has one, converting one bay and keeping the other answers most parking worries at once.
Detached garage. Used as a gym, workshop or office for the household, it stays part of the home, and the Planning Portal says a hobby workshop typically needs no permission. Turn it into a separate home and permission may be needed whatever the building work.
Gym or studio. On a semi, the garage often backs onto next door's. Insulate that party wall for sound before the weights rack goes up against it.
Cost and value. No prices here. A new foundation, raising the floor to house level and any damp work below it are what move a Maidenhead quote most.
Floors, groundwater and the river
A garage slab was laid for a car, not a carpet. Converting it means a new floor with a membrane that laps properly into the damp course in the old walls, and in Maidenhead that detail earns its keep. Thames Water's plan for the town records exceptionally high groundwater over the chalk in 2023 and 2024, and sewer flooding at Moneyrow Green and along parts of Ascot Road.
Flood risk is a separate question. The Environment Agency issues warnings for the Thames at Maidenhead and for the properties nearest the water. If any part of your project needs a planning application and the plot is in Flood Zone 2 or 3, the council's validation guidance asks for a flood risk assessment with it.
Check your address on the UKradon map too. Where the radon potential is high enough, LABC says new conversions need basic or full protection, and building control can tell you which applies.
In the Maidenhead Riverside conservation area, a new window where the garage door was will be read against the Arts and Crafts houses of the old Ray Lodge estate. A council report in 2010 proposed extra controls on doors and windows facing the road there, so ask whether a direction applies to your house before you order the frames.
Where these facts come from
- RBWM Cabinet, 28 April 2026: adoption of the Parking SPD
- RBWM: Parking SPD as adopted (Appendix B)
- RBWM: Parking Strategy (2004)
- Cox Green Parish Council: history of Cox Green
- RBWM: Maidenhead Riverside conservation area report (2010)
- RBWM: what to submit with your planning application
- RBWM: building control
- Thames Water: Maidenhead groundwater management plan
- Environment Agency: River Thames at Maidenhead to Windsor and Eton flood warning area
- Planning Portal: garage conversion planning permission
- Planning Portal: building regulations for a garage conversion
- Planning Portal: converting a garage into a workshop
- Planning Portal: running a business from a garage
- LABC: garage conversion tips from building control
- LABC: do I need to consider radon?
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Questions people in Maidenhead ask
Our 1970s garage in Cox Green is too narrow for the car. Does the council still count it as a parking space?
The 2026 Parking SPD says garages under 3.3m by 7.0m inside don't count on new developments, but it isn't applied retrospectively. What matters for an existing house is any condition on its original permission, so ask the council for the decision notice.
Will our car fit on the drive once the garage door is bricked up?
Measure it. The council's standard bay is 2.5m by 5.0m, plus 0.3m of width for each side boxed in by a wall or fence, and the car mustn't overhang the boundary. A short drive is a good reason to keep part of the garage.
We live near Boulters Lock. Is a garage bedroom a sensible idea?
Check the flood map for your plot first. In Flood Zone 2 or 3, a ground-level bedroom is the room most exposed, and any work needing planning permission there will need a flood risk assessment.
Can we put a window where the garage door is on Ray Park Avenue?
Talk to the council first. The street is in the Maidenhead Riverside conservation area, and extra controls on street-facing doors and windows were proposed for the Ray Lodge estate. Ask whether a direction covers your house.