If your garage, garden room, or outbuilding falls outside permitted development rights, the fee is the same flat £548 householder application rate that applies to house extensions. Most detached garages and garden buildings, though, don’t need planning permission at all, provided they meet a specific set of height, position, and coverage rules.
The fee question here is really a permitted development question first. Get that right, and the £548 often never applies.
👉 Use the calculator to confirm your exact fee
The rule most people don’t realise: attached vs detached
This is the distinction that trips up more homeowners than any single measurement:
- Detached garage or outbuilding (freestanding, separate from the house) — governed by Class E, the “outbuildings” rules
- Attached garage (built onto the side of the house, sharing a wall) — governed by Class A, the same rules that apply to house extensions
A detached garage can be up to 4m tall under permitted development; an attached one is instead assessed under extension rules — depth and height relative to the original house, not a flat metre cap. Two garages that look almost identical from the street can be judged under entirely different rule sets depending on whether that shared wall exists.
Permitted development limits for detached garages/outbuildings
Provided none of the exclusions below apply, a detached garage, garden room, shed, or similar outbuilding is usually permitted development if it meets all of the following:
- Height: up to 4m with a dual-pitched roof, 3m for any other roof shape
- Near a boundary: if any part is within 2 metres of the boundary, the whole structure is capped at 2.5m
- Position: must not project forward of the principal elevation — a garage in the front garden always needs planning permission, no exceptions
- Single storey only
- Coverage: combined with every other outbuilding already on the plot, must not cover more than 50% of the land around the “original house”
The “original house” date that catches people out
That 50% coverage limit isn’t measured against your garden as it exists today — it’s measured against the house as it was first built, or as it stood on 1 July 1948 if built earlier. If a previous owner already added a shed, garage, conservatory, or extension, that eats into your allowance before you’ve built anything new. Worth checking the property’s planning history with the local council before assuming the full 50% is available — a genuinely common reason “surely this is permitted development” projects end up needing the £548 application anyway.
Attached garages and party wall considerations
Because an attached garage shares a wall with the house (or sits immediately beside it), building close to a boundary shared with a neighbour can also trigger the Party Wall Act 1996 — a separate legal process from planning permission entirely, with its own notice requirements and potential surveyor costs. This applies regardless of whether planning permission itself was needed, and it’s a step several guides skip mentioning until after the planning stage, when it’s better addressed early.
Worked example
A semi-detached house has an existing 6m² garden shed. The owner wants to add a detached garden office measuring 18m², positioned 1.5 metres from the side boundary.
- Height check: within 2m of the boundary, so capped at 2.5m — a common design compromise, since many garden offices are designed for the fuller 4m/3m allowance available further from a boundary
- Coverage check: shed (6m²) + new office (18m²) = 24m², checked against 50% of the original plot’s garden area
- Result: if height and coverage both pass, no £548 fee applies
Move that same office to within 1 metre of a rear boundary at 3m tall, and it exceeds the 2.5m near-boundary cap, triggering the need for a full householder application.
Garage conversions are a different question entirely
Converting an existing garage into a habitable room is usually a permitted development matter and doesn’t typically require planning permission — but it always requires building regulations approval, a separate consent with its own cost, regardless of whether planning permission was needed.
When you definitely need the £548 fee
- The garage or outbuilding is in front of the house
- It’s a two-storey structure
- It exceeds the height or coverage limits above
- The property is in a Conservation Area, AONB, National Park, or is listed (Article 4 Directions can remove these rights locally too — worth checking with your specific council)
- You intend to use it for sleeping accommodation or as a self-contained annexe, which typically falls outside “incidental to the enjoyment of the dwelling” and out of permitted development altogether
For the official rules, see Planning Portal’s guidance on outbuildings.
Quick answer summary
- Detached garage/outbuilding within height, position, and coverage limits: £0 (permitted development)
- Attached garage, assessed under extension rules, within limits: £0
- Exceeds any limit, in the front garden, or on designated land: £548
- Garage conversion to habitable room: usually £0 planning fee, but building regulations approval still required separately
Use the calculator above once you’ve checked which category applies.