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Guide · Garage conversions

Garage Conversion Planning Permission and Building Regulations

When a garage conversion needs planning permission under section 55 of the 1990 Act, how conditions and Article 4 directions change that, and what building regulations Parts L, B, C, F and A require.

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Converting an attached or integral garage often needs no planning permission, because section 55(2)(a) of the Town and Country Planning Act 1990 says works affecting only the interior, or not materially affecting the external appearance, are not development. Replacing the garage door is the usual exception. Five building regulations parts (L, B, C, F and A) apply either way.

Planning and building regulations are separate regimes, and the regulations apply whether or not planning does. This guide takes planning first, then the five parts.

Key Takeaways

  • Internal works are not development under section 55(2)(a). A new wall or window in the old door opening may be, and then Class A of the General Permitted Development Order usually covers it.
  • Conditions on the original permission and Article 4 directions can remove those rights, so check both.
  • Garage conversion is a "change to energy status" under Approved Document L, so retained walls, floor and roof must meet stated U-values.
  • A new ground-floor habitable room needs escape, ventilation, a damp-proof floor and structural support for any new wall.

Do you need planning permission to convert a garage?

Often not. Section 55(1) defines development as building operations or a material change of use, and section 55(2)(a) removes works that affect only the interior of a building or do not materially affect its external appearance. Section 55(2)(d) also removes using buildings in the curtilage of a dwellinghouse for purposes incidental to the house.

Removing a partition, lining walls and laying a floor is not development. The question is the front elevation. Bricking up the garage door and adding a window changes how the house looks, and whether that materially affects its appearance is for the council to judge. Pushing the front wall out is an enlargement, and paragraph A.1(e) of Class A bars an enlarged part extending beyond the principal elevation of the original house.

Does a new window or infill wall need permission?

Usually not, because Class A of Part 1 permits the "enlargement, improvement or other alteration" of a dwellinghouse, and the government's technical guidance lists new windows and doors as general alterations. The main condition is paragraph A.3(a): exterior materials must be of similar appearance to those on the existing house.

The guidance says this means similar colour and style of brick, and similar window shape, colour and frame size, not identical materials. In a conservation area or other article 2(3) land, paragraph A.2(a) adds that Class A does not permit cladding in stone, artificial stone, pebble dash, render, timber, plastic or tiles. If your infill wall is to be rendered, check that first.

Can a condition on your planning permission stop the conversion?

Yes. Article 3(4) says nothing in the Order permits development contrary to a condition imposed on a planning permission. If the permission for your house or estate withdrew rights or required the garage to stay available, read the decision notice before drawing anything.

Planning guidance says a condition restricting permitted development rights has to be precisely defined by reference to the relevant provisions of the Order, and that blanket removal of small domestic alterations is unlikely to meet the tests of reasonableness and necessity (Use of planning conditions, paragraph 017). That is the council's test to apply, not yours to rely on, so raise any condition with the council first.

What does an Article 4 direction change?

Article 4 lets a council, or the Secretary of State, direct that permission under Schedule 2 does not apply to a Part, Class or paragraph, either across an area or for a particular development. Where Class A is withdrawn, an external alteration that is development then needs a planning application.

The direction does not turn internal works into development, because section 55(2)(a) is in the Act, not the Order. What changes is the front elevation: the window, the door and the infill brickwork. Our London borough pages name each covered borough's Article 4 areas, and the permitted development checker will tell you plainly if you need no application.

What about a detached garage?

A detached garage is treated differently. The government's technical guidance puts attached buildings under Class A and detached buildings under Class E, which requires a purpose incidental to the house. That purpose does not cover self-contained accommodation or primary living accommodation, such as a bedroom, bathroom or kitchen, in an outbuilding.

On that reading, section 55(2)(d) is unlikely to protect a detached garage turned into a bedroom. Ask the council, or apply for a certificate of lawfulness, first. Using it for a purpose that stays incidental to the house is a different question.

What does Part L ask of a garage conversion?

Approved Document L, paragraph 11.6, states that when a previously unheated space becomes part of the heated dwelling in a garage or loft conversion, a change to energy status applies to that space. Paragraph 11.7 then requires retained elements to meet Table 4.3 and new elements to meet Table 4.2.

Element New or replaced (Table 4.2) Retained: threshold, then improved (Table 4.3)
Roof 0.15 0.35, improved to 0.16
Wall 0.18 0.70, improved to 0.55 (cavity) or 0.30 (internal or external insulation)
Floor 0.18 0.70, improved to 0.25
Window 1.4, or Window Energy Rating Band B Replace if above 3.30 and separating heated from unheated space or outside
Other doors 1.4, or Doorset Energy Rating Band B Same test as windows

W/(m²·K), from the 2021 edition of Approved Document L. An existing element worse than the threshold should be upgraded to the improved value. If that is not feasible, or would not pay back within 15 years, upgrade it to the lowest value that is, generally no worse than 0.7 (paragraph 4.13).

The 2026 edition takes effect on 24 March 2027 and carries the same limiting values in its Tables 3.2 and 3.3. See our Part L guide for the changeover.

What do Parts B, C, F and A add?

Part B concerns escape and alarms, Part C a damp-proof floor, Part F ventilation and Part A the structure around the old door. Each applies to the new room. Your building control body applies these figures to the actual drawings.

  • Part B (fire). A ground-storey habitable room needs an opening onto a hall leading to a final exit, or an escape window or door (Approved Document B Volume 1, paragraph 2.1). An escape window needs 0.33m² openable area, at least 450mm by 450mm, with its bottom no more than 1100mm above the floor (2.10). A new ground-storey habitable room without a final exit also needs a fire detection and alarm system (1.8(b)). Any part that stays a garage needs REI 30 separation and an E 30 Sa self-closing door (5.6, Diagram 5.1).
  • Part C (moisture). A concrete floor needs at least 100mm of concrete on hardcore no deeper than 600mm, with a damp-proof membrane continuous with the damp-proof courses in the walls. Polythene membranes should be at least 300µm thick with sealed joints (Approved Document C, 4.7 and 4.8).
  • Part F (ventilation). Purge ventilation must give four air changes an hour; a window opening at 30 degrees or more needs an openable area of at least 1/20 of the floor area (Approved Document F Volume 1, 1.27 and Table 1.4). Whole-dwelling supply must meet both 0.3 litres a second per square metre of internal floor area and the bedroom minimum, 31 for three bedrooms and 37 for four (1.24, Table 1.3).
  • Part A (structure). Requirement A1 says loads must reach the ground safely. Approved Document A assumes wall loads are distributed where lintels bear at least 150mm, or 100mm for a clear span of 1200mm or less (2C24(a)). Its minimum strip foundation depth is 0.45m, or 0.75m, 0.9m or 1.0m on low, medium or high shrinkage clay (2E4).

What does a garage conversion cost?

Our garage conversion drawings cost from £695, and building regulations drawings are £795. The council fee is £548 if a householder application is needed, or £274 for a certificate for a proposed use or operation, which is half the full fee. Our own certificate service is from £950.

Council fees are paid to the council and are never part of our price. Beams over a widened opening need calculations, and our service is from £495. See the garage conversions page, our lawful development certificate guide and the Part B guide.

What else do people ask about garage conversions?

Most questions come down to the front wall and to whether the regulations apply. The interior of an attached garage is free of planning control, the front elevation sometimes is not, and the building regulations apply to the converted room in every case.

Do I need building regulations approval if I do not need planning permission?

Yes. Planning and the regulations are separate, and the five parts above are the ones that usually apply to the new room, depending on the work.

Does it matter whether the garage is integral, attached or detached?

For planning, yes: attached buildings fall under Class A and detached ones under Class E, as above. The building regulations apply to the converted room either way.

Where do these figures come from?

Every figure comes from legislation.gov.uk or a gov.uk document, fetched on 10 October 2026. The Act and Order supply the planning rules, the Approved Documents supply the building regulations figures, and the fees table supports the council fees. The links show where each sits.

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