Most loft conversions in England do not need planning permission. They are permitted development under Class B if they add no more than 40m³ (terrace) or 50m³ (other houses), stay below the existing ridge, avoid a front roof slope facing a highway, and the house is not a flat or in a conservation area. Building regulations always apply.
Class B covers anything that enlarges the roof, such as a rear dormer or a hip-to-gable. Roof windows fall under Class C, with lighter limits. Every limit below comes from the General Permitted Development Order 2015 (GPDO) or the government's guidance on it.
What are the loft conversion permitted development limits?
A loft conversion is permitted development when it meets every limit and condition in Class B of the GPDO, and the house sits on land where the right applies. Fail one and you need planning permission for the whole enlargement. The table sets each limit against its source in the Order.
| Limit or condition | What the Order says | Source |
|---|---|---|
| Volume added | No more than 40m³ for a terrace house, 50m³ for any other house | Sch 2 Pt 1, B.1(d) |
| Height | No part higher than the highest part of the existing roof | B.1(b) |
| Front roof slope | Nothing may extend beyond the plane of a roof slope on the principal elevation that fronts a highway | B.1(c) |
| Balcony or platform | No verandah, balcony or raised platform (a platform higher than 0.3m) | B.1(e)(i) and para I |
| Chimney, flue, soil and vent pipe | No installation, alteration or replacement | B.1(e)(ii) |
| Protected land | Not available on article 2(3) land: conservation areas, National Parks, AONBs, the Broads, World Heritage Sites | B.1(f) and Sch 1 Pt 1 |
| How the house came about | Not for houses created under Part 3 change-of-use rights or Part 20, or already enlarged under Class AA | B.1(a), (g), (h) |
| Materials | Similar appearance to the existing house | B.2(a) |
| Eaves | Original eaves kept or reinstated, and the enlargement at least 0.2m up the slope, so far as practicable | B.2(b)(i) |
| Outside wall face | Nothing beyond the outside face of an original external wall | B.2(b)(ii) |
| Side windows | Obscure-glazed, and non-opening unless the opening part is over 1.7m above the floor | B.2(c) |
| Flats and maisonettes | A "dwellinghouse" excludes a building containing flats, or a flat within one | Art 2(1) |
| Planning conditions | The Order permits nothing contrary to a condition on a planning permission | Art 3(4) |
Do I need planning permission for a loft conversion?
Usually not. A loft conversion that meets the Class B limits needs no planning application, and neither does one that only adds roof windows within Class C. You do need permission for a front dormer, an oversized enlargement, a balcony, or any loft in a flat, a conservation area or under an Article 4 direction.
Permitted development is a national grant of permission, so the council does not decide. The limits are exact: a dormer 1m³ over the allowance loses the right entirely.
Our free permitted development checker runs your project against these limits and says plainly when you need no application. It does not steer you towards a paid route.
How much roof space can a loft conversion add: 40m³ or 50m³?
A loft conversion can add up to 40 cubic metres of roof space to a terrace house and up to 50 cubic metres to any other house (B.1(d)). An end-of-terrace house counts as a terrace house, so it takes 40m³, as long as the row has three or more houses.
The Order's definition of "terrace house" is a house in a row of three or more used or designed for use as single dwellings, sharing a party wall or adjoining main wall with the house on either side. A house at the end of a row qualifies if it adjoins one that does (Sch 2 Pt 1, interpretation).
Every earlier enlargement of the roof space counts against the allowance, whether or not it was permitted development (B.3). The comparison is with the original roof space: the house as it stood on 1 July 1948, or as built if later (article 2, "original"). The government's guidance says any previous enlargement in any part of the house must be included.
Suppose, hypothetically, that a previous owner built an 18m³ rear dormer on a semi-detached house. A new hip-to-gable could then add no more than 32m³. The Order gives no method for measuring volume, so work from a measured survey. Our loft conversions page has a volume gauge showing how the allowance is used up.
Can I put a dormer on the front of the house?
No. A dormer or any other roof enlargement cannot extend beyond the plane of a roof slope on the principal elevation that fronts a highway (B.1(c)), so a front dormer always needs planning permission. Rear and side slopes are not caught by that rule, and front roof windows can still fall under Class C.
A highway includes an unadopted street or a private way. The government's guidance adds that the principal elevation can include more than one roof slope facing the same way, as with a bay window or an L-shaped front.
What are the permitted development limits for a dormer?
A dormer must stay below the ridge, sit at least 0.2m up the slope from the eaves where practicable, stay within the outside face of the original wall, use similar-looking materials, and have obscure-glazed side windows. It must also add no balcony or raised platform. All of these come from Class B.
The height limit uses the main ridge; chimneys, firewalls and parapets are ignored (technical guidance, Class B). The 0.2m is measured along the slope from the outer edge of the tiles or slates, not the horizontal, and guttering is excluded. "So far as practicable" is not a loophole: the guidance expects the set-back unless practical or structural reasons prevent it, for example where a side dormer joins a dormer on the main roof.
Materials need only look similar from the ground; the guidance accepts felt, lead or zinc on a dormer's flat roof.
Side windows follow a fixed rule (B.2(c)). They must be obscure-glazed, and the guidance says to level 3 on the usual one-to-five privacy scale. One-way glass does not count. They must also be fixed shut unless the opening part is more than 1.7m above the floor.
Does a hip-to-gable loft conversion need planning permission?
Not if it fits Class B. A hip-to-gable conversion, which replaces a sloping side with a vertical gable wall, is permitted development within the same volume, height and front-slope limits. The 0.2m eaves set-back does not apply to it (B.2(b)(i)).
That exemption is narrow. The added volume still counts in full against 40m³ or 50m³, the gable wall must not project beyond the outside face of the original wall (B.2(b)(ii)), and the work cannot rise above the existing ridge. A hip-to-gable and a rear dormer can be combined if the total stays inside the allowance.
A mansard is judged the same way. Class B applies to any enlargement of the roof, whatever the design is called, so test it against the same limits. Many mansards will struggle with the eaves set-back or the front-slope rule, so check before assuming permitted development.
Do roof windows need planning permission?
Usually not. Roof windows fall under Class C, which allows them if they protrude no more than 0.15m beyond the plane of the original roof slope and are no higher than its highest part. Class C has no conservation area exclusion, but side-slope windows must be obscure-glazed and non-opening unless the opening part is more than 1.7m above the floor.
Those limits are in Class C, paragraph C.1(b) and (c), and the side-slope window condition is C.2 (GPDO Sch 2 Pt 1). A conversion lit only by roof windows, with no dormer, therefore often needs no planning application even in a conservation area. Class C does not cover chimney, flue or solar panel work (C.1(d)). Article 4 directions and listed building controls can still apply.
Does permitted development apply in conservation areas, to flats, or under an Article 4 direction?
No to all three. Class B is unavailable on article 2(3) land, which includes conservation areas. Flats and maisonettes have no Part 1 rights, because a "dwellinghouse" excludes them. An Article 4 direction can withdraw Class B locally, and a planning condition can remove it for one house.
- Conservation areas, National Parks, AONBs, the Broads, World Heritage Sites: Class B does not apply (B.1(f), Schedule 1 Part 1). A loft dormer needs planning permission there. Roof windows under Class C are the exception.
- Flats and maisonettes: The definition of "dwellinghouse" in article 2(1) excludes a building containing flats or a flat within one, and the guidance says to seek planning permission for flats.
- Article 4 directions: Under article 4, the council can direct that specified permitted development needs an application. Check with the council before you design. Our London borough pages record each borough's Article 4 areas.
- Planning conditions: Article 3(4) stops the Order permitting development contrary to a condition on the house's planning permission.
- Listed buildings: Permitted development does not replace listed building consent. Under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990, altering a listed building in a way that affects its character needs authorisation.
Do I need a certificate of lawfulness for a loft conversion?
No, it is optional. A certificate of lawfulness for proposed work is not required to use permitted development, but it gives a buyer, lender or solicitor written proof that the loft was lawful. The council fee is £274, and our service fee is from £950.
The council charges the fee on submission. Our certificate of lawfulness service prepares the application with the volume calculation and drawings. It is most useful when you plan to sell, because it answers a buyer's solicitor in writing.
If the council decides the loft is not permitted development, you find out before the builders start. See our guide to planning permission fees in England for how this fee fits with the others.
Do I need building regulations approval for a loft conversion?
Yes, always. Permitted development covers planning only. A loft conversion is building work under regulation 3 of the Building Regulations 2010, and it must meet the structure requirement (Part A) and the fire safety requirement (Part B), whatever route you take for planning.
Regulation 3 treats the extension or material alteration of a building as building work, and an alteration is material if it affects compliance with requirements including Part A and paragraph B1 (regulation 3). The householder guidance says permitted development rights do not remove the need for building regulations or Party Wall Act consents.
The fire rules usually shape the layout. In Approved Document B, Volume 1 (2019 edition incorporating the 2020, 2022, 2025 and 2026 amendments, and also showing forthcoming 2029 changes), paragraph 2.21 applies when a new storey is created above 4.5m. The full escape route must be addressed, with fire-resisting doors (minimum E 20) and partitions (minimum REI 30). Paragraph 2.6 adds that a house with two or more storeys above 4.5m needs a protected stairway plus either an alternative escape route from each storey above 7.5m or a sprinkler system to BS 9251.
Measure from your survey, as the heights depend on the new floor level. Our Part B fire safety guide walks through the escape route, and beams, trimmers and floor joists need calculations: ours are from £495.
Do I need a party wall notice for a loft conversion?
Often, yes, if the house is semi-detached or terraced. The Party Wall etc. Act 1996 is separate from planning and building regulations. A steel beam bearing into a shared wall, or cutting into it, is work to a party structure that needs a notice at least two months before it starts.
The right to cut into a party wall is in section 2 of the Act, and section 3 requires a party structure notice at least two months before work starts. The government's Party Wall guidance has an explanatory booklet and example notice letters. Our Party Wall Act guide sets out the notice periods.
What does a loft conversion cost to get approved?
If your loft fits Class B you need no planning application. Building regulations drawings are £795 with us. If it needs permission, for example because of a front dormer or a conservation area, our complete planning drawing service is £895, plus the council's £548 householder fee.
Our fees are published on the pricing page, with the council's charges shown separately and passed on at cost. The loft conversions page sets out the whole sequence from survey to building control sign-off.
What else do people ask about loft conversion planning permission?
Two questions come up often once the main rules are clear: whether a Juliet balcony counts as a balcony, and what happens if a finished loft turns out to be slightly over the limits. Both are answered from the sources below.
Can I add a Juliet balcony?
Usually yes. The government's guidance says a Juliet balcony, with no platform and so no external access, would normally be permitted development. A balcony proper, or any raised platform higher than 0.3m, is not (B.1(e)(i)).
What happens if I exceed the limits by a small amount?
The enlargement is no longer permitted development, so the whole thing needs planning permission. There is no tolerance in Class B. If it is already built, the usual routes are a retrospective application or a redesign to fit the limits.
Where do these figures come from?
Every rule is from legislation.gov.uk, GOV.UK guidance or Approved Document B, read on 14 October 2026. The GPDO text is the live consolidated version.
- General Permitted Development Order 2015, Schedule 2, Part 1, Classes B and C (B.1 to B.4, C.1, C.2) and the interpretation of Part 1 (terrace house, highway, raised platform): https://www.legislation.gov.uk/uksi/2015/596/schedule/2/part/1
- The Order, article 2 (dwellinghouse, original), article 3(4) and article 4, and Schedule 1 Part 1 (article 2(3) land): https://www.legislation.gov.uk/uksi/2015/596/article/2, https://www.legislation.gov.uk/uksi/2015/596/article/3, https://www.legislation.gov.uk/uksi/2015/596/article/4 and https://www.legislation.gov.uk/uksi/2015/596/schedule/1
- Permitted development rights for householders: technical guidance, 2019 (ridge height, 0.2m measurement, level 3 glazing, Juliet balconies, previous enlargements): https://assets.publishing.service.gov.uk/media/5d77afc8e5274a27cdb2c9e9/190910_Tech_Guide_for_publishing.pdf
- Building Regulations 2010, regulation 3: https://www.legislation.gov.uk/uksi/2010/2214/regulation/3
- Approved Document B, Volume 1, paragraphs 2.6 and 2.21: https://assets.publishing.service.gov.uk/media/6aa3bb335f6e942efe37f150/AD_B1_2026.pdf
- Planning (Listed Buildings and Conservation Areas) Act 1990, section 7: https://www.legislation.gov.uk/ukpga/1990/9/section/7
- Party Wall etc. Act 1996, sections 2 and 3, and GOV.UK guidance: https://www.legislation.gov.uk/ukpga/1996/40/section/2, https://www.legislation.gov.uk/ukpga/1996/40/section/3 and https://www.gov.uk/party-wall-etc-act-1996-guidance
- Planning fees from 1 April 2026 (householder £548, proposed-use certificate at half the fee): https://assets.publishing.service.gov.uk/media/69a073bb07d7bff3604d6df6/Planning_fees_-_annual_indexation_from_1_April_2026.pdf