Barnet's new extension guidance leans on permitted development: it tells owners to use their rights for a rear dormer or hip to gable where they exist. A certificate is how you prove you did.
Barnet's Sustainable Design and Development Guidance SPD, adopted on 15 June 2026, keeps pointing owners back to their permitted development rights. Paragraph 4.83 says original hipped roofs can be converted to gables under permitted development. Paragraph 4.86 says that where rights exist at the house, an owner can exercise them for a rear dormer within the limits. Paragraph 4.94 says the same for an L-shaped dormer, provided the outrigger is part of the original house.
That makes the certificate the natural partner to a Barnet loft. Building under permitted development without one leaves nothing on the planning register to show the work was lawful. A buyer's solicitor will ask, and the honest answer then is a retrospective certificate with photographs instead of drawings. Applying first means the volume, materials and set-backs are confirmed before the roof comes off.
Barnet's page on whether you need planning permission says simply that if you would like formal confirmation your proposal falls under permitted development, you should apply for a certificate of lawful development, and the council decides whether it should be granted. The council fee for a proposed-use certificate is half of the planning fee for the same work.
Four common cases, checked against Barnet's own pages.
| Project | Route | Barnet source |
|---|---|---|
| Hip to gable on a house with rights | Certificate | SPD paragraph 4.83 |
| Rear dormer within Class B | Certificate | SPD paragraph 4.86 |
| Rear extension 3 to 6 m (4 to 8 m detached) | Larger home extension prior approval | Do I need planning permission page |
| House to small HMO | Planning permission | Article 4 since 29 May 2016 |
Barnet Council planning pages and SPD Part 4, read 25 October 2026.
The fee includes our measured visit. The bracketed figure applies if you already have measured drawings.
Three situations rule a certificate out. The first is a conservation area: Barnet lists 16, including Hampstead Garden Suburb, Mill Hill and Totteridge, and 10 are covered by Article 4 directions. Roof extensions under Class B are not permitted development in any conservation area, and Barnet says a single-storey rear extension in one needs a householder application rather than prior approval.
The second is a change of use. Since 29 May 2016 planning permission has been required anywhere in Barnet to turn a family house into a small house in multiple occupation, so no certificate can be issued for that change. The third is a deeper rear extension: between 3 and 6 metres on a terrace or semi, or 4 and 8 metres on a detached house, the route is the larger home extension prior approval, where work cannot start until Barnet replies or 42 days pass.
For example, a 1930s semi in Edgware with a hip to gable and a 48 cubic metre rear dormer fits inside the 50 cubic metre allowance and suits a certificate. Barnet decided 1,136 householder applications in the year to June 2026 with prior approvals set aside, 1,081 of them inside 8 weeks.
Every figure is linked to the page or document we read.
Barnet's SPD of 15 June 2026 says owners with permitted development rights can exercise them for a rear dormer within the limits of permitted development.
Source: Barnet Council, SPD Part 4, paragraph 4.86Barnet says a larger home extension under prior approval cannot start until the council replies or 42 days pass, and in a conservation area a householder application is needed.
Source: Barnet Council, Do I need planning permission?Since 29 May 2016 planning permission has been required anywhere in Barnet to change a house (C3) into a small house in multiple occupation (C4).
Source: Barnet Council, Article 4 Directions in BarnetBarnet lists 16 conservation areas, and 10 of them are covered by or have Article 4 directions in force.
Source: Barnet Council, Conservation areasThe council must decide a lawful development certificate within 8 weeks, and the fee for a proposed-use certificate is 50% of the planning fee.
Source: GOV.UK, Fees for planning applicationsBarnet decided 1,136 householder applications between July 2025 and June 2026, prior approvals excluded, and 1,081 of them were decided within 8 weeks.
Source: MHCLG, Planning application statistics PS2, July 2025 to June 2026Class B permits a roof extension of up to 40 cubic metres on a terraced house and 50 cubic metres in any other case.
Source: legislation.gov.uk, GPDO 2015, Schedule 2, Part 1, Class BTell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
It is not compulsory. Barnet says that if you would like formal confirmation that your proposal falls under permitted development, you should apply for one. It is the document a buyer's solicitor will ask for when a loft or extension has no planning history.
Usually yes, outside a conservation area. Barnet's June 2026 SPD says original hipped roofs can be converted to gables under permitted development, and the certificate confirms the volume stays within 50 cubic metres on a semi or detached house.
No. A single-storey extension deeper than 3 metres on a terrace or semi, or 4 on a detached house, goes through the larger home extension prior approval. Barnet must reply, or 42 days must pass, before work starts, and it is not available in conservation areas.
No. An Article 4 direction has required planning permission anywhere in Barnet since 29 May 2016 to change a house (C3) into a small house in multiple occupation (C4), so a full planning application is needed instead.
£715 inc survey (£515 if you supply measured drawings). That covers the measured survey, the drawings and the application. Barnet's own fee is separate and goes to the council.
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