For most houses in Barnet the answer is no: a typical rear dormer or rooflight conversion can be built under permitted development rights without a planning application. The exceptions matter, though, and the borough has more of them than many people expect. Here is how to work out which side of the line your home falls on before you spend money on drawings.
Permitted development is a set of national rules that lets you extend a house without applying to Barnet Council for planning permission, provided the design stays inside fixed limits. Most of the 1930s semis and terraces in places like East Barnet, Finchley, Whetstone and Edgware can take a rear dormer within these limits.
The main conditions are:
Permitted development rights apply to houses only. If you live in a flat or maisonette, including the converted Victorian and Edwardian houses common around Finchley, Golders Green and Hendon, you need full planning permission for any loft conversion, and usually the freeholder's consent as well.
Barnet also has a number of conservation areas where roof extensions are not permitted development. These include Hampstead Garden Suburb, Monken Hadley, Totteridge, Mill Hill, Wood Street in High Barnet, Finchley Church End and the Watling Estate in Burnt Oak. Hampstead Garden Suburb has extra controls on top, so even small external changes such as rooflights can need consent there. Listed buildings need listed building consent whatever the design.
You will also need to apply if your design goes over the volume limits, puts a dormer on the front, or raises the ridge. Some newer estates and previously extended homes have had their permitted development rights removed by a condition on an earlier permission, so it is worth checking the planning history for your address on the council's website.
If you do need permission, a householder application currently costs a little over £500 and the council aims to decide within eight weeks. Allow more time in practice for drawings, validation and any revisions.
Barnet's Residential Design Guidance is the document planners use. It expects dormers to sit comfortably within the roof rather than dominate it, which generally means no more than about half the width and half the depth of the roof slope, set in from the edges and below the ridge. This is noticeably smaller than what permitted development allows, so a house that qualifies for permitted development can often get a bigger dormer by that route than through an application. Overlooking of neighbours and the look of the street are the other main considerations.
If your conversion is permitted development, you are not obliged to tell the planning department. We would still recommend applying to Barnet for a Lawful Development Certificate. It costs roughly half the householder fee, usually takes up to eight weeks, and gives you written confirmation that the work is lawful.
That piece of paper is useful when you sell or remortgage, because solicitors will ask for it. It also protects you if a neighbour complains once the scaffolding goes up.
Planning is only one part of the picture. Every loft conversion needs building regulations approval, covering the new floor structure, the staircase, fire doors and escape routes, insulation and sound separation. As a rule of thumb you want around 2.2 metres from the top of the existing ceiling joists to the underside of the ridge for a workable room.
On a semi or terrace, steel beams normally bear on the shared wall, so you must serve a party wall notice on the adjoining owner, ideally at least two months before work starts. Building work on the loft itself typically takes 8 to 12 weeks, so with approvals included most projects run to five or six months from first drawings to completion.
Barnet Council publishes maps of its conservation areas and Article 4 directions on its website, and you can search your address on the planning pages. If you are near a boundary, the planning department can confirm in writing.
Not under permitted development, so you would need a planning application. Barnet rarely approves front dormers unless they are already a feature of the street, which is why most conversions use front rooflights and a rear dormer.
Usually yes on a semi-detached or detached house outside a conservation area, as long as the total added volume including any rear dormer stays within 50 cubic metres. It is one of the most common ways to gain usable space on Barnet's 1930s semis.
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