A lot of people in Mill Hill and Barnet put off a loft conversion because they’re worried about the council. I understand it – nobody wants to spend money on drawings and then be told no. The good news is that most loft conversions on ordinary houses don’t need planning permission at all. Here’s how it actually works.
Most lofts are “permitted development”
Permitted development rights let you make certain changes to a house without applying for planning permission. For loft conversions, the main rules are:
- You can add up to 40 cubic metres of roof space on a terraced house, or 50 cubic metres on a semi-detached or detached house (that includes any previous roof extensions).
- No part of the extension can go higher than the existing ridge.
- No extension on the roof slope facing the road (so rear dormers are fine; front dormers usually aren’t).
- The dormer must be set back at least 20cm from the eaves.
- Materials should look similar to the existing house.
- Side windows must be obscure-glazed and non-opening below 1.7 metres from the floor.
- No balconies or raised platforms.
A standard rear dormer or a hip-to-gable on a 1930s semi in Mill Hill, Edgware or Finchley almost always fits inside these limits. That’s why we can often start a loft within weeks rather than months.
When you do need planning permission
Conservation areas. Barnet has a number of them – Mill Hill village, Monken Hadley, Totteridge, Hampstead Garden Suburb (which also has its own Trust with tighter rules) and others. In a conservation area, permitted development rights for roof extensions are removed, so you need a full application and the design will need to be sympathetic.
Flats and maisonettes. No permitted development rights – but we don’t take on flats anyway.
Article 4 directions. Some streets have had permitted development rights withdrawn by the council. It’s worth checking before you assume.
Listed buildings. Listed building consent is needed for pretty much anything.
Going over the volume limit, or a mansard. A big mansard that changes the shape of the whole roof will usually need an application.
Houses that have already been extended. If a previous owner added a large rear extension under permitted development, some of your allowance may already be used up.
Get a Lawful Development Certificate anyway
Even when a loft is permitted development, I always recommend applying to Barnet Council for a Lawful Development Certificate. It costs a modest fee, takes around eight weeks, and gives you a piece of paper proving the work was lawful. When you come to sell, the buyer’s solicitor will ask for it. Skipping it saves a little now and causes headaches later.
Planning permission is not the same as Building Regulations
This is the bit that catches people out. Whether or not you need planning permission, every loft conversion needs Building Regulations approval. Building Control checks the things that actually matter for safety: the structural steels and floor, fire escape and fire doors, smoke alarms, insulation, the staircase, sound insulation and so on. You can use Barnet’s own Building Control or an approved private inspector. We deal with this on every job – it’s routine for us, and you get a completion certificate at the end that you’ll need when you sell.
The Party Wall Act
If you’re in a semi or a terrace, the steels for the loft will almost certainly bear on the wall you share with your neighbour. That means serving a party wall notice, at least two months before the work starts. If your neighbour consents in writing, that’s it. If they don’t respond or dissent, a party wall surveyor is appointed to draw up an award. It sounds heavier than it is – we work with good local party wall surveyors and can point you to one.
What we do for you
When you ask us to quote for a loft in Barnet or anywhere in North-West London, we’ll tell you honestly whether we think it’s permitted development, whether you’re in a conservation area, and what approvals you’ll need. If you don’t already have an architect or structural engineer, we can introduce you to the ones we work with regularly. We’d rather spend twenty minutes getting the paperwork right at the start than have a problem halfway through.
Thinking about a loft? Get in touch through the contact page or give us a call (Monday to Friday, 10am–2pm) and we’ll arrange a free consultation.
Planning rules change from time to time and every property is different – this article is general guidance for houses in the London Borough of Barnet, not formal planning advice. Always check with the council or your architect for your specific property.