For a council-specific deep dive on Barnet borough and Hertsmere, see our Barnet planning permission guide. This page covers the underlying rules.
Permitted Development for Lofts
Your loft conversion is likely permitted development if:
- Volume added is under 40m³ (terraced) or 50m³ (semi/detached)
- No part of the conversion is higher than the existing roof's highest point
- Rear dormers don't extend beyond the rear wall plane
- No balconies, verandas or roof terraces
- Side windows are obscure-glazed and non-opening below 1.7m
- Materials are similar in appearance to the existing house
- The property is not in a conservation area, AONB, or subject to Article 4
- The property is a house (not a flat or maisonette)
When You Need Planning
- Mansards (change roof profile)
- L-shaped dormers (usually exceed volume)
- Conservation area properties
- Listed buildings (also need Listed Building Consent)
- Flats and maisonettes
Applying for Planning
The specialist typically submits the application on your behalf, with drawings prepared by their architect or in-house team. Application fee in Barnet/Hertsmere is ~£258. Determination: 8 weeks target.
Lawful Development Certificate
For permitted-development conversions, it's worth applying for a Lawful Development Certificate from the council (~£128, 8-week determination). This is council confirmation that your conversion meets PD rules — important for future buyers and conveyancing.