The permitted development rules in detail
Under Class B of the Town and Country Planning (General Permitted Development) Order 2015, you can enlarge a dwellinghouse's roof by adding volume without planning, subject to: a maximum cubic content addition of 40m³ for terraced houses or 50m³ for semi-detached and detached houses (measured externally); no extension beyond the plane of the existing roof slope on the principal elevation (i.e. no front dormers visible from the highway under PD); rear and side dormers permitted if they do not exceed the highest part of the existing roof and are set back at least 20cm from the eaves; materials of similar appearance to the existing house; and the loft conversion must not result in the property having a separate, self-contained unit (i.e. cannot be used to create a flat).
Properties that cannot use PD for loft conversions
Permitted development rights are not available on: flats and maisonettes (no PD rights for any extension under Class A or B); listed buildings (any external alteration needs Listed Building Consent regardless of PD); conservation areas (PD rights for roof extensions are removed in conservation areas — any dormer visible from the public highway needs full planning); Article 4 Direction zones (local councils can remove PD rights for specific design reasons — common in conservation areas and design-sensitive zones); properties where PD has been removed by planning condition (some newer builds had PD removed when planning was originally granted). Builderr checks all these at the survey stage — we have a planning eligibility check process that runs the property against every restriction before we quote.
How to confirm your loft conversion qualifies for PD
There are three steps to confirm PD eligibility for your property: (1) Check that the property is a house (not a flat) and is not in any of the excluded categories — listed building, conservation area, Article 4 zone. The Planning Portal's interactive house guide is a good starting point; your local council's planning policy map shows conservation areas. (2) Check the design fits within the PD rules — volume, height, materials, no front dormer. The design needs to be drawn to scale and the proposed cubic content calculated. (3) Apply for a Lawful Development Certificate to obtain a formal written confirmation from the council that the proposed works are lawful. The LDC is not legally required but is strongly recommended — it gives you a permanent, bankable record useful on sale and against future enforcement risks.
