Side extension planning permission and permitted development

A side extension may qualify as permitted development in England, but there is no single width measurement that guarantees it. Check the original house, the full proposed enlargement and restrictions affecting the address together.

What are the main side extension limits?

Under householder Class A, an extension beyond an original side wall must be single storey, no higher than 4 metres and no wider than half the original house. Eaves must not exceed 3 metres where the enlargement is within 2 metres of the boundary.

Side extensions are excluded from these rights on designated land, including conservation areas. Further limits concern highway-facing elevations, materials, site coverage and other details. Flats do not have these householder rights.

These are selected tests from the government's householder technical guidance, which includes diagrams and the full conditions.

Does a side return count as a rear extension?

An extension beyond both original side and rear walls must satisfy both sets of rules. Joined existing extensions count when assessing the combined enlargement. Describing a proposal as a “side return” or building it in stages does not avoid those tests.

Read the rear extension planning guide alongside the side limits if your project wraps around the house.

How should you prepare the initial check?

Use an existing floor plan to mark the original walls, previous additions and the new footprint in different colours. Include the proposed roof profile and the distance to the boundary. Photographs from the street and garden help explain a corner plot or an irregular house shape.

Find your council's planning register and collect earlier decision notices. Flag any condition or Article 4 direction that may restrict the relevant right. Record uncertainties rather than treating missing history as evidence that the house has never been extended.

What if the proposal does not qualify?

A planning application is a separate route. Prepare a brief explaining the space you need, the proposed height and the relationship to neighbouring windows and gardens. That gives a designer something concrete to assess against local policy rather than simply trimming the drawing to a headline limit.

Start a property check or read the permitted development overview. If you want formal evidence that a qualifying design is lawful, consider a proposed lawful development certificate. Check building regulations separately before construction.

What does our planning service cost?

Phase 1 planning drawings and application support for a standard single-storey side extension start from £995, paid only when you are approved under an agreed pay-on-approval service. Wraparound, two-storey and combined schemes need an individual quote. Building regulations is a separate later stage, quoted individually. Council and Portal charges are separate.

Read our pricing and scope before instruction; we confirm the fixed fee for your project in writing.