Does it add value?
Usually, but not always by more than it costs. Nationwide's October 2025 house price research found that a 10% increase in floor area is associated with roughly 5% higher value, all else equal. An extension that creates a bedroom adds more than one that creates the same area of living space.
How to judge it for your house
Look at what extended houses on your street have sold for, ask a local agent for the ceiling price, and compare the uplift in pounds with the whole project cost, including fees and the kitchen. On streets where every house is extended, an unextended house can be worth less than its neighbours.
What adds the most?
A kitchen-diner opening to the garden, a downstairs WC or utility, and a layout that works for families. Over-specified extensions on modest streets rarely return their cost.
About this guide
Written by the Rear Extensions design team and checked against GOV.UK, Welsh and Scottish Government and Northern Ireland guidance in November 2026. It is general guidance, not legal advice; we confirm the rules for your house at the survey.