Glossary
Class AA upward extension
Class AA allows certain upward extensions of houses in England (adding storeys) as permitted development, subject to strict limits and a prior-approval process covering design, amenity and transport impacts.
Conservation areas, listed buildings and Article 4 directions often block or limit this route.
Class AA is an England GPDO right; other nations do not mirror it identically.
Official source: Upward extensions guidance (GOV.UK). Checked 27 October 2026.