Architects in Hillingdon

Hillingdon's semi-detached and detached houses on generous plots suit wrap-around and two-storey extensions, larger lofts and replacement homes. Its conservation areas and Areas of Special Local Character need a more careful approach to roofs and frontages.

Hillingdon's householder rules sit in policy DMHD 1 of its Local Plan Part 2, and its conversion rules are among the strictest in outer London.

Planning context in Hillingdon

• Householder extensions are assessed against Local Plan Part 2 policy DMHD 1, Alterations and Extensions to Residential Dwellings (adopted January 2020). Source
• Converting a house into flats needs an original internal floor area of at least 120 sq m, one unit per floor, and no more than 10% of a street converted (policy DMH 4). Source
• A borough-wide Article 4 direction has required planning permission for small HMOs since 11 December 2025. Source
• Additional HMO licensing for smaller HMOs started in August 2026, with a fee of £1,401 for a five-year licence. Source
• Hillingdon has 31 conservation areas. Source

Checked October 2026. Policy changes frequently; we confirm the position for your address at the outset of every project.