House Extension Cost in Muswell Hill: 2026 Price Guide

Plenty of homeowners in Muswell Hill skip the kitchen-only extension and go straight for a side-return infill or a double-storey addition, adding genuine square footage rather than moving house - a particularly obvious choice on terraces where the side return would otherwise sit unused.

Typical costs

• Side return infill: roughly £25,000-£40,000
• Single-storey rear extension: roughly £35,000-£70,000
• Double-storey extension: roughly £70,000-£130,000+

A double-storey extension isn't simply double the cost of a single-storey one - the roof, foundations and scaffolding are a large fixed cost, so the additional storey is often better value per square metre.

What affects the price locally

Muswell Hill sits within the London Borough of Haringey, and a meaningful share of its housing stock falls inside the Muswell Hill conservation area - designated in 1974 and one of the largest in London - plus the Fortis Green and Rookfield Estate conservation areas - which affects both what you're allowed to build and what materials you're expected to use. Matching original brick, slate or stone detailing on an extension in a conservation area typically costs more than a standard modern finish, and can extend the planning timeline too.

Access is again a factor on the tighter terraced streets: scaffolding, skips and material deliveries on narrow roads near Alexandra Palace often need council permits, which a local builder will usually have already dealt with before.

Planning permission

Side return and single-storey rear extensions often qualify for permitted development if they stay within set size limits, but double-storey extensions almost always need full planning permission from the London Borough of Haringey. Get a pre-application check if your street falls within a conservation area - it's a small upfront cost that can save a redesign later.