Home Extension Design in Haringey: Planning, Costs and What's Realistic in 2026

A home extension in Haringey typically costs £3,200 to £4,500 per m² to build in 2026, at mid-range specification, before VAT and professional fees. Whether you need planning permission depends less on the size of the extension than on the street: much of the borough is ordinary permitted-development territory, but Haringey's conservation areas and Article 4 Directions change the rules house by house. This page covers what the council allows, what it costs, and what we built for one Hornsey family for £140,000.

Studio MASS is a residential design practice led by an architectural technologist. We design and deliver extensions, loft conversions and refurbishments across London, from first feasibility check to completed build.

Do you need planning permission for an extension in Haringey?

Many Haringey extensions do not need planning permission. Outside conservation areas, a single-storey rear extension up to 3 metres beyond the original rear wall (4 metres on a detached house) usually falls under permitted development, as do most loft conversions within volume limits.

Inside a conservation area the position changes. Haringey requires planning permission for rear extensions beyond 3 metres, for any rear extension of more than one storey, and for side extensions. The council has also confirmed Article 4 Directions covering Noel Park, Peabody Cottages and Tower Gardens, which remove permitted development rights for smaller alterations such as window and door changes.

The practical rule: never assume permitted development applies in Haringey until someone has checked your street against the council's conservation area map and your property's planning history. That check is part of our Stage Zero review, before any design work starts.

How much does a home extension cost in Haringey in 2026?

Haringey sits in London's mid-price construction zone. From our 2026 Extension Cost Guide, built from BCIS indices, FMB build cost data and our own completed projects:

A single-storey extension in Haringey costs £3,200 to £4,500 per m² at mid specification in 2026. A loft conversion runs £3,200 to £3,800 per m². Conservation area projects carry roughly 15% on top for material restrictions and period-appropriate detailing. These figures are construction only; VAT at 20% and professional fees are additional.

Before a brick is laid, expect £8,000 to £16,000 in professional and statutory fees on a typical project, including the £548 planning application fee that applies from April 2026.

The full breakdown by extension type and specification level is in our free Extension Cost Guide 2026, no email required.

What does a real Haringey extension look like?

At Rathcoole Gardens in Hornsey, we designed a side-return kitchen extension and whole-house refresh of a Victorian terrace, built for £140,000 under permitted development, without a planning application. The project created a bright, open kitchen arranged around family life, and the full story, with real costs, is on the Rathcoole Gardens project page.

That project is also a useful caution against assuming you need planning permission. A good feasibility review sometimes shows the faster, cheaper consent route was available all along.

Who designs your extension if not an architect?

An architectural technologist designs buildings with a focus on how they are built: construction detail, building regulations, and buildability, alongside layout and light. In the UK "architect" is a legally protected title, so we don't use it. What matters for a Haringey extension is the same either way: design within the local planning context, technical drawings a builder can price accurately, and someone accountable from first idea to finished build. That is what we do, through one team and five stages, starting with a Stage Zero review that tells you what is realistic for your budget and what planning will allow before design begins.

Start with a conversation

The best starting point is our short questionnaire. It takes a few minutes and tells us about your home, your brief and your budget. We review it and arrange a free thirty-minute call, with an honest view on feasibility either way.

Start Here →