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Guide · Buying to extend

What to check before you buy a house you plan to extend.

Most people buy the house first and ask the architect second. By then the price is paid and the loft either works or it doesn't. Here is what we'd check before making an offer — most of it from your sofa, all of it before you fall in love with the kitchen.

The checklist

Eight checks. None of them needs a site visit; all of them change what you should pay.

01

Does the house still have permitted development rights?

Rear extensions, lofts and outbuildings can often be built without planning permission — but only if the house still has those rights. Flats never do; houses in conservation areas lose some; an Article 4 direction or a condition on an old permission can remove them entirely. If the rights are gone, every project becomes a planning application, with the risk and the months that brings.

02

What are the designations on the plot?

Conservation area, listed building, Green Belt, flood zone, tree preservation orders, Article 4, and — around Epping — the Forest's zone of influence. Each one changes what you can do and what it costs to do it. You can find most of them on the council's policies map; reading them correctly is the harder part.

03

What have the neighbours been allowed — or refused?

The planning history of the street is the best predictor of your own application. Three approved rear dormers on the same terrace is a strong hand. A refusal two doors down for exactly what you're planning is a warning you should read before you offer, not after.

04

Where is the ceiling price for the street?

Extensions add value up to a point; beyond the most anyone has paid on that street, every pound you spend is a pound you may not get back. Check the sold prices of the biggest houses nearby against the asking price plus your build budget. If the sum comes out above the ceiling, you're buying a home, not an investment — which is fine, as long as you know it.

05

Which way does it face, and where are the neighbours' windows?

A north-facing rear garden and a six-metre extension make a dark room. A neighbour's side window close to the boundary is the single most common reason a rear extension is cut back. Both are visible from the garden at the viewing.

06

Where are the drains and the sewer?

A public sewer within three metres of where you want to build means a build-over agreement with the water company, and sometimes a redesign. A manhole cover in the middle of the back garden is worth a photograph.

07

Is the roof the right shape for a loft?

Hipped roofs need a hip-to-gable to get a usable loft; low ridges rule it out altogether. Look at the neighbours who've done it — their dormers tell you what's possible and what the council has accepted.

08

Could the garage or the plot do more than you're asking of it?

A detached garage can become a room, an annexe or — sometimes — a separate unit; a wide plot can take a second house. You don't have to want that to benefit from it: the option is value, and it's a reason to pay a little more or to win a bidding war with confidence.

The short cut

All eight, for the address you're looking at, within 30 minutes.

The Property Insight Report pulls the designations, planning history, precedents, sale history and comparables for any address in England into one document — and comes with a 30-minute call with a RIBA chartered architect to go through it. £195, credited against your fee if you buy and commission us.

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Whether it is a first conversation or a scheme someone else has already started, we are happy to hear where you have got to.

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