Single Storey Extension Costs in Aylesbury: A 2026 Guide

What a single storey extension costs per square metre

In Aylesbury and the wider South East, most single storey extensions currently come in somewhere between £2,200 and £3,200 per square metre for the build itself, finished to a standard specification. A straightforward 4m x 5m rear extension of about 20 square metres therefore tends to land in the £45,000 to £65,000 range before you add a kitchen, bathroom or high end finishes.

Buckinghamshire prices sit a little above the national average because labour and material costs in the South East are higher than in much of the country. The per square metre rate also drops slightly as extensions get bigger, since costs like scaffolding, skips and setting up the site are spread over more floor area.

• Basic specification (simple layout, standard doors and finishes): roughly £2,200 to £2,500 per m²
• Mid range (bifold or sliding doors, underfloor heating, better glazing): roughly £2,500 to £2,900 per m²
• High end (structural glazing, bespoke joinery, premium flooring): £3,000 per m² and upwards

The costs that sit outside the builder's quote

The build price is only part of the picture, and this is where budgets most often go wrong. Architectural drawings and structural engineer calculations typically cost £2,000 to £5,000 depending on complexity. Building regulations fees, and planning fees if your project is not covered by permitted development, add several hundred pounds more.

If your extension will house a new kitchen, that is usually priced separately and can range from £8,000 for something sensible to £30,000 or more for a bespoke design. Other common extras include moving drains or a soil pipe, upgrading the consumer unit, a party wall agreement if you are close to a neighbour's boundary, and VAT, which most quotes from VAT registered builders will include but is always worth confirming in writing.

What makes one extension cost more than another

Two extensions of identical size can differ in price by £20,000 or more. Ground conditions matter a great deal: parts of Aylesbury Vale sit on clay, and where trees are nearby, foundations sometimes need to go deeper than the standard one metre, which adds concrete, muck away and time. Access matters too. A rear garden you can only reach through the house slows everything down compared with side access wide enough for a digger.

Glazing is the other big variable. A set of bifold or sliding doors across the rear can cost £5,000 to £15,000 depending on width and specification, and roof lanterns or large rooflights add more. Knocking through to create an open plan space usually needs steel beams, and the size and number of steels, plus the temporary works to install them, all feed into the price.

How to get an accurate price and keep control of it

Get at least two or three itemised quotes based on the same set of drawings, so you are comparing like for like. A single figure on one page tells you very little; a good quote breaks out groundworks, structure, roofing, glazing, first and second fix, and finishes, and states clearly what is excluded.

Agree a payment schedule tied to completed stages rather than dates, and hold back a sensible final payment until snagging is done. It is also wise to keep a contingency of around 10 to 15 percent of the build cost for the genuinely unforeseeable, such as poor ground or hidden drainage, so a surprise does not stall the project halfway through.