How much does a house extension cost in Herefordshire?

Nobody can price an extension from a phone call, and any figure given without seeing the property is a number chosen to win the job. What follows is a realistic framework for budgeting before you get quotes.

Rough per-square-metre ranges

For Herefordshire and Monmouthshire, at 2026 prices and for a standard specification:

• Single-storey extension: roughly £2,000–£2,800 per m²
• Double-storey extension: roughly £1,800–£2,400 per m² of total floor area — cheaper per metre, because one set of foundations and one roof serve two floors
• High specification or difficult site: £3,000+ per m²

So a 20m² single-storey rear extension — a fairly typical kitchen-diner project — commonly lands somewhere between £40,000 and £56,000 for the building work, before you fit it out.

What moves the number most

Ground conditions and foundations

Clay, made ground, high water tables, nearby trees and old drainage runs all change what the foundations have to be. This is the single biggest source of unexpected cost, and the main reason a proper site visit matters more than a quick look at photos.

Structural openings

Joining a new extension to an existing house usually means removing part of a rear wall and installing a steel. The wider the opening, the heavier the steel, the deeper the padstones, and the more propping is needed while it goes in.

Glazing

Bifold and sliding doors and rooflights are where budgets quietly disappear. A large aluminium sliding door can cost more than the roof structure above it. Worth deciding early, because it affects the steel too.

Access

If a digger and a lorry can reach the back of the property, groundworks are quick. If everything has to be barrowed through the house or round a narrow side passage — common on terraced streets in Hereford, Leominster and Monmouth — labour costs rise.

Older buildings

Solid walls, lime mortar and shallow historic foundations need a different approach and often more work. Conservation area and listed building requirements can also dictate more expensive materials.

Costs people forget to budget for

• Architect or designer's drawings: typically £1,500–£4,000
• Structural engineer's calculations: typically £500–£1,200
• Planning application fee, where an application is needed
• Building Regulations application and inspection fees
• Party wall surveyor, where a neighbouring wall is affected
• The kitchen, bathroom, flooring, decorating and landscaping — often excluded from a builder's quote
• A contingency of around 10–15% for what the ground reveals

Two quotes can differ by £15,000 simply because one includes the kitchen and the other doesn't. Compare scope before you compare price.

How to compare quotes properly

Ask every builder for an itemised written quotation that states what's included and what isn't, the payment stages, and who is responsible for drawings, engineer's calculations and Building Control fees. A single number on one side of A4 tells you nothing, and the cheapest of those is usually the most expensive by the end.

Questions

Is an extension worth it financially?

Usually, if you compare it with moving. Stamp duty, agents' fees, solicitors and removals on a house move in this area frequently total more than £20,000 before you gain a single square metre. An extension puts that money into your own property instead. It doesn't always return its full cost in valuation, though — particularly if you push the house well above the ceiling price for the street.

Should I get the cheapest quote?

Only if it's genuinely for the same scope of work. Most large gaps between quotes come from different assumptions, not different profit margins — foundations, glazing, whether making good and decorating are included. Line them up item by item first.

How much deposit should a builder ask for?

A modest sum to cover materials ordered up front is reasonable. Large payments before work starts are not. Staged payments tied to completed stages protect you and are standard for any builder confident in their programme.