Background info:

Before we delve into how much a house extension costs, let me give you some background. Building costs during covid saw a massive spike and post covid that spiked continued with the war in Ukraine pushing energy costs up. Most building materials are energy intensive to manufacture.

As a guide pre covid sqm rates for a mid spec extension (new building element) would be between £1500-£1800+vat. Post covid you’re looking at £2750-3300+vat for the same level of specification.

Note that the above only relates to new build elements to an existing property. If it’s a completed new build then you would be zero vat rated (for 99% of things), but not for and this is key, any consultants’ fees. If you want to know more about the zero vat rated exclusions and inclusions take a look here. We also work with specialist tax consultants who can advice on this and apply for the exemptions.

As well as the cost of the new elements to your existing home you need to consider the cost of any internal alterations. For refurbishment works you would now be looking at a range from £1000-£1500+vat per sqm. It’s very hard to give a flat sqm rate for this type of work as the work involved in one room can vary considerably to another.

Factors affecting the build cost:

• Exterior finish e.g. type of brick, render, stone, timber, or zinc.
• Window and doors e.g. aluminium, timber or uPVC, sliding or bi-folding
• Window and door size e.g. bespoke floor-to-ceiling or standard sizes
• Floor finishes e.g. polished concrete, ceramic tiles or engineered wood
• Wall finishes e.g. fair-faced concrete, painted plaster, exposed brick or blockwork.
• Kitchen design/supplier e.g. off the shelf, bespoke, handmade.
• Joinery e.g. bespoke handmade or off the shelf.
• Lighting/electrics/audio visual e.g. whole-house control, smart systems, dimming or simple switching
• Heating e.g. air conditioning, underfloor heating, smart systems or radiators.
• Heating and electricity sources e.g. solar panels, ground or air source heat pumps
• Soil conditions e.g. land may be contaminated, piled foundations may be required or the property is located on a floodplain.
• Construction methodology eg SIPS, non standard techniques.

Soil conditions: 

You may need to use piled foundations if there are protected trees in close vicinity to protect their roots, or there is contaminated land or you live on a floodplain and the building needs to be elevated off the ground (and for good reason I might add!).

Construction Method:

You may want to use an innovative building material that has top notch sustainability credentials. This would normally come with a premium price tag attached and required specialist contractors to install. Examples would be Passivhaus, EnerPHit or Zero Carbon.

Intricate Design:

You may want to have a copper roof or zinc cladding. These are considered non standard building materials for a house extension so expect to pay a premium and make sure the value of the house will reflect that premium. 

Be wary that the cheapest materials may not have the longevity as something slightly more expensive so it is a false economy if you plan to live in the property for more than a few years.

Cost calculator:

If you need some guidance on what the build cost for your home extension or renovation project might be take a look at our cost calculator.