how much does an extension cost 2026

there are simple methods to use to calculate but you have to be careful and do not just assume the prices will be somewhere near these calculations

Extension Costs in 2026 – Why Two Similar Extensions Ended Up Nearly £80,000 Apart

One of the questions we're asked most often is, "How much should an extension cost?" Unfortunately, there isn't a simple answer. While extension size plays a part, the final cost is influenced by the design, specification, construction method and how the project is managed.

To demonstrate this, here are two real projects that achieved a very similar outcome but had dramatically different budgets.

Project One – Main Contractor

For this project, we acted as the main contractor, delivering the entire extension from start to finish. As we are VAT registered, the price quoted below includes VAT.

The extension measured approximately 3 metres deep by 6 metres wide and created a large open-plan kitchen and living space. To achieve this, we removed the original rear external wall, internal walls and a dividing wall running through the property. This required extensive structural steelwork, including large RSJs to support a wide bifold door opening.

The specification was high throughout and included:

- Large aluminium bifold doors.

- Four Velux roof windows.

- A pitched roof construction.

- New concrete floor and drainage alterations.

- A high-end fitted kitchen.

- Premium flooring and internal doors.

- Relocation of the existing boiler and associated plumbing.

- Demolition of part of an existing garage before construction began.

The total cost for this turnkey project, including VAT, was £120,000.

Project Two – Project Managed

Our second example was completed using a completely different procurement route. Instead of acting as the main contractor, we worked as the client's project manager.

In this arrangement, we sourced and managed the subcontractors, prepared the working drawings and coordinated the build on the client's behalf. The client paid subcontractors and suppliers directly, meaning the construction costs were largely outside the VAT-registered main contractor model. Our project management fee was £2,500 plus VAT.

Although this extension was slightly smaller at 3 metres deep by 5 metres wide, the finished living space was very similar. The key difference was that every design decision was made with value for money in mind.

Cost savings included:

- A flat roof instead of a pitched roof.

- PVC French doors with glazed side panels instead of aluminium bifolds.

- No Velux roof windows.

- A revised structural design using larger masonry piers to reduce the span and the amount of heavy structural steel required.

- Reusing much of the existing kitchen by fitting new doors, end panels and trims, while adding only four new base units and one tall larder unit.

- No boiler relocation and significantly less plumbing work.

- A porcelain patio, but over a smaller area to retain more garden space.

Despite the lower budget, the extension still delivered an attractive, practical family living space.

The construction cost came to approximately £41,000, with our £2,500 plus VAT project management fee added separately.

What Can We Learn?

Comparing the two projects shows just how much extension costs can vary.

- Main contractor project: £120,000 (including VAT)

- Project-managed build: £41,000 (excluding our project management fee)

- Difference in construction cost: £79,000

The important point isn't that one approach is better than the other. Every client has different priorities, budgets and levels of involvement they are comfortable with.

However, these examples demonstrate that the biggest factor affecting the cost of an extension is often not its size. Specification choices, structural design, procurement route and careful project planning can make a remarkable difference to the final price.

If you're planning an extension in 2026, obtaining good design advice early in the process could save you many thousands of pounds while still achieving the additional space your family needs. 

want costings or project guidance please visit www.fryerpropertyconsultancy.com

project manged project £41,000.00