Extensions are complex projects that encompass a variety of different elements and trades, from laying foundations and building walls, to plastering, electrics and plumbing - and that’s before getting to features like adding a new kitchen or utility.


A large variety of things can affect the costs depending on what your use for the extension will be.


With our house extension price guide we hope to give you the basic knowledge to start planning your project. 

Basic Extension Costs

Flat Roof

Basic Doors

Basic Windows

Standard Extension Costs

Pitched Roof

Patio or Bi Fold Doors

Upgraded Windows

Stages of a house extension project

A home extension building project goes through several stages of building, which are broken down below. When completing a home extension we break down our costing in to stages, which is clearly outlined in our Schedule Of Work.

Each stage has an amount allocated to be paid on completion of work. Only when the stage of work is complete does the client make the payment allocated. We find this offers peace of mind and reassurance to clients.

STAGE 1 - Design, Planning & Building Regs

Planning permission is not always necessary for a home extension project, especially single storey extensions, but in some cases you may need permission from the City Council, which can be around £200.

Architectural drawings may come in around £500 to £1,000 depending on the scale and complexity of the work required and detailed in your build.

Building regulations are the standards to which all construction projects must adhere and are essential for all building projects in the UK. Building Regulations are designed to ensure buildings are safe, structurally sound, and water and energy efficient. The cost will vary depending on the size of the build and the type of work being carried out, but will typically be between £200 to £500. But don't stress...We can fill out all necessary forms for you to make the process as simple as possible.

STAGE 2 - Ground Works

The preparing of the site and digging of foundations is essential to making sure the extension is built safely and with structural integrity. Generally the ground work should be pretty straight forward. The general measurements for footings are around 450mm to 600 mm wide and up to 1 meter deep (This is where clay should be uncovered confirming the ground is acceptable to be built upon). Once clay has been revealed the building inspector will attend and confirm we can pour concrete to create the footings for your new extension.

If there is drainage that needs to be moved, under the ground, it will be uncovered during the digging process. Drainage may need to be diverted, which we can undertake for you. 

STAGE 3 - The Shell

This is where the main building takes place, building the basic structure with usually either brick or  block .

Choice & style of roof is erected, the building is insulated and interior elements such as plasterboard and a subfloor are added to ensure a watertight structure. Costs are related to the size of the build and materials used. The main building material of choice is at clients discretion. Decisions usually being made after consideration of cost.

STAGE 4 - Fitting

Fitting out your home extension with desired features usually include skirting boards, bifold/ patio doors, windows, electrical sockets, lighting, switches, as well as necessities like radiators etc. The costs of which will depend on whether you want to purchase high-end materials or standard. Sliding or bifold doors cost more than simple French doors do, although Bi folds seem to be the most popular choice at the minute.

STAGE 5 - Finishing

There is no upper limit to what you desire to spend when completing your extension – all finishes have a different cost dependent on the use of the room and desired finish. From standard wooden floor at £10 per square metre, to imported marble tiles that will cost a lot more to cover the same space.

Costs can also increase significantly if you are adding a new kitchen or bathroom to the extended space. As a benchmark, a new kitchen could cost between £7,000 and £15,000 on average, while a bathroom could cost between £3,000 and £8,000 average. This all dependent on your budget and the finish required.



9 Menlove Avenue, Liverpool, L18 1LS