House Extension – main factors impacting the cost

Many house owners at some point consider adding an extension to their home. It is quite logical as extending house increases usable space, allows to create open kitchen-dining area, and in general increases property value. But how much is it going to cost? What are the main factors shaping the price of such undertaking? Well, there are many. We have listed most crucial of them below.

Size of the extension and number of storeys

This is quite obvious – the bigger the extension, the higher the price is going to be. Most of the builders calculate the base price of extension-like project by simply multiplying number of square meters of each extension’s floor by their usual rate. Only then this number gets further amended by other factors specific to the project.

Depth and width of strip foundations

Foundation depth is dependent on type of soil specific to the area and weight of the proposed structure. This needs to be adequately designed by Structural Engineer. Furthermore, once foundation trenches have been dug, Building Control needs to inspect bottom of excavations and be satisfied with their findings. Otherwise, BC may request the builder to dig a bit deeper to reach suitable soil type.

Floor, walls and roof build-ups

These have significant impact on cost of materials and construction. Insulation requirements, bricks vs blocks and render for walls, size and grade of timber joists, flat vs sloped roof – these all affect the price of the build.


The steel required depends on what the structure will carry. It needs to be suitably designed by the Structural Engineer and is dependent on the structure over. The more steelwork is required and the bigger it needs to be, the higher the price.


Type of floor finishes, quality of the kitchen, existence of extra features like dropped ceilings, number of electrical points, etc. – it all has its part in shaping the cost.

There are many other factors which ultimately create the price of house extension. What is important when considering such project, is making sure that contractor you consider has sufficient experience in carrying out such works. Furthermore, when comparing quotes of different contractors, it is paramount to compare on like-to-like basis. Some contractors offer very detailed quotes, whereas others provide only brief description of works included within their pricing documents. This is very much advisable for the Client to only proceed with particular contractor when it is fully transparent what said contractor has included within their quote, and what will be for the Client to supply/arrange.

City Builders YK will always clearly state what is for the Client to supply and what is included within our pricing. We have necessary experience and expertise to carry out your project from the start to the very completion without involving you unnecessarily in the process. You can trust us to provide the very best and hassle-free service at all times. Should you be looking for professional contractor to carry out your house extension project, we would be delighted to hear from you. What we require in order to prepare the quote are construction drawings and a site visit – just so your requirements could be fully understood by us. Then, we provide a non-obligation quote for your perusal and we are eager to respond to all the queries you might be having. Should you decide to use City Builders YK services, the outcome you should expect is nothing short of magnificent.