HomeWhat an extension costs
What does a house extension actually cost?
You will find plenty of per-square-metre figures online. They are averages of jobs that are nothing like yours, and the honest answer is that the ground, the structure and the finish decide it. Here is what actually moves the number.
The five things that move the price most
Two extensions of identical size can be thousands apart, and it is almost always one of these:
- Ground conditions. What is under the lawn decides the footings, and you find out when you dig. Trees nearby, clay, an old drain or a high water table all mean deeper.
- Structure. How much wall is coming out, and what carries the load afterwards. One steel is routine; three steels and a corner post is a different job.
- Drainage. Whether the extension sits over a run, and whether anything has to be diverted or a manhole rebuilt.
- Glazing. Bifolds, sliders and roof lights are usually the single biggest line item after the shell, and the range is enormous.
- Finish. Whether we hand over a plastered shell for you to fit out, or a finished kitchen with the floor down and the decorating done.
What a written quote should actually contain
If a quote is one number on one line, you cannot tell what has been left out, and what has been left out is where the arguments come from later. Ours lists the work and the materials, so you can see what is in and what is not. Anything extra is agreed before it happens rather than appearing on the invoice.
Why we will not price it over the phone
Because it would be a guess, and a guess that is too low is worse for you than no number at all. The visit is free and takes under an hour. We look at the ground, the drainage, the access and what you actually want, and then you get a written price you can hold us to.
Common questions
How much does a house extension cost per square metre?
The per-square-metre figures you find online are averages across the whole country and every kind of job. They are a starting point for a daydream, not a budget. The same extension costs differently depending on the footings, the structure and the glazing.
Is a single storey or double storey extension better value?
Per square metre of room gained, a double storey is often better value, because you are paying for one set of footings and one roof and getting two floors out of them. Whether it suits your house and your planning situation is a separate question.
What is the cheapest way to add a room?
Usually a garage conversion, if you have a garage you are not parking in. The walls, roof and floor already exist, so you are paying for insulation, a floor, a window and a finish rather than for foundations.
Want a proper price for it?
Tell us roughly what you are planning and Scott will come and look. The visit, the advice and the written quote are all free.
Read more about extensions in Hertfordshire.
