The true cost of a home extension
How much does it cost to design and build a home extension?
This is the most common question we get asked. And our answer is always the same: it depends. Helpful, right?
But it’s true; the final cost depends on so many things. The extension type, the size and the fixtures and fittings all come into play.
We’ve broken down the true costs of different types of house extensions based on our experience across Nottingham, Derby and Leicester at the bottom of this page, but to start with we’re going to cover the basics costs:
Your architectural drawing fees
Your planning fees
Your building control fees
Your structural engineer fees
Your mortgage fees
Your build costs
The cost of any extras (kitchens, bathrooms, floor tiles etc.)
And that’s pretty much….wait, there are how many fees?!!
Don’t worry. It might seem like a lot, but let’s look at the numbers.
As architectural designers, we take our clients right through from initial design to approval and our fixed prices range from £649 (single storey side or rear extension on a semi-detached property) to £1399 (double storey and single storey extensions on a detached house). We also do price on request for other projects.
We handle applications for planning permission within our fixed prices, submitting them on our clients’ behalf. There is a fee payable direct to the council (usually £206 for a standard householder application) on top of our costs.
We also handle applications for building control within our fixed fees and then the costs for plan check and site inspections are payable direct to the building control company (or local authority if you choose to go with your council). Average costs here are around £600 - and remember, only around a third of this is due up front, and the rest only payable upon the first site inspection.
If you need structural calculations, we can take the load off and arrange these for you. We don’t charge anything extra here but you do need to pay the structural engineer directly. On a typical kitchen extension, taking out two structural walls, the cost would be around £350. Structural calculations are something we can help you avoid with some design modifications.
So, that’s costs 1-4 dealt with and if you’re planning a single storey rear kitchen extension on a semi-detached property under permitted development (so no planning fee - phew!), you’re looking at around £1,600 for your architect drawings, structural calculations and building control.
Once you’ve got your approved plans, you’re ready to get a builder on board. We can introduce you to local, reputable builders and arrange for them to provide quotes.
In our experience, average costs per square metre are £1,500 for ground floor extensions and then £1,100 for the first floor. Using these costs, a typical rear extension 3m x 6m would come in at £27,000. Bear in mind your kitchen and extra fittings would be on top of this. Keep an eye on our Instagram page where we break down the costs of our latest projects.
Now you’ve got your quotes, it’s time to get that money sorted. If you’re remortgaging, we would always recommend borrowing a minimum of 10% more than your build cost just to cover anything unforeseen. Also, if your build comes in on budget you’ve got a bit leftover to go on holiday (although we’re hoping you won’t need one because the process will have been totally stress-free!) and let the dust settle. Seriously, it takes two weeks to get the dust out after you knock through.
With the right team around you, you can get a good idea of the final cost at the very beginning with no nasty surprises. Obviously, things can happen on site, such as foundation issues, and you’re only going to find out when you start digging. That’s why we always recommend doing a trial hole - that way, if anything comes up and the remedy is going to be megabucks, you can stop before you’ve started. Or, perhaps that extra 10% we advised earlier will cover it and you’ll give yourself a pat on the back for planning ahead.
So, there you have it - the true cost of a home extension. Don’t forget to check out our ‘How to build a home extension’ step-by-step guide for more tips and guidance and follow us on Instagram to see our latest projects.