Cost of Building an Extension in 2019

What contributes to the cost of an extension?

The main governing factor on the cost of an extension is square footage or square meterage – how big it is. So, the bigger it is, the more it’s going to cost. Typically if you worked out a square meter at £1500, that’s a good base price. Then additional costs that you add on top of that would depend on questions such as;
Are you going to have a new kitchen?
Are you putting in large bi-folds or sliding doors?
Are you putting in big roof lights?
Are you redoing the floor throughout the house and having underfloor heating?
What kind of floor finish do you want?
Are you having new doors throughout? New radiators? New boilers?
All of these kinds of things contribute to the final cost of an extension.

Typically if you worked out a square meter at £1500, that's a good base price for the cost of an extension.

Extension Cost Guide

Single Storey Extension

Typically we always say that for a rear extension, budget £50,000 because you’ve got potential kitchens, opening up of walls to the original house, etc.

Two Storey Extension
Two storey extension could be around £80,000 because obviously on the second floor, you don’t have any foundations

Kitchen or Bathroom Extension
These kind of extensions don’t usually happen by themselves – they’re part of a greater extension. Kitchens can be anywhere from £7,000 to £50,000 but the typical kind of cost or price, people pay is about £7,000 to £15,000. But you’ve got to think about appliances – the better the appliances, the higher the cost. A super, duper, amazing bathroom could be £5,000 but obviously you could do that much cheaper.

Bungalow Extension
Again, that’s like a rear extension. You’re going to be opening up the existing house, so budget £50,000 but it could be up to £90,000

Loft Extension
Budget about £50,000 for a loft extension. You might have a bathroom or an en-suite in there or you could have a complicated roof so it could be £50-£60,000 but you obviously avoid, foundation costs and any costs associated in the ground. See more…

Fixtures & Finishings

There are many suppliers and prices for fixtures so you can pick your price point and search online to get an idea of cost. You can even go to IKEA and get a carpenter to fit your IKEA cupboards and make them permanent so they don’t look like IKEA furniture.
Again, for finishings like tiles on floors, tiles in bathrooms, etc. you can go to Topps Tiles, Porcelanosa or these kind of places and get prices per square meter and then associate that with how many square meters in your bathroom or on the wall. You can do it quite roughly and it’s a pretty good guide.

When doing fixtures and finishes, you can use Yoop’s Visual Finishes Schedule and that’s a schedule that organizes all these kinds of aspects of your renovation. and it does it room by room. It even drills down to what kinds of switches and sockets you want – are you having the white ones which cost £1 or are you having the brushed aluminium ones that cost about £10 each?

FREE GUIDE: Category: Home Extensions
FREE: Home Extension Cost Guide

Inside this easy to ready free guide, you will learn how much extensions, loft conversions and other renovations to your home are typically priced.

Building Site Constraints

Some of the key ones that you need to consider:

  • Have you got a tree in close proximity to where you’re doing an extension, especially if you’ve got a willow tree. They’re very thirsty and they can affect the foundation design which can have an impact on cost as well. Things like this should be sorted out prior to going onsite otherwise there’ll be a delay in the works while the contract is there and that will have a cost implication.
  • Organizing your kitchen and other big items like bi-fold doors/sliding doors. These can be subject to something called lead in times. A lot of window manufacturers will produce your windows on a six week order, but others, if they’re more specialty items can take 12 weeks so you really need to think about the time it will take for orders to be ready.

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Any other costs to consider?

  • If you’ve got a shared drain running across the back of your garden and you’re going to build over it or within three meters proximity, you’ll have to do a build over agreement there. So again, you’ll want to get that all sorted upfront – it’ll cost £335 with Thames Water. If you haven’t done that and you need to do one while you’re on site, then that can delay your works.
  • Are you moving boilers or installing new boilers?
  • Do you need a mega flow? A mega flow is a pressurized vessel which may be required if you’re adding a lot of bathrooms, or increased demand for hot water. Your combi boiler will only be able to accommodate so many hot water outlets before the pressure drops and someone feels it in the shower. If you have a mega flow, then it keeps the pressure in the vessel so you don’t get loss of pressure and you can serve more hot water outlets.
  • Are you going to move your consumer unit?
  • Are you going to move your gas meter?

You should establish these things upfron

To calculate the cost of your extension, Yoop Architects take a measured survey of your property, which captures all the information. Then we draw it all up in 3D and create sketches to show sometimes five or six options if it's not entirely clear how you want to achieve your brief.

Extension Cost Calculator

Unless you have a lot of information, about what your extension is going to be, then online extension cost calculators aren’t very helpful. Essentially, you need to create a bit of a scheme before you can start putting some numbers to it otherwise, there’ll be too many questions to answer.

To calculate the cost of your extension, Yoop Architects take a measured survey of your property, which captures all the information. Then we draw it all up in 3D and create sketches to show sometimes five or six options if it’s not entirely clear how you want to achieve your brief.

A lot of the times there are different ways of achieving your desired result and the more you work with the building, the cheaper, easier and faster your build will be. Once you’ve got a favorite scheme or a couple of favorite schemes, we have a phase called ‘Meet the Builders’. That’s when we can introduce you to a couple of builders, they visit the property and they give you a ballpark figure. They’ll also go through any twists and turns of what might be in the ground or any concerns that they have.

Getting an extension is also a great opportunity to ask about under floor heating. It’s getting quite popular to take out the entire floor on the ground floor and replace it with underfloor heating. It makes a huge difference in your life and would add huge resale value. Underfloor heating costs about £10-£15,000.

If you get ballpark figures from contractors early on, then if the cost of the extension is outside your budget or you don’t think you should spend that much money on your house in your street, then we can revisit the sketches. So, we’re at that very early stage, so it sorts out the cost of the project very early on.


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Post Author: yoopadmin