In the initial planning of your house extension, ensuring that you have the right budget for your project will be paramount to its success. However, during my initial discussions, I often find that potential clients tend to have a much lower budget in mind until I burst the burble with a more realistic estimate. And this is not to suggest that their budget is without some research, but whilst there is a plethora of information that can be found online, it’s important to find figures relevant to the location of your project and the period in which it will be carried out. So for those wondering how much does a house extension cost in London, here are my figures that will be relevant to common house extension projects in autumn 2017.
How Much Does a Single Storey Extension Cost in London?
The cost of your extension will be influenced by specification, so for example for a basic spec will cost £1,800 per m2, whilst a medium spec would be in the £2,200 per m2 region and a high spec in the £2,500 per m2 mark.
When we use the above figures to calculate an extension with a typical width of 5m and a depth of 6m and an area of 30m2, the basic spec would give an estimate of £60,000.
On top of this build cost estimate, you will need to add 20% VAT, which would be £12,000.
Architect and structural engineer fees will be approximately 15% of the build cost, which would be approximately £9,000.
Other additional costs on top of your build cost estimate will include 3% for party walls if required, 2% to cover planning and building control and 10% contingency.
So for a single storey extension in London, your project budget should be around £90,000.
How Much Does a Double Storey Extension Cost in London?
For a double storey extension with a basic spec, a quick calculation of adding 50% to the cost of a single storey extension will give you the estimate needed for your budget.
So the project budget for a 5m by 6m double storey extension should be around £135,000.
What Are the Items Likely to Turn your Project from Basic to Medium or High Spec?
If your extension is likely to involve redesigning the kitchen and installing new cabinets and appliances, this will increase your project cost. Kitchen fittings and installation can range from £10,000 + VAT to £50,000 + VAT.
If your extension involves adding a new bathroom, then the cost for sanitary fittings, installation and tiling can range from £6,000 to £10,000.
Bi-fold doors or sliding glazed doors like these will start from £5,000 for a 2.5m wide opening.
Other extras likely to noticeably increase your overall project cost will be UFH, new plumbing in connection with installing a new boiler, high spec lighting, bespoke joinery or installing a smart home system. If you would like to find out more about smart home systems, this post has some useful info.
If your project will involve demolition, this will add to budget as well the level difficulty accessing the rear of the property.
How Can You Control your Budget?
Agreeing a project budget with your architect is as equally critical as agreeing a project brief. In fact, I would go further and say designing in tandem with the project budget in mind will help to avoid unwanted surprises when requesting quotes from building firms.
For projects of a value of £100,000 or more, it may be beneficial to work with a Quantity Surveyor.
I hope have some useful square metres costs to work with as of autumn 2017 when asking the question, how much does a house extension cost in London? For readers outside London, please bear in mind that build costs and professional fees are likely to be different and perhaps significantly less in your region. For readers in London, I will aim to refresh this post at least once a year so that you can have the most relevant figures to work with when you come to carry out your project and when wondering the question: how much does a house extension cost in London?
As always, if you have any comments relating to the question of how much does a house extension cost in London, please leave in the comment box below.