How much does a house extension cost in London?
Whatever the driver, extending your home is a great way to add financial value to your property and improve your quality of life without the stress of moving. Whilst it's an exciting process to tailor your home to meet your needs, there are a number of costs to be prepared for before starting the journey.
Benchmark extension costs:
For the purposes of this article, we are focusing on the extension (up, down, round, in and out) of domestic residential projects in London to a standard finish. Whilst many factors affect cost, size has the greatest influence and has been used to indicate overall costs.
During the design process, we often find that making better use of existing space is key. Refurbishment of existing spaces is inherently cheaper where no new floors, walls or roofing is needed. Costs may be in the region of £1,500 per sqm (£140 per sqft) for new finishes, including lighting, with the potential to transform your home.
If you are proposing to enlarge an existing space, or add a new room, a single storey extension at ground floor can be a great option. Costs are typically in the region of £3,000 per sqm (£280 per sqft). Refurbishment costs should be considered where adjoining an existing space which requires updating as a result.
Where there is an opportunity to introduce a two storey extension, overall costs to floor area can benefit from economies of scale. For example, a two storey extension may only require one roof. A general guide is to add 50% to the footprint cost of a single storey extension.
With available site area often limited, garage and loft conversions offer the opportunity to expand within the existing building. With basic structure in place, costs are generally reduced from that of the new area to approximately £2,000 per sqm (£185 per sqft).
Basement development can be the most expensive route when extending but can provide much needed space where no alternatives exist with little to no change to the external appearance. Basement extensions are complex and involve structural works to carefully support the existing building. Costs can be in the region of £4,500 per sqm (£480 per sqft). Some Georgian/ Victorian properties have part basements which often simplifies the extent of works and associated costs.
Whilst this post is focused on London, it is worth noting that prices are generally lower across the rest of the UK with prices increasing in urban centres where material and labour costs may be higher than rural areas.
The benchmark costs are for construction only. They do not include VAT or professional fees which are expanded on below.
VAT:
VAT is often overlooked but plays a significant role in the overall cost of your extension, usually chargeable at the full rate, currently 20%. However, this is not always the case. There are instances where VAT is reduced to 5% or even 0%. An example of this is if a property has been vacant for more than two years, it may be eligible for the reduced rate of 5%. A good Architect can help work with you to understand this.
Professional fees:
Your Architect is an invaluable investment and will help guide you through the process. There are also other professionals who will support along the way such as a Structural Engineer and Building Control Inspector. On an extension project, you should allow for professional fees of 15-20% in addition to construction costs.
What's in the extension?
The variety of overall cost is heavily influenced by the level of specification. We've all done our share of scrolling through Instagram and Pinterest and it's very easy to be seduced by what's on offer. Overall extension costs are highly dictated by specification of what's within from the cheap and cheerful to high end luxury.
Bathroom:
With the introduction of a bathroom you will be looking at the starting cost in the region of £5,000 with scope to greatly increase costs based on specification of fixtures and fittings. This includes toilet, bath, shower and basin in a space of approximately 5sqm.
Kitchen:
Similarly with kitchens a starting cost of £20,000 is common. This will allow for a low to mid-level range of units and appliances in a space of approximately 10sqm. Keep in mind, there are some really creative ways to dress up basic units for a more lavish look.
Other expenses:
A worked example:
5 x 3 m kitchen extension
Footprint of 15 sqm @ £3,000 per sqm = £45,000
New kitchen @ £20,000 = £65,000
15 sqm refurbishment of adjoining dining area @ £22,500 = £87,500
Professional fees @ 15% = £13,125
Subtotal = £100,625
VAT @ 20% = £20,125
Overall budget = £120,750 including VAT*
Items such as large glazed openings, new heating systems or bespoke joinery will lead to increases.
*All prices estimated as of 2022.
Considerations:
Contingency - Not a direct cost but we advise allowing for contingency of 5-10% on extension projects. Whilst your Architect will most likely arrange a fixed price contract with the builder, there can be surprises and it's best to be prepared.
Insurances - It's worth contacting your insurer before starting building work to make sure you're covered. There may be an uplift to provide protection through the duration of the project. This may also affect insurance premiums on completion if the value of the property has increased.
Temporary accommodation - Consider whether you intend to stay in the property through the duration of the works or move to alternative rented accommodation if staying for the full duration is not possible or desirable.
Managing costs:
Ultimately, building work costs what someone is willing to do it for. We realise this is a strange statement but undeniably true. How much does a house extension cost in London? On most projects we advise tendering to three contractors. This inevitably provides prices which are the highest, lowest and a sanity check between. Once you have these prices, your Architect will work with you to ensure you appoint the contractor who is best value. When tendering a project with a budget of £200,000, it is not uncommon to have a £20,000 difference in the lowest to highest. The key is to understand where the cost difference exists in what you're paying for.
Some homeowners like to play a role in the project including supplying their own fixtures and fittings having the contractor install only as a means to make savings. This can provide an upfront saving but it puts responsibility on the homeowners time and technical knowledge to ensure fittings are correct and on site when required to avoid delay and abortive costs.
It pays to invest in a good Architect. On domestic residential projects, you are likely undertaking this type of project for the first time. Experienced Architects provide foresight on what lies ahead to help navigate potential risk, pitfalls and avoidable expense. It is beneficial to be transparent with your Architect. A good Architect will work within your means, helping to reduce costs where necessary and advise how best to make the most of your available budget to deliver the best possible result.