"I’d not hesitate to recommend Aura. They team are the perfect balance of creative and practical, imagination and solutions, to make whatever dream you have come to life."
"Aura kindly carried out some work for me on a small but compact development for me. It required precision, experience and haste, Aura were extremely efficient in all of these areas. I will 100% recommend and use Aura again."
"Aura Architecture is a highly professional firm of architects that always have the clients best interests at heart. The quality of their plans and drawings is superb and their turn-around when making amendments well within expected timelines."
When it comes to extension costs, there is no quick way to calculate the cost of a house extension or refurbishment proposal. Also, you will never truly know how much the cost of an extension on your dwelling will likely be until you have a full set of plans and a detailed Scope of Works drawn up – ideally with 3 to 4 tender quotes from contractors! And that’s not all.
You will also need to research and choose a new kitchen, bathroom finishes, sanitary ware, as well as many more variables. You may already have invested £1000’s in architects and design consultants and spend hours of time in order to get to that stage.
We would always advocate paying a Quantity Surveyor (QS)/Cost consultant to produce a cost estimate.
All this sounds rather expensive and time-consuming. Is there a quick way to anticipate your refurb or extension costs for free? Yes, and we’ll explain more in this article.
At Aura Homes, we’re committed to being transparent and upfront about costs and helping our clients avoid unnecessary expenses and mistakes in their property projects.
How Much Does An Extension Cost Per m2?
The cost to extend a house is not straightforward, in short, build costs per m2 will vary wildly. This cost of house extension guidance is by no means definitive, but it will give you a ballpark figure in which to help you move forward.
Let’s start by saying that this article is aimed mainly towards projects in London and the South East. Labour costs and some materials will vary depending on where you are in the country – we can only advise on our patch!
However, those of you outside London and the South East will still benefit from reading this, and we’re sure you will gain some valuable tips on what your house extension or refurbishment cost will be. Later in the article, we will show some real-world examples to help you piece together the information.
House Extension Cost Overview – Estimates
The table below gives an overview and estimated price range for how much your house extension or refurbishment may cost, based on our experience. These figures should be used as guidance only, as some building material prices have been very volatile recently.
Please note these figures were provided in 2022 so may have increased slightly.
The lower range would be a basic construction with uPVC windows/doors. The higher range would be a more complex construction with specialist glazing. Note that small extensions like side-return extensions will likely have a much higher £/m2 rate.
When creating an open-plan kitchen/living area, for example, this cost would be relevant if removing the house’s existing ground floor rear wall. Larger openings will need more steel beam.
£1,500 – £2,500 per m2 of additional floor space (above 1500mm ceiling height)
The cost of this will rise with the complexity of your existing roof structure or if its a new extension completely. If your roof and proposed layout are complex, it may be worth considering removing the existing structure completely and installing a new roof.
Up to £500: Cosmetic | £500 – £1,000: New wiring/plumbing and back to brick | £1,000 – £1,400: Including layout changes and minor structural work. All per m2 refurbished floor area
Back to brick? New wiring/plumbing? Or just a cosmetic uplift? This cost will vary greatly.
£6,000 + for basic spec | £15,000+ for mid-range | £40,000+ for high-spec. This is for a generic 20 kitchen units including appliances.
Assumptions: Basic – e.g. Howdens/Magnet, basic appliance spec, laminate worktops Mid-range – e.g. Wren/IKEA, better appliance spec (e.g. siemens), stone worktops High-spec – bespoke/designer manufacturer, top appliance range (e.g. Miele), stone worktop.
What Will Affect My House Extension Cost?
Drainage Location and Diversions
If you’re building over or near a Thames Water sewer that is classified as ‘Public’, you will likely need to submit relevant drawings and details to apply for a Thames Water Build-Over Agreement. We explain more about these in our blog which you can read here.
Ground/Soil Type
This will affect the type and depth of your foundations. Up to 25% of your overall budget may be spent in the ground! So doing your homework on ground conditions can really help nail down a realistic budget. A soil investigation will be required, or your structural engineer will advise on the likely ground conditions.
Nearby Trees
Tress absorb groundwater and can affect the shrinkability of the soil surrounding your house. This may require deeper foundations – therefore, adding extra cost. For example, Leylandii trees in a London clay soil close to your proposed extension can require 2.5m deep foundations and, in certain scenarios, make trench foundations unfeasible. We recommend that which our find out which trees are in your garden, and how deep your foundations may need to be using the handy NHBC Foundation Depth Calculator.
Property Age
Period and older properties will often bring unexpected costs and uncover hidden problems that were unforeseen. Therefore, if you are carrying out building works on older properties, ensure you have a healthy contingency in your budget and ensure you carry out a full structural survey of the property as early as possible.
Structural Complexity
This is where a good engineer can save you money. There will be many ways to design your supporting structure, and a good engineer will design a lean scheme with due regard to an easy installation on-site and good detailing in conjunction with your architect.
Procurement Method
This is another topic in itself that relates to the level of project management you wish to undertake yourself, the level of risk, your building contract, and many other factors. Many established interior designers and residential architects have extensive contacts and knowledge of suppliers, so can handle this for you.
Neighbours
Having a good relationship with your neighbours can keep your project moving swiftly, especially when your works require Party Wall Agreements in compliance with the Party Wall Act 1996.
Health & Safety
You have obligations as the homeowner under the Construction, Design, and Management Regulations (CDM) 2015. Your contractor will need to be aware of these as they will have the greatest responsibilities during your build project. Incorrect health and safety on-site can cause delays and even fines. We recommend that your contractor has sufficient costs in his tender to fulfil his duties.
What Professional and Statutory Fees Form Part Of My Refurbishment Cost?
You will need to notify your neighbours of any relevant works being carried out under the Party Wall Act 1996. More information can be found here, but in general, if you’re installing foundations within 3m of your neighbour’s property or putting steel beams within party walls, you will need to notify your neighbour and potentially draw up Party Wall Agreement. This can be a large part of your house extension cost if surrounded by leasehold flats. All leaseholders and freeholders need to be served a Party Wall Notice.
Cost: To serve notice, circa. £200. From £900 up to £2,000+ Per Award (if needed)
If you do not know the routes and flow direction of your property’s drainage, we’d suggest paying for a CCTV survey. This will give us the location and direction of drainage, manhole invert (depth) and cover levels, and detail whether there is any damage to the pipes.
If you’re building over or near a Thames Water sewer that is classified as ‘Public’, you will likely need to submit relevant drawings and details to apply for a Build-over Agreement. Most residential applications will be for pipes up to 160mm in diameter. There will be additional 4 hours of work for us to generate the design documents and manage the application on your behalf.
We will generally recommend instructing a private Approved Building Control Body instead of the Local Authority Council (*our preference only). A Building Control application is split into two sections.
Plans Check
This is where our drawings and the engineer’s calculations are submitted to the inspector, and a desktop study is carried out to check compliance with the Building Regulations Approved Documents. Payment for this is generally required on the submission of the application.
Inspection Checks
These are carried out at various stages of the build to check progress on site. The inspector will check compliance with the Building Regulations and comment on any alterations needed. Payment for this is generally required following the first inspection.
(*exc VAT)
Plans
Inspection
Combination of the above, side and rear extension
£400
£500
Combination of the above, side and rear extension
£400
£500
Combination of the above plus major internal structural alterations
£500
£700
Major works to 4+ bedroom property
£600
£900
Dont forget! Add 20% VAT and 10-15% on top of your builders quote for Professionals like AURA!
Our build cost analysis of 100's of projects suggested an average of 12% in professional and statutory fees above the base build costs from your builder
Build Cost – Example Case Studies
Case Study 1 – Large single-storey rear house extension costs (with internal reconfiguration and cosmetic upgrade)
Cost Overview
The table below gives an overview and estimated prices ranges for how much your house extension may cost.
*(Costs updated to 2023/2024 rates)
Work
Notes
Area (m2)
M2/Unit Price
Total
GF – New works
Basic rectangle, high-end doors/glazing
36.4
£3,000* per m2
£109,000*
GF – Major structural opening
Unit
£10,000
£10,000
GF – Remodel
minor structural alterations, new elec/plumbing, cosmetic upgrade
65
£1,000* per m2
£65,000*
FF – Internal works and additions
minor structural alterations, new elec/plumbing, cosmetic upgrade
Case Study 2 – Side-return Extension and Kitchen Refurbishment
This type of extension project is most common in London. It can be misleading when taking a £/m2 value because of the large number of engineering works needed to create a small amount of additional floor area. Despite this, the stunning open-plan kitchen/living space that this creates can really improve the home, adding value for both occupants and the house’s selling prospects.
Based on standard industry cost estimates, a value of £3,000/m2 would be taken here for the extension works. The additional floor area is approx. 15m2, so the guideline cost of this structural work is £45,000. Taking a figure of £750/m2 for the refurbishment of the remaining 20m2 = £15,000, plus approx.. £10000 for the major structural opening. But this would fall short of what this could be built for (!) because of the large number of works needed in just a small area. It skews the figures significantly.
The below breakdown gives a better reflection of what you should expect for this type of side return extension, bespoke glazing and large rooflights.
Work
Notes
Area (m2)
M2/Unit Price
Total
GF – Side Return Extension
Roof glazing, high-end doors.
15
£3,000 per m2
£45,000*
GF – Major structural openings
Unit
£10,000
£10,000*
GF – Refurbish
new elec/plumbing, a cosmetic upgrade
20
£750 per m2
£15,000*
Total (ex.VAT)
£70,000*
GF Side Return Extension
*This cost is likely to be more:
(ex.VAT)
£100,000-120,000
Excludes Kitchen and VAT.
The kitchen could be anywhere between £10,000 – £80,000+ (as is the case with this Tom Howley Kitchen shown)
We’d suggest budgeting circa. £140,000 – £160,000 for this side-return and refurbishment to include VAT and Professional Fees.
Graham, Mark and the Aura team have supported us on the planning permission and design of our building works. The service has been 2nd to none - white glove level. Mark our main contact is responsive and helpful. Using Aura was a superb… More decision and looking forward to completing the journey with them over the next months.
As main contractors with appreciation for good and efficient design, we were very impressed with Aura from day 1.
The tender pack had more information than some other projects we have done at completion, all the information is precise and… More carefully considered.
On top of that their ongoing project management is flexible and approachable.
Hope we get to work with them again in the future.
We instructed Aura Architects for a self-build project, they have seamlessly guided us through the process with great care and detail. We have thoroughly enjoyed with Francesco who was been extremely helpful and patient with the project,… More getting us to planning approval which took over 2 years but this did not deter his dedication to the project in what has been a very challenging process.
The whole process has been handled professionally with great communication and understanding from Aura who have taken great care to ensure we are happy and understand each of the key elements.
We are absolutely thrilled with what Aura have created for us and we can not wait to see the project come to life.
I am pleased to recommend Aura for any of your architectural needs! They have been fab and most importantly reliable! Thanks very much and a special thanks to Francesco.
Thanks, J&D.
I'm pleased to provide a review of Aura Homes for their work on our 4-bedroom self-built home in Hertfordshire. It has been a great experience working with them. Architect Francesco in particular displayed a good understanding of our… More vision and delivered a design that met our expectations. Their expertise and attention to detail were evident throughout the project.
Ben is firstly a great guy, full of ideas and creativity and positivity, along with experience and intelligence. Secondly, he isn't going anywhere, he is very trustworthy, a man of his word, stable and growing his business in and around… More London. Always looking to find the best solution for your needs and not afraid to show ambition for your project, whilst having a strong knowledge of all current rules/regs and an understanding of the objectives and constraints of the planning system. As an outgoing and gregarious networker, he has positioned Aura as introducer & deal-maker, so if you need introductions to trusted quality services like: Builders, Project Finance, Consultants (e.g. Traffic, Trees, Planning Law) - he usually knows someone!
I recently contacted Aura Homes Ltd to discuss a small development project. The project was unusual and a lot of factors needed to be taken into account due to the location, site surroundings and practicality of the proposal.
I originally… More discussed it with Ben Richards who I found to be helpful, knowledgable and very accommodating in that he listened intently to give a fair assessment of feasibility.
Iris Kouneni was assigned to me and met with me to thoroughly discuss and understand what my intentions were. Like Ben, she digested my layman’s view and proceeded to give me her professional opinion.
Iris and Ben were an absolute delight to work with, professional, knowledgeable, enthusiastic and communicative to mention just a few of their qualities.
Unfortunately due to the COVID19 lockdown we have had to shelve the project.
It's been a pleasure to work with Aura Homes Ltd, refreshingly honest and professional.
I look forward to working together with them in the future.
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Create Your Brief
We’d love to hear about your project.
Our easy ‘Create your Brief’ form will ask some additional information about your project, which will help us understand your project better so we can be more effective in our response.
Get in Touch!
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Create Your Brief
We’d love to hear about your project.
Our easy ‘Create your Brief’ form will ask some additional information about your project, which will help us understand your project better so we can be more effective in our response.
Get in Touch!
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Create Your Brief
We’d love to hear about your project.
Our easy ‘Create your Brief’ form will ask some additional information about your project, which will help us understand your project better so we can be more effective in our response.
Create Your Brief
We’d love to hear about your project.
Our easy ‘Create your Brief’ form will ask some additional information about your project, which will help us understand your project better so we can be more effective in our response.
Get in Touch!
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