Basement Conversions in London



Basement Conversion Reading Architects

Basement Conversion in London

This blog outlines some of the key things you should consider if you plan to convert your cellar in London.


The complexities of a basement extension mean it can be labour intensive, so we recommend hiring the right people to keep costs under control and help you plan; see our fees here.


Basement conversions and extensions in London are increasing in popularity, mainly because the area is short of buildable space. Expanding the floor footprint of the property is critical for creating more space in a growing family home. From a developer’s perspective, increasing the size of the property with a basement conversion is a great way to add substantial value and make a considerable return on investment.



Kensington - Studio Apartment

How Much Does A Basement Conversion Cost?

If you have an existing basement that has access stairs and is relatively dry, the cost of converting it into a more user-friendly space is comparable to above-ground fit-outs such as bathrooms or kitchens



If your existing cellar is the right height and dry, a conversion to living room space could be completed for as little as £1,200 – £1,900 per sq metre depending on specification.  In some cases, a cellar conversion can be easier than a loft conversion.



However, most basements need water-proofing and other engineering work to prevent damp ingress and guarantee structural integrity. 


Many of London’s older properties have coal cellars and larder basements that convert into living space well. 

Cinema Room


Reception Rooms

Swimming Pools


Utility Rooms

Wine Cellars

Home Offices

If the floor needs to be lowered, the cost can go up significantly as extending a basement in any way or creating one from scratch is considerably more involved than a conversion. Ease of access for excavation equipment and removal of soil will also affect the cost of this enlarging. Whilst additional surveys may help, digging down might uncover unknown costs – from buried services to rising water tables.


The first step to making basement design plans is to speak to your architect about the likely surveys that will be needed.  They should be able to give you independent advice and may even be able to recommend local surveyors.


A good residential architect will spend time discovering how you want your new basement space to feel and look. Some architects charge fees as a percentage of project cost, however, this doesn’t motivate them to suggest money-saving options for your consideration. Aura Homes are transparent with their fees, and you can ask for a quote to help you budget.

theobalds manor

The Core Values At AURA are:

  • Honesty and integrity

  • Innovation and creativity

  • Attention to detail

  • Understanding and respecting people

  • Sustainability

The values underpin our vision which is to:

  • Maximise your home’s space, ensuring that it’s tailored to your needs

  • Make use of natural light to improve your sense of well being and your home’s airiness

  • Create designs that are clean and simple, but use dashes of colour and textures to create added interest

  • Create energy-efficient buildings by thinking sustainably

Basement (under existing house plus underpinning):

£2,250-£4,000 per m2 of additional floor space (Site accessibility will play a large part in your basement extension hence the wide range in cost.)

Basement (under garden):

£2,000 – £3,000 per m2, additional floor space.

(This can be a great option in conjunction with walk-on roof lights to let light into your new basement space.)

Wondering how much will your basement conversion will cost?

Find out here

The Surveys You Could Need For Your Basement Conversion:

To limit all risks, completing several different surveys will help build a great understanding of your limitations and possibilities. This will help make a more robust Planning Application and give your engineers the correct information to design your basement safely.

The surveys we recommend completing are:

Geotechnical Survey

Flood Risk Assessment

Drainage Survey

Topographical Survey

Arboricultural Survey

How To Add Natural Light To Your Basement Conversion

Adding light is one of the more difficult challenges you may face when converting a basement. Lightboxes will be your source of natural light, so planning these strategically is important so that the room is filled with light and is not dark and dingy. Designers are full of basement conversion ideas and will strategically place the interior spaces and lightwells to maximise all opportunities for natural light. Basement conversions in London are particularly challenging, but the results are very much worthwhile.


Strategically placing rooms that do not need natural light will mean you can optimise the rooms which may need it. For example, adding a utility room or wine cellar in a problematic area to light means that you can place a living room or bedroom in an area with access to the window.


Minimising the number of interior walls decreases the amount of light that is being blocked off. This depends, of course, on your brief and needs for the project. If an open plan does not work for you, glass doors and separating walls will create separate spaces and create an airy feel.

Successful home extension

Achieving Planning Permission For Your Basement Conversion

Every planning office will have its policing regarding cellar conversion, so you must investigate and research your Borough thoroughly. Using an architect who has an excellent planning approval success rate and is local to your area means they should have previously worked alongside the planning office. Most London Boroughs now require a Basement Impact Assessment before considering your application, and some have taken steps to limit the depth and size of basements.

Getting the approval declined can often mean you have to go back to the drawing board, which can come with more delays and an increase in costs.


Hiring the necessary specialists will help you build a robust application – an experienced architecture firm like AURA Architecture will do this for you and recommend the correct guidance.

Methods to waterproof basements:

Waterproofing is a critical and vital stage of any basement conversion. It is essential that it is done correctly and no corners are cut. A leaking basement is a complicated issue to solve, and the basement conversion cost can rocket as it is not always easy to locate the origin of the leak – stress that you do not need! We recommend that you find a Waterproof Design Expert from the start to help you with the design process.


Through the rest of the project, your Architect should help you find and liaise with an experienced Waterproofing specialist. Water Proofing is a very skilled trade so hiring and finding the correct experts and construction companies is extremely important. Be sure that you are provided with the necessary Paperwork and Certification. This will help you with guarantees (should you look to sell the property) and be presented to your insurance provider (if the dreaded happens, and you get a leak). Typically a manufacturer’s warranty of 30 years will be provided. We are experienced in using DELTA Waterproofing systems.

Successful home extension

There are 3 main methods for basement waterproofing:

Type A


  • External Waterproofing: Great for new builds with lots of space around, it is a really effective way of preventing leaks. However, it needs a lot of space and cannot be done with neighbours close by. Therefore it is usually not appropriate for London basement conversions.

Type B


  • Waterproofing Concrete/Slurry: Concrete is positioned and laid around the perimeters to prevent the water from coming in. This is a suitable method for water prevention in London, although we usually see this leads to leaks after time.

Type C


  • Cavity draining tanking system: This is a draining system that gutters all the water in a trench around the perimeter of the conversion and pumps it out. We would recommend using this method as it is often more reliable as re-directing water is a lot more manageable and predictable than attempting to stop it.

Our Online Reviews

Scott Robertson
Scott Robertson
June 20, 2023
Professional, reliable, great to work with. Highly recommended if you are renovating your house.
Carina Isabel Lopes De Carvalho
Carina Isabel Lopes De Carvalho
May 2, 2023
It is a company of excellence
Emily Stuart
Emily Stuart
January 25, 2022
I used Aura for a side return and rear extension, and a renovation of my first floor bathroom. I wanted something unique and characterful, with lots of natural light. Aura really went above and beyond my expectations, creating me a space that truly is more than I could have imagined. From the initial consultation, where I felt immediately at ease with the team, to the transparency in their costings, all the way through the design process and project management, Aura have been consistently professional, communicative and flexible. It certainly hasn’t been an easy time for anyone in the industry, but Aura’s solution-first attitude and their adaptability made it so easy to work with them through lockdowns, supply chain challenges, pingdemics and everything in between. It was a true pleasure to work with the team - they really do their utmost to make the process as straightforward, simple and enjoyable as possible. 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.
Rob Birkin
Rob Birkin
November 18, 2021
February 9, 2021
I chose to use Aura based on their reviews in June 2020. At first it was a really good experience and I was impressed with their professionalisim. I received my drawings and wasn't completely happy with them. The 4 options I was given were all basically the same thing. They never came to my property to see the space or get a feel for where the light was coming in etc. The bathroom on the drawing didn't make sense as it was so small. (See below). The snug was also like a meter so again didn't make sense. I tried to escalate this to Ben, and I was offered another call but I had lost confidence in them. My neighbour was also doing work on her flat which is a similar layout and in contrast her drawings were really well thoughtout. In the end I had to pay again to get my drawings redone. (Attachment P&S - one example of my new drawings below - the more detailed drawings). I asked Aura for a partial refund as I never actually received a final drawing from them (despite paying for them) and they refused. It was just a disappointing and expensive experience.
Anthony Egan
Anthony Egan
May 22, 2020
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 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.
Brendan Quinn
Brendan Quinn
May 20, 2020
Thanks for reading this review. Ben is one of my monthly sponsors of the Property Events that I have run and also of the National Development Summit earlier in 2020. In a business setting I really appreciate Ben's support, particularly during COVid19- Ben had the option of pulling out of my events as a sponsor- as I have had to pivot- moving them online. Ben has continued to support these events as a sponsor, when he could have easily turned his back and moved on. Also at the National Development Summit 2020, Ben could see the effort I had put in to make the event, a great event, and himself and his team also equally put in huge effort. When you organise events, you ideally want things to go smoothly in terms of presenters turning up on time/before time, and with slides which are hassle free, and this Ben has done so. I have been to Ben's office several times and the staff have been really friendly. Ben's knowledge of working at Berkeley Homes, puts his company at a very high level.
Louise Hancock
Louise Hancock
April 13, 2020
Aura Homes is a highly professional firm of architects that always have the clients best interests at hart. The quality of their plans and drawings is superb and their turn-around when making amendments well within expected timelines. For bespoke projects, their research and recommendations (both in terms of quality and costs) is superb.
Harry Bucknell
Harry Bucknell
April 10, 2020
Couldn't recommend Ben and his team more. We were in a really tricky position with our building project and Ben navigated us safely out of it. Superb guidance, great technical knowledge and what I really valued the most was the communication. Always got back to me promptly which makes a real difference when stress levels are high. Thanks Aura!
Eugene Clarke
Eugene Clarke
April 9, 2020
The quality of work from Arua Architecture is to an excellent standard. We worked primarily with Ben and Gabby, they provide a friendly and professional service that minimised the worry and stresses associated with building projects. We hired Aura Architecture to assist us with our building project. We appointed them for the following work: - Regularisation on previous designs - Planning conditions discharge - Building regulation drawings - Detailed designs They came recommended from a Structural engineering company, and we were not disappointed.

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