The London Guide to Under Garden Basements

We've created a handy guide for those with a big garden or driveway who are thinking about a house extension. Read online or download the PDF and discover why we recommend an under garden basement or under driveway basement.
 |  Architecture

For those with a big garden or driveway who are thinking about a house extension, we recommend you consider an under garden basement or under driveway basement. Dig deep to get a high ceiling; put light-wells and roof lights in and you have an incredible space that feels just as good, if not better than your accommodation upstairs.

Cinema rooms, playrooms, games rooms, wine cellars, gyms, saunas, swimming pools, nanny, granny and teenage flats are just some of the ways we are seeing under garden basements being used.


This guide will explain how Ensoul Interior Architecture will take you from interest, to an approved planning application to proceed.

Under garden basements add significant value to your property. Ensoul has delivered more than 2x return on investment for under garden basements in terms of basement cost vs the uplift in property valuation. But aside from adding serious amounts of floorspace and value, here are 5 great reasons to go under your garden instead, or as well as under your house.

An under garden basement in London with lightwells and terrace

1. Brighter and lighter

By building a basement under a garden or driveway, we can architect in walk-on roof lights, lightwells and terraces to flood your basement with light.

2. Fresher

With lightwells and lower terraces you can throw open the doors to bring in fresh air and, with some planting and furniture you can even enjoy a small subterranean garden.

3. Quicker

If you have good side access to your garden, installing a conveyor belt is much easier and could save you considerable time and hassle on your construction.

4. Bigger

If you are fortunate enough to have a long or wide garden, you can create a large basement footprint as an alternative or in addition to an under house basement.

5. Lower impact to you and your neighbours

Under garden basements are less of a structural risk to both your property and your neighbours' properties as they are not underneath. They also create less noise and movement during the construction period as you are further away from your houses.

Step 1: Feasibility

Planning restrictions

Every planning office has a different policy regarding what you can and can't do with under garden basements and basements generally in the borough. So it's important that we investigate the latest basement policy and guidance of your local authority at the very start so you know what kind of basement is feasible and any design or cost impact. For example:

  • Wandsworth basement policy recommends that it would be good practice to retain a depth of at least a half of the back garden.

  • Merton basement policy stipulates not to exceed 50% of either the front, rear or side of garden of the property.

  • Royal Borough of Kensington & Chelsea basement policy limits the extent of basement excavation to no more than under half the garden and the depth of a single storey only.

  • And Westminster's new basement policy has introduced an £8,000 levy from 1 September 2016 for a ‘subterranean squad of basement nuisance busters' – charged with overseeing and controlling traffic impact, stricter working hours and complaints. It's the first of its kind in the country and assumed to be picked up by other boroughs.

Conservation Area restrictions

If applicable we will need to ascertain any additional restrictions placed on development in your area.


If you've got trees either in your back garden or your neighbours', in the vicinity of your new proposed basement, we will need to consider the impact. Viability will depend on how many, what species and their maturity.

Step 2: Ensuring Value

We conduct desk research and talk with local estate agents to establish what your newly proposed basement will add in terms of additional pounds per square metre. We can then ensure that the cost to value ratio is in check and that you get a great return on investment.

We have seen the ratio of property value per square metre to build cost per square metre at 2:1 or more in some cases.

Step 3: Surveys

We will need to get some surveys done to inform the basement technical design and satisfy your planning office requirements:

  • Geo-technical survey - this reports the soil structure down to the depth you are digging and presents information and any likely issues regarding this and the water table.

  • Drain survey to ascertain where the drains run around/under your house and garden to understand the impact of the basement construction. Depending on where the drains run, a separate “build over†agreement may be required from Thames Water.

  • Topographical survey to get accurate dimensions of the site to draw your plans to.

  • Arboricultural survey to investigate trees in yours and your neighbours' gardens to see what impact a basement dig may have on the health of any trees.

Step 4: Architectural Design

Once armed with local authority policy, the necessary survey results and an agreed budget, we will design your basement plan. This plan will include:

  • How big and what shape it will be

  • How we propose to connect your new basement to your existing house

  • What's the best space plan and room lay-out  

  • A high level interior design plan and furniture lay-out so that we know the architectural design is in perfect harmony with the interior plan

  • Where to put services i.e. drains, electric runs, ventilation, etc.

  • Access and exit points

  • Roof lights and lightwells to provide lots of natural light and ensure a high quality living space

  • A garden lay-out that will go back on top of your new basement

Step 5: Neighbour Support

At this stage and definitely pre-planning application, we recommend making the time to book 1:1 meetings with your close neighbours to talk about your plans over a coffee or a glass of wine. Ensoul will help to create a presentation pack for you and can even attend if its helpful for answering technical and build questions.

The main things to communicate are:

  • Explain why you're wanting to create your new space and what it will mean to you / your family. Neighbours are far more supportive if they understand that you need more space for music practice with contained noise levels; or space for a live in nanny so that you can go back to work etc.

  • Provide them with a top level overview of the proposed basement size and design.

  • Go through timings with them so they can understand the duration of works and impact to them.

  • Explain that it is being professionally designed, built and managed to quash any fears about cowboys potentially collapsing your houses.

  • Make a small gesture to them e.g. pay for a window cleaner once a month during works. The goodwill will go a long way and in the scheme of things the cost is tiny.

  • Critically, get any concerns or questions answered there and then, or written down so that they are dealt with immediately or if not there and then, before planning. This will prevent potential complaints or open comments on your local planning website when we file your application.

Step 6: Planning Application

Next we finalise your plans, write the necessary content and file your planning application which will take up to 8 weeks from acknowledged receipt by your local planning office.

Typically, your assigned planning officer will want to visit, will have some questions that need answering, and may sometimes indicate some conditions that may be required to give planning consent. We will handle all of this on your behalf through to conclusion and result.


Under garden basements add a fantastic amount of living space and can really improve your quality of life with extra room for kids; gyms and pools for fitness enthusiasts and much needed extra accommodation for those with older kids or live-in nannies or relatives.

Whilst there are many benefits over and above digging under your house, under garden basements are highly specialist structures that need an experienced parter to ensure a rigorous approach to design, waterproofing and build. 

Ensoul has a proven approach to getting clients through the initial planning application stage and beyond to a finished beautiful basement. We will be updating this document shortly with a new Chapter that outlines how we go from approved plans to a watertight basement with a beautiful fit-out. 

Want to find out more or get started?
Call us today on 020 3637 0700 or email 

Download a PDF
Download or read The London Guide to Under Garden Basements and learn how we'll work with you from concept to planning approval.


An under garden basement by Ensoul



Mike Lander - Residential Project Manager, Programme Director
Project Manager & Programme Director
Mike is a highly experienced programme director and engineer and runs Ensoul's project management and smart home operations with unrivalled precision.

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