Basement Extensions in London: DHA's Advice

According to a study by Newcastle University’s School of Architecture, Planning & Landscape, London basement extensions are now as normal as loft conversions. Researchers discovered that the City of London and its 32 boroughs approved 7,328 basements between 2008 and 2019.

 

 

The study revealed that Hammersmith and Fulham accounts for over 18% of all basement builds – 1,337 in total.  With Kensington and Chelsea and Westminster accounting for the second and third most excavations – 1,152 and 745, respectively.

 

The study also showed that the granting of planning permission to build basements has varied over time.   In 2009,  334 standard, 93 large and just 12 mega-basements were approved – a total of 439 across the year. The figures peaked in 2014 when 645 standard, 161 large and 36 mega–basements – a total of 842 across the year – being approved. Since that date, numbers have declined overall, with reasons being noted as the 'introduction of stricter subterranean planning regulations introduced by some boroughs, house price falls due to Brexit uncertainties and the impacts of the Covid-19 pandemic'. 

 

However over the last year, basement construction in London has gained significant traction.

 

What type of Basement Developments are there?

 

Here are the main types of basement development you can consider:

 

1. Basement excavation and extension:

i) Extending under the footprint of the house; and

ii) Extending under the garden.

 

2. Basement convergent:

i)  Converting an existing, underutilised basement into habitable space or a separate residential unit.

 

 

3.  Lightwell:

i)  Creating a lightwell to ensure natural light and air reach into the basement; and

ii)  Often visible from the street or within the private garden area.

 

Are the works I'm proposing Permitted Development or will Planning Permission be required?

 

Unless you're considering minor developments that don’t involve significant engineering or structural work, basement developments typically aren’t covered under permitted development rights and will require  planning permission.

 

Some boroughs, such as the London Borough of Camden, have introduced Article 4 Directions to remove permitted development rights for basement developments.

 

What Development Plan Polices do I need to consider?

 

As basement developments become increasingly common in central London, many boroughs have introduced detailed basement policies (Supplementary Planning Documents, or SPDs) tailored to their unique local context, challenges, and needs. The the key regulations and considerations you should be aware of before starting a basement development can be found here. 

 

What if my property is within a Conservation Area or is a Listed Building?

 

If your home is in a Conservation Area or is a Listed Building, basement development becomes more complex. These properties are protected due to their architectural and historical significance, meaning stricter regulations apply. Unlike some basement projects that may fall under permitted development, any basement work in these areas requires full planning permission.

 

To gain approval, you will need to submit additional documents and assessments to your Council, demonstrating that your proposal respects the character of the property and its surroundings. This often includes a Heritage Impact Assessment, explaining how the development preserves or enhances the historical integrity of the building. The Council will also carefully review any visible changes, such as lightwells, ventilation grilles, or access points, to ensure they are discreet and in keeping with the area’s character.

 

Beyond appearance, structural and engineering considerations are crucial. Many heritage properties have older foundations, requiring detailed structural impact assessments and careful construction methods to prevent damage.

 

How can DHA Planning help you?

 

Feeling overwhelmed by technical jargon and policies, or unsure where to begin with your basement project? Don’t worry, we’re here to help! With extensive experience in managing basement extensions and related applications across London, feel free to contact DHA Planning's Patrick Reedman or call us on 020 3005 9725 for professional advice.