In urban areas, where space and land are at a premium, it can be tempting to head underground in search of extra square footage. The maths is quite simple here; work out the value per square foot in sales value, the costs per square foot of adding a basement, subtract the latter from the former, and, bingo, you've got a pounds and pence answer to the value of adding a basement to a project.

But sadly, it’s not always that simple. Basements can add tremendous extra return on investment, but they don’t come without risk and significant expense for the developer. Here’s what you need to think about before adding a basement to your scheme.  

Key challenges with basements
Planning policy in your area
Each local council has a different approach to validating and determining a basement application. It is a constantly moving picture as new policies evolve. In most London boroughs, you must now provide construction management plans in a planning application. These plans may include a preliminary structural design or method statement and information on how many lorries will arrive and when. You may also need to complete a flood risk assessment and soil testing by a qualified professional. These all take time and add extra costs to preparing a planning application, increasing your risks.

The key planning issues for new basements often relate to the location of new light wells or lower garden areas, mainly if they are to the front of the property. This can be more pertinent in conservation areas or if the property is listed or considered a heritage asset.

Outside of London, we have found planning for basements to be much more straightforward, with no specific validation requirements.

Neighbour resistance to basements
There is often resistance to building new basements during the planning and construction phases. It’s no surprise, given the length of time of disruption and the potential risks. Whilst some of this fear of construction is unfounded, there are plenty of examples of basement projects going wrong. Consequently, we always recommend engaging your neighbours early in the process. The right project team of professionals and a skilled contractor will help to provide reassurance.