Chartered Surveyors London – A guide to basement developments

Basement and other subterranean developments have proved a strong trend in recent years, closely associated with London. The trend has increased significantly over the past five years thanks to a hike in land and property prices in the capital, which often makes it cheaper to dig down than actually move house.

It’s a great idea. In many cases it’s an outstanding success. But in some cases these developments can cause harm to the stability of the buildings above or to either side, cause drainage issues and floods, and even compromise the natural environment.

If you want to explore the potential for subterranean development in the capital, you need to make certain the work you propose won’t cause harm to the built and natural environment or affect local amenities like water sources, ground conditions, land stability and biodiversity. After all, the last thing you want is for your new basement to fall into the tube station below it, or flood every time it rains.

Approved document B of the UK building regulations, Fire Safety, Volume 1 Dwelling Houses, defines a basement as a storey with a floor which at some point is more than 1200mm below the highest level of ground adjacent to the outside walls. As you can imagine, this type of development almost always demands

planning permission, although in a few rare circumstances it can be classed as permitted development. If your property is in a conservation area, you will probably also need planning permission to cover any demolition works.

Every case is different, and some are more complex than others. Here’s some basic advice for you and your neighbours, which applies whatever the nature of your proposed basement development.

10 things for the property developer to consider

1. Consult your neighbours before you submit your planning application and before starting the work – it could save you all sorts of problems along the way
2. Give your neighbours at least a month’s notice for courtesy’s sake
3. Liaise closely with then throughout the project, keeping them in the loop about things like the completion date, changes of plan, particularly noisy or dirty times, when vibration from machines might happen, and dates for things like skips being delivered and removed
4. Make sure the builders plan noisy, dusty or vibrational work at the least inconvenient times
5. Make sure the builders comply with all the right highway licences and traffic orders, local parking restrictions and guidelines about materials left in the road
6. Make sure your builders keep other people’s drives and entrances clear
7. Ask your builders to join a considerate construction scheme
8. Provide the site Manager’s contact details and make it clear people know exactly who to get in touch with to talk about problems and make complaints
9. Make sure everyone complies with the approved drawings and plans
10. Get a signed party wall agreement via an experienced party wall surveyor like us

9 things for your neighbours to consider

1. Ask your neighbour or their developer for a timetable showing what will happen, when
2. Ask them to let you know when there’s going to be particularly noisy or disruptive work going on
3. If you want to give feedback on the planning permission, make sure you only address issues that affect planning legislation
4. Make sure you’re fully aware of the impact of things like construction traffic, parking, noise, dirt and vibration
5. Pin down any measures the developer will take to minimise the issues mentioned in number 4
6. Check your neighbour has had a proper party wall survey done
7. If you experience problems, talk to the site manager first. If it’s possible, collect photographic and date evidence
8. If the development doesn’t look like it’s proceeding according to the planning permission, get in touch with your local council planning enforcement people. The same goes if there’s a breach of the conditions set out in the Construction Management Statement
9. Bear in mind that an Environmental Health Officer can help you if levels of noise, dust and general disruption become unacceptable

While a basement development in London can be a great way to generate more space, it also comes with significant risks. The best way to ensure a smooth project that leaves you with happy neighbours is to tick every box and do absolutely everything by the book. We’re always happy to help developers achieve their goals.