Make sure a basement construction project is stress-free for everyone, by following our top tips.

1. Digging in Before Getting the Right Permissions

Attaining the correct planning permissions can be more challenging than the actual construction project itself sometimes, but it’s an unavoidable necessity that’s best done sooner rather than later – unless you’re happy to wait up to an additional eight weeks to start building.

It’s also important to keep in mind that there are certain restraints to consider when planning a basement extension.

For example, in the Royal Boroughs of Kensington and Chelsea, basements have been restricted to a maximum of one storey, so look into local planning permissions before drafting any sketches.

2. Trying the Neighbour’s Patience

No one wants to be the ‘talk’ of the town if said ‘talk’ is less than favourable. Show your neighbours that you care by hiring a reputable basement firm that is ‘Considerate Constructors’ certified.

A mindful basement contractor will prioritise keeping neighbours up-to-date on the project, keep work within normal business hours and make sure the lines of communication stay open throughout the duration of the basement extension project.

3. Waterworks

Both literal and proverbial.

Ensuring that the basement is watertight is one of the most important aspects of the design but sadly, there are basement companies out there that are not fully experienced with the latest methods of effective waterproofing.

If a basement is not waterproofed properly, it will let you know – with leaks, damp, structural damage and even collapsing walls. Definitely something to be avoided at all costs.

There are two main kinds of waterproofing involved in basement design. The traditional chemical method is called ‘basement tanking’ and uses cement based renders to waterproof basement excavations, however this method is becoming less popular as water table levels rise and lead to greater hydrostatic pressure on a lot of properties.

A more reliable and common technique is the use of a textured membrane made from Polyethylene sheeting called a Cavity Drain Membrane. This covers the new subterranean walls, much like lining your basement in giant bubble wrap. As well as being impervious to water, a Cavity Drain Membrane is also vapour proof and provides extra insulation to properties.

Whichever method you deem best though, always ensure you are using a reputable and experienced basement construction and design firm like Knowles.

4. Letting the Garden Become a Rubbish Heap

Don’t upset the locals by turning your garden into a massive eyesore. Retrofitting a basement is a massive undertaking and the debris coming from under the house can quickly accumulate.

To avoid this, ensure that you use a basement construction company that prioritises a tidy building site.

5. Cutting Costs

Inarguably, the cost of fitting a basement reflects the quality of the work undertaken. Some basement construction companies may offer comparatively low prices, but the question to ask is whether cutting back on initial cost is worth the hassle (and added expense) of ongoing problems often seen in below-par basement conversion projects.

6. Not Utilising Space

At an average cost of £500-1000 per square foot in London, you want to make the most of a basement conversion. If you’ve hired a basement construction firm that prioritises ‘value-engineering’ like Knowles ( expect a design that utilises the space to its full potential. For other inspiration on maximising on space, consider choosing versatile features, like moving floor swimming pools that allow you to have both a swimming pool and a room coexisting in the same space.

7. Stress

Could creating the perfect basement extension wreak havoc on stress levels? In one word, yes. High expectations, ballooning budgets, things that go creak (and crash and boom) in the night, a cluster of strangers coming and going and limited access to those amenities you’ve grown accustomed to – like running water and working appliances – can get to anyone. While you can’t escape the anxieties tied to a major renovation like a basement extension, you can definitely lay the foundation for a less stressful one.

Some ways to help manage stress levels during the basement conversion process are being realistic about your expectations (depending on local planning permissions, you might not be able to have exactly what you had in mind initially, (i.e. a 3 storey basement in Kensington), expect waiting times (depending on the materials and feature you want – it could sometimes take months to be delivered) and using a reputable and experienced basement contractor.

Knowles is one of the leading authorities in basement construction in London, designing and building hundreds of basements yearly. If a basement conversion project is on the cards, contact Knowles for some specialised assistance.