Basement Conversion and Extension: A Detailed Guide

We have talked a lot about ideas for various extensions and conversions but let’s explore these possibilities in more detail. So, if you don’t have enough space for an extension at the back or side of your property or even a garage you can convert, have you thought about the basement? While loft conversion is the best way to create additional bedrooms because of the location, the basement has a more flexible range of uses since it is closer to the existing living areas. (more ideas and tips here)

Why should you convert your basement?

Our first reason is the most beautiful one - a growing family. But what about an office? A gym? An arts studio or a music recording space? Even a games room? The list really is endless - so what do you need the extra space for? Even if you want your basement to be a place to store things, why not make it exceptional? A place that you’d want to spend time in.

What are the options when it comes to basement renovation?

1. New build basement

2. Renovating an existing basement or cellar

3. Extending out into the garden, front or side of the house, or directly underneath.

Is this project worth it financially?

In some parts of London and more and more elsewhere in the country, where property values are at a premium and stamp duty is high, many people are turning to basement conversions and extensions as a viable option. Hiring professionals for your basement extension will be essential for most of the tasks, but there are certain jobs you could do on your own.

So, the cost will vary depending on the type of the project – converting an existing cellar or building a new one.

Converting an existing cellar will cost £1,150-1,800/m² (including cost of tanking and insulation of the walls). Additional costs for lowering the floor level and underpinning in the existing cellar will be £1,500-2,000/m².

Costs for digging a basement under an existing house will always cost more and will result in a longer and more invasive build. If you are making a decision between a loft conversion or a basement extension, they cost about the same.

You always have to be prepared for obstacles - documents that are needed or poor land conditions can significantly increase your costs, so, be prepared!

●       Planning application (if needed) – about £170

●       Building Regulations application – £750 or more (depending on the project)

●       Party Wall Agreement – £700 per neighbour

●       VAT – 20% extra on top!

So all building projects with the home are always fairly costly but remember in most cases the overall value added to your could be between 10-15%.

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When is Planning Permission required?

Planning permission is not required if you are converting an existing cellar or basement since it falls under ’change of use’. This will be covered by Permitted Development (unless you are in a Conservation Area or your home is a Listed building).

Still, if you are significantly expanding your basement or building a new one, you will have to submit a planning application to your local planning office.

Building Regulations approval

Whether you are doing an extension, conversion or project to build a new basement, Building Regulations approval will be required since it is statutory minimum construction standards that ensure buildings are safe, hygienic and energy-efficient for you and your neighbours too (including verifying fire escapes, electrical wiring, waterproofing, and water supply).

The renovation or the repair of an existing habitable basement does not involve a change of use and therefore is excluded from the Building Regulations.

Party Wall Act

The Party Wall Act serves to protect neighbours’ rights and interests. It also relates to protection against distruption while work is ongoing.

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Here at STAAC we can handle all the planning, Building Regulations approval or planning applications for you, so contact our expert team today on 0808 1699964, email us at support@staac.co.uk or get out free Project Planning Pack right now on the website!