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As a basement conversion specialist we offer you a complete design and build package and you can discover more about our work right here.

We can draw up designs for your perfect new basement space then bring them to life.

From cinemas, gyms or bowling alleys to spas, play rooms or swimming pools, all types of basement conversions allow Londoners to transform a house into a dream home; even if their dream is simply more space for the kids.

Call us today on 07751583714 or fill out an online enquiry form. We will arrange a free visit, no obligation site survey of your home.

We offer a full no-stone-unturned service, which includes designing, excavating and rebuilding London basements into anything that residents can imagine, including playrooms, gyms or even swimming pools.

We have years of experience in creating extraordinary basement conversions and we can meet the most demanding and outlandish of client ideas.

London Basement Conversions

It can be more cost effective to expand beneath your current property with a basement excavation. It is also easier to get planning permission for them than another story.

They add substantial value to your home. If you’re thinking of selling up and taking advantage of the London house price boom, you could gain even more with a glamorous signature basement.

Underground rooms can add between 10 and 15% to the value of a home, while basement conversions in the centre of London can add as much as 20% to the price tag.

Call us today on 07751583714 or fill out an online enquiry form. We will arrange a free visit, no obligation site survey of your home.

Planning permission for a London Basement conversion

Planning permission differs from borough-to-borough, however, in some of London’s swishest neighbourhoods the council are clamping down on large-scale basement excavations. The Royal Borough of Kensington and Chelsea and Westminster, amongst others, have changed their planning laws after a slew of complaints from residents and businesses.

Almost all London basement conversions need planning permission, however, there are rare circumstances where it may fall under permitted development. Typically you will need some or all of the following permissions:

  • Planning permission

  • Building control

  • Listed building consent

  • Party Wall Agreement

  • Highway licence

  • Skip licence

  • Parking suspension

  • Streetworks licence

  • Freeholder consent (if you live in a flat or leasehold house)

Your basement project may be refused planning permission because of ‘over-development.’ What this actually means can be wide ranging. The London Borough of Richmond-upon-Thames describes it as ‘Just as overly large extensions above ground level can dominate a building, an extension below ground can be of an inappropriate scale.’

Other things you may need to think about are:

  • Tree and root protection: if you damage street trees or ones on adjoining sites some boroughs may refuse your application.

  • Drainage and rainwater: A basement development may have to provide an appropriate proportion of planted material to allow for rainwater to be absorbed.

  • Basements being used as living accommodation: if you plan on using your basements to house living accommodation, such as family or staff bedrooms you may need to ensure the rooms have sufficient daylight, outlook and privacy.


Cellar conversions

Many historical properties in London already have cellars. This offers the home owner the option of converting what used to be a storage space into a liveable space. Depending on what you plan to use the space for you may not have to ask for planning permission, however, if you wish to turn your cellar into a basement flat, this will require planning permission.

What are the steps to getting a basement conversion in London?

There are three main steps to basement conversions. These include

  • Design and planning process

  • Structural phase

  • Fit-out

1)Design and Planning process

1) Site survey. A surveyor will come and visit the property and will be able to advise if a basement conversion is feasible for your home. If the project is feasible, the surveyor will give advice on what can be achieved and will take measurements for a quotation.

2) Once this is done, a quote and specification will be supplied and a contract drawn up.  Once the contract is signed, the design and planning process can then take place.

If your property has a wall connected to another property or it’s detached and the basement conversion comes within 3m of their property, a Party Wall Agreement will need to be sorted. One of our certified party wall surveyors will help you through this process.

3)Once the planning permission and Party Wall Agreements are in place, the construction phase can begin. On average it can take between 6-10 months to complete a basement conversion.

2)Structural phase

This part of the process involves the following:

  • Securing the site with hoarding

  • Weatherproofing

  • Ensuring it passes all health and safety requirements

  • Securing the Underpinning

  • Digging out the soil and disposing of it correctly

Once all the above have been completed, it is time to waterproof the basement. This is usually done with sump and pump drainage systems and we also add a delta membrane system. If your specification includes any lightwells or windows, it is in this phase that they will be installed.

3)Basement Fit out  

When the structural phase is complete – it’s time for our team to take over. This means transforming the shell into liveable space. What will be done and how long this will take is dependent on your specifications, but as a rough guide, here is what will be completed:

  • Utilities such as gas, electric and plumbing will be installed

  • The flooring will be finished, including any underfloor heating

  • Any bespoke carpentry and joinery are carried out

  • Pool, bathroom or kitchen installation

  • Any other specifications that need to be added

At the end of this phase, one of our representatives will meet with you to give you your completion pack. This includes details of all guarantees, your gas and electrical safety certificates and building control sign-off.

Contact Cadman Design and Build today!

We can oversee every step of the basement conversion process with our team of architects; from gaining the essential planning permission and approval needed to create your dream home, right through to the actual digging out, construction and fit out. Alternatively, we are more than happy to cater to your specific needs, for example if you have your own architect and/or structural engineer that you would prefer to use, then we are happy to work alongside them.

Every Basement conversion in London that we complete, is tailor-made to the customer’s specific needs, so all your requirements will be discussed in detail when you meet with our team of surveyors –  and if you only wish to use our construction team, then this isn’t a problem.

We work closely with a group of approved building and basement conversion contractors to deliver our work, all of which have been carefully vetted by the experts and, as a client, you will have a direct contract with one of our approved contractors, with all payments going to the appointed team.

Our strict trading agreements with all of our contractors set out how they need to operate, and allow us to effectively manage the whole process. This gives us the control on rare occasions to deal with any issues or problems affectively.

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