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  • Writer's pictureJulie Bliss

The Downward Dig - how about extending down?

If you can’t go up (or you already have and still need more space), then why not think about extending down? If you’ve got a basement or cellar, then this is a great way to add significant value, particularly if you can access the garden directly from the lower space.


Basement and cellar conversions are very popular in denser urban areas where space is a premium and you often don’t have anywhere left to go but down! Many pre-1930s houses were built with cellars, and they’re particularly common in Victorian terraces.

Cellar and Basement conversions are usually covered under Permitted Development, unless you’re in a conservation area (check with your local council).

An existing cellar or basement conversion will cost around the same as a loft conversion, but can be more if you have to excavate or create an entirely new space.

Extending down is often a great idea in hilly areas where many houses are built on land that slopes away to the rear of the house and already have storage or other redundant space under the house.

Cellar structures can be really interesting in their own right...make the original architecture a feature for your modern build.


Bringing in as much natural light as possible is key. This can be done by high windows, light tubes and glass ceilings, or light from an open stairwell. If possible, it’s best to also dig out an area of garden behind the cellar or basement in order to create natural light via windows, sliding or bifold doors that can lead out onto a patio.

What to look out for that can end up costing more than you bargained for:

  • Poor drainage

  • Soggy land; clay, sand or marsh is not ideal

  • Need to move drains

  • A high water table

Always make sure you consult an expert on damp-proofing. Often older houses do not have an existing membrane or damp proof course and require tanking (applying a layer of waterproof material directly to the structure) or the creation of a cavity membrane (if there is a cavity!).

You must also factor in adequate underpinning and pay particular attention to party walls if you’re attached to another house. This doesn’t have to be any more of a drama than it would be for a loft conversion or knock-through within the above ground space, but you must always get advice from a surveyor or structural engineer.

Cellar and basement conversions with their own access can create the perfect guest annexe, rentable room, teenage retreat, home office, studio or games room can be a great way to increase your living space without having to move.

If you’re thinking of ways to improve or increase your home space, give me a call.

Photo credit - feature photo: Billy Bolton for Rose & Partners

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