AdviceConversionsExtensionsPhil Spencer

Phil Spencer on Attic Conversions & Basement Extensions

As many of us are choosing to improve rather than move, the question that follows is: what improvements do we make? Not only do these improvements need to provide an alternative to moving, they need to be cost effective/ add value to the property. Put simply, if you like the area you’re living in and it costs less to turn your 3-bedroom house into a 4-bedroom house than it does to move, why move?

Whether you need more storage space, larger communal living areas or more bedrooms, the two projects that deliver the greatest increase in living space are the loft conversion and the basement conversion. Of course building work can be messy and stressful but so can moving! For me it’s all about location. The house can change, the location can not.

I chose my house for its location and modified it to suit my family over the years — I’ve converted the basement and extended the kitchen and in my previous home I did a kitchen extension and installed dormer windows into the loft.

attic conversions

Image source: Wentworth Studio

Attic conversions

The first thing that comes to mind is the one thing that puts people off – planning permission. However, in many cases you don’t need to seek planning permission for either a loft or basement conversion under Rights of Permitted Development, which allow you to extend and change the external appearance of your home.

For instance, I’m about to start work on a place I own in Brixton where, in theory, it’s possible to extend the original house by up to 6 metres without needing planning permission. The local rules have been changing quite frequently of late — so its well worth exploring!

Not all properties will qualify but the regulations have recently been relaxed (in order to encourage/stimulate building work etc). Properties such as listed buildings or those in conservation areas will require planning permission however and local interpretation can vary, so it’s best to contact your local planning authority in advance.

If you do need planning permission you must seek this before commencing any work or you could face a heavy fine, be forced to tear down the work and even get a criminal record!

loft conversion

Image source: Pinterest

You also need to check that you own the loft space. If you’re a leaseholder you may need to get permission from the freeholder, landlord or management company and in some cases all three. If you do need planning permission you’ve got a far better chance of it being accepted if you keep within the same style of the original building, using the same/similar materials.

loft extension

 Image source: Pinterest

Attic conversions are most commonly used to create extra bedrooms, making them relatively easy and cost effective to convert. I recommend you work with your builder/ architect to decide upon a configuration that makes the plumbing work as simple and cheaply as possible. It’s also worth checking that your current heating system will be able to serve the extra living space. You do need to be realistic — the ceiling height needs to be no less than 2.3 meters to give enough headroom. Generally the stepper the pitch of the roof the better suited it is to conversion.

A few well placed sky lights can create a space that’s bright and open. Again ask your builder’s advice on where these should go. Dormer windows extend out from the original roof and they can be a good way to add head height and bring in light. These will require planning permission.

The cost of a loft conversion can be anything from £10,000 for a basic conversion with a Velux window to £30,000 for a larger conversion with structural changes, such as dormer windows.
attic extension

Image source: Pinterest

Basement extensions

A loft conversion is the quicker and cheaper conversion but it’s not suitable for everyone. For those who can’t extend out or up, or have already converted their loft and still need more space, a basement conversion may be the only viable option.

basement conversion

Image source: Fresh Palace

A simple cellar conversion can be completed in just a few weeks, whereas extending the cellar under the entire house can take months as the house will have to be underpinned. If there is access from the garden to street level for the soil to be removed, you can probably stay living in your home while the conversion is taking place. If there is no access and the soil has to be carried through the house or your ground floor has to be replaced, you will unfortunately need to move out while the conversion is underway.


Basement extensions are best suited to terraced or semi-detached homes in need of a bigger kitchen or even a pool/ projects that are best situated on the ground floor(s). You can expect to pay about £2,000 – £2,500 per m² for the structural work and fit-out costs are around £750-£800 per m².

cellar conversion

Image source: 1 Design Per Day

basement extension

Image source: The Telegraph

This basement in Chelsea has faux-windows and computer controlled lighting so you wouldn’t even know you’re underground!

Well designed loft or basement conversions can add a significant amount of value to a property. Not only do they increase the valuation of the property, they change how you live in your home and as far as I’m concerned this is where they can really add value. When I bought my family home I bought it for its location. I always knew I would make changes as we live in it and our requirements change. There’s no need to move, as long as you can improve.



Looking for help and advice with converting a loft or basement? Find a qualified and trusted specialist builder on Rated People and start enjoying more living space at home.

Phil Spencer

Phil Spencer doesn’t need much of an introduction, he’s TV’s most well-known property presenter, having co-presented Location, Location, Location and Relocation, Relocation for over 10 years. Phil'ls blog posts focus on adding value and advice/ tips for when you're buying or selling your house.

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  1. ist class pictures and workmanship I have been in the building trade 45 years started as a plasterer then extensions and the last 12years doing loft -garage-conversions and basements due to illness I have had to just design advise and project manage best wishes to you phil

  2. Great article with some inspiring photographs. Can I suggest a better proof reader as I found 6 errors with a potential, questionable two more.

  3. Very informative, and easy to understand. I have considered a loft conversion, but we are purpose built maisonettes and have on
    e below me, would I get permission for this?

  4. We have just moved into a ground floor flat with a large living room but the interior of the room is very dark, except by the windows at the far end. This means turning on lights at all times to illuminate the room away from the windows. How can we give the effect of daylight in that part of the room, at a reasonable price please? Thank you.

  5. I live in a top floor flat in a block of 12. We have a flat roof do you think it would be possible to extend up?

  6. Thanks everyone for your comments. They’ll be passed on to Phil so he can address your questions in his next blog post, next month.

  7. we have a basement under our house with patio doors, just need some kick to get the project moving. Can you advise and recommend any in wales?

  8. Great article! I definitely agree with you, basement and cellar conversions do add great value to the property and extensive extra space.

  9. Either/or, make sure you have the area surveyed, damp proofed, and with this, you can go ahead and add serious value to your home.

    Dean Webster

  10. Very informative blog, it is very nice and expressive information shared here that is really most helpful.

  11. Amazing pictures. I’m looking forward at loft conversions in Barnet but never thought about permissions as such. This was a really informative post. Thank you for the images. Truly inspiring!

  12. Both lofts and basement conversions can make incredible, unique spaces. Just look at those fantastic photos you’ve shared; who couldn’t fail to be impressed and inspired with such a room?


  13. WOW Basement conversions are best suited, very clean and kitchen and big place. very nice article I like it. thanks.

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