Loft Conversion in London – What costs do I need to consider?

Loft conversions are one of the most cost-effective ways to increase the space in your home. In London, in particular, where space is at a premium, basement and loft conversions are a common feature.

Whilst excavating a basement is a more costly affair, a loft conversion is a relatively more ‘value for money’ kind of project. Of course, you can go to town with how much you spend on your internal specs, but if you had to choose a way to increase your living space in a way that won’t break the bank, a loft conversion is probably your best bet.

Loft conversion costs depend mainly on two factors:

  • The size of the project
  • Where you live

Though loft conversions generally increase the value of a property, how much any potential increase could be is governed by where you are in the country. Space is hugely expensive in the South so a loft conversion there would add more value to a property than it would in the North. Loft conversions can cost between £20,000 at the bottom end and £40,000+ at the top end. A conversion in a small house in rural England may cost £16,000, while the same job would cost a London resident upwards of £30,000.

Before considering a loft conversion, make sure your home will meet the current eligibility criteria, so you don’t find yourself building illegally. As long as your loft has a height of 2.4m+ (approx. 8ft), it’s eligible for conversion.

Loft extension or conversion prices also vary according to the type of loft conversion project you are undertaking.

  • Room in Roof Loft Conversion

This is one of the simplest kinds of loft conversions and prices start at around £15,000. The primary costs associated with this kind of conversion are a staircase, insulation, fire safety considerations, skylights, electrics, heating and lighting.

  • Hip to Gable Loft Conversions

This involves converting the hip (sloped) side of the roof into a flat edge which provides added space inside the loft. The hip-to-gable loft conversion price will also vary depending on what else you have done to the loft.

Average prices range between £30,000-£35,000.



  • Dormer Loft Extension

Dormer loft conversions extend outwards from the back or side of the roof in a box shape. These are sometimes referred to as kennel or box conversions and provide added space in the loft room. Dormer loft conversion prices vary depending on how many dormers you add and what else you do to the loft, but on average, they range between £19,000-£30,000.

  • Roof Structure Alterations

If you decide you want to completely overhaul the roof of your existing property and create living space at the top of the house, you will need planning permission. This is the most expensive of all kinds of loft conversions and prices are likely to start at around £40,000 as they will require the removal and rebuilding of the entire roof. This may be necessary either because the existing roof is not an appropriate shape, or because it is not structurally sound to undergo any of the simpler extensions.

You will also need to consider the costs of adding natural light into the space in the form of skylights, dormer windows and rooflights.

Rooflights that follow the pitch line of the roof are the most economical and can be done without planning permission. It is fitted by removing the tiles and battens where the rooflight will be fitted. The rafters are cut to make way for the rooflight after suitably reinforcing the remaining rafters. The rooflight frame is then fitted and flashings added before making good the surrounding tiling.

We found this handy cost guide that might give you a region-by-region idea of the average cost of a loft conversion.

At SDA Build London, we offer a complete design and build service, project managing your conversion or extension from start to finish. If you are considering converting your loft, give us a call on 0208 191 7595 or email us at for a no-obligation quote. We are specialists in all kinds of building work, especially in London, and we’ll be happy to share our recommendations with you.