How much does a loft conversion cost in London?

Unsurprisingly how much a loft conversion costs varies depending on the scale and complexity of the work.

How much does a Velux rooflight / basic room in the loft cost?

This is the cheapest type of conversion and will typically be somewhere in the region of £25,000-£40,000. With this type of renovation you can expect the floor to be reinforced, two skylights, a staircase for access, full electrics, fire safety measures and insulation.

How much does a dormer loft conversion cost?

You get all of the above with something like this plus the addition of dormer windows. Dormer roof construction increases floor space, adds height and gives you more natural light. They help with staircase access too.

You won’t get anything cheaper than £35,000 and if it’s a dormer conversion with a double bedroom and en suite you'll be looking at anywhere from £50,000 upwards.

How much does a hip-to-gable loft conversion cost?

At this point, you’re talking serious construction work. You will need scaffolding to be fitted with an appropriate cover as most of the roof structure will be removed – this will bump up the price. Here the time estimates of the contractor have to be realistic; if not the price can rise quickly.

Also as you will be raising the flank wall, you might have to build the wall in masonry, which may require a specialised trade such as bricklayers. It could be good to confirm the adequacy of the foundation of the existing flank wall before raising it. In London, you should be budgeting for at least £60,000 upwards. 

The main types of loft conversion

Dormer loft conversion

Most loft conversions use dormer windows. Here, you’re building out so that inside you often have an area of flat, full-height ceiling, and your window is vertical. As well as the extra space created, a dormer window will be less noisy when it rains, and is easier to look out from than a roof light.  

There is a huge variety of conversions using dormers: you can have multiple dormers on the same side of the roof, or dormers front and back, narrow dormers or wide dormers. 

Hip-to-gable loft conversion

If you live in a detached, semi-detached or end-terrace house, you might have a hipped roof. With a hipped roof, the roof slopes on three (semi-detached/end terrace) or four (detached) sides.

With a hip-to-gable loft conversion, one of those slopes is removed and you build out to a vertical wall (gable). Sometimes this type of roof extension is used in combination with a dormer on one of the remaining sloped sides of the roof. 

Rooflight/Simple room loft conversion

This is the simplest option. You’re not extending the roof – you’re adding windows that lie at the same angle as the rest of the roof.

Most of the work will take place on the inside, where you will need to build a new staircase – unless you are already lucky enough to already have one. You will also need to lay down a proper floor, and probably insulate the room. 

Mansard loft conversion

This is the most ambitious and expensive option is mansard loft extension. (It’s also almost certainly the only one that has a pop song named after it). Essentially, with a mansard you’re replacing at least half your existing roof, and sometimes all of it, with a gently sloped or sometimes flat roof with sharply sloped sides.

You get much more new space than with the other types of conversion, but you will need planning permission, and in some areas (eg a conservation area) that could be difficult. And, as you’re getting your builders to do much more work, you will pay a lot more too.

Next up in our ultimate guide, some of the details of your loft conversion you might want to consider.