Cost of a loft conversion in London 2021

25th September 2021

Keen to gain extra space with a loft conversion? In this article we outline the latest cost of a loft conversion in London 2021, the cost of different types of London loft conversion – from a first-fix loft conversion to a generous Hip-to-Gable loft conversion – and how we can help you keep costs down, so you achieve your dream home for less.


How much does a basic loft conversion cost?

A basic ‘First-fix’ loft conversion is the ideal solution if you’re watching your finances and/or have a serious DIY habit. Also known as a shell loft conversion our loft conversion experts undertake key preliminary planning, such as a site survey and architectural drawings, and the major parts of the build.


A typical first-fix conversion includes installing a suspended floor, Velux windows, steel beams, the loft extension itself – such as Dormer or a Mansard – and internal components, such as a staircase and doors.


The beauty of a basic conversion is that it gives you a large space which you can continue to develop yourself or wait and call the experts back in (hello!) when you’re ready. The average cost of a 1st fix (shell loft) conversion is £10,000 to £15,000 less than a full conversion *


How much does a dormer loft conversion cost?

A dormer loft conversion is one of the most popular types of home extension in central London and is a great way to achieve extra space.

A dormer extension projects vertically from your existing sloped roof creating extra headroom and floor space. It typically creates one spacious extra bedroom and an extra bathroom.

Depending on the size and layout of your loft, the average cost of a dormer loft conversion is £35,000 to £40,000*.


How much does an L-shaped dormer conversion cost?

An L-shaped dormer can house multiple rooms, increasing the size and value of your home substantially. They are well suited to the structural layout of Edwardian and Victorian London terraces, providing impressive additional space.


The build involves constructing two connecting dormer conversions – one on top of your main roof and another on the rear roof. The increase in space is huge, often creating room for two new bedrooms and a bathroom or a super spacious bedroom and en suite.


Besides adding lots of liveable square footage, and a great return on your investment, L-shaped dormers generally do not require planning permission – although you will still need Building Regulations approval.


The extra materials and build time mean that this type of conversion is up to a third more expensive than a regular Dormer, with the average L-shaped dormer costing between £38,0000 and £48,000*.


How much does a mansard loft conversion cost?

A mansard loft conversion is a full-width conversion on the rear of the home that nearly always requires planning permission. It is a popular conversion for London terraces and comprises a flat roof with softly sloping back wall – unlike a Dormer which extends vertically upwards.


A factor that pushes up the cost up of a Mansard extension is additional work required to construct the Party Wall – the wall you share with your neighbours. Once complete, a Mansard creates space for a sizeable double bedroom and an en suite bathroom.


The average cost of a mansard loft conversion is between £38,000 and £48,000*.

How much does a L-Shaped mansard loft conversion cost?

An L-shaped mansard loft conversion adds even more space than a regular Mansard. If you have a rear bedroom (or kitchen) and bathroom, the new L-shaped Mansard will usually sit directly above them.


Due to work needed to the shared Party Wall, you will need planning permission. However, the room and potential return you gain from an L-shaped Mansard is substantial.


The new space can accommodate multiple living spaces, from two large bedrooms and a bathroom to a luxurious master bedroom with en suite – with room to possibly slot in a stylish home office.


The average cost of an L-shaped mansard loft conversion is between £42,000 and £50,000*.

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

At the top of the loft conversion tree, is the hip-to-gable loft conversion. A hip-to-gable conversion is ideal for semi-detached and detached homes in London with hipped roofs that slope down evenly towards the four walls.


One of the reasons these conversions are more expensive is due to the complexity of the build, which involves replacing the sloping roof with vertical, triangular end walls. The upside is the abundance of living space you acquire.


A hip-to-gable can usually accommodate two spacious master bedrooms – ideal for growing children – and a sizable bathroom. Or if you’re planning a secluded sanctuary, a stunning super-sized loft bedroom with en suite and dressing room.


The average cost of a hip-to-gable loft conversion is between £45,000 and £55,000*.

Recent articles

We use cookies to show you personalised content and improve your experience of our website. You can manage the use of these cookies in your browser. By continuing to use this site you consent to the use of cookies in accordance with our Privacy Policy and Cookie Policy.