Loft conversions can add so much more space to your home, and add value too. A mansard loft conversion will maximise the space available in your loft, giving you the opportunity to transform a once unused space into a luxurious bedroom, a living area and more. But how much does a mansard loft conversion cost? We’ll explore the costs in this guide.

How much does a mansard loft conversion cost?

Mansard loft conversions tend to be one of the more pricey loft conversions, because there’s more construction involved and they have a unique look. Expect a mansard loft conversion to cost around £60,000 on an average semi-detached home.

Mansard loft conversion size	Average cost
Small terraced house	£52,500
Semi-detached house	£60,000
Large detached house	£67,500

These costs are just averages; the final price of your mansard loft conversion could be higher or lower. One of the biggest factors affecting the cost of loft conversions is location, so HaMuch uses its database of hourly and daily rates to determine how much a mansard loft conversion may cost in your area. Take a look at the table further down the page to get a more accurate estimate for your town or city, then post a job to get real quotes from our builders.

What is a mansard loft conversion?

A mansard loft conversion is usually built to the back of your property and has a flat roof, with an almost vertical 72-degree back wall. They tend to be one of the most expensive types of loft conversion, but you get lots of room space with good proportions.

Mansard loft conversions work particularly well for open-plan, modern layouts, so a stylish bedroom/living area with an en-suite works well in this types of loft conversions. This is ideal if you have an older child living with you that needs more of their own space.

Factors that affect the cost of a mansard loft conversion

• Size: As you’d expect, the bigger your mansard loft conversion is, the more it will cost. Many builders charge per square metre of floor space, and you may find that they charge slightly less per square metre for larger conversions.

• Standard of finish: You’ll be able to choose the quality of a lot of the materials for your mansard loft conversion, and that can affect the cost. Of course, higher quality or luxury brands of things like paint, tiles and flooring will cost more.

• Party wall agreements: If you live in a semi-detached or terraced house, you’ll need to get a party wall agreement drawn up before work can start on your loft conversion. Specialist surveyors tend to charge anywhere between £100-£400 per hour, and you’ll need to pay your neighbours’ costs if they want to use a different surveyor.

• Whether you’re adding bathrooms or kitchens: Adding extra plumbing will drive up the cost of your mansard loft conversion as there will be more work involved. However, adding an en-suite or creating an entire living space from a loft conversion will often pay for itself in value that it adds to your home.

• Type of roof tiles: The type of roof tiles you choose will affect the cost. You usually will have to keep the roof in style with the rest, so if you want to change it you could end up having to re-roof your entire house. The supply and fit of clay tiles tends to cost £100 per square metre, while slate tiles usually cost around £110.

• Location: Where you live has one of the biggest impacts on your mansard loft conversion cost. Conversions in the south east and London will cost much more than those in the north of England. It’s important to get a range of quotes to ensure that you get the best price possible for your area.

Additional costs to consider with a mansard loft conversion

Architect costs

You may decide to use an architect to design your mansard loft conversion. Architects are great at designing spaces that maximise and use the space available efficiently, so it can be well worth hiring one to draw up your plans. They can also help you navigate planning permission and building regulations, and you can even have them manage your project from start to finish.

An architect’s fees start anywhere from around £400 and can reach as much as £2,000 or more.

Skip hire

Any loft conversion creates a lot of waste, so you’ll need a skip – or skips – during your project. Most builders will have a skip hire company that they use regularly and will include the cost in your quote, but if they don’t expect skip hire to cost around £300 per week.

Roof repair

Having a mansard loft conversion is a great opportunity to look at your roof and decide whether any repairs are needed. You may also want to consider pressure washing your existing roof tiles to ensure the colour matches the new ones as closely as possible.

Pressure washing your roof can often cost as much as £500, but because you’ve already got scaffolding erected you will probably pay much less. Replacing roof tiles can cost as little as £50 up to £250 depending on the type and number of tiles you need to replace, while a brand new roof can cost up to £10,000.

Boiler installation

If you’re adding an en-suite or new bathroom into your loft conversion, you’ll need to check that your boiler is still suitable to supply water to all your outlets. Adding more showers and baths to your system can mean you need a more powerful boiler to ensure you still get enough hot water when you need it.

A Gas Safe-registered engineer will be able to tell you whether your current boiler is still suitable for your home. If it’s not, a new boiler installation can cost anywhere between £1,500-£4,000, depending on the type of boiler you need, how complex the installation will be and if you need to move it to a new place.

Painting and decorating

Once your mansard loft conversion is finished, you’ll want to put your own stamp on it. That means you’ll need to get painting and decorating!

While it’s perfectly possible to decorate your home yourself, you might not have the time to spend on it – and even if you do, you’ll get a better finish if you use a professional.

Painters and decorators tend to charge between £130-£400 per day to decorate a room, plus the cost of paint. How long it takes them to decorate your room will depend mainly on its size.

How long does a mansard loft conversion take?

On average, a mansard loft conversion will take between 8-10 weeks. However, remember that every loft conversion is different, and it’s not uncommon to hit snags that hold your project up.

We’ve put together a timeline so you know when to expect different parts of your loft conversion to take place.

Mansard loft conversion timeline

Week 1: Scaffolding and materials

A scaffolder will come to erect the scaffolding around your home to make it safe for the builders to work. Materials that your builders will need straight away will be delivered to your home and stored somewhere safe and convenient for you.

Week 2: Roof structure changes

The builders will open your roof and add extra supports if required. They will also create the openings for your windows.

Week 3: Roof tiles and insulation

The builders will finish constructing the roof, then replace your roof tiles and add any new ones that are required. They will add roof insulation up to building regulations standard. Inside, your loft conversion will be prepared for any plumbing or electrical work.

Week 4: Windows and flooring

Your new windows will be installed along with plasterboard and any internal walls you’ve specified. Then, your floor will be laid with ventilation added if required.

Week 5: Electrics and plastering

An electrician will finish wiring your power supply so your plasterer can skim the walls.

Week 6: Plumbing and carpentry

If you’re having a bathroom installed, a bathroom fitter and plumber can work together to do this while a carpenter fits your staircase and hangs your internal doors.

Weeks 7-8: Snagging

You and your builder can assess the work done, and if there’s anything you’re unhappy with you can add it to the snag list to be rectified. Once you’re happy, the scaffolding will be removed and skips will be taken away.

Weeks 9-10: Finishing touches

Painters and decorators, interior designers and any other professionals you may need can come in and start helping you put your own stamp on your mansard loft conversion and make it feel like it’s always been part of your home.

Do I need planning permission for a mansard roof?

You’ll almost always need planning permission for a mansard roof. Mansard loft conversions involve quite a drastic change to your roof, so there are stricter rules surrounding where and how they can be built. However, if you see many mansard roofs in your area, your local council may have produced planning guidance to help people get their plans approved.

Typical guidance from local authorities, particularly London boroughs, includes stipulations such as:

• A maximum internal floor to ceiling height

• Matching or being sympathetic to your existing property

• A maximum pitch of the roof, e.g. 70 degrees

• Only allowing mansard loft conversions when other houses in the row have already been extended or the roofline is broken

Ask an architect or go directly to your local building control to find out more about how to get your mansard roof through planning permission.

What is the difference between a dormer and a mansard?

The main difference between a dormer and a mansard loft conversion is that they look different. While mansard loft conversions extend your roof out to make a flat roof and a 72-degree wall angle, dormer loft conversions suit high pitched roofs as they create a box-like structure in your loft.

Dormer loft conversions tend to be much cheaper to build as there’s less construction involved, but they don’t blend as seamlessly into the aesthetic of your existing property. They also don’t add as much space to your home as mansard lofts.

A huge benefit of dormer loft conversions over mansard conversions is that dormers often fall under permitted development rights, meaning you won’t need to apply for planning permission. However, you’ll still need to make sure you follow all building regulations and get sign off by your local building control.

If you’re ready to get quotes for a mansard loft conversion, post a job on HaMuch and we’ll match you with builders in your area.

Estimates for common extension builder jobs;

Rates for other trades