An Ultimate Guide About Mansard Loft Conversion

Mansard Loft conversion is one of the best choices if you want to add an extra storey to your building. Want to know more about what is mansard conversion, cost, permissions, and feasibility options? Stay tuned with this ultimate guide on mansard loft conversion.


Planning to move? Go for improve!

It is always convenient and affordable rather than shifting to a new house than extending the current one.

Mansard Loft conversion helps you add that extra room from the unused attic space in your home and make it look bigger, stylish and whoppingly spacious!!

What is a Mansard loft conversion?

What is a Mansard loft conversion

A mansard loft conversion involves giving two pitches to the sloping roof. The top of the roof is less steep while the sides are extremely steep.

Typically, the roof is either flat or equivalent to a flat roof. This helps you add an extra floor to the existing property with dormer windows.

All four sides of a mansard roof have two sloping roofs of which one is steeper than the other. This means the whole rooftop of your property is extended.

This loft conversion is usually done on the rear side of the property. One of the walls is removed and the height of the party wall is raised to create more space.

The new roof slopes have almost a vertical slope of no less than 72 degrees.

History of mansard roofs

The word mansard is coined after the famous French architect François Mansart (1598 – 1666) who is believed to be the father of this innovation.

Even before Mansart another architect Pierre Lescot designed a similar roofing style for a part of the Louvre Museum in 1550. Some sections of the former Royal palace in the 16th century were also designed by him.

It was later in the 17th century when Mansard got inspired and started adopting this style in his drawings of buildings for his clients.

The mansard roofs became immensely popular and fashionable in the 19th century during the era of Napoleon (The Third). By now, the mansard roofs were widely accepted internationally as well.

 How is Mansard roof loft conversion performed?

 How is Mansard roof loft conversion performed

Mansard roof loft conversions are indeed one of the most complex and expensive than other similar conversions because it involves a complete makeover of the internal roof space.

Check out the steps involved:

Step1: The existing roof is removed.

Step2:  Party walls are raised in height.

Step3: Interior walls are created.

Step4:  A new roof is constructed at a different angle.

Step5: Dormer windows and access points (staircase) are added.

Scaffolding is created to work externally.  Apart from that, to continue the work in bad weather, a rood cover is needed.  Along with roof construction, the existing attic floor will be strengthened. All the plumbing and electrical connections are added.

Once your entire work is inspected and approved as per the building regulations, you are all set to furnish and decorate your new living space.

Types of Mansard loft conversion

A mansard roof is one of the most aesthetically appealing amongst all loft conversions. The reason is it doesn’t appear as a box-like dormer as well as flushes out those gable ends.

Mansard loft conversion completely alters the slope of the roof to an angle of 72 degrees. Mansard loft conversions are mostly suitable for terraced houses in highly populated areas.

They are mainly of three types:

  • Rear Mansard
  • Front Mansard
  • Front and Rear Mansard

Apart from that, there are three more types of mansard roof extensions.

  • Flat-topped Mansard Extension
  • Double Pitched Mansard Extension
  • Butterfly roof

Benefits of Mansard loft conversion

Delve into the magical and beautiful experience of transforming your unused space into a spacious living area by undergoing a mansard roof loft conversion.

Now, make your dream of having an extra bedroom(s) with an attached bathroom come true with this roof conversion.

Check out the benefits:

  • Mansard roof conversion doesn’t require much structural reinforcements.
  • The straight mansard walls are easy to furnish than the sloping roofs of other loft conversions.
  • Mansard roofs have dormer windows which are an excellent source of natural light in your new living space.
  • These roofs are versatile

Planning Permission for a mansard loft conversion

Undergoing a mansard loft conversion means alerting the pitch of the roof till the top is flat or the walls are almost vertical.

As a major portion of structural alterations is involved, mansard loft conversions do require planning permission.

Apart from that, it will also need to comply with building regulations and be inspected by local authorities. In case the alterations may impact the adjoining properties, a Party Wall Agreement may be required.

The construction cannot be started until the approval has been gained and may take up to 8 weeks to get the approval.

The mansard conversions are visually less imposing; therefore these are more likely and easily granted the planning permission for people living in the conservation area.

How much does planning permission cost?

For applying to the planning permission for your loft conversion, you need to pay an application fee. The costs of planning permission vary from place to place.

The fee generally starts from £202 in Scotland, England and Ireland for all the extensions and alterations made to a single dwelling house.

For the residents of Scotland, Wales and England, the mansard loft conversion cost for planning can be calculated online as well using ePlanning and planning portal.

How long does planning permission take and how long does it last?

The local authorities are bound to share a reply as soon as possible. For a simple application, the applicants can expect a response within eight weeks.

It may take up to 13 weeks for complex applications. If an application involves carrying out an environmental aspect assessment, 16 weeks can be expected for the application to be processed.

Until specified, the notices from planning permission are valid for three years from the date of grant.

The applicant can start anytime within this three years’ time, anyhow the work can be completed after three years.

If any short, long or specific time has been granted, it would be stated on the letter of approval.

What are the loft conversion building regulations?

Building regulations play an important role in deciding whether the loft conversion is stable or not and ensuring that the structural integrity of the building is not hampered.

Irrespective of the type of loft, every conversion has to comply with the building regulations.

Depending on the type of extension you are planning, you need to be aware of the respective building regulations for loft conversions.

Planning for storage space

Even if you want to convert your unusable attic space for storage purposes, you need to get approval from the local authorities regarding compliance with building regulations.

Mostly, the joists of the ceiling of the rooms below (attic floor) are not designed to bear any weight. Putting excessive weight on the can affect the overall strength of the property. So, it’s a must to get the design approved by the building regulations to ensure additional safety.

Planning a habitable space

Converting your unused attic space into a liveable space also requires you to get approval from the local authorities.

Whether full or partial, loft conversions do need a lot of alterations to be made. Complying with building regulations ensure maintaining the structural integrity and safety of the occupants as well.

Each and every step of the loft conversion should be inspected and approved by the Local Authority Building Control department and signed off.

All the following categories of the building regulations must be complied with to get approval.

  • Headroom ( > 2.2 m)
  • Proper Insulation
  • Fire and Electrical Safety
  • Staircase and Stairs Design
  • Sound and Water Proofing
  • Structural

How much does a Mansard loft conversion cost?

A loft conversion mansard gives you a completely new storey over your existing property. It’s complicated and massive building alteration.

The cost depends on:

  • Scale of the work
  • Design
  • Style and finish
  • Additional spaces such as bathroom

In general, the bigger the property higher will be the price.

The mansard loft conversion cost starts from £40,000 to can go up to £70,000.

The cost is pretty high from other conversions such as hip to gable or dormer as it involves changing the entire structure of the roof.

But, every penny spent is worth the investment made.

How location affects the loft conversion cost?

There is no one-size-fits-all approach for the cost prediction.

Typically, the cost of construction depends a lot on the market prices of the property. If the property prices are lower, the construction works are affordable and vice versa.

The location of the property is also one of the deciding factors for your loft conversion cost. The more the locality is densely populated, busy and is deeply inhabited, the higher are the costs.

The reasons for high costs are due to:

  • Space constraints in a metropolitan city raise the cost as there is very little space available for parking, scaffolding, machinery set up etc.
  • The cost of labour in such areas is pretty high as the workers are getting good daily wages or salaries.
  • The transportation and materials cost is high as the production plants are far away from the metropolitan areas.

How long does a mansard loft conversion take to build?

Around 8 to 12 weeks are required to convert your normal looking roof to a mansard roof. Time also depends on the architectural design and size of the property.

Mansards are quickly becoming popular in the London area as they add a whopping 20% increase in your property value.

A mansard roof loft conversion is a great investment giving you the ultimate headspace and adding usable living space to your home.

What other things do you need to make Mansard Loft Conversion?

  1. Look around your neighbourhood

Just step out in your locality and find if any house in your locality has undergone mansard loft conversion. If you find a one, approach the owner and have look from inside and make your brain cells visualize your home regarding this conversion.

  1. Measure headspace

The minimum headspace required for any type of loft conversion is 2.2 m. The best way to measure it is by using a measuring tape and run it from the floor to the tallest part of the ceiling.

If it is 2.2m or more, then your loft is suitable for conversion.

There is a possibility that some homes such as Victorian homes that were built before 1930 may not have that much headroom.

  1. Roof type

A lot of things depend on the type of roof you have.

Whether it’s newly built, ages-old or whether your roof has rafters or trusses etc. One can easily tell a lot about the roof by looking at the loft hatch.

Mansard loft conversion with trusses is possible but additional support would be required to replace the trusses. This can ultimately affect the overall cost.

  1. Consider the floor below

Most people ignore the changes that will be made to the floor post-conversion. Placing, even a staircase in a minimal way could take a sizable chunk of the room. Make sure you are happy to lose that space!

Pros and Cons of loft conversion mansard


  • A loft conversion mansard adds a new storey to your property making it more spacious.
  • All types of properties are eligible to undergo mansard loft conversion until they comply with building regulations.
  • Versatile and can be matched up with the existing style of the building.
  • Gives a “room in the roof”.


  • Mansard conversions are indeed expensive option than other loft conversions.
  • Requires planning permissions for mansard conversion while for other types, they fall under permitted development rights.
  • Requires a good amount of construction work.

Is my home suitable for mansard roof loft conversion?

The best part of mansard loft conversion is that they are suitable for all home types, be it semi-detached, detached, terraced homes, chalets or bungalows.

It is best suited to properties where the space on the side and rear of the homes is restricted and the homeowners don’t want to use the garden space by adding a ground floor extension.

Modern semi or a Victorian townhouse, loft conversion mansard is now a common feature seen in densely populated, urban and suburban areas.

The residents just love to bring out the aesthetics of the external walls by going for cladding with tiles or slate or brickwork- whatever makes them exclaim “wow”.

Bottom Line

Winding up, Mansard conversions are best suited for properties in densely populated areas where there are space constraints to expand the property in front or rear.

Mansards are great for adding a whole storey and carving out a beautiful living space from the unused attic space. The space can be used as office space, guest area, playroom, lounge or extra bedrooms!

A mansard conversion involves restructuring the slopes into two pitches where one is heavily steep than the other. It’s more like an extension than a conversion.

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