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How much does a mansard loft conversion cost?

Mansard loft conversions are usually one of the most expensive loft conversion options compared to a dormer or hip-to-gable conversion but they offer the maximum floor area and interior design opportunities. The final cost of a Mansard loft conversion will depend on the size of the roof and your choices for the interior fit but a good average figure to work on is £50,000.

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What is a mansard loft conversion?

Mansard loft conversions are named after their creator, a French architect called Francois Mansard. They are usually sited to the back of the property and feature vertical, square sides which slope inwards at an angle ranging from around 70 to 75 degrees with a flat roof on top. Dormer windows can be fitted to the flat roof to create even more usable space. The sides are usually constructed in brick, finished with cladding or tile-hung, the choice of styling usually selected to match the house.

Why are mansard loft conversions popular?

The popularity of loft conversions just does not diminish as a cautious housing market due to Brexit gives way to a looming economic recession. A Mansard loft conversion opens up possibilities in lofts which lack conversion appeal due to size and headroom but some people choose them simply because they can maximise the already generous space they have available.

  • Mansards can be an alternative to a rear dormer loft conversion if planning restrictions forbid the latter
  • Some people choose Mansards to really change up the style of their home and because they like the external look
  • Mansards offer architectural flexibility with different size and shape options to suit varying styles of house
  • Mansards make the most of smaller loft spaces which would otherwise be gloomy and dark and rather pokey – a Mansard loft conversion can hugely open up these roof voids
  • A Mansard can re-design the exterior appearance of your home and offer exciting design possibilities for bold, creative external makeovers
  • Mansards can have the added and distinctive feature of French windows in the roofline
  • Mansard loft conversions are most commonly seen on the rear of Victorian terraced properties but are actually a style which can suit many types of house
  • There is flexibility in the choice of covering for the external walls – use bricks which are matching or complementary to the house, render or clad the walls depending on your preference

What should you expect on the estimate for a Mansard loft conversion?

Building quotations or estimates are usually split between labour and materials. The breakdown for the materials should be very detailed for a project as complex as a Mansard loft conversion. There may also be third-party costs listed such as the hire charges for scaffolding and waste disposal skips.

A breakdown of mansard loft conversion costs

  • Professional fees for the architect which will average £800-£1,000 to produce the drawings
  • The fee to apply for planning permission which is in the region of £200 payable to your local council
  • Whilst the Mansard loft conversion is in build, the works will need to be inspected by a Building Inspector to ensure they comply with the latest building regulations. The plans have to be submitted for inspection and then the Buildings Inspector will make visits at pre-arranged stages during the construction process. This usually costs somewhere between £500 and £1,000
  • Your architect will commonly cover the requirement for a Party Wall agreement if your house is in a terraced row or semi-detached and shares one or more walls with neighbours. If you have more than one neighbour then you will need separate agreements with both sides. If your neighbour/s choose to appoint a surveyor to act for them then you will also be liable for their professional fees. The Party Wall agreements referred to as ‘Awards’ are to protect your neighbours from damage and disruption whilst you convert your loft
  • Bats are a protected species under the 1981 Wildlife and Countryside Act and depending on your location you may need to have a bat survey and show that you have made clear provision to accommodate them in your plans. Bat surveys from specialist ecologists can cost up to £400

Which properties are the best suited to a mansard loft conversion?

If you take an overground tube ride on the edges of London where the tube line runs through residential areas, you will see numerous Mansard loft conversions on the rear of Victorian terraced properties. Houses built before the 1930s usually had smaller roof voids and urban terraces also often have less garden or yard space hence the popularity of Mansard loft conversions. However, Mansards can suit many styles and types of property and some people even with spacious lofts, opt for this style in order to maximise the style and size of the accommodation within the conversion. Click here to see mansard bungalow loft conversions costs.

If your house is listed and/or in a conservation area then the planning authorities may impose restrictions on the type of loft conversion you can have mainly because of the structural changes to the exterior of the roof and the visual impact this will have both on your house and surrounding properties.

How is a mansard loft conversion built?

Mansard loft conversions are usually constructed in the following order:-

  • A structural floor is installed made from steel and timber floor joists
  • The old roof at the rear of the property is removed from the exterior accessed by scaffolding
  • The walls are raised and the new roof added
  • If appropriate and in the design, dormer windows are added at this point
  • Interior walls are fitted plus insulation
  • Windows are next
  • Electrics are wired in and pipes run for the plumbing
  • Carpentry follows such as skirting boards
  • The walls are plastered
  • Final decoration and fitting takes place

Throughout this process, there will be stage inspections from the Building Inspector to ensure the work complies with building regulations. The full job from start to finish will usually take between six to eight weeks – this excludes the time spent by the architect producing the drawings and obtaining planning permission.

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Mansard Loft Conversion Cost Frequently Asked Questions

What are the downsides to a Mansard loft conversion?

Apart from a roof lift loft conversion, a Mansard is probably the most expensive and disruptive to your home. Even a roof lift which means taking off the old roof and then dropping a new roof which is bigger or higher in place via a crane is probably less disruptive than a Mansard. Because of the works on the roof, a Mansard project is more complicated and will take longer than other alternatives. You will also require planning permissions whereas other types of loft conversion which do not interfere with the exterior of the roof and its structure, often do not.

Is a mansard loft conversion better than a dormer?

It depends on your style of property, the likely response from the planning authorities and what your plans are for the interior accommodation. A dormer conversion offers the best use of floor space and headroom but the external appearance won’t work for some types of property and some planning authorities will reject applications for dormer roof conversions in certain circumstances. A Mansard can look softer from the outside or be styled to really make a statement depending on your preference but it won’t give you the same headroom as a vertical dormer.

Can I get away without applying for planning permission?

It’s very unlikely that any mansard loft conversion would be deemed to fall within PD or ‘Permitted Development’ due to the major structural changes to the roof shape and structure. If you want to avoid the need to apply for planning permission then you will need to consider a loft conversion which leaves the roof unchanged apart from the addition of skylights or roof lights.

What is an L-shaped Mansard loft conversion?

An L-shaped Mansard conversion just refers to the shaping of the conversion and is popular if you are opting for an open plan look for a studio or workspace or want to use the new area for a bedroom with en-suite bathroom.

How long will the conversion take?

Instructing the architect, drawing up the plans and liaising with a builder can take two to three months or longer before the final design is agreed and work can commence. The actual building works usually take around six to eight weeks from start to finish. Your plans for the interior accommodation will also affect the timeline; new bathrooms and kitchens will take longer to install then rooftop studios or extra bedrooms.

What is the uplift in value on my home if I add a Mansard loft conversion?

A standard loft conversion which creates another bedroom and en-suite bathroom will add at least 20% to the value of a property so research suggests, some data shows that the figure could be nearer 25%. A Mansard loft conversion doesn’t just add extra accommodation however; the exterior impact can also create a design wow factor to the appearance of a property. A Mansard loft conversion represents the chance to change up conventional accommodation and do something radically different from the main styling in the house without compromising it or working against the existing aesthetics of the property. For traditional period homes, this can be a striking feature.

Are there ways to reduce the cost of a Mansard loft conversion?

The biggest way to lower the cost is to avoid adding extra kitchens and bathrooms although these rooms might be central to your loft conversion plans. Some people source individual contractors themselves and put the project together piecemeal, this can work out cheaper than hiring one firm to complete the whole installation. But all-inclusive packages will include the drawings as well so can be cheaper than instructing a separate architect.

What are the best funding routes to cover mansard loft conversion costs?

Some homeowners obtain finance from their mortgage lender if they have sufficient equity in the home and can satisfy the lending criteria on the monthly repayments. Most lending institutions will require the equity to be present pre the loft conversion and will not allow the borrower to rely on borrowing against the new uplift in value to the property that the Mansard loft conversion will create.

Where is the best place to find a good roofing company?

A personal recommendation from family, friends or work colleagues is a good way to go and this is where social media can be helpful if you belong to a local community group. Using local companies will allow you to check out their work for other people. Always obtain at least three estimates before you choose and you will learn something from each quotation. If the roofing contractor of your choice comes in over your budget then most companies will be happy to work with you to get the project under budget (within reason) by altering some of the specifications or materials which are being used to reduce the overall cost.

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