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The average cost of a loft
conversion is around £40,000
Pricing guides

How much does a loft conversion cost?

When you run out of space in your home and extending or moving isn’t an option, then the only way is up - into the loft. Many of us manage to get some use out of the space about the ceiling, even if it’s just for storing Christmas decorations or old books, but if you’re serious about adding more space to your home, a loft conversion can be one of the most effective ways to address it. Whether it’s a dormer style conversion, a mansard conversion, or a hip to gable, each method can give you new rooms to enjoy and add value to your home. But before you get started, you need to know how much a loft conversion costs, so you can set a budget and begin your planning. We spoke to some of the experienced loft conversion specialists on MyBuilder to find out how much you should expect to pay.

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Loft conversion cost calculator

The cost of your loft conversion will depend on a variety of factors. The two key factors are the style of loft conversion you choose, and the size of the your property.

As most lofts cannot be simply altered into habitable rooms due to building regulations, there will almost certainly be structural work that needs to be carried out to convert the loft. The main kinds of loft conversion are:

  • Adding a loft room: If you have the space already in the loft (i.e the height between the bottom of the ridge timber and the top of the ceiling joist is 2.2m or greater), then converting it into a room simply involves adding a staircase, skylights, insulation, and often reinforcing the floor, along with final fitting and decoration.
  • Dormer loft conversions: The most common style of structural loft conversion, these are an extension to the existing roof, building out sections with vertical walls from the roof to add floor space and room for windows. These are suitable for most types of home, including terraced house loft conversions. 
  • Hip to gable conversions: An option for detached and semi-detached homes where the roof has at least three slanting sides, a single hip to gable conversion fills out one of the sides by building a vertical end wall, giving you a larger amount of interior space. A double hip to gable conversion can be done on detached houses, building out on both sides.
  • Mansard roof conversions: These are the most dramatic style of conversion, involving changing the entire roof structure, adding a flat roof with sloping “walls” at 72 degree angles, and dormer windows added. It adds the most room, but significantly changes the exterior appearance of the property.

Room in loft conversion costs

As the simplest method of converting a loft, this is the cheapest way to proceed, though it is only suitable for some homes. The cost is generally between £15,000 and £20,000, with prices tending to be higher in London and the south east where tradespeople are more in demand.

Dormer loft conversion costs

As dormer conversions are relatively straightforward to add to a home, they are a cheaper type of conversion, with the cost typically coming in at around £31,000 to £58,000 depending on the size of the conversion and other factors, with an average of around £45,000.

Hip to gable loft conversion costs

The added complexity of hip to gable conversions means they are typically more expensive, with a starting price of around £42,000, going up to around £65,000, with an average of around £54,000.

Mansard loft conversion costs

As a mansard conversion involves the most complex and complete overhaul, it is the most expensive option, beginning at £45,000, and going up to around £70,000, with an average cost of £58,000. 

Bungalow loft conversion costs

Any of the three main styles of attic conversions can be done to a bungalow if the property is suitable and planning requirements are met, so the costs of a bungalow loft conversion can vary from around £30,000 to £70,000.

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Stages of a loft conversion

A loft conversion project goes through several stages of building, which are broken out below. Establishing individual prices for each section is difficult, as many builders will not separate costs for individual elements which form part of the main build. However, if you are having a loft conversion carried out, many homeowners will agree to pay their tradesmen in stages, typically after some of the following elements are competed.

1

Loft conversion plans costs 

It is advisable to get comprehensive plans drawn up for your conversion, either from an architect or an architectural technician. This will lay out exactly what changes will happen and how the finished project will look, taking into account all of the relevant structural changes that need to be made, including all the necessary calculations. A price of around £1,000 plus VAT is fairly typical for this service.

2

Planning permission costs 

For the majority of loft conversions, planning permission will not be needed, as the changes will count as permitted developments. However, there will be instances, depending on the scale of the conversion and factors such as if your home is in a conservation area, where planning permitted may have to be applied for - this is currently £172 in England.

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3

Building regulation costs

Regardless of your planning status, your conversion will have to be inspected by the building regulations department of your local authority to ensure it is being constructed in accordance with the rules, making sure it complies with things like fire safety, access, floor strength and so on. Submitting the plans for inspection and having on-site inspections can cost between around £400 and £800. You may also need a Party Wall Agreement if your work will impact any adjoining properties, for example if you live in a terraced house or a semi-detached home. This requires your neighbours to agree to the work taking place. You are liable for costs such as their surveyor and any damage to their home which may occur as part of the works - it can cost several thousand pounds depending on how complex the agreement is. Another potential cost, though not always needed, is a bat survey if you believe your loft may have bats - this can cost up to £400.

4

Loft building costs

Once all the plans have been finalised and approved, work can commence. Typically initial work will be carried out externally with the use of scaffolding and in some cases a roof cover to allow work to continue effectively even with bad weather. At some point, access will be created into the loft from the interior and the floor will be strengthened. The dormers will be constructed and the roof altered. Interior walls will be then be fitted along with insulation, and features such as the staircase will be installed, followed by windows. Electrics and plumbing will go in, before it is plastered and carpentry such as skirting boards are fitted. Electrical sockets and elements like the WC and sink, if needed, are then added, before the final conversion is ready for final inspection, and decoration can then take place. This is where the bulk of the costs are spent.

5

Other loft conversion costs

The ultimate finish of the loft will have a large impact on the cost of the project - for example, if you are simply planning to use the space as a large bedroom, it will cheaper than if you are putting a bathroom in the space, where you will need to purchase the suite, which can cost several thousand pounds. Other factors include things like moving water tanks, if needed, and the number of windows being fitted.

A slate roof will usually cost more to alter than one with concrete roof tiles. Another factor is whether the roof was built with a frame - often found in pre-1960s homes - or with wooden trusses, which are easier to construct but can take less weight. Replacing or reinforcing the trusses can take more work and thus increase the costs.

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MyBuilder Top Tip

Pay attention to fire safety - this will be a key part of building regulation inspections of your plans and the building work. You may need to install special fire safety doors and mains-powered fire alarms, or make changes to your window plans to allow ladder access. The person who creates your plans should help address this, but be prepared that you may have to alter your original vision to make your conversion comply with the rules.

How long does a loft conversion take?

The actual building portion of a loft conversion will typically last between six to eight weeks, depending on the complexity and scale of the project. However, the planning stage can also take a considerable amount of time, especially if planning permission is required and a Party Wall Agreement needs to be negotiated. You will typically be able to stay in your home throughout the duration of the work though, with only minor disruption.

How to keep your loft conversion costs down

The best way to ensure your loft conversion is not needlessly expensive and runs to budget is to hire reliable and experienced tradespeople who are adept at dealing with any complications and managing successful projects. At MyBuilder, we usually advocate hiring particular specialists for each role, however, with loft conversions, there are a number of ways of hiring the necessary tradespeople. This could involve hiring an architect to plan and then oversee the entire project, hiring a team of builders and other necessary trades, or hiring a specialist loft conversion firm who will have a team with all the needed skills. You can also project manage the work yourself, hiring different tradespeople for different elements of the work, however, to help ensure everything runs smoothly and the timings all work, this can introduce more risk, as one part running late can impact later work.

Adjusting your plans to try and ensure the plumbing needed in the conversion is over plumbing already in your home can also help keep the price down as it eliminates the need for more complex plumbing work.

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