Loft conversion costs and how to reduce them

Converting your loft space is a great way to add more space to your home. But how much does a loft conversion cost and can you do it for less?

Loft conversion costs 2023

In 2023 the average loft conversion costs around £50,000 in the UK, according to Checkatrade. But the cost can vary considerably depending on the type of loft conversion, the size, the complexity of the project and your property’s location.

Types of loft conversion and typical costs

The most common types loft conversion and average costs are as follows:

1. Velux loft conversion cost

Velux loft conversions are the cheapest and easiest to do as they involve the least disruption to the existing loft space. However, Velux loft conversions offer the least amount of additional space to the property. The average cost of a Velux loft conversion is £27,500.

2. Dormer loft conversion cost

Dormer loft conversions are the most common type of loft conversion. They involve adding a small flat roofed extension with a window which means you gain additional space. The average cost of a dormer loft conversion is £50,000.

3. Hip to gable loft conversion cost

A hip to gable loft conversion involves altering the shape of your roof structure to gain space. It straightens an inwardly slanted end roof to create a vertical wall, therefore changing the hip roof into a gable one. The average cost of a hip to gable loft conversion is £60,000.

4. Mansard loft conversion cost

With a Mansard loft conversion, the whole shape of the existing roof is changed. You end up with an essentially flat roof and vertical outer walls. The average cost of a Mansard loft conversion is £65,000.

For help with your loft conversion design, an architect or architectural technologist can help. See our guide on architects and do you need one. Use our free tool to find local architects and architectural technologists.

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Loft conversion costs by house type

Loft conversion costs for semi-detached house

This will vary depend on the size and type of your loft conversion but the average cost of a loft conversion on a semi-detached house is £50,000.

How much does a detached loft conversion cost?

The costs of a loft conversion in a detached house are typically higher that for a semi-detached house. The average detached loft conversion costs £62,500.

Bungalow loft conversion costs

Bungalow loft conversion are generally larger in area than regular houses and tend to cost more. The average cost of a bungalow loft conversion is £75,000.

Terrace house loft conversion costs

While the cost of a terrace house loft conversion will depend on the type of loft conversion you choose, if you opt for a dormer loft conversion, the average cost is around £50,000.

All prices quoted are from Checkatrade.

Loft conversion cost calculator

Online Loft conversion cost calculators may sound like a good idea but they will only give you averages. To get an accurate idea of the costs involved is to approach firms in your area, book a consultation and get a quote.

Find quality local contractors to provide accurate quotes for your loft conversion project with our find a builder service

Cost breakdown of a loft conversion

Using the example of a £50,000 dormer extension with roof light, here’s how the costs could break down:

• Loft conversion stairs cost: This will cost around £1,000-£1,500 for basic stairs although expect to pay substantially for custom built stairs
• Loft conversion flooring costs: This will depend on the flooring type, for example vinyl may cost £15-£25 per m2, while carpet may cost £10-£65 per m2.
• Loft conversion labour costs: Depending on the type and size of your project, average loft conversion labour costs are between £14,000-£35,000
• Other costs will include things like: General building costs such as electrics, beams, joists and masontry, bathroom suite and architects’ plans if using – read our guide on Architect fees and how to cut them
• If you are adding loft insulation, for the average three-bedroom semi-detached home in the UK you can expect your loft insulation cost to be around £900, according to the Energy Saving Trust. That price can rise to £1,100 for a detached house and £1,200 for a detached bungalow. It is estimated that you will save £300 per year on your energy bill with loft insulation so it’s worth the investment.
• If you need planning permission, then there is also the cost of planning permission to factor in.

Loft conversion ideas to reduce costs

1. Choose a simple design

To keep costs down, keep the design simple. For example:

• Lowest cost: A rooflight conversion that simply involves fitting out the existing roof space, requiring limited structural alterations and the addition of insulation, plumbing and heating, staircase, plaster and decoration, will be the least expensive option. 
• Mid-Cost: Adding one or more dormer windows to add more usable space will involve more structural alterations and so will typically cost more money, especially if access is limited.
• Highest cost: A mansard loft conversion, or converting a modern engineered truss roof, can effectively mean replacing the whole of the existing roof structure with an additional attic storey and is the most expensive.

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2. Pick off-the-shelf materials

Choice of materials and finishes will also affect cost, with simple off-the-shelf standard rooflights, stairs and standard design details being the most cost-effective, and bespoke windows, stairs and cabinetry all adding significant cost. Choice of fixtures like tiles, sanitaryware, lighting, sockets and switches can be another big variable, with scope to really economise or to splash out on luxury.

3. Manage the project yourself

The simplest option to convert your loft is to hand the project over to a specialist design and build contractor, or to an architect who then helps you find and manage a builder, but there is a cost for paying someone else to manage the project for you and take on the stress. If you have the time and knowledge required to hire subcontractors, buy materials and manage the build, you can reduce costs by 10-20%.

4. Use your DIY skills

If you have DIY skills, you can reduce labour costs cutting the overall cost by as much as 40%, but only take on what you have the time and skill to complete cost effectively.

At a basic level, this could include:

• Painting and decorating
• Laying floor tiles
• Installing shelves and curtain rails

5. Avoid changes that require planning permission

Loft conversions can be completed within permitted development rights. By doing so you will avoid the time and costs involved in seeking planning permission. Read our guide Do I need planning permission?

6. Plan around existing plumbing

This applies to all building works. Moving plumbing across the room to fit with a plan you have might deliver the best aesthetic but can also add to the final bill, as well as time the project takes to complete.

7. Choose your trades carefully

A loft conversion firm is often the most expensive option but might be the most cost effective in the long run. Or, if you have a clear idea of what you want to do then a builder may be right for your project. Whichever route you take, remember to get at least three quotes and carefully compare them. Read our guide on Getting builders’ quotes for more information.

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What is the loft conversion cost per m2?

The cost per square metre will typically vary from around £1,250/m2 to £2,500/m2 depending on the design and on who builds it and where. Your loft conversion costs will be calculated by multiplying the usable gross internal area (the area with headroom of 1.5m or above) by the finished build cost per square metre (£/m2).

Generally the smaller the project, the lower the total cost, but larger projects can end up costing less on average per square metre (£/m2) due to ‘economies of scale’. Be aware, that a very small loft conversion that only creates a small amount of additional useable space – typically because of the limited available area with full height headroom, can be very expensive per square metre and may not be worthwhile doing, especially after deducting the space lost on the floor below to accommodate a new staircase.

Loft conversion costs in London vs outside London

The location of your property will have a major impact on loft conversion costs and this is especially the case in London. This is for a number of reasons such as the contractors you use will likely charge more and transporting materials can also be a challenge.

However, as with any loft conversation, to to get an accurate idea of the costs involved, you should approach firms in your area, book a consultation and get a quote.

Find quality local contractors to provide accurate quotes for your loft conversion project with our find a builder service

How will you fund loft conversion costs?

The main ways of funding loft conversion costs are:

• Using savings
• Taking out additional borrowing on your mortgage with a ‘further advance’
• Remortgaging to release equity
• Homeowner loan

If you are planning to pay for your loft conversion by remortgaging or with a further advance, it’s important that you speak to a fee-free mortgage broker first. Not only will they highlight any fees you might need to pay if you remortgage, such as an early repayment charge if you remortgage during the initial term of your mortgage, but they’ll search the market for the best deal for you too.

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Get fee-free remortgage advice from our partners at L&C. Use the online remortgage finder or speak to an advisor today.

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Alternatively you might want to consider a homeowner loan or second charge mortgage, in which case read our guide on Homeowner loans explained where we explain the pros and cons and can connect you with expert brokers

Do I need to replace my roof?

Doing a loft conversion may prompt you to consider replacing your roof.  For what to consider, see does my roof need replacing?

Where can I see loft extension ideas?

The best guide to costs is to look at similar projects to your own that have recently been completed by other homeowners on sites such as homebuilding.co.uk.