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How much does a loft conversion cost in 2023?

Loft Conversions

We all know someone who has had their loft converted.

Only last week, a friend and his wife were kind enough to give me the grand tour of theirs.

Both were keen to point out how cool they would be during the summer due to their new air conditioning unit.

It all looked stunning, and truth be told I was a little jealous – I wondered how much their loft conversion cost, but it was only later over a coffee that they dropped the bomb regarding how much it was. I must say I was a little surprised.

Bearing that in mind, I thought it might be useful to write a comprehensive article about how much a loft conversion costs.

In this post, we will cover:

I hope you find it useful.

1. Loft Conversion Cost: By Type

Loft Conversion TypeAverage Cost
Velux Loft Conversion£15,000 – £20,000
Dormer Loft Conversion£40,000 – £60,000
Hip to Gable Loft Conversion£50,000 – £70,000
Mansard Loft Conversion£70,000 +

1.1. How much does a Velux Loft Conversion Cost?

This is the best way to lower your loft conversion cost. That’s because it simply involves inserting windows into your existing roof slope. There are therefore few labour and material costs. When it comes to a Velux conversion, you should first consider the size of your existing loft space. If the amount of existing usable space is large, this is a great idea, but if you need a little extra height or floor space the three options below might suit you better. Velux conversions make existing space more usable but don’t create any extra space. In terms of cost, an average size Velux window costs £700 – £1,200.

1.2. How much does a Dormer Loft Conversion Cost?

Dormer windows are a fantastic and cost-effective solution to create that much needed extra space in your loft. As most roofs in the UK are pitched, the dormer will substantially increase the internal head height. This creates a larger area of usable space within your loft.

1.3. How much does a Hip to gable loft conversion Cost?

This is one of the most popular types of loft conversion found in the UK. It can create a huge amount of extra space. This type of conversion can add a large master bedroom and en-suite bathroom to most detached and semi-detached houses. In terms of loft conversion cost, they are a little more expensive than the two options above because they involve rebuilding the entire side and rear roof slopes.

1.4. How much does a Mansard loft conversion Cost?

This type of conversion is found mostly on terraced properties. It involves rebuilding your existing roof by increasing the roof pitch at both the front and rear of your house. By raising the pitch angle, the amount of usable space beneath it substantially increases. These are typically the most extensive of all the four options because your entire roof needs to be rebuilt.

2. Loft Conversion Cost: Breakdown

To give you a better idea of the individual costs associated with an average size loft conversion, we have prepared this useful table.

JobAverage Cost
Professional Fees£6,000
Internal preparation£1,500
Alterations to roof structure£15,000
Steal to support£6,000
New roof materials£12,000
New staircase£3,500

3. How long will it take to build my loft conversion?

Type of Loft ConversionDuration
Velux Loft Conversion4 – 6 weeks
Dormer Loft Conversion2 – 3 months
Hip to Gable Loft Conversion3 – 4 months
Mansard Loft Conversion4 months +

4. Loft Conversion Cost: Explained

4.1. Architect Fees

Traditional Architect: In my opinion, it’s always best to approach an architect before carrying out a loft conversion. All architects will have spent a minimum of 5 years studying and will have at least 2 years practical experience before being able to call themselves an ‘architect’. They will therefore have a huge amount of experience and can work with you to create some fantastic options. They can recommend new materials and even prepare different layouts that work best for you. Architects’ fees range quite a bit depending on who you go to. We would expect their fees to be in the region of £2,400 – £4,000 for a straightforward rear dormer loft conversion.

Architectural Technician: You may not have heard this term before. Architectural technicians can prepare drawings but without the same levels of formal training that you would expect from a traditional architect. The difference between these groups of professionals and traditional architects is that technicians have less overall experience but also charge lower fees. If your loft conversion is relatively straightforward, some experienced technicians would be able to carry out the associated work. Their fees to prepare both planning and building regulations drawings for a simple dormer window extension could add from £1,100 – £1,900 to your loft conversion cost.

4.2. Loft construction method

Insert Image

There are typically two different types of loft construction method. Rafters run along the outer edge of the roof and trussed roofs cross through the middle of the roof space. If your current loft is supported by trusses, your loft conversion would be more expensive because they would need to be removed and supported in a different way.

4.3. Materials

When it comes to materials, there is a huge pool to pick from. Velux windows are relatively inexpensive, but if your loft conversion involves a dormer window the materials and labour will be more expensive. The cheapest building material for a dormer window would be clay hung tiles to match those of the main house. If you would like something a little more unique, you might opt for a zinc clad dormer which looks incredible, but is a little more expensive.

4.4. Repair existing roof

If you’re about to create a stunning new loft conversion it might also be a good idea to make any repairs or upgrade your existing roof depending on its age. Replacing all the tiles on a typical semi-detached house would cost approx. £1,500 while replacing all the guttering could be an additional £2,500.

4.5. Underfloor heating costs

Retro fitting underfloor heating can be expensive and can add a great deal to your loft conversion cost. But, as most loft conversions involve upgrading the existing floor, this is a great time to install it. The two main advantages are an even distribution of heat while also creating additional usable space usually taken up by radiators.

4.6. New bathroom

No new master bedroom would be complete without your own bathroom. The size will depend on the size of your loft and how big you’d like your bedroom to be. The cost of a new loft conversion bathroom ranges from £4,000 – £7,000.

4.7. Building regulations costs

When reviewing quotes from various architects, bear in mind they will typically only include their fees. Before instructing an architect, I would suggest asking them to estimate other fees you might be expected to pay once the design process starts. Once complete, all new loft conversions need to be signed off by building control. Your architect has two options here. They could either apply to your local planning authority or to an approved inspector. The average building control application fee is approximately £700 – £1,200.

4.8. Party Wall Survey Costs

Party Wall Surveys would usually only apply if you were converting a loft within a terraced or semi-detached house. The reason for this is that some of the supports for the new roof or dormer will be close to or on top of your shared party wall. It’s difficult to predict the cost because it depends on whether your neighbours are agreeable or slightly more difficult. We would expect the costs associated with a Party Wall Agreement for an average size loft conversion to be in the region of £1,000 – £1,800.

5. What factors affect the cost of a loft conversion?

5.1. Type of loft conversion

One of the main influencing factors on loft conversion cost is the type of loft conversion you wish to build. We have written a separate blog highlighting the most popular types of loft conversion here. That article also includes the estimated construction costs of each one.

5.2. Type of Roof Tiles

If you’re replacing your existing roof tiles, there is a huge range of materials to replace them with. Clay tiles are usually the cheapest option, while more modern versions made of zinc or copper can substantially increase the overall cost. Below is a list of some poplar options ranging from cheapest to most expensive.

  • Clay roof tiles
  • Concrete roof tiles
  • Reclaimed roof tiles
  • Interlocking roof tiles
  • Slate roof tiles
  • Modern roof tiles (e.g zinc or copper)

5.3. Size of Loft Conversion

As with any extension, the larger the space you are trying to create, the greater the cost. The cheapest type of loft conversion would be a Velux conversion. This simply involves placing new windows into the existing roof slope.

A medium sized loft conversion might be a dormer window including a hip to gable. This is more expensive than the Velux option because it requires rebuilding both the side and rear roof slopes of your home.

A large loft conversion would be either a new crown roof or mansard roof. These cost more because they involve replacing the entire roof structure. The average cost of a new crown roof for an average sized house would be approx. £50,000 – £70,000.

5.4. Loft conversion cost: window choices

Velux window: This depends on the size of the window. An average size Velux window (62cm x 78 cm) would cost approx. £360. A large Velux window (94cm x 160 cm) will cost approx. £1,600.  

Dormer window: This depends on the size of your existing house. It also depends on the type of materials you would like to use. A typical clay hung tile dormer window would cost between £10,000 and £13,000.

Gable window: The cost of these types of windows depends on the materials. uPVC is usually the cheapest option, where a single window would cost between £500 and £1,000. Aluminium frame windows look a little more modern but cost slightly more (between £700 – £1,200). The most expensive type of window would be a bespoke timber frame, costing in the region of £900 – £1,800.

5.5. Internal Walls

You may be fortunate enough to have a very large existing loft space, giving you the opportunity to create more rooms. In these instances you might opt to have an ensuite bathroom or perhaps a bedroom and a playroom. This would involve slightly more labour and materials to erect new partitions. The average cost for every new stud wall is approximately £800.

5.6. Plumbing Cost

This is where the skill of the architect will help save you money. If you are planning a new loft conversion, your architect will do their best to link the new bathroom to the existing system. If that isn’t possible your builder may need to install a new drainage system which can be more expensive.

5.7. Electrics Cost

This depends on the type of lighting you would like. A single pendant light in the middle of the room could cost as little as £350 on top of your loft conversion cost. If you want something more contemporary, you could opt for evenly spaced LED spotlights throughout your new space. The labour and fixtures/fittings for this more elaborate option can range from £1,500 – £2,500.

6. What Steps are involved in a loft conversion?

Step 1: Structural strengthening and support

Before construction starts, you will have received a set of detailed drawings from your architect. Your structural engineer will also have provided a set of calculations and drawings.  With regard to construction costs, there are lots of factors at play here. For example, can your existing loft floor support the new structure above? If not, it will have to be strengthened and reinforced.

Step 2: Install new windows

This is where the exterior shell of your loft conversion is built. If you are proposing a new gable wall and rear dormer window, both the side and rear roof slopes will be removed and rebuilt. If you’re simply adding Velux windows to an existing roof that will take less time and expense.

Step 3: Build new staircase

In most cases, existing loft spaces are accessed through a pull-down ladder. When converting your loft to a habitable space you will need a new bespoke staircase to take you upstairs.

Step 4: First fix (electrics and plumbing installation)

At this point, your plumber would carry out what’s called the ‘first fix’. This means running all the water and waste pipes to the correct place if you’re having a new bathroom, as well as fitting the shower tray or bath. If your new ceiling included spotlights your electrician would also prepare all the new wiring.

Step 5: Install insulation

Insulation acts in two different ways. It’s often fitted in between your new rafters and is sufficiently thick to retain as much heat as possible to keep you warm in winter. The outer surface is also reflective, helping reflect the heat during periods of hotter weather to keep your new loft cooler during summer. The benefits of having insulation are more than worth the addition to your loft conversion cost.

Step 6: Fit internal partitions

At this point, depending on the layout, your builder will erect all the dividing walls. Here is when you really start to visualise the different rooms and spaces.

Step 7: Plasterboard and plastering

Once the internal walls and partitions have been built, they will be plaster boarded. There are again lots of different types. We would always suggest a slightly thicker option as it helps better insulate each room which saves on heating bills. Once the plasterboard has been installed, your builder’s plasterer will get to work and plaster all the new walls, so all the surfaces are completely smooth.

Step 8: Carpentry

At this point you’re almost there. This stage involves fitting new doors, architraves, skirting, handrails and spindles to stairs.  

Step 10: Second fix (electrics and plumbing installation)

At this stage, the entire loft is nearly complete. Your builder will now install the final bits and pieces including: radiators, bathroom suite, underfloor heating, wall tiles and floor tiles.

At the same time, your electrician can work on fitting the light switches, power sockets, lights, TV points and smoke detectors.

11. Do I Need an Architect for a Loft Conversion?

Option 1: Traditional Architect

Advantage: In my opinion, an architect is the best place to start before planning a loft conversion. There are so many advantages, despite the addition to your loft conversion cost. First, they’ll have a huge amount of experience and can help turn your ideas into something truly unique. Second, they will understand all the local planning polices to help you obtain the necessary consents. Finally, they will be perfectly placed to prepare all the technical drawings you require as well as liaising with both the structural engineer or builder on your behalf.

Disadvantage: The only disadvantage of some architects are their fees. But, like any profession, there are those that charge more and those that charge less. We would always suggest obtaining 3 or 4 quotes from different architects so you can compare the scope of works they include within their services as well as the fee itself.

Option 2: Specialist loft conversion company

Advantage:  Going directly to a company who specialise in loft conversions means there will be less work involved for you in terms of managing the process. Rather than dealing with an architect, engineer and builder, these companies will do everything in house.

Disadvantage: It is unlikely that loft conversion companies will employ qualified architects to carry out the design and detailed work. They will probably have architectural technicians, who might have less experience. The only other disadvantage is that it is not in the loft conversion companies’ interests to keep your costs down. An architect, on the other hand, will be paid the same fee regardless of construction costs and can work with you to reduce the total build cost.

Option 3: Use an experienced builder

Advantage: There are some design and build contractors who manage the entire process on your behalf. Similar to the specialist loft conversion companies, they have few incentives to keep your loft conversion cost down.

Disadvantage: Builders are good at construction, but they are not as creative as traditional architects. So, if you’re looking for something modern, unique and jaw dropping, they may not have the expertise to deliver your dream loft.

Can my existing loft be converted?

Check the neighbours

The first place we would suggest starting is having a walk up and down your street or looking at google’s 3D maps. In most cases, houses on the same street are similar in terms of design and scale. If your neighbours have converted their lofts, the chances are your loft would also be suitable.

Check head height

One of the main limiting factors when it comes to converting your loft space is the distance between the top of your joists and the bottom of your rafters. If there is spare space above your head, your loft is more than likely tall enough for a loft conversion. If you struggle to stand up in your existing loft it might be too low. Remember that when converting your loft, the floor might have to be increased in height and the ceiling may drop slightly to accommodate additional insulation or support. The minimum finished head height for a loft conversion is 2.2m.

Space for a staircase

The best case is where your landing is sufficiently large at first floor level so you can simply continue your existing staircase up into your loft. If your landing is relatively small, you may need to take away space from an existing bathroom or bedroom to fit in the new staircase.

Is your home listed?

If you own a flat or house, any internal work such as building a new staircase does not require planning permission. If you live in listed building you would be required to apply for ‘Listed Building Consent’ for any internal changes. This is where a specialist architect will be of assistance.

12. Loft Conversion Ideas

12.1. Children’s Bedrooms

A picture of a loft conversion children's bedroom
A bright and airy children’s bedroom

If your children are like mine, they can make quite a bit of noise from time to time. Creating a new bedroom in the loft gives them that little bit of freedom. This reduces the need for you to wear ear muffs and means you will spend less time tidying up in other parts of the house.

12.2. Master Bedroom with En-Suite

A picture of a large loft conversion with en suite bathroom
A modern loft conversion with master bedroom and en-suite bathroom

If you’re lucky enough to have a large existing loft to convert, you will be able to fit in both a large bedroom and an ensuite bathroom. This not only gives you a little more privacy but may be a good retreat from what’s happening downstairs.

12.3. Home Office

A picture of a loft conversion home office
New loft conversion with bespoke home office

I recently began working from home which is fantastic as it saves me 2 hours of commuting each day. I transformed my loft into a fantastic home office which is quiet and helps me focus.

12.4. Loft Home Cinema

A picture of a loft conversion home cinema room
Loft conversion with home cinema

Here is something a little different. If you love watching films, creating an incredible home cinema in your loft can be a great idea. Just make sure you leave some space for a popcorn machine.

13. How to save costs on a loft conversion

13.1. Larger windows rather than more windows

We know how important it is that your new loft conversion is flooded with natural light. In terms of saving money one way is to opt for larger windows rather than more windows.

This comes down to labour. It will take your builder a similar amount of time to fit a rooflight measuring 50cm x 80cm to a slightly larger one measuring 80cm x 150cm. If you opt for more rooflights, each opening requires quite a bit more labour, thus pushing up the overall cost.

13.2. Set a loft conversion cost budget

It’s very easy when designing and planning a loft conversion for costs to quickly spiral out of control. If you sit down with your architect at the start of the project to talk about your budget, it will certainly save you money in the long run. Part of your architect’s role will be to make sure the project stays within budget. For example, if you decide last minute to add lots of LED spotlights rather than a pendant light in the centre of the room, your architect will point out this could take the project over budget. They can then work with you to think of alternative ways to save money.

13.3. Explore different designs

When working with your architect, we would always advise that you ask them to prepare different options within your brief. It may be that you like some elements of different options and end up merging them together. For example, you might opt to have one larger bedroom rather than two smaller bedrooms. This saves on the number of partitions and also the labour required to build them. A second option is to have one huge master bedroom rather than a smaller bedroom and ensuite.

13.4. Off the shelf rather than bespoke

The most fun part of planning your loft conversion is picking the materials and finishes. Along with the huge array of options comes a huge variance in the prices. If you’re looking to save money, a great place to start is making sure you buy standard products from manufacturers. For example, you could opt for an Ikea wardrobe rather than finding a carpenter to make something bespoke.

When it comes to bathroom fixtures, you might find an incredible hand painted glass basin, but these can be hugely expensive. Lots of high street brands make stunning products at a fraction of the cost to those who make items to order.

13.5. Trade discounts and sales

Your builder will have trade accounts with bathroom, kitchen and general builder suppliers. We think it’s always a good idea to ask them if you can use their account to order fixtures and fittings as those discounts can take the price up to 40% lower when compared to the rates a normal shopper might be asked to pay.

13.6. Finishing touches

This depends how good your DIY skills are. One good cost saving measure is to ask your builder to complete the shell, electrics and plumbing. But, perhaps you can fit the floor and paint the walls yourself? These tasks are relatively straightforward to carry out and can end up in big cost savings.

13.7. Cheap Builder Quotes

It’s always important to obtain at least 3 quotes from prospective builders before starting a loft conversion. The cheapest quote is not always the best. Lots of builders know the tender process is very competitive and will quote on the low side to get the job. The problem here is that if the price of materials or labour rises (as they certainly have over the past year) your builder might not be able to stick with the agreed price. They could therefore ask for additional fees once work has started. To avoid this happening, make sure your architect or quantity survey prepares a very clear schedule of works for your builder to work with.

14. FAQs

14.1. Do You Need Planning Permission for a Loft Conversion?

Permitted Development

In the majority of cases, if you own a house, you benefit from something know as ‘Permitted Development Rights’. These are specific extensions you can build without the need to apply for planning permission. There is however specific legislation you must adhere to.

Below is a summary of Permitted Development requirements for loft conversions:

Materials: Any materials you use must be similar in appearance to the existing house.

Volume: The volume (measured externally) must not exceed the original roof space by more than 40 cubic metres for terraced houses or 50 cubic metres for detached or semi-detached houses.

Height: Your loft conversion must not exceed the height of the existing roof.

Location: Your loft conversion must not extend beyond the existing front roof slope.

Side-facing windows: Any windows located in the side elevation must be obscure-glazed and, if opening, must be 1.7 metres above the floor of the room in which they are installed.

Set back from the eaves: Any enlargement should be set back, so far as practicable, at least 20cm from the original eaves. The eaves are typically where your first-floor rear wall meets the underside of your roof.

No overhanging roofs: The roof enlargement should not overhang the outer face of the wall of the original house.

Planning Permission

If you do not meet the requirements of the Permitted Development legislation sited above, you would need to apply for planning permission, but that’s not necessarily a bad thing.

Your local planning department will have more discretion when it comes to interpreting their policies. For example, if you choose to construct a new loft conversion under Permitted Development, your external materials need to match those of the existing roof. If your roof is made up of red clay hung tiles, this means your dormer window would also have to be made of red clay hung tiles.

However, when applying for planning permission (depending on your area’s character) you will have more materials to choose from. For something a little more modern and unique you could opt for zinc, aluminium or even copper.

14.2. Do I need Building Regulations for a loft conversion?

Building Regulations approval will always be required when converting a loft. A building control surveyor will come to site to inspect your conversion at various stages and will be responsible for issuing a completion certificate upon final inspection.

Here are some of the technical criteria your new loft conversion will need to meet:

U-values: U-values show whether your new loft conversion meets the relevant thermal efficiency criteria.

Head height: a minimum headroom of 2m for all escape routes including the stairs is required.

Windows: Openings should be at least 450mm x 450mm and at least 0.33m2 in area.

Rooflights: These are usually top opening — you must ensure the bottom of the opening is between 800mm and 1,100mm from the floor.

14.3. Do I need a party wall agreement for a loft conversion?

All loft conversions involving a wall or structure shared with one of your neighbours requires a party wall agreement. For example, you’ll need a written agreement if you want to:

  • Remove a chimney breast
  • Use the wall as a load-bearing wall
  • Rebuild or remove sections or all of the wall
  • Insert a damp course proof
  • Underpin the entire length of the wall
  • Increase the wall’s height or thickness

Ask your architect if they can recommend a Party Wall surveyor who will be able to offer you advice as to the best way to approach it.

14.4. Can I Live in the House While my Loft is Being Converted?

The short answer is, YES, you certainly can.

Here are some steps to take:

Construction Timeline: Ask your builder to give you a clear indication of exactly when the work will start and finish. The shorter the time period, the less disruption there will be for your household.

Builder references: Ask your builder to provide references. When you speak to homeowners they have previously worked with, ask them how the process went. Did the builders tidy up after the end of each day? If the builder needed to turn the gas or electrics off at any point, were they given a lot of warning in advance?

Tin Hat Scaffolding: Ask your builder if they offer a tin hat service. This essentially means putting pieces of aluminium over the scaffolding which keeps the elements out. Not only will this prevent any leaks, but it will mean your loft conversion is finished more quickly because the builders won’t need to cover the exposed roof each evening.


The process involved in designing and building a loft conversion can be complex.

If you would like to discuss any ideas or have questions you would like answered, please feel free to call a member of our team anytime.

We offer a free 30-min consultation where our architects can discuss design options, planning and budgets.

We look forward to hearing from you.

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