New Loft Conversion Cost: Price Guide

Most lofts and attics fall into the same role – storage. And while this is undoubtedly useful, as we all have boxes of stuff we just don’t know where else to put, it isn’t exciting, inspired or adding value to your home. The solution to this is simple. Build a loft conversion. However, if you’re thinking of doing this, one question likely comes to mind: how much does a loft conversion cost?

The main factor affecting the price of your loft conversion will be the size of the loft. Yet there are also a lot of smaller details to consider, each of which will affect the final price.

You may be asking other questions alongside this too. There are a lot of front-end considerations, such as: whether you need planning permission, what kind of light you can add and how long it will take to build. Because of this, Quotatis have put together this comprehensive price guide to new loft conversion costs for 2023. It covers the price of loft conversions as well as any related questions you might have about the renovation process.


  1. What types of loft conversions are there?
    1. Dormer
    2. Hip to gable
    3. Mansard
    4. Roof light
  2. Can I convert my loft?
  3. How much does a loft conversion cost in 2023?
  4. What do I need to know before I build a loft conversion?
    1. Building regulations
    2. Planning permission
    3. Stairs and staircases
    4. Ceiling joists
  5. Do I need a designer, or can I convert my loft myself?
  6. How can I add light to my loft conversion?
  7. What types of insulation can I add to my loft conversion?
  8. Which fire regulations do I have to follow for new loft conversions?

What types of loft conversion are there?

There are three main types of loft conversion: dormer, hip to gable and mansard. There is also a fourth kind, roof light, which we mention separately as the nature of the renovations are different to those of the first four.

Before you decide which of these four is best for you, you need to consider a few things. Firstly, what shape is your roof/loft currently? This will determine if you can just renovate the interior of your loft or if you’ll have to drastically alter the structure of the building. This will obviously greatly affect the final loft conversion cost. You’ll also have to consider planning permission and development rights, as well as how much your budget permits for spending.

Make sure to research some loft conversion ideas before you commit any finances though. It’s always best to approach these large projects with a vision in mind. Knowing what you want, even generally, is a good way to stay focused, saving you time and money.

With that in mind, let’s look at which option best suits your needs.

Dormer loft conversion

dormer window loft conversion
Dormer loft conversion

This is the most common form of loft conversion, due to its affordability and flexibility regarding the existing house structure. Often called a flat roof dormer, this loft conversion involves adding an extension to a slanted roof. This is achieved by erecting a vertical wall starting from the bottom of the roof. A new flat roof is then built out horizontally from the existing roofing, connecting to the new wall. Two side walls are then finally added to create a box-like shape.

As this extension only requires to you to add to a roof, it doesn’t require any interior structural changes. This keeps the new loft conversion cost lower than if you had to dramatically alter the roof’s original shape.

There is a sub-type of dormer conversion called an L-shaped dormer. This creates, as the name suggests, an L-shaped room that folds around a corner of a house. Most commonly this will be the rear/side corner.


  • Creates more room – great for small/tight lofts
  • Assuming it doesn’t extend out from the roof and hang over the property, it should fall within your development rights. This means you don’t have to apply for planning permission
  • Relatively cheap when put against other choices
  • Let’s you add large windows, letting in lots of natural light and strong ventilation
  • Straight walls make designing/building the interior easier


  • Shape of extension can be visually unappealing, potentially looking incongruent with the rest of the house
  • Affordable materials can also look unstylish

It should be noted though that these visual issues can be rectified with what’s called a “gabled dormer”. This increases the new loft conversion cost, but makes the extension look more in line with the existing roof. Instead of having a flat roof, a gabled dormer has a more typically shaped top – an inverted “v”.

Hip to gable loft conversion

These conversions are newer and therefore less common. A hip to gable extension has a higher loft conversion cost than dormers, but still isn’t the most expensive option.

This type of loft conversion involves taking an existing, inward angled wall and straightening it. As a result, existing attic space is increased without adding new construction, furthering separating it from dormer extensions.


  • Blends in with existing roofing, making it visually appealing
  • Ideal for bungalows, terraced and detached homes
  • Adds plenty of extra space
  • If you have the finances, you can add both a hip to gable to the side of your property (filling out a slanted side) with a rear dormer for maximum extra space


  • Doesn’t work for mid-terrace homes
  • Less affordable than dormers, creating a moderate loft conversion cost
  • Requires some interior structural changes, which can be costly

Mansard loft conversion

Mansard loft conversion costs are the highest of the three, due to the more involved process of renovations. Nearly always built at the property’s rear, a mansard conversion extends out from a sloped roof with a flat roof and wall that is angled inwards at 72 degrees. They can be installed on a greater number of house types than most other conversions.

That said, they are most typically seen on terraced housing. This is because they are often built by raising the party wall first – this is the wall that separates one terraced house from another. Fitting a dormer or hip to gable conversion on a terraced house can be challenging, so this is a viable alternative.


  • Lots of headroom
  • Despite being new, it can blend in effectively with older brickwork – essential for adding to terraced housing
  • Let’s in lots of light
  • Visually more appealing than a dormer


  • Most expensive option
  • Lengthy construction times
  • Almost always needs planning permission

Roof light loft conversion

rooflight loft conversion

Unlike the previous three options, roof light loft conversion prices are much lower. This derives from the fact that roof lights don’t expand the existing space at all. Instead, they simply reinforce the floor so that windows can be added to the slanted attic walls.

If you’re worried about planning permission or are short on funds, these are a great alternative to the options above. This is so long as you’re focused more on changing the aesthetics than the dimensions of your loft, of course.


  • Planning permission and development rights can get more complicated to navigate in conservation areas. Roof lights are much easier to approve in these areas than other options
  • Much cheaper than dormers, mansards or hip to gables
  • Still allow for extra storage, if you make creative use of your eaves


  • Doesn’t create additional space
  • If the windows are front facing, then you may still require planning permission
  • 2.25m of head height is needed in the centre of the room to raise up the floor
  • As no additional room is created, it can limit where you can have stairs come up into the room

Can I convert my loft?

Another point we should cover before getting onto actual prices is whether your house is able to support a loft conversion. Aside from having a loft to convert in the first place, there are a handful of other factors you need to consider:

  • Roof structure
  • Head height
  • Roof pitch
  • Other limitations

There are more issues regarding the nature of your house that can affect your decision to renovate. However, these topics are here because they cannot be ignored – everything else is more about your preferences. If you’d like to cover all your bases, make sure to read the section on what you need to know, below.

Roof structure

Roofs are structured differently depending on who originally built them, and during what period they were erected. A typical roof structure that leads to difficult conversions are trussed roofs. Because of their shape, their structural integrity will be compromised if you don’t take out extensive work on them. This includes inserting steel beams to support loadbearing walls, which can drive up the cost of a new loft conversion.

One of the roof types most suitable for loft conversions are those that use traditional frames. They lend themselves well to an affordable conversion, as they can be easily altered. Follow the advice of a structural engineer, but usually all that needs to be added is support for existing rafters.

Head height

This is arguably the most important factor to get right. From the bottom of your loft’s ridge timber to the highest point of the ceiling joist must be at least 2.2m. While there is technically no minimum height, you’ll require 2m when you account for the stairs you need to build.

If you don’t have 2.2m of headspace to spare, there are options available to you:

  1. Increase your roof height: While technically possible, this can be challenging. Partly because of the structural resign involved, but also because of expenses and planning permission needed. This process can take a while too and will necessitate the set-up of scaffolding while you’re without a roof.
  2. Decrease the ceiling height of the room below: Even more labour intensive than the first option, this requires removing the entire ceiling underneath the loft. Doing this will also mean you need to install plates, bolted to your walls, that the new ceiling joists will connect with. A tie between the walls and the roof structure is necessary on top of that, to inhibit the roof from spreading.

Roof pitch

The roof pitch is the angle at which a roof extends from a wall. The higher the roof pitch, the sharper the angle upwards the roof takes. A higher roof pitch therefore equates to a higher central head height, which is better for loft conversions.

Other limitations

There are a few other practical issues to make sure you have squared away before you can appraise the cost of a new loft conversion. Namely, will your heating system be affected by your renovations?

By altering the shape and contents of the loft, you may remove space for your plumbing and hot water tanks. In this case, you may need to replace your current domestic heating system. A sealed system is a common alternative.

How much does a loft conversion cost?

The price you pay for a loft conversion is dependent on a lot of factors. Roof pitching and overall structure can have a large effect, as can the cost of adding stairs. There are plenty of other potential costs too.

Financial costs

The lowest general figure you can expect to pay is around £15,000 for a regular room-type loft conversion. This includes: reorganising the electric and heating systems, insulation, appropriate fire safety precautions, new supports in the floor and a handful of windows or rooflights. This is, of course, an average figure. As such doesn’t take into consideration the unique costs involved with specific types of loft conversions.

If you choose a dormer style, for example, your loft conversion costs can increase dramatically. Larger floor space and creating more head height are key reasons for this. Dormer loft conversion costs can be closer to £35,000 to £40,000, albeit the very cheapest can be anywhere from £20,000.

Additionally, if you decide for whatever reason to alter your roof structure then there will be extra costs. The most likely reason for this is that you’d need to create more head height, usually to install a staircase. Alternatively, this can be a necessary cost in a mansard or hip to gable loft conversion. These types of projects can raise your total loft conversion cost to over £40,000.

Time costs

Another cost to take into account is the length of time it will take to complete. The planning phase can a variable length of time – anywhere from a month to three. If you need a Party Wall Agreement for a mansard conversion, this will greatly increase the time spent here. After that, the actual renovations can take from six weeks to two months.

What do I need to know before I build a loft conversion?

While the price of a loft conversion is likely your key concern, it’s not the only thing you need to be aware of. Here are a few things to consider before buying any materials.

Building regulations

Building Regulations approval is mandatory for any loft conversion. To get this, you’ll need a building control surveyor to inspect your project at multiple points throughout construction. If, upon completion, they are satisfied that you’ve met various parts of the Building Regulations then you will be granted a completion certificate. This will signify that your new loft conversion is legal.

Specifically, you need to be aware of these sections of the Building Regulations while you’re building:

  • Part B and P – Fire and electrical issues. The most complicated of the regulations. If your home has 2+ storeys, and your escape window is found over 4.5m from the ground, then a “protected staircase” needs to be installed. This must reach down to an exterior door. Bear in mind that this may be tricky if your existing staircase doesn’t come from a hallway on the bottom floor. Plan accordingly.
  • Part K – Falling and collisions. A lower bound of 2m in headspace is required for every escape route. This includes any stairs, albeit the regulations are laxer when it comes to staircases providing entry to a loft conversion.
  • Part L – Thermal efficiency. Certain U-value targets must be met for newly converted rooms. This means that your loft conversion must have a desired level of thermal efficiency in order to be considered a habitable space.

Finally, if you’re converting a home that is semi-detached or terraced, you’ll need to let your neighbours know that you’ll be conducting these renovations. However, this is only true if the alterations are counted under the Party Wall Act.

Planning permission

loft conversion cost
Building a loft conversion

As you can see from the types of loft conversion section, whether or not you need planning permission for your loft conversion will depend on the choice of conversion you go for.

In most cases loft conversions fall under Permitted Development (PD), meaning they do not require planning permission. That said, it’s worth considering researching any specific issues that might arise on websites like Planning Portal. For example, while dormers do fall under PD you will need to apply for permission if you build one forward of the roof plane.

If you decide to build a mansard conversion, or even a larger hip to gable, then you may need to apply for planning permission. This is also true if your property belongs to a conservation area or is a listed property. Any renovation that changes the shape and/or height of the roof will generally require planning permission too.

Stairs and Staircases

There is a minimum height requirement of at least 2m above the pitch line for any stairs you’re installing. This is the key requirement, but there are a series of other stipulations that must be met.

You cannot have more than the maximum number of steps, which is 16 in a straight line. The minimum height of any balustrading is 900mm over the pitch line. Spindles must have a separating distance of at least 100mm between them. Additionally, a step rise can only be as much as 220mm. Step depth meanwhile has a minimum of 220mm. Step width is however unregulated, but this doesn’t necessarily mean you can install an extremely narrow staircase. You’ll need to ensure appropriate access to your loft – as well as considering any furniture that you want to put up there.

Ceiling joists

One thing you might consider, with all the questions surrounding what a new loft conversion cost arrives at, could be whether you need to replace your ceiling joists when converting your loft. In fact, you likely will. New joists are necessary in order to meet sections of the Building Regulations. This is because existing ceiling joists are unlikely to support a conversion floor.

In order to know what you need, we recommend hiring a structural engineer. They will advise as to what grade and size of joist you’ll need. New joists don’t replace old joists however – they are installed alongside the old systems.

Do I need a designer, or can I convert my loft myself?

It is possible to design a whole loft conversion by yourself. But unless you have prior design or construction experience, we don’t recommend taking on so much by yourself. This is especially true if this is your first large scale home renovation. It’s one thing to redesign a room that already exists, such as your living room or kitchen. It’s another altogether to plan a room from the ground up – literally – accounting for construction as well as refurbishment.

The other benefit of hiring someone else comes from the rigmarole surrounding planning permission. Whichever type of professional you choose; they’ll make sure you get planning permission and comply with Building Regulations.

If you do decide to hire someone to help with design, you have two main avenues you can explore:

Design company

This is the simplest solution, in that companies will charge you one fixed price for the total service. It’s also easy to check how reliable a design company is through websites like Trustpilot. Because the services they provide are likely part of package deals, you may find that prices are standardised.

However, be prepared to have less creative control when working with a company. This is especially true if they’re a large organisation with lots of clients, as they simply won’t have as much time to spend with you individually.


This option is more suitable if you want that personal touch. Working with an architect is as co-operative an experience as it sounds. Between the pair of you, you’ll work to realise a design that fits the potential of the space, the needs of your home and your own sensibilities. They will do this by taking your notes and producing drawings, which you will then discuss before you settle on a final design.

Hiring an architect may require you to hire a structural engineer as well.

Because of the small amount of work involved for the architect however, their design costs may be high. This is because they need to account for inconsistent work periods and peaks and troughs in demand. For more information on the architect costs see our cost guide.

How can I add light to my loft conversion?

The last thing you want when you’re transforming your loft into something new is to finish renovating, only to realise there’s no source of natural light. Being ideally positioned to receive natural light, it would be a waste of potential not to let some of the outside in. Additionally, being the highest room in the house means that it will also have the best views.

When it comes to natural lighting options, you have a couple of options:

  • Rooflights
  • Dormer windows

Alternatively, you can add artificial light, if neither of these options seem appropriate for your new loft conversion.


We covered rooflights earlier in the section above, however it’s worth going into more depth. Rooflights are a relatively inexpensive option when it comes to how they’ll affect the loft conversion cost.

Installing them requires fitting tall/long windows along the roof’s pitch line. This is achieved by taking away any tiles or materials where the rooflights will need to be. Obstructing rafters are also removed, though those that remain must be made stronger. Otherwise the structural integrity of the roof can be compromised.

Planning permission is only required if you install them on a front-facing part of the house.

Dormer windows

Smaller than rooflights, more like traditional windows. They work great when the pitch angle of your roof is incredibly high. This allows you to maximise the utility of your floor area underneath.

Mansard and hip to gable conversions can also have windows, and they too help create more space.

Dormer windows can also be quicker to install than other choices. Many design and building companies will make their own dormer windows and then place them into renovated properties. This leads to quicker install times as they don’t have to measure and construct the windows on-site.

Artificial lighting

There are 3 kinds of artificial light that you can add to a room:

  • Ambient: A replacement for actual daylight
  • Task: Provides light for work and tasks, ideal for reading
  • Accent: Creates atmosphere

The best loft conversions will combine these 3 options to great effect. You can add ambient lighting, for example, by adding table lamps. These can be connected to the main wall switches as well for ease of control. Another source of ambient light can be created by installing downlights in the ceiling, or even within dormer windows.

What types of insulation can I add to my loft insulation?

As you’re converting your loft, you may want to consider how you’re going to insulate your new room. While it may increase the initial loft conversion cost, it’s critical in order to save on energy down the line. There are two forms of wall insulation – warm roof and cold roof – as well as a couple other ways to insulate your rooms.

Warm roof insulation

Warm roof insulation involves inserting a layer of insulation on top of the rafters but before the weatherproof layer. This option is most used on dormer conversions, particularly those that have a flat roof. That said, slanted roofs also make use of warm roof systems.

The methodology of warm roof insulation is as follows:

  • 100mm Celotex insulation is used to cover the rafters
  • Then a covering cap is added
  • Then finally regular tiles and tile battens are put in place

Sound insulation as well as heat insulation is provided by an internal partition wall too. This wall utilises a 100mm quilt on one side, with plasterboard on the other.

Cold roof insulation

loft conversion cost insulation
Cold roof insulation

Contrary to what the name might suggest, cold roofing isn’t a euphemism for choosing no insulation. Instead, it involves packing the spaces between the rafters with insulation (rather than putting an insulating layer above them). As there’s nothing normally between rafters, this doesn’t require you to remove or restructure anything too drastically.

The difference between these two methods is that, while both create insulation, cold roofing doesn’t insulate the rafters themselves. As a result, the rafters will get cold in winter. This chill will therefore radiate through the roof and into the loft conversion.

This method is easier than warm roofing, as you don’t have to get in between various roof elements. It can, however, take longer. It also actually has a bigger negative impact on your new loft conversion price than warm roofing.

Floor insulation

You can install additional insulation in the floor as well as the roof. The material used for this is a kind of mineral fibre quilt, which is placed between your joists. These quilts come in a variety of makes, including a style that is heavier and insulates against sound.

Party wall insulation

If your property is part of a terraced development, you may also have to account for the party wall. If you build a mansard loft conversion, you’ll also increase the size of this wall, so keep this in mind. As with the examples above, you can insulate the party wall against sound and heat.

Using mineral fibre materials matched with timber is a common solution to insulation problems. They’re also well priced so investing in this kind of timber studwork shouldn’t affect your loft conversion costs too much.

Which fire regulations do I have to follow for new loft conversions?

When building new loft conversions, you must make sure that you meet any and all necessary fire safety regulations. The last thing you want to do is spend thousands in loft conversion costs only for it to be unsafe. There are four key areas to make sure are fire safe:

  • Windows (single storey and two storey)
  • Doors
  • Smoke alarms
  • Floor joists

Windows – single storey

The critical thing to remember with windows is that they need to be low enough to the ground, and large enough to fit through, so that you could reasonably escape from them. Specifically, openings must be at least 450mm by 450mm.

Additionally, any first-floor windows must be egress openings (though this doesn’t include bathrooms).

Windows – two storey

While the above guidelines are still useful for multi-storey homes, there are also extra considerations to take into account. Escape windows are not allowed if they’re over 4.5m from the ground. Instead, you need to install “protected stairs” (see above – What do I need to know before I build a loft conversion). These must reach down to the exit door on the ground level.

Therefore, if your staircase emerges from a room, not a hallway, then you can do one of two things:

  1. The bottom of the stairway can lead into a lobby which closes it off. All walls and doors in the lobby must be made of fire-resistant materials. Doors opening outwards into connecting rooms is also ideal. Specifically, you must have two doors in the lobby – this way you can vacate the fire at the front or rear.
  2. You can erect walls around the base of the stairway in such a way that it creates a hallway. This hall must lead to a door to the outside and must be totally enclosed.


At the top or bottom of new stairs, you must install a fire door. This separates the loft from the rest of the house. 20 minutes of fire protection is the regulation standard for what all doors should provide. If your current doors on the ground and/or first floor don’t meet this, they’ll need to be replaced.

The only glazing allowed on these doors is fire-rated glass. Therefore, if you want a way of getting natural light in, think about rooflights or windows. These will lighten up the stairwell without violating any fire safety regulations.

Smoke alarms

Smoke alarms are necessary on every floor and should be mains-powered. Additionally, they need to be interconnected so that if one goes off, they all do. It’s common that, in case of a power cut, most smoke alarms have rechargeable batteries as back-ups.

Floor joists

New floor joists must be of suitable quality that, in the event of a fire, they offer at least 30 minutes fire protection. To achieve this, you may have to renovate the ceilings in the rooms below. This is likely to involve replastering and could significantly increase your new loft conversion cost.

With all that information in hand, you’re now able to make an informed decision about what kind of loft conversion is right for you. If you decide that any of these types of loft conversions are right for you, fill out the form below. Quotatis will put you in touch with local, qualified tradespeople who can help you realise whatever vision you have.