Last updated 30th July 2020
Looking to have a dormer loft conversion? Want to know how much it costs? Check out this article and find a breakdown of conversion prices for all types of dormer lofts. By providing a cost for labour and materials, and by square metre, we've made it easy for any homeowner to calculate a estimated price for their job.
The main types of loft conversion are Velux, Dormer, and mansard. Velux conversions are the least expensive and typically cost in the region of £20,000. Dormer is the most common type of loft extension and entails a small flat-roofed extension with a window. Typically, a dormer loft conversion will cost in the region of £30,000. A Mansard loft conversion is the most extensive and means replacing one entire side of the roof to form a whole new storey. The is a major renovation and will involve planning permission. Typical costs are around £50,000. But this article will simply deal with the most common type of loft conversion in the UK, the dormer conversion.
A small dormer loft conversion typically costs around £2,000 to £7,000, while a mid-range dormer would be priced at £10,000 to £30,000. A larger-scale loft conversion could cost anywhere from £40,000 to £60,000 depending on the type of installation that is chosen, and other customisations (roof type, en-suite conversion, etc.) can change the cost accordingly. The change in price is due to the materials needed and the additional time/labour that’s required for the tradespersons to complete these additions.
The average cost of loft conversion will also depend on the type of dormer you choose. The most common applications include:
Below are some estimated costs of a dormer loft conversion.
|Job description||Avg. Cost||Duration|
|Fit a small flat-roofed dormer with uPVC window||£4,000||5 Weeks Approx.|
|As above - with a pitched roof||£5,000||5 Weeks Approx.|
|Typical double dormer full loft conversion||£30,000||8 Weeks Approx.|
|Large double bedroom dormer conversion with en-suite||£40,000||8-10 Weeks Approx.|
Below we explain the cost per square metre for different types of dormer loft conversions:
|Type of dormer loft||Avg. Cost per m2|
|Barrel roof dormer||£1,076|
|Hipped roof dormer||£1,237|
|Flat roof dormer||£1,345|
|Pedimented roof dormer||£1,776|
There are several additional costs you may need to consider when planning your dormer loft conversion, including:
|Moving the water tank||£300 to £800|
|Replacing roof trusses||£12 to £40 per m2|
|Roof modifications||£11,500 to £15,380|
|Ventilation||£250 to £400|
|Underfloor heating||£20 to £30 per m2|
|Scaffolding||£11 to £40 a day|
Below we explain the supply only costs of common expenses you may face when converting your loft.
Individual costs of a small dormer loft conversion (flat-roofed) - Total Cost: £4,000
Due to the long-term nature of the work being completed, the average cost of labour will be higher than usual, but tradesmen may charge a lower daily rate due to the long timescales involved. For example, a discounted daily rate could be around £120 - for 5 workdays each week for 5 weeks (for a small dormer installation) - this could still cost around £3,000 for the time and labour alone.
You will also need to consider the costs of each contractor. Here is a breakdown of the different labourers, how much they charge and the duration of each job.
|Tradesman||Avg. Cost per hour||Duration|
|Builder||£65||4.5 to 5.5 weeks|
|Plumber||£55||2 to 4 days|
|Electrician||£50||3 to 7 days|
|Plasterer||£40||1 to 2 days|
|Joiner||£12||1 to 2 weeks|
|Structural engineer||£50||2-4 Days|
|Glazier||£16||1 to 5 hours|
|Roofer||£50||1 to 2 weeks|
The above time frames may vary depending on the size and quality of the dormer loft conversion. For example, a basic dormer window installation may only take around 3 weeks, while a larger dormer loft conversion with a bedroom and bathroom could take anywhere from 6 to 8 weeks.
There are several steps involved when installing a dormer loft conversion, including:
The first step is to find out if you need planning permission to build a dormer loft conversion. The majority of loft conversions fall within the permitted development rights. However, you may be restricted if your home is classified as a listed building or your dormer exceeds the legal limitations. If you do require planning permission, you must apply before any construction begins. It is also important to obtain building control approval before building your dormer loft, as this will prevent you from any fines or wasted time.
To ensure you meet building regulations, you can seek help from professional architects and structural engineers who can design a foolproof plan for your dormer loft which will prevent legal issues and could also increase your return on investment. This will include detailed drawings of headroom, stair design, electricals, insulation, fire safety, and even soundproofing. They will also work with other tradesmen to ensure that everything is done properly.
Once the plans are in place, the building can commence. The first trip is to erect the scaffolding around the area being converted. A roofer will then remove sections of the roofing tiles to accommodate the dormer structure. Steel supports are then hoisted onto the roof then bolted together to construct a solid steel frame across the loft and above the ridge of the roof.
Once the internal structure is in place, joists will then be positioned along with boards which form the base of the roof. The frame and boards will then be bolted on each side both inside and outside of the property. The front boarding will then be measured and fixed accordingly, making sure to accommodate for windows and doors.
To protect the dormer from water damage, a waterproof membrane will be installed along with lead strips which act as a barrier against rainwater.
If your roof is not the right pitch or size, then changes must be made to comply with building regulations. If you have a truss roof, it will be easier to remove and raise. A typical roof raise involves the removal of the existing roof, which is then replaced with a higher roof.
If raising the roof is not possible, then you may be able to higher the ceiling in the room below. This will involve bolting a plate to the wall with shield anchors to make room for the new floor joists.
Other modifications include rafter strengthening, which involves adding more supports to ensure your loft conversion is stable. A trussed roof will also have to be strengthened with steel beams inserted between loadbearing walls to prevent any damage or potential caving.
There are two ways to insulate the roof, the first being the cold roof method which requires 70mm slab foam insulation to be installed between the rafters, making sure there is 50mm space between the roof material and the insulation. 30mm of additional insulation should then be added to the inside of the rafters for a total of 100mm of insulation.
Warm roof loft insulation involves 100mm of Celotex insulation covering the rafters. This is then secured with a covering capping, tile battens and tiles. This is a common application for a flat roof dormer, although it does not tend to work with other applications.
If you live in an attached or semi-detached home it may be necessary to insulate party walls to tackle noise and heat reduction. This will involve mineral fibre insulation combined with timber stud work which can be attached to sound-rated plasterboard. To insulate the floor, mineral fibre insulation and a denser sound insulation quilt should be laid between joists.
The electrician you hire will start by installing first fix electrical work which could involve installing a temporary consumer unit for the site, followed by fitting an earth rod, carcass wiring and backboxes. They may also need to cross bond and earth the plumbing pipework.
Wiring should then be installed into walls, making sure there is a 150mm tolerance for each cable. Once these are fitted, the walls will be plastered and more wiring will be put in place for the permanent consumer unit, as well as installing lighting, power sockets, security systems, and more. Tests will then be completed to ensure the safety of all electrical installations.
Dormer lofts are usually sloped, so the right lights must be chosen and fitted properly. The most common choices include track lighting and downlights, which are usually installed on a flat ceiling or inside a dormer window.
To enhance natural light, an electrician or roofer may install roof lights by removing the tiles and battens. The roof rafters will then be cut to make room for the roof light, which will then be framed and flashings will be added to secure it.
Adding a dormer window to your loft conversion involves opening up the roof to install the right size timbers. They may be cut to size off-site for quicker installation and better weatherproofing.
To meet fire safety regulations, you will need to have a fire door installed at the top or bottom of the new stairs. This door should provide 20 minutes of fire resistance and must not be glazed to comply with the rules. This should be fitted by a fully-trained individual.
To access the loft, you will need an adequate staircase fitted. This will involve installing a staircase on line with the roof ridge to make the most of the space. It is vital that the minimum height remains at least 1.8m to the side of the stairs, 1.9m in the centre and 2m above the pitch line. The stairs must not exceed 16 steps, although the most common application is 13 steps in a dormer loft.
To fit the stairs, part of the landing ceiling will need to measured and cut to accommodate the fixture. The corner steps should then be fitted on the level below and then connected to the main staircase. This will be bolted together and hoisted into place, making sure it is leading to the right spot in the dormer.
If you're adding a bathroom to a dormer loft conversion, then you will need to bring in a plumber. The first thing they will do is located the existing facilities which can be used to power the new toilet, sink and bath/shower. Soil pipes must be connected, which is easily done in homes where pipes are fitted at roof level, although it may be possible to connect pipes on the floor below also.
When fitting a shower and toilet, you must measure the headroom before installation. You may also want to consider installing your bath by tucking it under attic eaves to create more space. Wall-mounted installations are also great space-saving options, especially in a smaller loft conversion.
When adding a dormer loft, you may need to update the boiler, especially if you are having a bathroom fitted. When installing a new boiler, a qualified plumber will more than likely place it in the space of the existing boiler to avoid any changes or complications.
You may also want to have radiators fitted. To do this, all existing radiators must first be disconnected then the area must be scoped to find the best to install the radiator. Popular options include under windows; however, this may not generate heat throughout the entire room, especially in larger conversions.
If you are installed a large dormer extension, then you may consider underfloor heating installation, which is especially effective in bathrooms. You can choose either a wet or dry system. For the first option, pipes will be laid out to cover the entire floor area, and the manifold should be placed on the floor to ensure the plumbing connection is easy. An electric system will involve sticking electric mats to the floor, and attaching a floor sensor below a wall thermostat to help monitor usage. In both applications, the screed will be applied to the floor, which insulates and increases heat flow.
When laying the flooring in a loft, it is important to measure the area and use part of the flooring as a template before sticking it down, as some pieces may need to be cut to fit properly.
Before laying down the floor, an underlayment will be installed, which will act as a thermal and noise barrier. Once the underlay is in place, it should be secured with tape on the seams.
The actual flooring itself should then be placed down spacers which will help to achieve at least a ¼ inch gap. The floor should be laid out from left to right and once complete a rubber mallet should be used to join the flooring together while keeping the seams and joints are tight with no caps. Once complete, the mouldings and trim will then be added to the edges of the floor.
Plasterboards should be placed on each wall and bolted into place. This will then be followed by the application of adhesive, which is one of the most important layers as it will ensure the plaster dries evenly.
The plaster itself should be mixed into cold water and should only be applied when it has a custard-like consistency. The plaster will then be painted onto walls in an upwards motion. After the first coat has been laid on, it can be smoothed over after 20 minutes of drying time. The surface can then be scraped, and the process begins again.
To finish off, a small amount of water is applied to the surface; then a trowel is used to smoothen out the area. To ensure there is no excess plaster, sandpaper can be used to remove any unnecessary debris.
Once all walls have been plastered, decorating can commence. If the design involves painting the walls, this can be completed by a professional painter and decorator or by yourself. To ensure a clean paint job, the walls will be thoroughly cleaned with a sponge and clean water to remove all dust and debris. Primer should then be used to prepare the wall; then once this is dry, the chosen paint will then be applied carefully, making sure to let it dry between coats.
Hanging wallpaper is slightly more complicated and may take longer. This involves measuring and cutting the wallpaper to size then pasting it onto the wall with adhesive, making sure that everything fits perfectly with no creases or bumps.
A dormer oft conversion is a huge job so there are a lot of factors which will change the overall cost you pay for the work. Below we have split up all the factors which will change the price and give an indication of what you can expect the cost to be.
Any loft conversion is a major job and beyond the scope of the typical DIY enthusiast. You will need a builder to construct the walls and install insulation and soundproofing. A glazier for the new windows, an electrician for lighting and new sockets for electrical equipment, and a plumber for additional radiators and perhaps to fit a bigger boiler to cope with extra heating demands. A joiner may be required for new ceiling joists, and a plasterer will be needed for the new walls.
A painter and decorator will also come in handy, although this is one part of the loft conversion which most of us can tackle to save some cash. If you plan to tackle the painting or wallpapering yourself, you should consider investing in the following tools:
The majority of homes can be converted, although some may have more space than others to convert their loft. For example, if you have a traditional cut rafter roof or purlin roof which both form an M-shape in the centre of your loft, then the minimum height will usually be 2.2 metres at its highest. In contrast, a modern trussed roof will have just that bit extra with a minimum of 2.4 metres at its highest point.
To determine the extent of your conversion, you will also need to consider the pitch of your roof, as the higher it is, the taller the head height will be. However, many roof modifications can be implemented to accommodate enough headspace.
Measuring the internal walls is also a key indicator of whether your loft can be converted. To accommodate a dormer conversion, your loft’s walls should have a minimum of 7.5 metres from front to back and 5.5 metres from one side to the other. If your loft space is smaller than this, work can be done to increase wall space.
You should also make sure there is enough room for a staircase without being too cramped. There must be enough space for a head height of 1.9 metres with a steepness pitch of 42 degrees. In smaller lofts, space saver stairs can be used if they only lead to a single room.
|Flat-roof dormer||£16,000||- One of the most affordable dormer loft conversions
- Offers the largest amount of living space
- Versatile application
- Works well in lofts with minimal headspace
|Hip-roof dormer||£6,000||- Features three sloping planes
- Larger hipped roofs can maximise space
- Adds a contrasting appeal on gable roofs
- Enhances natural light
|Gable-fronted dormer||£6,500||- Has a simple pitched roof
- One of the most popular choices for period homes
- Provides shade to dormer windows
- Installed to enhance the architectural appeal and enhance light
|Shed dormer||£15,000||- A single-planed flat roof which slopes downwards
- A simple installation can reduce construction costs
- Maximises loft space
|Blind dormer||£4,000||- Can be constructed to form any of the above shapes
- Does not penetrate the roof
- Used for smaller loft conversions
- The cheapest loft conversion available
When planning out your dormer loft conversion, you need to consider the best ways to utilise the space.
For a small dormer loft conversion, such as an en-suite or an office, you should consider the positioning of your furniture and where the best placement is to create more space. You should also choose light décor for your walls and flooring to create the illusion of more space. Storage is also an important element in smaller spaces, for example, if you’re planning to implement a small spare bedroom, then you should consider purchasing a storage bed which will free up space.
For larger conversions which may include multiple rooms, you may want to opt for an open plan design which will allow you to maximise the space as much as possible. In contract, you may want more privacy with separate space, especially if you are building a bedroom dormer with an en-suite, which will require a doorway, so you may have to sacrifice some space in either one of the rooms.
To assist you with the planning and design of your dormer loft conversion, you could hire an architect, who will charge around £50 to £60 per hour. While this may seem expensive, it can actually be extremely beneficial as an architect will help you create a design that is both unique and practical, while also making sure building regulations are met.
There are alternatives you could consider including a structural engineer, who typically costs around £50 per hour. Their main job is to help you understand the basics of the structure and what you can or can’t do when building your loft conversion.
You could also hire an interior designer to help you with the internal finishings such as the flooring, walls, appliances and any other decorations you will need. You can expect to pay around £100 an hour for interior design services. However, it may be worth it if you’re looking for a professional and sleek loft conversion.
One of the most important things you need to consider is a staircase for your loft conversion, as this will provide you with an entry and exit doorway to the rest of the house. Typically, a staircase will be fitted on your upstairs landing where corner steps will be added for better access.
The legal parameters for a loft staircase are as follows:
There are various staircases you can choose from with varying prices, such as:
You could also consider a space-saving staircase which is perfect for small loft conversions, although under building regulations should only be used to access a single room. This is a compact staircase which features alternating steps enabling you to get to your loft much quicker. A space-saving staircase can cost anywhere from £150 to £600 depending on the design and materials used.
Lighting is another important element in your loft conversion, as roofs tend to be the darkest part of the home. There are various ways to enhance the light in your home, through both natural and artificial means.
To heat the rooms in your loft, you should consider the following options and their costs:
Another great way to retain heat in your loft is by investing in double-glazed (£300 per window) or triple-glazed windows (£400 per window), which will prevent any heat from escaping.
Insulation is also vital in heat loss prevention, so you should consider installing either slab foam or Celotex insulation in your walls (£100 per m2), floor (£3 to £20 per m2) and roof (£35 to £80 per m2)
You must have controlled ventilation installed in your dormer loft conversion to prevent a build-up of condensation, while also keeping the air as clean as possible. Here is a breakdown of the different types of ventilation, the material costs and price for the installation:
|Type of ventilation||Material cost||Installation cost|
|Background ventilation||Airbricks (£260)
Trickle vents (£15)
|Rapid ventilation||Double-glazed window (£300)
Triple-glazed window (£400)
|Extract ventilation||Extractor fan (£50)||£200|
If you’re planning to add a bathroom or en suite in your loft conversion, then you will need to make sure that you have a plan in place before you start. You will also need to consider your budget, as additional plumbing costs and furnishings will increase the cost of your dormer loft conversion.
The first steps in building a bathroom dormer extension will involve installing the plumbing (£700) and soil pipes (£1,000). It may be possible to extend the plumbing, as long as the bathroom is located in proximity to the existing waste and supply pipes. You may have to extra to move the pipes, which could add up to around £2,500 depending on how far it needs to be move.
You will also need to consider the installation costs of your toilet (£250), sink (£320), shower (£600) and bath (£700). You should also make sure that you have available floor space measuring at least 1.7m by 2.3m to accommodate all bathroom fixtures.
Ventilation is also an important factor, as bathrooms tend to accumulate a significant amount of condensation. To prevent a build-up, you should consider installing an extractor fan and one or two windows to provide the right ventilation in line with building regulations.
When planning your dormer loft conversion, it is important to consider fire safety regulation which will ensure the installation is safe. You also need to ensure compliance by covering the following safety criteria:
There are many reasons why people choose to convert their loft, with the most common being it provides more space, especially in a small home.
It is also a great alternative to moving home, say for example you have another child and do not have a spare room, you can transform your loft space into a bedroom instead of dealing with the stress of moving out.
A dormer loft conversion is also a cheaper alternative to other roof conversions, which are most costly, can be risky and also take up a lot more time.
There are several advantages for constructing a dormer loft conversion including:
If you are thinking about a loft conversion to provide some extra accommodation for you and your family, then this could also help your home should achieve a better price when you come to sell. Homeowners can reap the most financial benefits by adding on a bedroom and bathroom, which could see an increase of property value up to 20%, as you will be able to sell your home at a much higher value than what you bought it for. So, provided you get the renovation done properly using high-quality material, a loft conversion is a great idea as it offers the additional space you need. You will likely recoup the entire cost of the project when you come to sell.
Planning permission is not typically required for a loft conversion, as long as you stick the following requirements:
If any of your plans do not adhere to the guidelines, then you will have to apply for planning permission which should cost around £206 to apply.
You should choose tradesmen/companies which are listed on the government's Registered Competent Person Scheme so they can give you a BS7671 certificate which complies with Building Regulations. You should also check that your plans meet the following criteria:
If your dormer does not meet these regulations, then you will need to make a building regulations application, which can cost around £240.
If you have a low budget, you could consider the following ways to keep your costs down.
You may want to remove your dormer loft and install a new loft conversion, or maybe you have moved into a new home and do not like the look of the staircase leading to the conversion. For a basic removal, you should expect to pay around £400, which includes professional labour and materials. This price will, of course, depend on the size and type of dormer loft you have, as other installation may be tricky.
You could always remove the installation yourself, especially if it just involves removing the staircase and filling in the ceiling. All you will need to purchase is a ladder and hatch which would cost around £150 and will be put in the place of the old staircase.
More complicated removals include bathroom dormer loft conversion, which will require the help of a plumber who will usually charge around £55 per hour to remove any pipes or bathroom fixtures. Roof modifications may also need to be made, which can cost up to £15,000.
If you decide that you want to convert your loft into a dormer conversion then you’re going to need to hire multiple different tradesman to work together on the build.
To ensure all the tradespeople you hire are reliable, always request references and evidence of work. Planning permission may be needed and building regulations will need to be followed so its key to test their knowledge on any standards, so you know they understand them, and you can trust their guidance. Don’t be afraid to ask questions and don’t hire the first local contractor you find. You need to hire an expert in their field as without doing so you can put your home, yourself and your family in danger.
It’s recommended that you get at least three quotes from different loft conversion specialists before you make any hiring decisions. If you’d like to find local loft conversion contractors who can give you an estimate, click here.