The Cost Of A Dormer Loft Conversion

All you need to know about dormer loft conversions and windows, including costs of installation, materials, labour and time frames.

Dormer Loft Conversion

What the job entails

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, so provided you get the renovation done properly, a loft conversion is a great idea as it offers the additional space you need and you will likely recoup the entire cost of the project when you come to sell. However, like many areas of life, cutting costs or rushing in without the proper research or advice, can give you major headaches - act in haste, regret at your leisure. It's important to take some time to research loft conversion costs and the types available. The type of loft conversion you decide on will depend on a number of factors, not least of which is your budget. Plus, there's also the question of whether or not the space or type of roof is suitable and whether you're likely to get any necessary planning permission.

A 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 though this is one part of the loft conversion which most of us can tackle to save some cash! 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. Whether or not you need your local authority planning department approval depends on the type of conversion and if your home is listed in a conservation area.

The most popular type of loft conversion in the UK is the traditional flat roof dormer conversion. As well as being the most popular, this is the cheapest type of dormer conversion to build, while offering the largest amount of additional living space. A dormer conversion can also often be possible even in lofts with minimal headroom. A flat-roofed dormer conversion is relatively inexpensive to install and offers a versatile space in all type of properties whether a Victorian terrace, post-war semi or even a modern detached home.

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The Cost Of A Dormer Loft Conversion

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.

Due to the long term nature of the work being completed, the cost of labour will be higher than usual, but may well charge a lower daily rate due to the longer timescales involved. For an 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 £3000, for the time and labour alone.

Depending on the type of installation that is chosen and other customisations (roof type, en-suite conversion, etc) can change the cost accordindly. Usually due to the materials required and the additional time/labour that is required for the tradespersons to complete these additions.

Below are some estimated costs of a dormer loft conversion.

Job Description Avg. Cost Duration
Fit a small flat-roofed dormer with uPVC window £4000 5 Weeks Approx.
As above - with a pitched roof £5000 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.

Cost Breakdown

Individual costs of a small dormer loft conversion (flat-roofed) - Total Cost: £4000






Waste Removal


In most cases, a dormer loft conversion falls under permitted development and will not require planning permission, but there are specific conditions and limitations attached to permitted development rights so you should always double check with your local planning department and obtain a Lawful Development Certificate from your local authority as written proof that your loft conversion is lawful for when you come to sell your home.
Yes - Building Regulations Approval is required on any loft conversion whether or not planning permission is required. Building Regulations ensure that the structure is safe and includes elements such as structural strength, stability, sound insulation, safety and emergency fire exits.
This is a common question, but it's difficult to give an exact figure without knowing exactly what kind of conversion you want and the existing roof structure. An ordinary, simple dormer conversion can cost less than a new bathroom or kitchen.
Since 2011, as long as you aren't extending your roof space, planning permission rules have been changed which means most loft conversions now falls within the category of permitted development. However, it is vital that you always check directly with your local planning department as permission is your responsibility as the property owner.
A water tank or chimney does not mean that you can't have a loft conversion. Both water tanks and chimneys can be removed or worked around. However, it is likely that this will increase the overall cost of the conversion to cover the extra work involved.
You might be surprised what can be achieved with a flat-roofed dormer window, but of course, there does need to be enough floor space to make it practical and a minimum of 7 feet and 6 inches of height in the highest part of the room.
A simple loft conversion can be completed in around 5 weeks, but larger conversions can take up to 8 weeks. Obviously, any complications such as removing or working around chimneys and water tanks will take longer as will rerouting water pipes and electrics if required.