Whether it’s because your family is growing and you’re in desperate need of another bedroom, or because you need a quiet place to work from home, a rear dormer extension is a home renovation worth considering. Characterised by a ‘box’ shaped extension protruding from a sloping roof, a dormer extension adds space and headroom to a property.
Though there are various types of extension to choose from, dormer extensions are hugely popular in the UK, with many homeowners using one to add value and space to their property. Before you go ahead and start planning a dormer loft extension, it’s helpful to have a rough idea of the costs involved.
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Types of Dormer Extensions
Dormer loft conversions are typically used to add an extra bedroom - and sometimes an en suite bathroom - to a home. There are various types of dormer extensions to choose from including flat roof, gabled, hipped and shed dormers. Though the different types of dormers are similar, they have some key differences.
- Flat Roof Dormer - This type of dormer has a flat roof that extends vertically from the property’s existing roof, providing extra headroom and floor space. It’s one of the more cost-effective dormer options because of its simple design, but it’s often considered to be one of the less appealing in terms of aesthetics. It’s a good option if you are trying to keep things as budget-friendly as possible.
- Gabled Dormer - This type of dormer has a roof that slopes down on two sides, forming a sort of triangle shape. It’s a more traditional type of dormer extension and one that’s commonly seen in the UK, and it’s often considered to be more visually appealing than a flat roof design. However, this does mean that gabled dormers tend to be a slightly more expensive choice, as the structure can be complex.
- Hipped Dormer - A hipped dormer has a roof that’s sloped on all sides, which makes the extension look integrated and ‘in line’ with the rest of the property. Compared to flat roofs and gabled dormers, hipped dormers have a more cohesive design. But, this requires a lot more construction, which increases the cost.
- Shed Dormer - Unlike other types of dormer, a shed dormer has a single sloping roof, which extends down from the property’s existing roof. This creates a contemporary look, making it a popular choice for modern homes. Shed dormers don’t tend to be as expensive as hipped dormers, and it’s a mid-range option.
What Impacts the Cost of a Loft Extension Dormer?
- Extension Size - One of the biggest influences on the cost of a dormer extension is the size. It will come as no surprise to learn that the larger the dormer, the more it is likely to cost. This is because large extensions require more materials, labour and time. There’s also a chance that a larger dormer extension will require more extensive structural modifications to the existing roof, which also increases the materials, expertise, labour and time required.
- Choice of Materials - The cost of a dormer extension is also impacted by your choice of materials. Premium materials tend to come with a higher price tag, and the cost of high quality options quickly adds up. You should also expect the cost of an extension to be higher if you need to use specialised materials for custom features and finishes.
- Location - Your location will also impact the cost of a dormer extension, especially if you live in an urban area, such as London. This is because labour and materials are usually more expensive in cities, and in areas with a high demand for construction services. It’s usually cheaper to have building work carried out in more rural locations.
- Design Complexity - The complexity of the dormer design will affect the cost. Dormer extensions with intricate roof structures - such as those with unique angles or custom features - usually require more labour and expertise to build, which comes at a price. Tradespeople capable of complex designs are able to charge more for their services.
- Planning Permission - Planning permission is often needed for a dormer extension, and the cost of this can add up. Planning permission fees, application costs and any surveys required will all need to be factored into the budget.
Average Dormer Extension Cost
The average cost of a basic dormer extension in the UK is £45,000, depending on the size and complexity of the project. The cost ranges from £30,000 to £60,000, with some large and complex projects going beyond this. For a dormer extension that’s large enough for a master bedroom with an ensuite, you should expect to pay between £35,000 and £45,000.
| Small Dormer | Mid Dormer | Large Dormer | |
|---|---|---|---|
| Price Range | £2,000 - £7,000 | £10,000 - £30,000 | £40,000 - £60,000 |
| Average Cost | £4,500 | £20,000 | £50,000 |
Cost of Dormer Extension Windows
You can expect to pay between £150 - £200 per 0.5m x 0.5m window. The cost increases depending on the size of the window, to £200 - £250 per 1m x 1m window, and £250 - £300 per 1.2m x 1.2m window.
Cost of Dormer Extension Flooring
The cost of flooring for a dormer extension varies depending on the type of flooring you choose.
- Vinyl - £7 to £30 per m2
- Wood - £10 to £70 per m2
- Carpet - £4 to £40 per m2
- Tiles - £10 to £60 per m2
You can reduce the cost of a dormer extension by choosing a more affordable flooring option, such as vinyl or a budget-friendly carpet.
Cost of Dormer Extension Insulation
Insulation is a key part of dormer extension construction, as it helps maintain comfortable indoor temperatures throughout the year, whilst also reducing energy use. The cost of dormer extension insulation depends on the type of insulation that you choose.
- Sheet - £15 to £25 per m2
- Loose Fill - £5 to £15 per m2
- Blanket - £12 to £27 per m2
It’s important to use proper insulation in the walls, roof and floors of a dormer extension to ensure thermal efficiency. This reduces heat loss during colder months and keeps the heat out during the summer.
Breaking Down the Cost of Dormer Extension Building Materials
A large part of the total cost of a loft dormer extension comes from the building materials.
- Roofing - You should expect to pay between £1,500 and £3,000 for roofing materials, depending on whether you choose tile or slate.
- Windows - Windows for the dormer extension are likely to set you back between £1,500 and £3,500 depending on the size, material and the type of glazing.
- Insulation and Heating - On average, it costs between £1,000 and £3,000 for insulation material, the install and extending the property’s existing heating system.
- Electrics - Ensuring a dormer extension is equipped with electrics costs between £1,000 and £3,000 for electrical outlets, lighting and installation.
- Plumbing - Plumbing will set you back between £1,500 and £4,000 for the installation of plumbing fixtures, with dormers with a bathroom costing more.
- Finishes - The cost of finishes will depend on the quality, style and material used. It tends to cost somewhere between £2,000 and £5,000 for flooring materials, painting and decorating. This is a cost that is completely dependent on how much you want to spend.
Cost of Professional Services for a Dormer Extension Project
You can expect to pay between £1,000 and £6,000 for the planning and technical design elements of a dormer extension project. This includes architectural drawings, planning permission and calculations. The cost of this will vary depending on the size and complexity of the construction.
As part of this cost, you will need to pay for the planning application, plus any additional charges for complexities. Building regulations usually cost between £850 and £1,200 for inspections and any necessary certifications. If you share a wall with a neighbouring property, you might need a party wall agreement. This costs between £700 and £1,600 per adjoining neighbour.
You will also need to enlist the services of an architect to put the dormer plans into place. In the UK, architects charge between 5% and 12% of the whole construction cost. You might also need to hire a structural engineer and they charge from £50 to £90 per hour.
Average Cost of Hiring a Dormer Extension Tradesman
Unless you have a wealth of experience and building knowledge, you will need to hire a tradesperson to complete your dormer extension project. The cost of doing so is usually included in the overall price, but it’s helpful to know roughly how much you can expect to pay per hour of their time. Depending on the type of dormer extension, you might need to hire a range of people.
| Service | Cost Range (per hour) | Average Cost (per hour) |
|---|---|---|
| Builder | £20 - £35 | £27.50 |
| Plumber | £35 - £45 | £40 |
| Tiler | £20 - £40 | £30 |
| Decorator | £20 - £50 | £35 |
| Electrician | £50 - £120 | £85 |
| Plasterer | £30 - £50 | £40 |
Planning Permission and Regulations
If you need to acquire planning permission to extend your property with a dormer extension, you will need to have permission granted. To do so, you need to submit a planning application. The cost of planning permission depends on the type of extension you are planning, the size and how much it alters the existing property.
A householder planning application is the most common type of planning application, and it’s used for projects that extend the house, whilst staying within the boundary or garden. This costs £258 and is what’s needed for a dormer extension. If you are planning to significantly change your property with a much larger dormer extension, you will need to submit a full planning application.
Funding and Financial Assistance
Funding a dormer project can be done in a variety of ways including personal savings, loans or with government grants. Using personal savings is a straightforward and popular option, allowing you to cover the costs upfront without incurring any debt. However, using savings often requires a lot of careful budgeting and saving over time to build up the necessary funds. This could delay the start of the build, especially if you are waiting to have enough in your savings pot.
Alternatively, you could choose to take out a loan, such as a home equity loan or a personal loan to finance the dormer extension. With a home equity loan, you use the equity built up in the property as collateral. This could provide you with access to a larger amount of money compared to other types of loans. Personal loans are also an option and don’t use the equity of the property, but they may have higher interest rates, and you could be limited in regards to how much money you can borrow.
You might be eligible for government grants towards your dormer extension, which will help you to cover the cost. These grants tend to be linked to energy efficiency and insulation, and are given on a case-by-case basis.
DIY vs Professional Dormer Construction
There is a big difference between the cost of hiring a professional for your dormer extension, compared to handling everything yourself. Though there are potential cost savings with a DIY approach, there are also key risks to be aware of. Before going ahead, you need to compare the pros and cons of DIY versus a professional.
The Pros and Cons of DIY Dormer Extensions
- Cost Effective - One of the main benefits of a DIY approach is the fact that it’s cheaper. By doing the work yourself, you avoid having to pay for labour. But, though a DIY approach is cost effective to begin with, it’s not necessarily an affordable solution in the long run. There is a risk of things going wrong with DIY, and mistakes could be expensive to fix. Plus, without the experience and expertise of a professional, there is no guarantee of a long lasting finish that you are completely happy with.
- Flexibility - There is a lot of flexibility that comes with a DIY approach to dormer extensions, as you can manage the project in a way that works for you and your schedule. You can complete tasks as and when you can, without having to worry about strict workman schedules and deadlines, or unavoidable disruption to your home life. However, this can also mean that construction takes longer. You are likely to have other commitments and responsibilities - such as work deadlines, family life and hobbies - that the project will need to work around.
The Pros and Cons of Hiring a Professional
- Expertise and Experience - Professional tradespeople have years of expertise and experience to ensure a flawless construction process from start to finish. Even if you do have a lot of DIY experience, it’s unlikely that you have the same skills and knowledge as them. Their experience allows them to build a high quality and professional dormer, one that adheres to safety standards, whilst also ticking every box.
- Efficiency - There’s a lot of work that goes into building a dormer extension, but professionals are able to work quickly and to tight deadlines. Thanks to their experience, professional tradespeople are able to complete tasks efficiently and to a high standard, reducing the chances of unexpected delays.
The decision between a DIY approach and hiring a professional usually comes down to a variety of factors such as the complexity of the job, your skill level and the desired outcome.
Key Takeaways
It’s hard to give an exact cost for building a dormer extension in the UK, as there are a lot of variables. You can expect to pay between £30,000 and £60,000 for a dormer extension, depending on size, materials, location and design complexity. As there’s such a range in the cost, it’s important to plan and budget beforehand, to ensure that you have a successful and cost effective project. You need to find a balance between having a dormer extension that works for you and your property, but also one that’s affordable with your budget. It’s also a good idea to have a contingency fund to cover the cost of unexpected costs or changes to the project along the way.
Sources
https://extensionarchitecture.co.uk/blog/dormer-loft-conversion-cost-guide/
https://www.gov.uk/guidance/fees-for-planning-applications/