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What Is the Cost to Add Dormers to a Loft Conversion?
- Adding a dormer to an existing loft conversion in the UK costs between £6,000 and £22,000.
- The price varies based on the dormer’s size, design, and materials.
- Dormers extend from the roof slope, adding windows, space, light, and ventilation.
Adding a dormer to an existing loft conversion is a smart way to increase the usable space and improve the appearance of your home.
Dormers are extensions that project from a sloped roof, featuring windows that let in more natural light and provide extra headroom. They can make cramped loft spaces feel bigger, improve ventilation, and even increase your property’s value.
Financially, any loft conversion can substantially boost a property's market value. On average, homeowners see an increase in home value of approximately 15% to 20%, according to The Guardian.
In this article, we’ll explain the costs of adding a dormer, including factors like size, design, and materials. We’ll also explain when planning permission is needed and share practical tips for keeping costs down.
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Cost of adding a dormer to an existing loft conversion
Adding a dormer to an existing attic conversion in the UK costs between £6,000 and £22,000, depending on several factors like size, design, location, and materials. To get an accurate estimate for your project, it’s best to consult a qualified architect or builder.
Here are the key factors that affect how much it will cost to add a dormer to the existing loft conversion:
- Type of dormer: Simple designs, such as flat-roof or shed dormers, are the most affordable. More complex styles like hipped or gable-fronted dormers cost more due to their intricate construction and added materials.
- Size of the dormer: The bigger the dormer, the higher the cost. Larger dormers require more materials, labour, and often additional structural reinforcement to support the new load.
- Materials used: Premium materials, such as bespoke windows, high-quality roofing, or decorative siding, will raise the cost.
- Structural modifications: If your current roof isn’t suitable for a dormer, you may need reinforcements or changes to the existing structure. This could include strengthening roof beams or adjusting the loft layout, which adds to the cost.
- Location: Where you live matters. Labour and material costs tend to be higher in urban areas, particularly in London, compared to rural regions.
- Access to the loft: If access to your loft or roof is tricky, builders may need extra equipment, like scaffolding or cranes, which increases costs.
- Regulatory requirements: In some cases, you’ll need planning permission and must meet building regulations. This is especially true if you live in a conservation area or a listed building, where stricter rules apply.
What is the cost to convert a Velux to a dormer?
Converting a Velux window to a dormer costs between £6,000 and £17,000, depending on factors like size, dormer design, and materials. Costs can rise if significant structural reinforcements are needed to support the new dormer.
Here are the main factors that affect the final price of dormer loft conversion:
- Type of dormer: Simple styles like flat-roof dormers are the most affordable upgrade from a Velux conversion. More intricate designs, such as gable-fronted or hipped dormers, are pricier due to their complex construction.
- Size and design: Larger dormers or those with custom features, like bespoke windows or high-end finishes, will cost more.
- Structural changes: Converting from a Velux to a dormer often involves adjusting the roof structure. If your loft needs reinforcements to support the dormer, such as strengthening beams or rafters, this will increase the overall price.
Because every project is unique, it’s important to get loft conversion quotes from several contractors to understand the costs specific to your property and desired design.
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Different dormer window types and their costs
When adding a dormer to an existing loft conversion, the style you choose will impact the cost. Here’s a table showing the types of dormers and their average cost ranges:
| Dormer type | Average cost range |
|---|---|
| Flat roof dormer | £6,000–£12,000 |
| Shed dormer | £7,000–£13,000 |
| Side dormer | £6,000–£8,000 |
| Rear dormer | £11,000–£16,000 |
| Gable dormer | £10,000–£17,000 |
| Double dormer | £9,000–£14,000 |
| Hipped dormer | £12,000–£20,000 |
| Full-width dormer | £14,000–£22,000 |
Adding dormers to an already converted loft is generally cheaper than the cost of a dormer loft conversion from scratch.
Let’s go over how each of the dormer types looks. We’ve arranged them from the cheapest to the most expensive in this list:
- Flat roof dormer: A rectangular box-like structure with a flat, horizontal roof that sits parallel to the ground. It protrudes vertically from the sloped roof, creating straight walls and a flat ceiling inside the loft.
- Side dormer: Smaller and positioned on one side of the roof. It projects outward with a small, boxy structure, featuring a single window. The design is subtle, blending with the existing roof while introducing extra light and ventilation.
- Shed dormer: Features a single sloping roof plane that angles downward, slightly less steep than the main roofline. This design creates a wide, elongated dormer that runs along a significant portion of the roof.
- Rear dormer: Spans a significant width of the roof at the back of the house. It has a flat or slightly sloped roof and vertical walls, transforming the angled roof space into a large, box-like structure.
- Gable dormer: Has a classic triangular shape with two sloping roof planes that meet at a central ridge, forming a peak. The dormer extends vertically from the main roof, with a window set into the vertical face.
- Double dormer: Consists of two dormers, either placed opposite each other on both sides of the roof or side-by-side on a single side. Each dormer projects outward, forming two distinct structures with their own windows.
- Hipped dormer: Has three sloping roof planes that gently meet at a central ridge, mirroring the look of a traditional hipped roof. Inside, the sloped sides reduce headroom slightly but maintain a sophisticated design.
- Full-width dormer: Stretches across nearly the entire length of the roof, creating a large, rectangular structure with straight walls and a flat roof. From the outside, it significantly alters the roofline, giving the loft a modern, boxy appearance.
Adding a dormer to an existing loft conversion on a budget
If you're adding a dormer extension on a tight budget, a flat-roof dormer is the most cost-effective option. Its simple, box-like design is easier and quicker to construct, which reduces both labour and material costs.
To keep costs down further:
- Stick to standard sizes: Avoid bespoke windows or complex designs — standard materials are far more affordable.
- Choose cost-friendly materials: Use durable but budget-friendly options for cladding and roofing, like uPVC or composite panels.
- Minimise structural changes: Position the dormer where minimal reinforcement is needed, such as over load-bearing walls.
Some builders offer discounts during quieter periods, such as winter months, when demand is lower.
Factors influencing the cost of adding a dormer to a loft conversion
The cost of adding a dormer to a loft conversion varies widely based on multiple factors. To help you plan this project more effectively, let’s go over the most significant of them:
- Dormer size and type: Larger dormers or those with custom designs cost more. Standard flat-roof dormers are cheaper than more elaborate gable-fronted or hipped dormers.
- Structural modifications: Reinforcements to the roof structure or adjustments to support the new addition may be required. The level of complexity of these modifications significantly impacts costs.
- Materials used: The choice of materials for the dormer, such as cladding, windows, and roofing, affects the price. Premium materials or those matching the existing house raise costs.
- Planning permission and building regulations: If planning permission is needed, application fees, specialist reports, or amendments add to the total cost. All dormers must comply with building regulations, which may involve additional inspections or modifications.
- Labour and location: Labour costs vary by region, with higher rates in areas like London and the Southeast. The availability of skilled contractors can also influence pricing.
- Additional features: Adding extras like windows, insulation, lighting, or interior finishes will increase costs. Skylights or bespoke window designs for the dormer can further add to the budget.
These factors directly impact how much you’ll spend on your dormer addition and highlight the importance of careful planning. Once you understand the main cost drivers, the next step is finding the right professionals to ensure quality work within your budget.
Comparing multiple quotes is a practical way to do this, as it allows you to find competitive prices, evaluate expertise, and avoid hidden costs.
Here’s how comparing quotes can save you money:
- Find competitive rates: Different installers may offer varying prices for the same project. Comparing quotes helps you identify the most cost-effective option.
- Spot hidden fees: Multiple quotes allow you to see exactly what’s included, helping you avoid surprise charges for materials, labour, or additional work.
- Negotiate better deals: Multiple offers give you leverage to negotiate lower prices or request added value, such as free upgrades or faster timelines.
- Evaluate expertise: Comparing services ensures you choose an experienced professional who offers quality work at a fair price. Cheap doesn’t always mean best!
- Save on materials: Specialists may offer discounts on materials or suggest budget-friendly alternatives that still meet your needs.
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