Find out the costs of a dormer loft conversion. A dormer loft conversion creates extra headroom, fills your room with natural light, and adds significant value to your property— all without the need to move house.
A dormer loft conversion is one of the most cost-effective ways to add space and value to your home. But how much should you expect to pay?
The cost of a dormer loft conversion varies depending on the type of dormer, property size, materials used, and additional features like an ensuite or bespoke windows.
This guide breaks down the costs of dormer loft conversions by type, size, and key factors to help you plan your budget effectively.
How much should you expect to pay for a dormer loft conversion? The cost of a dormer loft conversion varies depending on the type of dormer, the level of structural work needed, and the overall design.
A simple dormer window might cost as little as £5,000, while a full-width rear dormer could range between £40,000–£55,000. If you're adding an ensuite, L-shaped dormer, or hip-to-gable extension, expect higher costs due to increased complexity and materials.
Below, we break down the typical costs for different dormer loft conversions, helping you budget for your project with confidence.
Remember: The most common dormer conversion (flat roof rear dormer) typically costs between £40,000–£55,000, depending on specifications.
Our cost calculator helps you estimate the cost of a dormer loft conversion based on your chosen dormer type, size, and key project factors. Simply select your loft type, enter your project details, and get an instant estimate tailored to your requirements.
This tool considers roof structure, materials, window choices, insulation, and interior finishes, giving you a clear breakdown of expected costs before planning. While actual costs may vary depending on location and contractor rates, this calculator provides a realistic starting point to help you budget effectively.
Try it now to see how much your dormer loft conversion could cost!
Dormer loft conversions come in various styles, each offering unique benefits and aesthetics. Here are the most common types, explained in an engaging and easy-to-read way:
A flat roof dormer extends straight from your roofline, creating a boxy structure with a flat top. It’s one of the most popular types because it’s simple and gives you much extra space.
Benefits:
Ideal for: Those looking to add living space without breaking the bank.
Cost range: £35,000 - £55,000
Also called a doghouse dormer, this has a pitched roof that forms a triangle at the top. The sides are vertical, and the front wall has windows to let in light.
Benefits:
Ideal for: Those who want a visually appealing addition that complements a traditional home style.
Cost range: £40,000 – £55,000
This dormer has three sloping sides, with the front typically having a window. It’s designed to match homes with hipped roofs.
Benefits:
Ideal for: Homes with hipped roofs that need an elegant, seamless addition.
Cost range: £45,000 – £60,000
An L-shaped dormer combines two dormers, usually at the back of the house, creating an L-shaped space. It’s great for homes with existing rear extensions.
Benefits:
Ideal for: Larger homes or those with extensions needing maximum space and flexibility.
Cost range: £45,000 - £70,000
A Mansard Dormer has a flat roof with steeply sloping sides, forming a box-like structure. It’s often used in cities to maximise space while keeping within building rules.
Benefits:
Ideal for: Homes that need lots of extra space with a classic, stylish design.
Cost range: £50,000 - £80,000
Each dormer loft conversion offers unique benefits. Choose the style best suits your home, and enjoy your new space!
*Please note that these costs are average estimates and can vary based on factors such as the loft's size, the project's complexity, the quality of materials used, and the region where you live.
Understanding the cost per square metre for different types of dormer loft conversions helps in budgeting and planning. Below is an overview of typical costs:
These approximate figures can vary based on location, materials, and specific project requirements.
For instance, a recent loft extension in North London exceeded its £75,000 budget due to unexpected structural issues, highlighting the importance of thorough planning and contingency budgeting.
When planning your dormer loft conversion, consider obtaining multiple quotes and consulting with professionals to get a more accurate estimate tailored to your needs and circumstances.
A dormer loft conversion costs can vary widely depending on several key factors. From structural modifications to finishing details, understanding what impacts the price helps you plan your budget effectively. Below, we break down the biggest cost factors and what you need to consider.
The larger and more complex the dormer, the higher the cost. A simple rear dormer adds space without major structural changes, while an L-shaped dormer extends over two sections of the roof, requiring more time, materials, and expertise.
The type of roof also affects costs. Trussed roofs (common in post-1960s homes) need additional steel beams for support, adding £3,000–£6,000 to the project.
The type of roof you have plays a huge role in how complex and costly – your dormer loft conversion will be. Older homes with traditional cut roofs are generally easier to modify, while modern trussed roofs (common in post-1960s properties) often require additional reinforcement, adding time and expense to the project.
The materials used for your new dormer also impact costs. Matching roof tiles to your existing home can be straightforward with concrete tiles, but natural slate or clay tiles come at a premium. Understanding your roof’s structure from the start helps avoid unexpected costs. Here's a quick analysis:
The choice of roofing materials also plays a role in pricing:
Remember that if you live in a conservation area, you may need to use matching materials, which can increase costs.
The right windows can greatly affect how light and airy your dormer loft conversion feels. Dormer windows, which extend vertically from the sloping roof, cost between £500–£1,500 each, depending on size and material.
Velux roof windows sit flush with the roofline, are a more cost-effective alternative at £300–£800 each and work well for sloped sections where dormers aren’t feasible.
For added comfort, triple glazing improves insulation and reduces noise but comes at an additional cost of around £150 per window.
While more windows enhance the look and feel of the space, they also add to the overall budget, so it’s worth balancing aesthetics with cost.
Every loft conversion must meet building insulation and fire safety regulations. Proper insulation is required under Part L to improve energy efficiency, with costs ranging from £1,500 to £3,000.
This investment helps retain heat in winter and prevent excessive heat buildup in summer, keeping the loft comfortable year-round. Fire safety is equally crucial, particularly in dormer conversions that create new living spaces.
Fire doors and smoke alarms, required under Part B, add an extra £500–£2,000 depending on the number of doors and necessary safety measures. While these upgrades are essential for compliance, they also contribute to a safer and more energy-efficient home in the long run.
The final stage of your dormer conversion determines how comfortable and stylish the space will be, the interior finishing costs can range based on what additional elements your have fitted and the level of quality of the finishing. Costs to consider are:
While a dormer loft conversion can add value to your home, unexpected costs can arise. These hidden costs can catch homeowners off guard, leading to budget overruns. Here are some hidden costs to consider:
By considering these potential hidden costs, you can better prepare for your dormer loft conversion and avoid unexpected financial strain.
Considering a dormer loft conversion raises many questions, from planning permission to potential costs and benefits. Our experts answer the most frequently asked questions to help you make informed decisions about your project.
£35,000 - £80,000 depending on type & complexity. Here's the full cost breakdown for a dormer loft conversion, including time frames.
Yes, a dormer loft conversion can increase your home's value by up to 20%, particularly if you add extra bedrooms or bathrooms. This varies by location and the quality of the conversion.
A single dormer window costs around £5,000–£8,000, while a full-width flat-roof dormer starts at £40,000 and can go higher depending on finishes.
