Dormer windows are one of the most effective ways to add space, light and character to a loft conversion. Whether you're planning a simple rear dormer or looking to include a Juliet balcony or full-height glazing, our guide breaks down everything.
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Dormer loft windows are one of the most practical upgrades you can make, they increase headroom, improve natural light, and add valuable floor space without altering your home’s footprint.
This guide breaks down everything you need to know before choosing a dormer window, including:
Choosing the right style of window is just as important as selecting the right dormer structure. The window shape, glazing style, and opening mechanism all influence how much natural light you get, how the room looks from the inside, and how your home appears from the outside.
Here are the most popular dormer window types used in loft conversions:
Flat-roof dormers typically feature wide casement windows or horizontal sliders, as they allow maximum light and airflow across the full width of the dormer.
Common window styles: Triple-panel casement, horizontal sliding.
Best for: Maximising light in bedrooms, offices, or bathrooms.
Design tip: Add equal-width glazing sections to maintain visual balance from the outside.
These windows are set within a pitched (triangular) gable structure and are often styled to match traditional sash or mock-sash windows for added character.
Common window styles: Vertical sash or casement with divided panes.
Best for: Period homes or adding charm to a front-facing dormer.
Design tip: Use vertical glazing bars or arch details to echo traditional architecture.
With their sloping roofs on three sides, hipped dormers suit smaller, square window styles, often in symmetrical pairs to keep the look balanced.
Common window styles: Small casement or fixed-panel.
Best for: Bungalows or side dormers where space is tight.
Design tip: Match the frame colour to the roof to blend the look.
L-shaped dormers offer more wall space, so you’ll often see double or triple casement windows installed side by side. Some homeowners mix fixed and opening panes for a sleeker look.
Common window styles: Double casement, fixed and opening combinations.
Best for: Maximising width and creating consistent lighting in larger lofts.
Design tip: Keep symmetry across both dormer faces for a clean finish.
These feature full-height glazing or large fixed panes with minimal frames, creating a dramatic, contemporary look. They’re often combined with Juliet balconies or frameless glass.
Common window styles: Floor-to-ceiling fixed glass, bi-folds, or French doors with glazed balustrades.
Best for: Stylish loft lounges, home offices, or master suites.
Design tip: Use slimline aluminium frames for a sleek architectural finish.
Dormer window costs vary depending on the size, style, materials, and whether you’re installing a balcony or upgrading the glazing. Below is a breakdown of typical prices to give you a ballpark figure before getting quotes.
Read our specialist guide on loft conversion costs to understand costs in detail. You can also reach out to any of our experts to get a better understanding on the moving parts.
Dormer window costs can vary significantly depending on a few key factors. Here’s what typically influences the final price:
Materials play a major role. uPVC windows are the most affordable option and require minimal maintenance, making them popular. Timber frames offer a more traditional look but are more expensive to supply and install. If you opt for a contemporary design, aluminium or composite frames tend to sit at the higher end of the price range.
Size and style also affect the cost. Larger or more complex windows, such as wide casement windows or Juliet balconies with French doors, require more materials and labour, which drives the price up. A small window in a flat dormer will cost far less than a feature-rich modern glass installation.
Labour and location can make a noticeable difference. Installation costs are typically higher in areas like London and the South East, while prices in the North or Midlands are usually more competitive. The complexity of the job also affects labour time and cost.
Access and scaffolding are often overlooked but can add hundreds to the project. If your loft is difficult to access or you’re working at height, you may need extra scaffolding or safety measures, typically costing between £500 and £1,500.
Additional features such as bespoke glazing, integrated blinds, premium finishes, or Juliet balconies will all increase the price. While these upgrades can elevate the look and feel of your loft, they’re best planned with a clear budget in mind.
We recommend reading out detailed guide which breaks down the costs of a dormer loft conversion in full to give you an exact idea.
Balcony dormers are a modern, eye-catching upgrade that combines added loft space with a touch of outdoor living. Whether you’re opting for a Juliet-style opening or full French doors with a glass platform, this feature brings in light, fresh air, and serious kerb appeal to your loft conversion.
A balcony dormer is a type of dormer window that extends your loft space with large glazed openings. It's usually floor-to-ceiling doors rather than traditional window frames.
Most include either:
These dormers are almost always installed at the rear of the property to maintain privacy and improve your chances of planning approval.
There are two main styles of balcony dormers, and the cost can vary significantly depending on size, materials, and structural requirements.
Juliet balcony dormers are the most popular. These feature inward-opening French doors or sliding glass panels, paired with a fixed glass or metal balustrade. Expect to pay £4,000–£6,000 extra, on top of your core dormer build.
Full French door dormers with a walk-out platform or steel balcony are more complex. These often require deeper structural support and bespoke design. Prices typically range from £6,000–£10,000+, depending on the materials and finish.
In most cases, planning permission is required for balcony dormers due to privacy concerns and design regulations, especially when installed at the rear of the home.
Balcony dormers provide exceptional natural light and ventilation, making them ideal for master bedrooms, home offices, or loft lounges. They can instantly transform how a space feels, adding height, openness, and value.
They do require a considerable amount of headroom and structural support, so they may not be suitable for compact lofts or low roof pitches. Unlike standard dormers, they often can’t be built under permitted development rights and will need formal planning consent.
Dormer windows don’t just change how your home looks from the outside, they also have a big impact on how your loft feels inside. The right design can make the space feel bigger, brighter, and more livable.
Whether you’re converting your loft into an office, a bedroom loft conversion, or creating a unique bathroom loft conversion, here are a few cool ways to make the most of the space around your dormer:
Not always. But sometimes, yes.
Most dormer windows built at the rear of a property fall under permitted development rights, meaning you won’t need full planning permission. But you'll likely need formal approval when you add certain features, like a front-facing dormer, balcony, or raised roofing.
Here’s a breakdown of when planning permission is required, what qualifies as permitted development, and the building rules that still apply either way.
Not all dormers qualify for permitted development, and if yours doesn't, you'll need to apply for planning permission before building. This applies when the design affects the look of the home from the street, alters the roof shape significantly, or adds elements like a balcony or terrace.
You’ll usually need to apply if:
If your dormer ticks the right boxes, it may be built without planning permission under permitted development rights. You won’t usually need permission if:
Even if you don’t need planning permission, it’s a good idea to apply for a Lawful Development Certificate (LDC) to confirm the work is legal. This can be especially useful when selling your home later.
Got questions about dormer windows? You’re not alone. Below, we’ve answered homeowners' most common queries. From costs and planning rules to whether you can fit a bedroom or bathroom in your dormer space.
A flat-roof dormer with a basic uPVC casement window is usually the most cost-effective option. It’s simple to build, maximises headroom, and often falls within permitted development rights, reducing the need for planning permission.
In most cases, yes. A well-designed dormer can create a usable bedroom, home office, or bathroom, increasing your floor area and overall appeal. This often adds 10 to 20% to your property’s market value, especially in areas with underutilisation of loft space.
Read our detailed guide on loft window and loft conversion ROIs to understand how much value you could gain on your dream loft.
There’s no fixed size, but under permitted development, your dormer must not exceed:
It must also sit below the existing roof ridge and be set back at least 20cm from the eaves. Here are three specialist guides to read below on this:
Absolutely. Dormers are ideal for adding full-height space for a bedroom, ensuite, or compact bathroom. The added headroom and natural light make these rooms more functional and comfortable than standard loft spaces with sloped ceilings.
