Find out how much a dormer window costs in the UK

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How much does a Dormer Window Cost?

Dormer windows are commonly found in attic conversions as a small extension on the side of your roof. Popular options include Velux windows (one of the best-known dormer window brands), and the average dormer window costs are from £2,000 to £20,000.

Projects can be priced at closer to £30,000 depending on multiple variables, the nature of your loft conversion, and the window design options you choose!

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Factors That Impact the Average Dormer Window Cost

A small dormer window conversion to improve the space and light in your loft costs from £2,000 to £7,000 for the window itself, assuming you're not undertaking any further structural work.

Mid-range dormers with a slightly more generous size cost from £10,000 to £30,000, and a larger-scale project can be from £40,000 to £60,000, again reliant on whether your attic conversion includes any changes to the roofline, en-suite bathrooms etc.

A further option could be to use a mansard loft conversion - although this project starts from £50,000 as it involves far more than fitting a small window extension.

Mansard roof fitters remove one side of the roof to construct a new storey, making it more expensive.

Price factors change considerably because of the required materials and labour hours.

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Additional Considerations in Fitting Dormer Windows

Below we've created a table with some average costs for a dormer window conversion in your loft space.

Dormer window specification Expected installation time Average cost
Small flat-roofed dormer window with a UPVC frame Five weeks £4,000
Small dormer with UPVC frames and a pitched roof Five weeks £5,000
Double dormer window (full loft conversion) Eight weeks £30,000
Large double dormer conversion with an en-suite bathroom Eight to ten weeks £40,000

Window fitters will likely want to measure up to determine your capacity to fit a new dormer window, which is an important factor in providing an accurate quotation. The type of dormer you have (and whether that's part of a larger attic conversion project) will dictate the price.

Dormer window type Average cost per square metre
Recessed £750
Blind £862
Barrel £1,076
Hipped £1,237
Gable £1,291
Flat roof £1,345
Pedimented £1,776

If you're unsure which dormer window type would be best for your property; an experienced installer will be able to show you designs and styles so you can make an informed choice!

Extra Costs of Installing an Attic Dormer Window

Along with the window, frame, construction work and labour hours, several other pricing elements will likely feature on your quote:

  • Moving a water tank from your attic costs £300 to £800.
  • Replacing any roof trusses that need to be moved costs around £12 to £40 per metre square.
  • Modifications to the roof usually require a professional roofer and can be anything from £11,000 to £15,000 or above.
  • Appropriate ventilation mechanisms typically cost £250 to £400.
  • Underfloor heating in your attic comes at £20 to £30 per square metre.
  • If your window fitter needs scaffolding, this cost varies depending on how long the work is expected to take and whether you already have scaffolding in place for more complex loft conversion projects.

Costs of Heating and Insulation in a Dormer Loft Conversion

You may already have sufficient heating and insulation within your attic space. Still, it's a consideration if you are fitting a dormer to use a loft currently utilised for storage.

There are many options, from electric or gas radiators, plug-in heaters, carpeting and underfloor heating.

One of the best ways to ensure your dormer window keeps the room warm and comfortable is to opt for high-performance glazing.

Window fitters can offer several options, from double-glazing, triple-glazing, acoustic glass and reinforced glass.

Insulation is also vital, so if your attic needs additional work to replace the wall, roof or floor insulation, this is another factor to build into your budget.

Costs of Ventilating a New Dormer Window Attic Installation

Ventilation is extremely important to avoid building up condensation and keep the airflow sufficient within your converted attic to use as a regular room.

The window itself is an excellent way to boost ventilation and natural light, but you may opt for secondary ventilation to ensure your attic room doesn't experience dampness.

Example options include:

  • Air bricks - cost around £260 to supply, with a total £1,200 installation cost.
  • Trickle vents - from £15 to buy, up to around £100 including labour.
  • Double-glazing is usually included within your dormer window unit price. If you buy the glazing separately, the average panel will cost approximately £2,000.
  • Upgrading your glazing from double-glazing to triple-glazing usually adds around £500 to the budget.
  • Extractor fans are useful in attics that have previously been exposed to mould or dampness - this should cost in the region of £200, including supply and installation.

You might also opt for a different window opening mechanism if you are concerned about ventilation and dampness - a window fitter will be able to recommend the best styles depending on the size of the window and the amount of opening space you have.

Benefits of Choosing Dormer Windows for Your Home

The most common reason homeowners opt for a dormer window is that it can transform a dusty, dark attic space into a usable room - perhaps a home office, extra bedroom or play space for children.

Most houses have a loft, but they're typically a little unused and unloved, primarily because a pitched roof makes the space difficult to move around in.

Installing a dormer window can give you extra space, free up capacity for an additional bedroom, and add value to your home.

Other benefits include:

  • Boosted natural lighting - attics don't normally have any windows, so a dormer window will add sunlight to your new space. A fitter will advise on the right direction, size and type of dormer window depending on the aspect of your home.
  • Ventilation - a stuffy attic isn't a healthy environment for a bedroom but can be transformed with a dormer window! Fresh air helps to keep the whole property well ventilated and stops heat from accumulating in the attic during the summer.
  • Increased room size - as we've mentioned, a steeply sloped roof can make an attic room tricky to use without stooping. There are regulations in place dictating minimum headroom, and one of the easiest ways to achieve this is through a dormer window.
  • Enhanced property exterior - you can choose a huge range of windows, frames, and styles to ensure your dormer is consistent with the rest of your property's appearance and looks stunning.

Dormer windows open access to the views surrounding your home, so you can reimagine an attic storage space into one of the most used rooms in your property.

Checkout this video which talks you through a few considerations when thinking about installing your dormer window:

Frequently Asked Questions - Dormer Window Costs

Below, we've answered some frequently asked questions about dormer window costs and attic conversions.

Do I Require an Architect to Install a Dormer Window?

Not necessarily, but it can be helpful to have an architect or designer on hand to deal with structural implications, designs and assist with submitting a planning permission application where relevant.

Architects tend to charge from £50 to £70 per hour, although that may vary depending on where you live and the project's complexity so add this to your domer window cost.

As with your dormer window quotations, it's advisable to agree on a total project price upfront or confirm the maximum anticipated hours so you are comfortable you can cover the costs within your budget.

What Are the Main Types of Dormer Window Design?

There are several different designs and finishes you might choose from, which could depend on the size of your roof, the headroom in your attic, and the appearance you'd like to achieve.

Popular designs include a hip to gable loft conversion, adding a dormer to the side. Contractors may be able to reuse tiles removed from the roof to create a consistent finish.

Flat roofs and pent roofs are also common, with waterproof felt over the top of the dormer extension to keep it weatherproof.

Do I need Planning Permission to Install a Dormer Window?

You may do - the regulations differ and depend on:

  • Where you live and the guidelines from the local planning office.
  • The size and style of your dormer window loft conversion.
  • Whether you have neighbours, and if so, how close they are.
  • Any impacts on privacy or general appearance.

Planning permission is usually stricter in denser city areas or conversation areas, where you will likely need approval before you can fit a new dormer window.

Whether or not you need planning approval, your dormer window will need to be professionally installed with building regulations compliance. It's, therefore, sometimes best to work with an architect or structural engineer to ensure all the materials and design choices you make are fully compliant.

Can I Install a Dormer Window Without Converting My Attic?

You certainly can - we've covered some of the average costs for a more involved dormer window project, assuming that most homeowners will want to convert the room for regular use.

However, there is no reason you can't install a dormer in a loft space to add brightness and fresh air without any additional conversion work. Get in touch if you need more information about dormer window costs!