Blog>Cost Guides>How much does dormer window installation cost?
Last updated: 20 September 2024
How much does dormer window installation cost?
Thinking of adding a dormer window to your home? Read on to find out the average dormer window installation cost.
Fast Facts
Dormer window installation costs start at £1,000
Prices can vary depending on factors like the dormer window style, size and material
Make sure to budget an additional £500 - £1,500 for scaffolding
A dormer window can add kerb appeal to your home. But how much does dormer window installation cost?
Here, we’ll share some ballpark estimates to help you budget for the project.
How much does dormer window installation cost?
Dormer window costs start at £1,000 for supply and installation.
However, costs can quickly climb depending on factors like your dormer conversion type, the size of your dormer windows and their material.
| Item | Low-High | Average |
|---|---|---|
| Full dormer conversion – 2 large wooden frame windows | £3,500 - £5,000 | £4,500 |
| Side dormer conversion – 1 small uPVC window | £800 - £1,200 | £1,000 |
| L – shaped dormer conversion – 3 small uPVC windows | £2,400 - £3,600 | £3,000 |
| Rear flat roof dormer conversion – 2 uPVC windows | £2,000 - £3,000 | £2,500 |
| Rear gable dormer – 1 uPVC window | £800 - £1,200 | £1,000 |
| Rear hipped dormer – 1 uPVC window | £800 - £1,200 | £1,000 |
| Scaffolding to install window(s) | £500 - £1,500 | £1,000 |
| Last updated: September 2024 Our costs are ballpark averages - get a local tradesperson to quote now | ||
Bear in mind that these costs are just for the supply and fitting of the windows, along with scaffolding for access.
They don’t include planning, structural calculations, building regulations approval, roofing, insulation, floor coverings, stairs, doors or any other conversion costs.
Keen to get the full lowdown? Head over to our loft conversion cost guide.
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How much does it cost to install various dormer window styles?
A dormer is a vertical window with its own roof, which sticks up from the slope of a pitched roof.
But there are lots of different dormer window styles, many of which are named after their roof type.
Here are some common dormer window styles in the UK, along with the typical cost to install them.
Cost to add dormer windows to a full dormer conversion
A full dormer conversion is a dormer that spans the entire width of your roof.
In this way, it can vastly increase the usable space in your attic.
The average cost to add two large wooden frame windows to a full dormer conversion is £4,500.
Cost to install a dormer window to a side dormer conversion
If the slope of your property’s roof faces out from the side of your property, you could look into building a dormer conversion at the side of your home rather than at the rear.
Typically, you’re looking at around £1,000 to install one small uPVC window to a side dormer conversion.
Cost to add dormer windows to an L-shaped dormer conversion
Many Edwardian and Victorian properties have a wing at the rear, known as a two-storey outrigger.
In this case, an L-shaped loft conversion can be a great way to increase your usable space – especially if yours is a mid-terrace property.
Essentially, you build a dormer on the rear outrigger roof and another dormer on the main roof, in a way that allows them to join together in an L-shape.
As a rough guide, you can expect to pay around £3,000 to add three small uPVC windows to an L-shaped dormer conversion.
Cost to add dormer windows to a rear flat roof dormer conversion
Flat roof dormer conversions involve extending a pitched roof outwards from the peak to create a flat section – imagine a box shape where you once had a sloped roof.
Flat roof dormers are amongst the most popular dormer window styles in the UK as they’re cost-effective to build and they create lots of internal space.
Adding two uPVC windows to a rear flat roof dormer extension typically costs £2,500.
Cost to add a dormer window to a rear gable dormer
Instead of flat roofs, gable dormers have their own pitched gable roofs.
They’re often seen as the most attractive and traditional option when it comes to dormer conversions – and they’re especially popular in period homes.
You’re looking at roughly £1,000 to add a uPVC window to a rear gable dormer.
Cost to add a window to a rear hipped dormer
A hipped dormer is similar to a gable dormer.
But instead of a gable roof, hipped dormers have hipped roofs, which consist of three sloping planes.
In this way, they make a great matching feature in properties that also have hipped roofs.
The cost of adding a dormer window to a rear hipped dormer is normally around £1,000.
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Dormer window cost calculator UK
As you can see, the cost of putting in a dormer window can vary widely.
So, it can be difficult to know how much to budget for your project.
Aside from your dormer window style, here are the main factors that will affect your overall cost.
Size
The bigger your windows, the more they’ll typically cost.
Not only do bigger windows require more materials, but they’re also heavier, which can increase your labour costs.
Material
You can get dormer windows in all kinds of materials, from timber to aluminium, uPVC to composite.
uPVC will generally be the most cost-effective material. Composite and aluminium will be at the higher end of the price range, but could be worth it due to their durability and longevity.
Quantity
The more windows you install, the higher your overall price will be.
That said, if you’re installing several windows at the same time, you could end up paying less than if you were to install them each separately, as your installers will already be on-site.
Location
Labour costs vary across the UK.
Generally, costs in London and the South East tend to be higher than in other areas of the country.
Access
If your property is difficult to access, the job is likely to take longer, which can raise your costs.
We recommend budgeting around£1,000 forscaffolding. But if your building is especially tall or the roof is tricky to access, you may need to budget more.
Additional costs
Remember that the costs in this guide are for the supply and installation of your dormer windows only.
If you haven’t converted your loft yet, you’ll need to factor in many other costs, such as roofing, insulation, floor coverings, structural calculations, stairs, doors, and more.
Our loft conversion planning guide can walk you through the whole process step-by-step.
Do I need permission for a dormer window?
Before you start installing dormer windows, you’ll need to consider whether you need planning permission.
Often, if you’re installing a dormer window at the rear of your property, this will fall under your permitted development rights.
As such, you may not need planning permission, as long as you abide by certain rules – for instance, your dormer can’t exceed the top of your existing roof.
On the other hand, if you’re hoping to add dormer windows to the front of your home, this normally will need planning permission.
Similarly, planning permission is a must if you live in a listed building or a conservation area.
If you’re unsure, it’s always best to check with your local planning authority, as they won’t all have the same criteria.
Head over to our planning permission cost guide to learn how much it will set you back if you do need to put in a formal application.
Get an expert to estimate the cost of putting in a dormer window
As you can see, there are lots of variables at play when it comes to calculating your dormer window installation cost.
That’s why it’s always best to get quotes from loft conversion specialists near you.
They’ll be able to visit your property and put together a quote based on your unique requirements.
Luckily, it’s easy to find the right tradesperson for the job here at Checkatrade!
All our tradespeople have to pass up to 12 checks and are regularly reviewed by homeowners on everything from punctuality to professionalism.
Simply enter your postcode into the search box below to get started.
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FAQs
How much to install a dormer window in the UK?
Dormer window installation costs start at £1,000.
How long does it take to install a dormer window?
How long it takes to install a dormer window can vary depending on the scope of the project.
That said, as a rough guide, you can expect the job to take somewhere between a few days and several weeks.
How much does dormer window replacement cost in the UK?
Dormer window replacement costs will vary depending on the size, material and type of dormer window.
That said, prices typically start at around £1,000.
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