cost of dormer window

What Is The Cost To Add Dormer Windows To A Roof?

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What Is The Cost To Add Dormer Windows To A Roof?

A medium sized dormer window measuring around 6 inches by 10 inches will cost in the region of $1800 to add to an existing roof. However, it is not always the individual unit cost of each dormer window but the installation charges which can mount up. Dormer windows require extensive renovations to the roof structure; this is where the real cost lies. 

Are you looking for a more accurate average cost of dormer windows? The best thing to do is speak to local roofers in your state or area and compare quotes. Fill out the form below and we'll put you in contact with dormer roof experts in your local area. Time to complete: 30 seconds.

Do you know that adding three dormer windows during a new build construction can increase the cost of the roof by up to 20%?  You might think that retro fitting dormer windows into an existing home would be cheaper than this but in fact it can be even more expensive with costs ranging from $3,500 to $20,000 per window depending on the style and size. Here are some average costs.

The average cost to add one dormer by roof type

Type Cost per square foot
Shed dormer $75-$120
Flat dormer $80-$125
Gable dormer $110-$150
Hip dormer $115-$135

Now some different costings for building a dormer on an existing roof which are based on the type/style of house or the addition.

Type of House or Addition Cost per square foot
Cape Cod $110-$150
Bungalow $110-$150
Attic $75-$120
Bathroom $24,000 average
Window $4,000 average

Converting attic or roof space is very popular especially for homeowners who don’t have the option to extend their homes either to the side or to the rear. But attic rooms situated under curved or arched ceilings can be very difficult to light effectively. Skylights are one option but they are surprisingly expensive and offer no views. Unsurprisingly, dormer windows are a very popular choice in this situation as they can provide the perfect amount of lighting and ventilation and if they are designed correctly, can also significantly improve the design aesthetic of the property.

Dormer windows will also add space to the room interior and help with higher furniture placement which is not always an option in a simple attic conversion. The extra space is offered because the dormer windows project vertically beyond the plane of the slanted roof. Dormer windows have their own roof structures for protection and so from a construction viewpoint, are completely sound and a good designer will be able to blend them into the main roof design and actually improve the look of the existing roofline. Find local expert roofers and quotes for a new roof.

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What are the other cost considerations with dormer windows?

Apart from the actual cost of the dormer windows themselves, there are other expenses which are associated with fitting this type of feature to your current roofline and these include:-

  •         Building permits - it doesn't matter where you live in the USA or in which state, you're more than likely to need a building permit and these can sometimes take months to be issued. Building permits also incur the levy of a fee which can typically range from around $200 to a few thousand dollars on large projects
  •         Professional fees – a roof redesign normally requires the submission of drawings particularly if the project forms part of an attic upgrade
  •         Window style - The window that you choose and its style, will have a big impact on the overall costs
  •         Dormer window size - some window styles consist of a single pane whereas others will have a number of window panes arranged together, the style of the window and the projection of the dormer will directly impact on the costs
  •         Roof upgrades – often dormer windows are part of a project to convert roof space for accommodation or to upgrade living space that is already there, dormer windows are therefore not usually the only part of the cost. Some homeowners combine a dormer window project with a roof re-model or refurbishment project

What is a dormer window?

The word ‘dormer’ comes from the French verb, ‘dormir’, meaning to sleep, which is a style of window always associated with the upper levels of accommodation within the property.

A dormer window is a vertical unit with its own integral roof which is partly positioned within the slope of the existing roof. They are popular for people seeking to convert their attics and who are restricted by not being able to extend their home sideways or to the rear. Dormer windows can come in all shapes and sizes.

Why add dormer windows?

The main reason for adding dormer windows to a roof is in order to create light for an attic conversion. This may be an attic conversion that is already in place but which lacks light and roof height or it could be a completely new design and remodel which is being planned alongside a new roof.

Dormer windows can be a difficult design to get right; the style of the roof, the roofline and the way in which the dormer windows impact on the house as it sits with other properties, will need to be carefully considered by the designer or architect. Dormer windows which look awkward or clumsy or which are not proportional to the house will not enhance either its appearance or uplift its value.

Badly designed dormer windows can ruin the entire look of a property and will always have a negative impact on its value and curb appeal even if they do the required job of adding light and ventilation to the roof space.

What are the main costs associated with dormer windows?

The main costs with dormer windows are not just the windows themselves but the actual cost of the attic conversion and much of this will depend upon what type of accommodation you are seeking to create. Adding bathrooms or self-contained units with kitchens will always cost much more than just extra bedroom accommodation.

Different types of dormer window

Whichever type of dormer you choose will dramatically impact on the cost and there are many different types of dormer that you can select for your home. The most common type of dormer window is called a gable fronted dormer and this usually has a simple pitched roof which slopes down to either side creating a cottage type appearance. A vertical frame supports the planes and forms a triangular section below the roofline.

A shed dormer window features a sloped single flat roof in the same direction of the roofline but at a shallower angle. There is a popular design called a Nantucket dormer window style which is a shed dormer connecting two gable dormers.

A hip roof dormer slopes on three planes and converges at one point over the window pane whereas a Gambrel dormer has a gable at the peak of the roof but two steeper slopes on the sides like a barn roof.

An eyebrow window dormer has a curved roof and no sides and creates an eyebrow effect which is why these roofs are sometimes called an eyelid dormer. The other two types of dormer window are a bonnet dormer which has straight walls with a curved roof and a wall dormer which features a window situated directly above the exterior wall instead of in the middle of the roof.

The cost of shed dormers versus gable dormers

Gable dormers are also known as doghouse or kennel dormers and are usually best suited to homes with a steep roof pitch and an angled roof. Gable dormers are cost-effective and attractive and are usually one of the more budget-friendly dormer window options.

Shed dormers are a bigger investment but they do offer increased square footage and are one of the best ways to add headroom and space to smaller homes.

A Nantucket dormer is a combination of a shed and a Gable dormer and is created by erecting two gable dormers and connecting them with a shed dormer.

What are the pros and cons of dormer windows?

There is no doubt about it, dormer windows are a highly desirable window style with great curb appeal and they can completely revolutionise an attic conversion, adding floor space ventilation and natural daylight to what can be an otherwise unappealing space. However, these windows are expensive and inconvenient to install and despite their numerous advantages, can be off putting for some homeowners. Here are some of the pros and cons associated with installing dormer windows which might help you make a decision:-


  •         Internal lighting - the attic or loft conversion will be much brighter and will benefit from natural light and also views which can become a real feature depending on your location. Natural light has plenty of proven health benefits
  •         Increased space – dormer windows add extra space in the conversion and make it possible to have tall furniture
  •         Ventilation - dormer windows that can be opened will allow fresh air to circulate around the room and solve a number of the ventilation problems associated with attic conversions
  •         Aesthetic appeal - Dormer windows which are well designed and proportionate to the size of the property can really improve curb appeal and add character and style to what can otherwise be a plain roof


  •         Roofing eaks - unless dormer windows are very well installed, they can be vulnerable to leaking as essentially they are built into the main roof structure so dormer windows do create a weak point for the ingress of water. Their integrity should be checked as part of an annual roof inspection
  •         Cleaning - cleaning dormer windows can be challenging unless they are able to be completely opened and rotated by 360 degrees. Some dormer windows can't be opened at all
  •         Cost – dormer windows are expensive regardless of the style and type you choose as most of the cost relates to the installation

Finding the right roofing contractor

Installing dormer windows is not an insignificant cost and often forms part of a larger project. The roofing element of the plans needs to be undertaken by a professional roofing contractor following a thorough inspection of the existing roof (if it is not to be renewed) and working to drawings and plans usually provided by an architect or surveyor. If you are replacing skylights with dormers then you may be able to just work with your roofer on this project.

If you need to find a roofing contractor then try to go word of mouth and get a personal recommendation. Ask friends, family or neighbours for info or you could consider putting a post on social media groups in your area to see if you can find someone.

Installing dormers is a professional job so you want to avoid the lower end of the market and firms which tend to just specialise in roof repairs rather than more substantial roofing projects.

Questions to ask your roofing contractor?

  •         Is the roof suitable for dormer windows?
  •         How many does he recommend?
  •         What is the best style for your needs and to suit the property?
  •         What are the different types of glass available in terms of eco-friendly and self-cleaning options?
  •         How long will it take to install them?
  •         Does the roof need any upgrading or repair in the areas where the windows will go?
  •         What guarantees and warranties are offered for workmanship and products?
  •         How long has the company been in business?
  •         Are there previous customers you can speak to who will act as references?

Are there any grants available to help with the cost of dormer windows?

Most roofing grants are aimed at repair or renewal to keep homes watertight; dormer windows tend to be bracketed in the category of home improvement and would not be viewed as an essential roofing need unless they were pre-existing, old and letting in water. Adding new dormer windows is a matter of preference and usually the homeowner would have to bear all of the cost himself.

Frequently Asked Questions

What are faux and prefab dormers?

Prefabricated dormer's usually cost between $8000 and $14,000 and these figures do not include labour and installation. The high price comes because of their size -normally they tend to be larger - and the cost associated with manufacturing them, supporting them and then lifting them into place. You can purchase fake dormers at home improvement and roofing retailers and they can be a more affordable option but the downside to them is that they do not create any increased square footage and there will not be any return on investment. Prefab or faux dormers tend to be more popular with DIY projects but they are still quite complicated even for a competent DIYer and could need professional installation.

Will dormer windows add value to my house?

Dormer windows will add value to your house, this is typically described as the return on investment or ROI. Usual return on investment is around 40% but they also have the added value of creating savings on electricity bills over the longer term because of the increased natural light which comes into the house; dormers can reduce the reliance on artificial light in attic conversions.

How much square footage does a dormer add?

On average, dormer windows typically add about 250 square feet but this can be more depending on the style and number of the installation.

I want to have dormer cladding, how much does this cost?

Dormer cladding varies in price depending on local material and labor costs, budget for anywhere from $2 to $15 per square foot but the cost could be higher if you choose a high-end, premium cladding and of course dependent on the overall size of the area which needs to be covered. Cladding is popular because it helps keep the installation looking good and protects it from the elements.

How long does it take to build a dormer?

It can take from 4 weeks to 6 months to build dormers depending on where they sit in your roofing project. Factors which influence the timeline are style, any required permits which can be a slow process, surrounding roof work and interior finishing.

What is a full dormer?

A full dormer is a shed dormer, same window, different name and this style is one of the most popular. The term ‘dormer’ is used interchangeably to refer to the window itself but also can mean a converted room on the second floor of a house and a horizontal extension of a room.

How much do permits cost?

A building permit can cost anywhere from $390 to $1,930 and they can take a long time to be issued. The permits all need to be in place before the project starts.


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