How much does it cost to add a dormer?

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How much does it cost to add a dormer?
Dormers add light and living space to an attic. (Hemera Technologies/ Images)

A well-designed dormer can add light, living space and selling value to your home. However, a dormer doesn't come cheap and the return on your investment may not cover the building costs. The actual cost of a dormer will depend on a number of factors, such as how much work you are willing to do yourself, the type of dormer you want and the structural characteristics of the property where you wish to install it. The average do-it-yourself dormer project costs around £1,170 in materials, while hiring a contractor for a medium-sized dormer will cost from £1,625 to £3,250, according to

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Design and Building Permit

Installing a dormer in an existing building is a major project. It is certainly not a weekend do-it-yourself project for your average construction enthusiast. Because it will alter the structure of the roof, you will need to apply for a building permit from your local building authority. The application must include a description of the work and plans designed by a qualified professional. Include in your budget the cost of hiring a contractor, engineer or architect to create the design, as well as the building permit fees applicable in your area.

Dormer Types

The cost of your dormer will also depend on the style, model and materials you choose. Many types of dormer styles are available to choose from, all with their own structural and design requirements. Tudor revival, Gothic and Queen Anne styles, for instance, require a gabled structure in their installation. More basic styles, such as prairie and shingle dormers are much less involved and require minimal changes to the roof's structure.


As in all projects, the quality and type of materials you use will determine the final cost. For example, the type of lumber you use for the dormer's form work, whether you choose drywall or panelling, the kind of insulation you use and the quality of the window you install will all affect the bottom line cost of your dormer.

Attic Remodel

Installing a dormer is often only part of the larger project of remodelling an attic into a bedroom or office. As mentioned above, adding dormers to an attic will increase the amount of natural light, the home's living area and the selling price of the property, but you must weigh this against the investment cost of this project. The national average cost of remodelling an attic bedroom was £33,428, according to 2010-2011 Cost vs Value Report of Remodeling Magazine. The average resale value for an attic bedroom project is £24,142, according to the same survey. This means you will probably only recoup 72 per cent of your investment if you sell your home. So, dormers may only make sense if you are planning to stay in the home for the long term, not as a short-term home improvement investment.

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