Attic Home Addition Calculator: Get an Instant Price Estimate

Estimate how much it will cost to build an addition in your unused attic using this Home Addition Calculator. The estimate will include the cost of cutting out a roof section, building a shed dormer, installing new windows, insulation, roof, and building a bedroom + bath / shower room in the former attic space.

Building a Shed Dormer / Attic addition increases the usable living space in your house by an average of 200-250 sq. ft. This project's resale value of 84.3%, making it a great investment in your home. Select from the options below to calculate your home addition costs:

Addition Size: x Sq. Ft.
New Windows
New Roof Skylights
Bath / Shower type
Your Region:

Low End
Mid Range
High End

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Example of a Shed Dormer Addition:

Attic Addition

Home Addition Calculator Specs:

To make this home addition cost estimate as accurate as possible, the following set of assumptions is used:

A "Medium Quality" addition includes the following:

  • New Hardwood Floors in the bedroom
  • 5x8' Standard Bathroom With Shower, and Tiled Floor / Shower Surround
  • Spray Foam Insulated ceilings and walls, with a sheetrock / plaster finish
  • 4 new construction windows and 2 Velux skylights
  • Existing stairs leading up to the attic with new railings (does not include building new stairs)
  • New electrical wiring and and HVAC(Radiators or Air Ducts) installed

A "Luxury Quality" home addition makes use of better materials. A "Basic Quality" addition has materials quality, suitable for a Rental property, with carpet floors, basic ceramic tile and an acrylic shower in the bathroom.

The actual home addition costs can and will vary based on many factors. For a more accurate calculation, use the "Regional" setting to choose in which part of the US you live. Otherwise, use the "National Average". This unique feature of the Home Addition Calculator allows you to get a truly custom estimate for your project.

Some Notes About Building a Shed Dormer Addition

If you live in a cold climate, the roof of a shed dormer will be susceptible to Ice Dams build up. This happens because in order to build the shed dormer, you have to increase the ceiling height of the addition to at least 8 ft. making the dormer/addition roof almost flat. This flat or low slope roof increases the chance of ice dam leaks. To avoid these leaks and ice dams build-up, we recommend using a single ply membrane for low slope roofs, such as Rubber or PVC. These can increase the cost of building an addition by $1,400-2,500 on average. Use roofing calculator to compare costs between using asphalt shingles, rubber or PVC single ply material.

Ins some cases, unexpected HVAC issues, such as difficulty in connecting existing system ducts / pipes to the attic, can also increase total cost. Published/updated on: April 30, 2014

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2 thoughts on “Attic Home Addition Calculator: Get an Instant Price Estimate

  1. Alexander

    I am interested in a shed dormer on both sides of the attic of a classic cape cod to out a master bedroom with bath, and some extra storage space in.