Attic Addition Calculator

Estimate the cost of building an addition in your unused attic. This includes 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 an average of 200-250 sq. ft. and has a resale value of 84.3%, making it a great investment in your home. Select from the options below to calculate these construction 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

Addition Specs:

To make this 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" 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 cost of this remodel 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".

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.

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