Home Addition Calculator: Estimate Your Cost To Build A Shed Dormer

Home Addition Calculator lets you estimate how much it will cost to build a shed dormer addition in your unused attic. The quote 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 converted attic.

Building a Shed Dormer / home addition increases the usable living space in your house by an average of 200-250 sq. ft. This project's resale value is arounf 84.3%, making it a smart investment.

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 cost estimate as accurate as possible, the following set of specs 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 higher quality, premium looking materials.

A "Basic Quality" addition will have materials suitable for a Rental property. This includes: carpet floors, basic ceramic tile and an acrylic shower in the bathroom.

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 allows you to get a truly custom estimate for your project.

Factors That Increase The Final Shed Dormer Cost

The actual home addition price can and will vary based on many factors.

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 our 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.

Central Air HVAC Costs
Central AC only
$3900 - $5600
AC + Hot Air Furnace
$7900 - $10400
Central Air + Ducts
$12100 - $17900

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Shed Dormer Design Considerations

Many homeowners stay away from building a shed dormer because they are often perceived as being ugly and ruining the overall curb appeal of the house. Unfortunately, there is some truth to this, as a poorly designed and positioned shed dormer can in fact look like an eye sore on the roof.

However, if you plan everything correctly, this home addition can actually enhance the beauty and functionality of your home. Consider the following tips:

- The dormer should look like its a section of the main roof. Build it with just enough space for windows and headroom to avoid having an oversized, protruding structure.

- Ideally, the dormer should spring from a line that is below the primary roof ridge.

- The roof slope of your shed dormer should be minimum 4-in-12. If its flatter, the wall of the dormer will appear disproportionately tall, creating a highly unbalanced design.

- It is best to avoid building a dormer than runs the whole length of the house. These types of additions look strange, because they are mistaken for being the main roof. Instead, nest the dormer within the eaves of the main room, so it clearly looks like a subordinate structure.

- Contact 3-4 local construction pros to get their free estimates and design suggestions. This way you will be able to choose the best price and a contractor who you feel comfortable with trusting this huge project.

Published/updated on: November 20, 2017

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3 thoughts on “Home Addition Calculator: Estimate Your Cost To Build A Shed Dormer

  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.

  2. Joan

    I am trying to find out the cost of a shed dormer for our Cape house. We have two bedrooms in the attic and would like to add a bathroom.