How to Install a Shed Dormer


So you want a little headroom up in the attic. Installing a shed dormer will give you more space. Follow these steps to get the job done.

Things You'll Need

  • 2-by-4's
  • 2-by-6's
  • Plywood
  • Hammer
  • Circular saw
  • Measuring tape
  • Chalk line
  • Nails
  • Mark dormer's outline across ceiling and down rafters. Build a brace from 2-by-4's and brace it 8 inches from outside top of dormer opening to support the roof before cutting out the hole for the dormer.

  • Frame front wall with 2-by-4's. Extend top plate 3 1/2 inches beyond end studs to catch side wall studs and rafters. Frame opening for window.

  • Outline dormer on outside roof with a chalk line. Set the blade depth on a circular saw to cut through roof sheating, but not deep enough to cut through rafters. From inside, knock roofing off in sections. Cut rafters.

  • Install a doubleheader at top of dormer and single one at the bottom. Remove brace. Set front wall into position, check for square, level and plumb and nail through the soleplate into the floor joists. Secure to the rafters.

  • Nail rafters from top of dormer to the top plate of the front wall. Install soleplates on double side rafters and notch in studs along each side. Sheath finished frame, then cover with felt. Install window and add roofing, trim and siding to match the rest of the house.

Tips & Warnings

  • Consult with a contractor before beginning.
  • Obtain proper permits and check local building codes.
  • Have tarps or large sheets of plastic on hand to cover hole in case it rains.
  • If your roof is supported by webbed trusses, do not attempt to install a shed dormer. This can add stress on the trusses and cause the roof to collapse.
  • Shed dormers must be waterproofed and adequately ventilated and insulated.

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