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Project Difficulty:
Difficult
Estimated
Project Time: 6 hours
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Skylight with curb assembly
Safety goggles
Dust mask
Drywall saw or saber saw
Measuring tape
Pencil
Power drill with screwdriver attachment
Spirit level
2x4s for temporary bracing
Framing materials to match existing joists and rafters
2x6s for framing shaft
Trimmer joists
12d or 16d common nails
Metal framing ties
Hammer
Plumb bob
Utility knife
Circular saw with carbide-tipped blade
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Aluminum step flashing
Replacement roofing shingles
Roofing compound
Caulking gun and caulk
Adjustable bevel gauge
Fiberglass batt insulation
Staple gun and staples
6-mil polyethylene vapor barrier
Drywall
Drywall knife and tape
Joint compound
100-grit sandpaper
Wood molding
Paint
Paintbrush
Tarp (optional)
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Skylights, also known as roof windows, are an excellent way to brighten up any room and, if they open, improve ventilation.
Ideally, the square footage of a skylight should be at least 10 percent of the total square footage of the room. Because many building codes have natural light and ventilation requirements, as well as maximum allowable ratios of glass to floor area, check with your local building department to stay in compliance.
Before you start, have the skylight on site, along with rough opening dimensions and manufacturer's installation instructions. Follow their instructions carefully, but be aware that some steps may not be fully covered. Use the instructions below as a guideline. If installing your skylight requires cutting into rafters, consider hiring a professional contractor to do the job.
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1.
Locate and Mark the Opening
Using a drywall saw or saber saw, cut a 2-foot-square test hole in the ceiling, near the center of the proposed light shaft. Inspect the ceiling and roof framing around the test hole to determine the optimal opening location. Take into consideration electrical and plumbing installations. Position and mark the opening so that the need for cutting existing framing and joists will be minimized. (Fig. 1)
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2.
Cut the Opening
Using a drywall saw, cut along the guideline and remove the ceiling material. Install temporary bracing. Cut through the ceiling joists and framing as necessary for the skylight opening. (Fig. 2)
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3.
Frame the Ceiling Opening
Double up the last uncut joist on each side of the ceiling opening, and install double headers across the opening, perpendicular to the ends of the cut joists. Use lumber the same depth as the existing ceiling framing. Next, nail trimmer joists to frame the exact opening for the light shaft. Using 12d common nails, nail through metal framing ties to connect joists more securely than with simple toenailing. (Use 4-inch ties for 2x4s, 6-inch ties for 2x6s, and so on.) (Fig. 3)
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4.
Locate and Mark Out the Roof Opening
Hang a plumb bob from the bottom edge of the roof rafters down to each corner of the ceiling opening. (Fig. 4)
Transfer the corner locations vertically to the rafters, and then project these points up to the underside of the roof to locate the rough opening to be cut through the roof. Then drive a pilot nail up through the roof at each corner of the proposed opening.
The corners should fall on the inside of the skylight curb framing.
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5.
Cut and Frame the Roof Opening
Most prefabricated skylights come premounted on their own curb assembly. Take the assembly up to the roof and, using the pilot nails as guides, outline the curb opening on the roof. For an asphalt-shingled roof, use a utility knife to first cut along these marked lines and then remove the asphalt shingles, baring the roof sheathing below.
Then, using a circular saw, cut through the sheathing. If you have a wood-shingled roof, use a circular saw to cut through both the shingles and the roof at the same time. To allow the saw to glide freely over the shingles, place a board beneath the saw. Save the shingles for later patching around the perimeter of the skylight. (Fig. 5)
Frame the roof opening. Double the rafters at the sides of the roof opening and, at the ends of the cut rafters, install double headers across the opening at each end.
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6.
Install the Skylight
Follow the manufacturer's instructions for installing the skylight. Secure it temporarily while testing for proper positioning. A misaligned skylight would be very noticeable from the inside once the interior side is finished. Use a spirit level to check the sill and measure the diagonals to ensure square corners. Be sure to screw the brackets into the roof over a layer of building paper. (Fig. 6)
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7.
Flash the Curb and Repair the Roofing
Install aluminum sill, head, and step flashing, as recommended by the window manufacturer, carefully interweaving the flashing and the replacement shingles as you move along. Apply roofing compound under both the flashing and the shingles as you proceed. (Fig. 7)
Lastly, caulk around the perimeter of the window unit.
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8.
Frame the Shaft and Finish the Interior
Frame the sides of the shaft with 2x6s. Using an adjustable bevel gauge, carefully mark, cut, and install the framing.
Next, insulate the walls using R-19 fiberglass batts. Staple a 6-mil polyethylene vapor barrier on the interior sides.
Finish the shaft with drywall, and then tape the joints using drywall tape and joint compound. Use 100-grit sandpaper or drywall sanding mesh to smooth the joint compound, and then apply finish paint.
Install wood molding to hide the joint between the skylight and the drywall.
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