How to Install an Acrylic Square Skylight

Measure the length and width of the skylight with a tape measure to determine the size hole you’ll need to make in your ceiling and roof to create the mount and the straight shaft for the skylight. Locate an area of the ceiling between the ceiling joists in the room where you wish to place the skylight that’s large enough to hold the measured dimension. Use a wall stud finder to locate the joists, and then choose a section of ceiling between a pair. Mark the dimensions of the skylight on the ceiling with a straightedge and pencil at the chosen location.

Drill a hole through the ceiling at the inside corners of the marked lines. Use the holes to pass the blade of a keyhole saw through the ceiling in order to cut out the marked area.

Remove the ceiling panel you’ve just cut out, and cut through any insulation you find over the hole with a utility knife. Remove the insulation.

Locate the cut hole from the attic side of the ceiling. Hold a plumb bob against the roof over the four corners of the hole, marking the ceiling at each location where the bob is even with the corner. Connect the markings with a straightedge and check the measurements of the rectangle created with the dimensions of the skylight. The measurements should be the same. If they aren’t, repeat the plumb-bob process to get the positions of the marks correct. Drill holes through the inside corners of the marked square.

Climb a ladder up to the roof and find the holes that you just drilled. Use the straightedge to guide you in connecting the holes into a skylight-sized square. Mark the roof with a piece of chalk so that the lines show clearly. Remove any shingles over the marked square, and then redraw the square lines onto the roof felt. Use a circular saw to cut through the felt and the roof along the chalk lines, and then remove the roofing piece.

Return to the attic and create a frame to attach your skylight to in the roof. Measure the roof rafter planks with the tape measure to determine the size of boards used. Create your frame using the same sized boards. Cut the boards to fit at the top and the bottom of the roof hole, using the length of the space between the rafters adjoining the space as the length of the planks. Use the circular saw to cut each plank. Place the planks between the rafters with the edges of the planks flush with the hole in the roof. Nail the planks in place using 16d nails.

Create a frame for the hole in your ceiling identical to the one for the roof. This frame helps hold the skylight shaft frame, as well as provides a surface to place the lower acrylic panel.

Use a T-bevel to measure the rafter angles along the roof. Measure the distance between the corner of each hole on the roof frame and the edge of the corresponding hole on the ceiling frame. Cut four 2-by-4-inch planks to match the distance of each corner, and the angle of the rafter. Nail the boards at the sides of the frame at each of the corners with 8d nails, making a skylight well frame that connects the two holes.

Return to the roof, and set the skylight in place over the hole in the roof. Screw the skylight to the roof using the mounting holes in the base of the skylight.

Place 8-inch-wide strips of roofing felt beneath the shingles surrounding the skylight. Begin with a strip running along the base of the skylight and extending about 4 inches to either side, then place paper along the sides of the skylight before finishing with a strip against the top edge. Cut the felt with the utility knife when needed. Lift the shingles where necessary with a prybar to place the roofing felt and nail the shingles back into place.

Replace the shingles around the skylight that you removed from the roof when you cut the hole. Place the skylight step flashing along the base of the skylight and around the sides. Slip the side pieces of flashing beneath the side shingles. Attach the step flashing by nailing it to the sides of the skylight rather than to the roof, using the mounting holes provides in the flashing.

Place the solid flashing onto the base of the skylight, over the skylight edge and the step flashing at the side. Screw the solid flashing in to place, and then place the side pieces followed by the head flashing along the top. The head flashing sits flush with the roof, so slip the piece that sits on the roof under the shingles along the top of the skylight before screwing it in place.

Go back to the attic and measure the sides of the framed skylight well. Cut drywall sheeting using a utility knife to score the cutting lines and then snapping the sheets to fit the measurements. Attach a sheet of drywall to the 2-by-4-inch corner studs on the interior of the skylight well, using drywall nails spaced every 5 inches along the stud length and along the sides of the frames at the top and bottom.

Place drywall tape over the joints in the corners of the drywall, and along the joint between the well and the ceiling. Cover the tape with joint compound using a drywall knife to seal the joints and allow the mud to dry. Sand the compound smooth after it dries with a medium-grit sandpaper and paint the well the same color as your ceiling to blend its drywall in with the rest of the ceiling surface.