In addition to the sklight, you will need 2-by-4s for the frame, drywall and finishing supplies for the ceiling, roofing paper, roofing nails and 16d galvanized nails, step flashing and continuous flashing.

Your toolkit should include a circular saw, hammer, flat pry bar, tin snips, and a utility knife.

This is not an easy project as it involves cutting the roof and installing new structural framing members as well as drywalling and finishing the ceiling beneath the skylight. The roofing paper and metal flashing must be installed correctly or the roof will leak around the skylight. If you have good carpentry skills, follow the manufacturer’s directions precisely; otherwise, hire a professional.

The instructions presented here will give you an idea of the work involved. Some skylights use different installation methods and different types of flashing.

Bubble lights and plastic skylights are inexpensive, but you cannot see clearly out of them. A fixed skylight will produce heat in the summer, but the effect will be minimal if it has low-e glass.

Some manufacturers sell remote-controlled shades or Venetian blinds for their skylights. At the high price end, a ventilating skylight can open to allow hot air to escape, significantly cooling a house and replacing or at least reducing the need for air conditioning.

1. Cut & frame the opening.
Follow the manufacturer’s specifications for cutting the hole in your roof. From the inside, drill a locator hole where you want the center of the skylight to be and then work on the roof to cut the opening with a circular saw.

Frame the opening so it is strong, installing header joists perpendicular to the rest of the joists (Figure 1). If you have a standard ceiling (one that does not follow the angle of the roof), cut and frame the ceiling as well, and frame a vertical passageway for the light to flow through.

2. Cut back the roofing & attach the skylight.
Using a utility knife and a straightedge, cut the roof shingles about 3 inches back from the opening on all four sides. Set the skylight in place, centered on the opening, and attach it to the roof with nails or screws.

3. Slip in the underlayment.
Cut strips of roofing paper about 8 inches wide and slip them under the shingles (Figure 2). Install the bottom piece, then the sides, and then the top. Sneaking the paper under the shingles will be tricky. Use a flat pry bar to lift all the roofing nails that would get in the way, taking care not to damage the shingles.

4. Install bottom & step flashing.
Install the bottom flashing, a single piece that wraps partway around the skylight and sits on top of the roof shingles (Figure 3). Drive roofing or flashing nails horizontally into the skylight, not vertically into the roof.

Next, slip individual pieces of step flashing under the shingles. On each side, start at the bottom and work up. The step flashing pieces must overlap each other by 4 inches or so. Attach the flashing pieces to the skylight, not to the roof.

5. Install the solid flashing pieces.
These pieces are designed to fit tightly onto the skylight and ensure that water cannot enter between the step flashing and the skylight. Attach the bottom piece first and then the side pieces (Figure 4). Install the top piece (called the head flashing) by slipping it under the roofing and attaching it to the skylight.