OPENING THE ROOF
Rain or shine, you can easily create a skylight in one day using the following instructions. Since nature could prove to be uncooperative, it's best to prepare for rain as a precaution. Purchase a tarpaulin large enough to cover the roof opening with plenty of leeway. The tarp should be big enough to skirt the ridge to the other side of the rooftop, providing a runoff for water. Should it rain, you can make a "sandwich" over the roof opening with 2X4's, tarpaulin, and additional 2X4's.
MAKING THE FRAME
According to most building codes, the skylight should be, at minimum, 5 inches above the roofing material with the aid of the curb. Generally, you should select 2X6 pressure treated lumber for the construction of your roof curbs. Check the manufacturer's instructions for dimensions for the roof opening and match these to the inside dimensions of the curb. Note where the lumber is to be cut, working with a tape measure and a combination or carpenter's square. Avoid knots at the ends. Cut your wood and protect against split ends by drilling pilot holes for the nails. Then nail the pieces together. You'll want to test for squareness by measuring diagonals of the curb from corner to corner, or by using a carpenter's square.
Until you are ready to nail it in place you'll want to keep the curb square by bracing two opposite corners together. Lightly drive 2" nails into wood or triangles cut from plywood about 1/2" thick.
Items needed: Tape measure, combo square, circular saw or crosscut saw, electric drill and claw hammer.
PREPARING THE ROOF
For a curb-mounted model, use a rope to dolly the curb to the roof. Align the curb with the four protruding nails so that each corner houses a nail. (For a heavy shake roof, chalk your lines about 1/2" away from the edges of the curb, permitting space for the eventual step-flashing. For asphalt shingle or wood roofs, make your chalk lines directly in line with the outside edges of the curb.) The curb can be put aside for now.
Items needed: Chalk line or utility knife, or tape measure and straight edge.
Select a saw and blade appropriate to the roof you are working with. Circular saws perform well for wood shingles and shakes (use a combination blade) and for asphalt shingles (use a carbide-tipped blade). Disposable blades are essential for built-up roofs since the blade will later be useless. When cutting the rough opening, take care that the saw's blade pierces the roofing material and sheathing, but not the rafters. Line up the saw blade with the chalk line. Now turn on the saw and lower it so that its base plate is on the roof. Follow your marked line until you hit a corner. When you have sawed the entire square, remove the roofing section.
Items needed: Circular saw, chalk line, claw hammer, pry bar and an appropriate saw blade.
REMOVAL OF SECTION
Different skylights will require varying amounts of roofing material to be removed. If step-flashing is necessary (those mounted on a site-built curb are included), use a pry bar to remove the nails and then make a 10" clearance, removing shingles on all sides of the opening. These shingles will be needed later to flash the unit.
COMPLETING THE FRAMING
You'll have to install jack rafters between the headers parallel to the rafters if your skylight does not fit between the rafters. You'll need pieces of lumber the same size as the rafters to fit between the two headers. Nail these pieces in joist hangers nailed to the headers.
ALL ABOUT JOIST HANGERS
To create a secure butt joint between a header and a rafter or a joist and a beam, you need a framing connector called a joist hanger. Typically U-shaped, these are secured with special framing anchor nails available when you purchase your joist hangers.
PLACING THE CURB
Use a rope to elevate the curb to the roof and place the curb over the roof opening, ensuring that the two are correctly aligned. With a carpenter's square or by measuring the diagonals, be certain that the curb is square. With 2 1/2" nails, toenail the curb through the sheathing to the frame rafters and headers. Corner braces can now be eliminated. Fasten the curb to the roof opening using 2 #10 galvanized nails or 2 #8X1.5 deck screw per side.
Roofing felt should be attached around all sides, under the edges of the existing shingles, and allowed to curl up the sides of the curb. Once the felt is cut to align perfectly with the top of the curb, it can be stapled to the curb itself. Cut the felt, curl it around and staple it to the adjacent side of the curb when working on a corner. Felt on the top piece should overlay edges of the felt at the side piece and these should overlay the felt on the bottom piece.
Items needed: Hand stapler, utility knife, claw hammer and a carpenter's square or tape measures.
PLACING THE SKYLIGHT
The skylight is ready to be positioned once you have successfully framed the roof opening. The following instructions are suitable for most models but check the manufacturer's specific recommendations. Be sure to install flashing correctly to prevent rain from leaking in through the roof. (Various flashing kits are available for low-profile and high-profile roofing materials.) As a general rule, when you have overlapping roofing felt, flashing or shingles, the piece that is higher on the roof should be topmost.
For curb-mounted skylights, install the curb as directed, follow with the flashing, and finish by fastening the skylight to the curb as described below. For a step-flashed unit, attach the skylight to the sheathing with the mounting brackets provided and install the flashing.
A. Bottom Saddle Placement
Replace shingles up to the bottom of the curb or to the step-flashed skylight's frame, then line up the saddle flashing with the bottom of the curb. Don't prick the roofing felt since this will cause leakage when it rains. Using 1" nails, nail the saddle flashing to the curb. Avoid the sheathing.
B. Step-flashing Placement
Place shingles and step-flashing at every side of the curb, weaving each new piece of step flashing with each course of shingles. Avoid cutting the roofing felt or nailing the shingles through the flashing. Lower pieces of step flashing and shingles should be under higher pieces. Holding each piece of flashing flat against the roof using your hand or foot, nail it into the curb. It may be necessary to cut the flashing to fit the top of the curb. Cut the flashing with tin snips and then curve it around the corner and nail it to the top of the curb.
Items needed: Tin snips, claw hammer
C. Positioning the Top Saddle
Secure the top saddle flashing along the top of the curb, holding the saddle in place while you nail it in. (If you have a very thick roof, the saddle may not fit snugly against the curb and you will need to employ the filler piece in your flashing kit. The filler should be sandwiched between the saddle and the curb and then the whole bundle can be nailed together.) You may now replace shingles over the saddle flashing, but do not use nails. Unless the manufacturer advises it, cement or sealant is unnecessary.
ATTACHING THE FRAME TO THE CURB
You will need to run a line of silicone rubber sealant across the top of the curb once it is flashed. Before gluing firmly, be sure the skylight is positioned directly over the curb. Use the pre-drilled holes in the frame to attach the skylight's frame to the side of the curb.
Items needed: Claw hammer, caulking gun
ATTACHING THE FRAME TO THE ROOF
If the manufacturer instructs you, remove the sash from the frame once you have framed the rough opening. Attach the mounting brackets to the frame and align the frame over the opening. Screw the brackets to the sheathing. Use a carpenter's square or measure the diagonals to be certain that the frame is square.
Place roofing felt around the frame, positioning the material under existing felt at the top and sides, and over existing felt at the bottom. Once you have wrapped the roofing felt around the frame's edges, staple it in place. Cut the material, curl it around and staple it to the adjacent side of the curb when you reach a corner. If you have done this properly, roofing felt at the top of the skylight will be on top of the side pieces and these will be on top of the bottom piece. Before installing the step-flashing, replace shingles up to the bottom of the frame.
Items needed: Utility knife, hand stapler, tape measure or carpenter's square, electric drill or screwdriver.