SKYLIGHT II THE ULTIMATE "OPEN HOUSE"

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Recheck the rough framing to see if it's square and is sized correctly, then drive nails through the roof sheathing from the inside corners to locate the hole's perimeter. At this point, you'll have to get on the roof and snap chalk lines between the nails to guide the cuts you'll be making.

Up on the Roof

For most owner-installed skylights, manufacturers recommend removing the shingles and the felt below them for a distance of about 10" around the top and sides of the opening. Do this with a flat bar and a utility knife. You can then snap your chalk lines directly onto the roof sheathing and make your four penetration cuts with a circular or reciprocating saw.

More than likely, the model you've chosen has a built-in curb, which raises the glazing panel several inches above the roof surface and directs water and shingle debris around the glass. If a curb's not included, you'll have to make your own from treated 2 X 4 stock, and toenail it to the header box, flush with the rough opening. Simple butt joints at the corners are sufficient.

You're now ready to set the skylight in place. Flashing kits that come with the unit may be of several different designs, depending upon the product. The simplest is a perimeter flange that relies upon nails and mastic to secure the unit and prevent leaks. With this type, a heavy layer of roofing cement is used as bedding between the plywood sheathing and the flange. Then after the flange is nailed to the roof, you apply a second layer of mastic over the nails and flashing, and cover that with patch strips of felt underlayment and shingles, starting from the corners of the-base flange, working up along the sides, and finishing across the top. The base flange extends over the lower course of shingles to shed water away from the cut.

Another common sealing method uses head and base flashing along the top and bottom walls, and strip flashing along the sides. The skylight and frame are fastened to the header box with nails, screws, or special clips. With this type of arrangement, both the head and base flashing sections are usually well designed and intended to last the life of the roof. Unfortunately, strip flashing, no matter how well made, probably will not. If the manufacturer offers a step flashing option (comprised of individual, overlapping sections), you might take it just to avoid leakage problems in the future.

It's important, no matter what the flashing method, that you follow instructions carefully and use the materials provided with your purchase. The fact that both are specific to your skylight will mean a sound installation and one that can be backed up by a manufacturer's warranty if necessary.

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