Part 5 of a six-part series, Green Renovation: Adding Skylights
In parts 1 through 4 of this series you learned about the green benefits of adding skylights, types of skylights, structural and other considerations, where and how to position your skylight and how to cut the hole and frame the well. If you have purchased curb mounted skylights without built-in curbs, the next step to installing skylights is building your curb and preparing to add the flashing.
Curbing Your Skylight
Your skylight instructions will tell you the framing dimensions. Standard sizes fit over rafters that are 2 ft. on center, so the outside dimension probably will be 25 ½ in. or 49 ½ in.
The curb usually is built from 2x6 lumber, mounted on edge so that it is 5 ½ in. above the roof. The curb is simply nailed or screwed to the rafters/trusses and headers, which should line up with the dimensions of the curb.
If you want to be overly cautious about waterproofing, you can overlap the corners in your curb to help reject water. Cut the top piece longer so that the side pieces butt up against it, leaving a solid 2x6 across the top and no seam for water moving downhill to penetrate. Conversely, cut the bottom piece shorter so that its ends abut the side pieces; the seams will be on the downhill side of the skylight, away from the flow of water.
As an added precaution, run a bead of caulking around the base of the curb. You probably will never need it, but it serves as a last line of defense should water penetrate the flashing.
If You Never Felt this Way Before…
Before flashing, you must wrap the curb in roofing felt, the same type of tar paper that you removed when you cut the hole in the roof. If you have composition shingles, use 15-lb. felt; wood shakes require 30-lb. felt.
The felt is fitted much the same way as the metal flashing described in the last article. The lower section of felt should overlap the sides of skylight by several inches and be worked between the existing felt and shingles/shakes at the bottom of the cutout.
Work side pieces of felt under the shingles/shakes, and overlap the lower piece by at least two inches. Cap it off with a top piece of felt that overlaps the side pieces by at least 2 in. and fits up under the existing roofing felt at the top of the cutout.
You are now ready to tackle the final and single most important step to installing skylights. Part 6 will explain how to install the flashing.
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