Installation Instructions – SIG Deck Mount (FM)Skylights SIG Skylights are designed for homeowners or professional installation. Sizes have been selected to eliminate or minimize cutting of structural members. Many sizes fit conveniently on 24” o. c. roof rafters or pre-fabricated roof trusses.
Materials You Need 1. Roofing felt for replacement of worn or damaged areas 2. Top quality roofing sealant and trowel or spreader 3. Galvanized roofing nails, 3” or longer nails, 2” stainless or aluminum screws 4. Lumber the size of roof rafters for headers to frame skylight openings 5. Self-adhered roofing underlayment such as Ice and Water Shield ™ or Storm Guard ™ (amount = 4 ½ x length + 3 ½ x width of opening, if using full 36” width of underlayment)
Helpful Hints Plan your installation for a dry, calm day. Allow a full day to complete the installation.Check the ceiling and space above the proposed skylight location. Avoid or relocate any wiring, plumbing, duct work, etc.
Determine the location of the skylight after reviewing the spacing of the existing roof rafters. Consult local building code requirements in the event that existing roof rafters or trusses have to be cut. If the roof pitch is 2:12 or lower, the skylight should be structurally raised above the roof deck.
Be sure the wood decking is sound, with no signs of rot or decay. Repair any existing problem areas. Use a top quality, non-cracking sealant.It is beneficial to install a diverter above the skylight, especially when skylights are mounted low on the roof.
You may require special guidance if you encounter unconventional interior construction. If you have tile, slate or heavy wood shingles, you may require professional assistance.
Installing Your SIG Deck Mount (FM) Skylight
PLAN AND MARK THE OPENING On the underside of the roof, select and mark the area to be cut. Avoid wiring, plumbing, duct work, etc. Make sure the area is square. Drive 3” or longer nails through the roof from the underside to mark the planned opening.
PREPARE AND CUT THE OPENING Carefully remove 24” to 36” of shingles (but not roofing felt) from the top and sides of the planned opening. Remove one less row of shingles from the bottom to allow lapping of underlayment several inches over the shingles in Step 4.
Mark the rough opening, then cut the hole in the roof. If you must cut a rafter, cut it back an additional amount of the thickness of the rafter to allow for framing . FRAME THE OPENING Frame the skylight opening, installing headers perpendicular to the rafters with lumber the same size as the rafters. This rough opening will typically be 1” larger than the SIG skylight nominal dimension, which should match the finished opening. (Ex.: a SIG 24 x 48 FM (Deck Mount) Skylight fits a 24” x 48“ finished opening or a framed 25” x 49” rough opening).
PREPARE THE ROOF AROUND THE OPENING Remove sawdust around the opening. Starting at the bottom, apply 12” to 36” wide strips of self adhering underlayment around the four sides of the opening. (The lower the roof pitch, the wider the strips). First apply the bottom strip.
Overlap it several inches onto the shingles below the opening and continue it up to the edge of the opening. Next do the sides, first overlapping the bottom strip of underlayment. Finally apply the top, overlapping the side strips. Replace shingles only up to the bottom of the opening.
PLACE THE SKYLIGHT Temporarily position the skylight evenly over the opening and mark its exact location using two finishing nails driven through the pre-punched top holes.
Remove the skylight and apply sealant to the top of the shingles below the opening, where the skylight will sit, and to the ridged undersides of the skylight flange.
Place the skylight back over the nails with the edge marked “TOP” at the top of the slope. THE BOTTOM FLANGE SHOULD SIT ON TOP OF THE SHINGLES. Remove the finishing nails.
FASTEN THE SKYLIGHT Fasten the skylight to the roof with stainless steel or aluminum screws through the pre-punched flange holes.
DO NOT NAIL THROUGH THE SKYLIGHT FLANGE.
Start at the top corners of the skylight, then work down the sides. No screws are needed along the bottom flanges.
APPLY SECOND LAYER OF UNDERLAYMENT Especially with lower pitched roofs, apply a 10” to 30” second layer of underlayment over the skylight flanges on the sides and then the top, only as close to the curb as the flange rib nearest to the curb.
Start at the lower sides, lapping the underlayment first over the bottom shingles then up the sides, then lap the top strip over the side strips.
DO NOT APPLY UNDERLAYMENT OVER THE EXPOSED LOWER FLANGE.
REPLACE THE SHINGLES Starting at the bottom, replace the shingles up the sides and then over the top, trimming shingles to within ½” of the skylight and sealing them firmly to the flanges.
DO NOT NAIL THROUGH THE SKYLIGHT FLANGE.
If desired, for cosmetic purposes only, you may spot glue additional shingles on the bottom flange to conceal the bright aluminum. ENJOY YOUR NEW SKYLIGHT!
What Our Clients Are Saying
“Why do I use SIG? Simple. They have the best skylight out there. It is the most durable, simplest to install, and easiest to maintain. They have plenty of stock sizes, and they will cheerfully make complicated custom skylights, with by far the fastest turnaround time. They are a pleasure to work with – and have been for twenty years!”