A properly assembled skylight curb flashing is essential to prevent leaks and ensure long-term roof integrity. This guide walks you through a clear, step-by-step process for assembling skylight curb flashing. Before starting, gather these tools and materials: measuring tape, utility knife, tin snips, roofing nails, hammer, caulking gun, roofing sealant, and flashing materials (both step flashing and counter-flashing).

Step 1: Measure the Curb. Begin by measuring the skylight curb's dimensions. The curb is the raised frame that sits on the roof. Measure its length and width. This data determines the size of the base flashing.

Step 2: Cut the Base Flashing. Using a metal sheet or pre-formed flashing pieces, cut a base layer that extends at least 4 inches beyond the curb on all sides. Bend the edges upward slightly to direct water away from the curb.

Step 3: Install the Step Flashing. Step flashing is applied along the side of the curb L-shaped metal pieces. Start from the bottom, sliding each piece under the roof shingle above it. Nail the flashing to the curb side, but do not nail through the shingle. Overlap each piece by at least 2 inches. Continue this up to the top of the curb.

Step 4: Install the Continuous Flashing at the Bottom. Cut a continuous piece of flashing that spans the entire lower side of the curb. Slide it under the shingles below, leaving a slight overhang to shed water. Seal all edges with roofing sealant.

Step 5: Install the Counter-Flashing. Counter-flashing covers the top edge of the step flashing. Cut strips to match the length of each curb side. Insert the top edge of each strip into a pre-cut groove in the skylight frame, then bend the bottom edge down over the step flashing. Seal the groove with caulk.

Step 6: Seal All Joints. Run a continuous bead of roofing sealant along every seam and nail head. Pay special attention to corners. Use a putty knife to smooth the sealant.

Step 7: Test for Leaks. Lightly spray water from a garden hose over the assembled flashing. Wait 10 minutes and inspect the attic interior for any moisture. If you see water, re-apply sealant to the affected area.

Step 8: Final Inspection. Check that all edges are securely fastened and that the flashing overlaps with shingles without gaps.

This method works for both asphalt shingle and metal roofs. Always work on a dry, non-windy day and follow safety practices like using a harness and ladder stabilizer. Well-assembled flashing protects your home and extends the life of your skylight. With patience and attention to detail, you can achieve a professional-grade installation. Remember, if you are uncomfortable working at heights, or if your roof has multiple penetrations, consult a licensed roofer. Happy building