Estimate skylight flashing kit requirements based on skylight dimensions and roof pitch. Includes step flashing, head/sill flashing, and ice shield.
Skylights are one of the most common sources of roof leaks when improperly flashed. Proper skylight flashing involves multiple components: sill (apron) flashing at the bottom, step flashing up both sides, head (saddle) flashing at the top, and often a cricket behind the skylight to divert water.
Most skylight manufacturers offer integrated flashing kits sized to the skylight model, but custom flashing or additional materials may be needed for unusual installations or steep pitches. This calculator estimates the flashing material for each zone around the skylight.
Proper skylight flashing also requires ice and water shield membrane extending at least 6 inches beyond the flashing in all directions. This provides a secondary seal layer if the flashing ever develops a gap.
Understanding this metric in quantitative terms allows construction professionals to compare design alternatives, evaluate cost-effectiveness, and select the optimal approach for each project. Accurate calculation of this value helps construction professionals plan projects more effectively, reduce material waste, and ensure compliance with building codes and industry standards.
Skylight leaks are the #1 complaint among homeowners with roof windows. This calculator ensures all flashing zones (sill, step, head, and ice shield) are properly sized, reducing the risk of leaks. Regular use of this calculation supports compliance with building codes and inspection requirements, helping projects proceed smoothly through the permitting and approval process.
Step Flashing = 2 × Skylight Height + 12" extra per side Head Flashing = Skylight Width + 12" overhang Sill Flashing = Skylight Width + 12" overhang Ice Shield Area = (Width + 12") × (Height + 12")
Result: 10 step pieces per side, 42" head/sill flashing
Height = 48 in. Step flashing at 5-in exposure: (48 + 12) / 5 = 12 pieces per side. Head/sill flashing = 30 + 12 = 42 inches wide. Ice shield = 42 × 60 = 2,520 sq in (~17.5 sq ft).
Deck-mount skylights sit directly on the roof deck with integrated low-profile flashing. They work best on slopes of 4:12 and above. Curb-mount skylights sit on a raised wooden curb (frame) and work on any slope, including nearly flat roofs. The curb raises the skylight above the water plane.
The critical principle is "layer like fish scales" — every piece must overlap the piece below it so water always runs over, never under. Start at the bottom with sill flashing, work up the sides with step flashing woven into each shingle course, and finish at the top with head flashing that covers the final step flashing pieces.
Not all moisture around skylights is from leaks. In cold weather, warm moist interior air can condense on the cool skylight frame and glass, dripping water that appears to be a leak. Proper interior ventilation, double- or triple-pane glass, and insulated frames minimize condensation.
Use the manufacturer's flashing kit whenever possible — it's engineered for the specific skylight model and ensures warranty coverage. Custom flashing is needed for unusual sizes, very steep or low slopes, or non-standard roofing materials.
A skylight cricket (or saddle) is a small peaked structure behind the skylight that diverts water around it. Crickets are required for skylights wider than 30 inches on shingle roofs and recommended for all skylights to prevent water pooling.
Skylight leaks are usually caused by: worn/cracked flashing, missing ice and water shield, improper overlap sequence (head flashing under instead of over step flashing), or condensation (not an actual leak). Proper installation prevents all but condensation issues.
When re-roofing, always replace the skylight flashing. Leading manufacturers recommend new flashing with every roof replacement. Between roof replacements, inspect the flashing annually for gaps, corrosion, or sealant failure.
Yes, but use a curb-mount skylight (not deck-mount) for slopes below 4:12. The raised curb provides better drainage and allows for taller flashing that prevents water intrusion at the low slope.
Always flash from bottom to top: 1) Sill (apron) flashing first, 2) Step flashing up both sides (woven with shingles), 3) Head flashing at the top (overlapping the top step flashing). This ensures every layer sheds water over the layer below it.