Installing a skylight adds natural light, improves ventilation, and boosts home value—but it’s not a weekend DIY project for beginners. This tutorial walks you through a standard curb-mounted, fixed acrylic skylight installation on an asphalt-shingle roof. Expect moderate difficulty (intermediate), 12–16 hours over two days, and strict attention to framing, flashing, and sealing.
Overview
| Category | Details |
|---|---|
| Skill Level | Intermediate — requires roofing, framing, and waterproofing experience |
| Time Required | 12–16 hours (plus 24-hour caulk cure time before final inspection) |
| Tools Needed | Circular saw, reciprocating saw, chalk line, framing square, caulk gun, ladder (24-ft extension), roofing nailer |
| Estimated Cost | $550–$1,200 (skylight unit + flashing kit + shingles + sealants; excludes labor) |
Tools & Materials
| Item | Specs/Notes |
|---|---|
| Skylight Unit | Fixed curb-mounted acrylic unit, 22" × 46" (e.g., Velux FS C06 or Fakro LTP); verify roof pitch compatibility (3:12–12:12) |
| Flashing Kit | Manufacturer-matched step-flashing kit (e.g., Velux EDL 2246 for that size); never substitute generic flashing |
| Roofing Underlayment | Ice & water shield (minimum 36" wide), plus synthetic underlayment (e.g., GAF Tiger Paw) for full deck coverage |
| Framing Lumber | 2×6 pressure-treated lumber (for curb); 2×4 blocking; exterior-grade plywood (½" thick) for interior ceiling frame |
| Sealants & Fasteners | Butyl tape (1/8" thick), silicone roof sealant (ASTM C920 Type S), galvanized roofing nails (1-1/4"), #10 stainless steel screws (1-1/2") |
Step-by-Step Instructions
1. Plan & Mark the Opening Location
Choose a rafter bay that avoids electrical wires, plumbing vents, and structural beams. Use a stud finder and infrared thermometer to confirm no hidden heat sources. Mark the opening centerline on the roof with chalk—then transfer that point to the attic ceiling using a plumb bob. Cut a 1/4" pilot hole in the ceiling drywall and feed a wire through to mark the exact spot on the roof surface.
2. Frame the Roof Curb
Build a 2×6 curb frame sized to match your skylight’s rough opening (check manufacturer specs—typically 1/2" larger than unit width/length). Anchor it to rafters with 3" structural screws, not nails. Shim as needed to ensure levelness within 1/8" tolerance across all four sides. Leave a 1/8" gap between curb top and roof sheathing for butyl tape compression.
3. Cut the Roof Opening & Install Flashing
Using your marked lines, cut the shingles and roof sheathing with a circular saw set to 7/8" depth—stop before cutting into rafters. Remove debris and inspect for rot. Lay ice & water shield 12" beyond all edges of the opening. Install step flashing first: slide each piece under shingles above, then nail to sheathing with one nail per leg. Integrate counterflashing into the curb’s metal flange per manufacturer diagram.
4. Mount & Seal the Skylight Unit
Lift the skylight onto the curb. Press firmly to compress butyl tape. Secure with manufacturer-supplied screws—do not overtighten. Apply ASTM C920 silicone sealant continuously along the entire perimeter where the skylight meets the curb. Wipe excess immediately with mineral spirits and a lint-free cloth. Let sealant skin over for 2 hours before proceeding.
- Tip: Work on a dry, 45–85°F day—cold temps make butyl tape brittle; heat causes premature sealant slump.
- Warning: Never skip the ice & water shield layer—even on low-slope roofs. The U.S. EPA estimates 22% of skylight leaks stem from missing or improperly lapped underlayment (2022 Home Performance Report).
Pro Tips
Skylight failures most often trace back to flashing misalignment—not the glass itself. Always follow the manufacturer’s flashing sequence exactly. A single reversed step-flashing piece can channel water behind the curb instead of shedding it away.
"I’ve replaced over 170 leaky skylights in New England homes—and 9 out of 10 were installed without proper step-flashing overlap or ice shield extension. It’s not the product; it’s the installation discipline." — Carlos Mendez, RCI-certified roofing consultant, 2023
- Test fit the curb before cutting the roof—use scrap wood to simulate height and check clearance from ridge vents or chimneys.
- Drill pilot holes for curb screws—pressure-treated lumber splits easily if driven blind.
- Label every flashing piece with masking tape before removal—reassembly order matters more than you think.
How do I choose the right skylight size?
For rooms under 150 sq ft, a 22" × 46" unit provides balanced daylight without glare. Larger spaces (200–300 sq ft) benefit from two smaller units spaced 4–6 ft apart rather than one oversized unit—this prevents hot spots and improves air circulation. Avoid units wider than 30" on roofs steeper than 8:12 unless reinforced with internal bracing.
Can I install a skylight on a flat roof?
Yes—but only with a curb-mounted unit specifically rated for low-slope applications (≤ 2:12 pitch), and you must add a 4" minimum curb height with integrated drainage channels. Standard residential skylights are not rated for flat roofs and will pond water. See our flat roof skylight options guide for compliant models.
Do I need a building permit?
Almost always. In 47 states, skylight installations require permits when altering roof structure or adding penetrations (International Residential Code §R105.2, 2021 edition). Your local authority will inspect framing, flashing, and fire-rated assembly compliance—especially in attached garages or townhomes.
What’s the best time of year to install?
Early fall (September–October) offers stable temperatures, low humidity, and minimal rain—ideal for sealant adhesion and shingle self-sealing. Avoid February–March in cold climates: shingle granules don’t reseal below 40°F, increasing leak risk. Spring is second-best, but watch for sudden downbursts that wash away uncured sealant.
How do I prevent condensation inside the skylight?
Condensation forms when warm, moist indoor air hits cold glass. Install a dehumidifier in rooms with high moisture (bathrooms, kitchens), use exhaust fans during showers/cooking, and ensure attic ventilation meets 1:150 net free area ratio (per IRC §R806). Double-glazed, low-E coated units cut condensation by 65% versus single-pane (Velux Technical Bulletin TB-017, 2022).
Should I hire a professional or DIY?
If you’ve framed walls, flashed chimneys, and sealed roof valleys successfully, you’re qualified. If not, hire an installer certified by the skylight manufacturer—Velux, Fakro, and Sun Tunnel all maintain searchable contractor directories. According to the National Roofing Contractors Association’s 2023 survey, DIY-installed skylights are 3.2× more likely to leak within 3 years than professionally installed ones.
A properly installed skylight should last 20–30 years with minimal maintenance—just annual gutter clearing and biannual sealant inspection. Keep your roof’s integrity intact, and that burst of morning light will stay bright, dry, and worry-free. For related help, see our chimney flashing tutorial and roof leak detection checklist.