Before You Start

Skill Level: Advanced (Professional recommended)

Time Required: 1-2 days per skylight

Cost: $500-1,500 (skylight + materials, DIY) vs. $1,500-3,000 (professional installation)

Skylight Types

Curb-Mounted (Recommended):

• Skylight sits on raised curb (4-6 inches)
• Better water shedding
• Easier to flash properly
• More durable
• This guide covers curb-mounted installation

Deck-Mounted (Not Recommended):

• Skylight sits flush with roof
• Prone to leaks
• Difficult to flash correctly
• We do not recommend this type

Required Tools

Cutting Tools:

• Reciprocating saw (for roof deck cutting)
• Circular saw (for rafter cutting if needed)
• Utility knife
• Tin snips

Installation Tools:

• Drill with bits
• Hammer
• Pry bar
• Tape measure
• Chalk line
• Level (4-foot)
• Square
• Caulk gun

Safety Equipment:

• Fall protection harness
• Safety glasses
• Work gloves
• Dust mask
• Tarps (for weather protection during installation)

Materials Needed

• Skylight unit (curb-mounted)
• Skylight flashing kit (usually included with skylight)
• 2x4 or 2x6 lumber (for curb construction)
• 2x6 or 2x8 lumber (for headers if cutting rafters)
• 3/4" plywood (for curb top)
• Ice & water shield
• Roofing nails
• Framing nails/screws
• Roofing cement
• Butyl tape sealant
• Shingles (to match existing roof)

Step 1: Choose Skylight Location

Considerations:

• Rafter Spacing: Ideally install between rafters (avoids cutting structural members)
• Interior Ceiling: Avoid electrical, plumbing, HVAC in ceiling cavity
• Roof Slope: Minimum 3:12 pitch (steeper is better for water shedding)
• Sun Exposure: South-facing for maximum light, north-facing for diffused light
• Tree Coverage: Avoid areas with heavy debris accumulation

From Interior:

1. Locate rafters: Use stud finder or drill small test holes
2. Mark desired location: Between rafters if possible
3. Drive reference nails: Through ceiling at corners of opening

Step 2: Mark Opening on Roof

From Exterior:

1. Locate reference nails: Driven from interior
2. Measure skylight rough opening: Check manufacturer specs
3. Mark opening on roof: Use chalk line
4. Verify square: Measure diagonals (should be equal)
5. Check for obstructions: Ensure no rafters in opening (unless you plan to cut them)

Step 3: Remove Shingles

Process:

1. Mark removal area: 12 inches beyond opening on all sides
2. Remove shingles carefully: You'll reinstall some around skylight
3. Remove nails: Pull all nails in removal area
4. Expose underlayment: Clean deck surface

Step 4: Cut Roof Deck Opening

Process:

1. Drill starter holes: At each corner of opening
2. Cut from above: Use reciprocating saw with metal-cutting blade (hits nails)
3. Cut carefully: Stay inside chalk lines
4. Support cutout: Have helper hold from below as you finish cuts
5. Remove cutout section: Carefully lift out
6. Inspect framing: Check for damage or rot

Step 5: Frame Opening (If Cutting Rafters)

If Opening Fits Between Rafters:

Skip to Step 6 (no structural cutting needed).

If Cutting Rafters:

Framing Process:

1. Install headers: Double 2x6 or 2x8 (same size as rafters) at top and bottom of opening
2. Use joist hangers: Secure headers to full-length rafters
3. Cut rafters: Only after headers are secured
4. Install trimmers: Vertical supports between headers on sides
5. Verify structural integrity: No sagging or movement

Step 6: Build Skylight Curb

Why This Matters:

The curb raises the skylight 4-6 inches above the roof, allowing water to shed around it. This is critical for leak prevention.

Construction:

1. Cut curb sides: 2x4 or 2x6 lumber to match opening perimeter
2. Miter corners: 45-degree cuts for tight joints
3. Assemble curb: Nail or screw corners together
4. Install curb: Center on opening, nail to deck and rafters
5. Check for level: Curb must be level in all directions
6. Install curb top: 3/4" plywood, sized to match skylight base

Step 7: Waterproof Curb

Critical Waterproofing:

1. Apply ice & water shield:
   • Start at bottom of curb
   • Wrap up sides and over top edge
   • Overlap seams by 6 inches
   • Press firmly to ensure adhesion
2. Seal all seams: With roofing cement
3. Ensure complete coverage: No exposed wood

Step 8: Install Step Flashing (Sides)

Why This Matters:

Step flashing is the most critical component. 90% of skylight leaks are caused by improper step flashing.

Installation (Each Side):

1. Start at bottom: First piece of step flashing at lower corner
2. Overlap shingles: Flashing goes OVER shingle below, UNDER shingle above
3. One piece per shingle course: Each shingle course gets one step flashing piece
4. Nail flashing to deck: High on flashing (will be covered by next shingle)
5. Overlap pieces: 2-3 inches where flashing pieces meet
6. Seal to curb: Apply butyl tape where flashing meets curb

Step 9: Install Base Flashing (Bottom)

Installation:

1. Position base flashing: Covers bottom of curb
2. Extend under shingles: Flashing goes under shingles above
3. Seal to curb: Butyl tape along curb edge
4. Nail to deck: Along top edge (will be covered by shingles)

Step 10: Install Head Flashing (Top)

Installation:

1. Position head flashing: Covers top of curb
2. Goes UNDER shingles: Critical - water flows over flashing, under shingles
3. Seal to curb: Butyl tape along curb edge
4. Overlap step flashing: Head flashing overlaps top of side step flashing

Step 11: Reinstall Shingles

Process:

1. Cut shingles to fit: Around skylight perimeter
2. Maintain proper overlap: Shingles over flashing at sides and bottom
3. Slide under flashing at top: Shingles go under head flashing
4. Seal cut edges: Dab of roofing cement under cut shingle edges
5. Nail properly: Above flashing, not through it

Step 12: Install Skylight Unit

Installation:

1. Apply sealant to curb top: Continuous bead of butyl tape
2. Position skylight: Center on curb
3. Secure with screws: Through skylight flange into curb (follow manufacturer specs)
4. Check operation: If operable, ensure smooth operation
5. Install interior trim: From inside (drywall, trim, etc.)

Step 13: Final Sealing

Critical Final Steps:

1. Inspect all flashing: Ensure proper overlap and sealing
2. Seal any gaps: With roofing cement or caulk
3. Check shingle alignment: Ensure water will flow properly
4. Clean debris: Remove all installation debris from roof

Common Mistakes to Avoid

1. Improper Step Flashing

Installing step flashing incorrectly (or skipping it) is the #1 cause of skylight leaks. Each piece must overlap properly.

2. Cutting Rafters Without Proper Headers

This compromises structural integrity and can cause roof collapse.

3. Installing in Bad Weather

Once you cut the roof, you're exposed. Rain during installation causes interior water damage.

4. Using Deck-Mounted Skylights

These are prone to leaks. Always use curb-mounted.

5. Inadequate Sealing

Skimping on sealant causes leaks. Use butyl tape generously.

The Bottom Line

Skylight installation is complex and risky. You're cutting a hole in your roof and trusting your flashing skills to keep water out. Mistakes cause expensive water damage.

At RJ Roofing Bros, we've installed hundreds of skylights. We know the flashing details that prevent leaks. We warranty our work. The $1,000-1,500 professional installation cost buys peace of mind and leak-free performance.

Want a skylight installed right? Call (604) 997-1292 for a free quote.