Why We Wrote This Guide

My dad Johnny and I have installed skylights on homes from Hope to Abbotsford, and the single biggest pattern we see is leaking skylights that were installed by someone who underestimated the flashing. The Fraser Valley dumps 1,500 to 2,000 millimetres of rain on our roofs every year. That volume of water finds every shortcut, every gap in butyl tape, every step flashing piece that was nailed too low. We wrote this guide so homeowners understand exactly what a proper skylight installation involves — and why it matters more here than almost anywhere else in Canada.

If you read through these steps and decide you want to tackle it yourself, you will have the knowledge to do it right. If you read through and decide to call us instead, we respect that decision too. Either way, an informed homeowner is a protected homeowner.

Before You Begin: Planning the Install

Skill Level: Advanced — structural framing and precision flashing experience required

Time Required: 8-12 hours spread across 1-2 dry days

Material Cost (DIY): $500-$1,200 CAD depending on skylight size and brand

Professional Installation: $1,500-$3,500 CAD including unit and all materials

Curb-Mount vs. Deck-Mount: Why We Only Install Curb-Mounts

There are two fundamental skylight styles, and in the Fraser Valley, only one makes sense.

Curb-Mounted Skylights sit on a raised wooden frame (the curb) that lifts the unit 4 to 6 inches above the roof surface. Water hits the curb and sheds around it. The flashing integrates with the shingle courses in a predictable, repeatable pattern. When we pull off a failed skylight on a roof in Chilliwack or Harrison, it is almost always a deck-mount that someone installed flush to the surface. Deck-mounted units rely on gaskets and sealant alone to keep water out, and in sustained BC rain events lasting three or four days, those gaskets lose. We install curb-mounts exclusively and this guide covers that method.

Tools You Will Need

Cutting and Framing:

• Reciprocating saw with a bi-metal blade (you will hit nails in the deck)
• Circular saw for rafter headers if structural cutting is needed
• Utility knife for shingle trimming
• Tin snips for custom flashing bends

Layout and Fastening:

• Drill with assorted bits
• Hammer and pry bar
• Tape measure, chalk line, and framing square
• 4-foot level
• Caulk gun
• Stud finder

Safety Gear:

• Fall protection harness with roof anchor — non-negotiable
• Safety glasses and dust mask
• Work gloves rated for sheet metal
• Tarps large enough to cover the opening if weather turns

Materials Checklist

• Curb-mounted skylight unit (VELUX and Fakro are the two brands we see most in BC)
• Manufacturer flashing kit — usually ships with the unit but confirm before your install day
• 2x6 lumber for curb framing (we use SPF-grade kiln-dried)
• 2x8 lumber for headers if you need to cut through a rafter
• 3/4-inch plywood for the curb cap
• Ice and water shield membrane — a minimum of one full roll
• Butyl tape sealant (buy more than you think you need)
• Polyurethane roofing caulk
• Matching shingles from your last re-roof (if you kept extras)
• 1-1/4 inch roofing nails and 3-inch framing screws
• Joist hangers if cutting a rafter

Step 1: Scout the Location from Both Sides

This step is where most DIY skylight installations go sideways. People pick a spot on the ceiling, cut, and discover a rafter, a duct, or a wiring run right in the opening.

From inside the attic or ceiling cavity:

1. Map every rafter with a stud finder. Mark their edges on the drywall with painter's tape.
2. Look for obstacles: electrical wiring, plumbing vents, HVAC ductwork. In many Fraser Valley homes built in the 1980s and 1990s, bathroom exhaust ducts run through the attic space at odd angles — verify clearance.
3. Position the opening between rafters whenever possible. Avoiding structural cuts eliminates the need for headers and saves hours of work.
4. Drive four reference nails through the ceiling at the corners of the proposed opening so you can locate them from the roof surface.

From the roof:

1. Find the reference nails poking through the shingles.
2. Confirm the pitch is at least 3:12. Many single-storey ranchers in Abbotsford and Chilliwack sit right at 4:12, which is workable. Anything under 3:12 requires a specialized low-slope skylight and different flashing methods beyond this guide.
3. Evaluate sun path and tree debris. South-facing skylights capture the most winter light (valuable in our overcast months). North-facing skylights deliver softer, more even illumination year-round. Avoid spots directly under cedar or fir branches — needle accumulation clogs skylight channels fast.

Step 2: Lay Out and Strip Shingles

1. Snap chalk lines for the rough opening using the skylight manufacturer's dimensions plus 1/2 inch clearance on each side.
2. Measure diagonals. If the two diagonal measurements differ by more than 1/4 inch, your layout is not square. Adjust before going further.
3. Strip shingles 14-16 inches past the chalk lines on all four sides. Pry carefully — you will reinstall some of these shingles later. Pull every nail in the removal zone.
4. Clean the exposed underlayment and inspect the deck surface for soft spots or rot. In older Fraser Valley homes, we occasionally find moisture damage in the deck plywood near ridge vents or bathroom exhaust penetrations.

Step 3: Cut the Roof Deck

1. Drill starter holes at each corner of the opening.
2. Cut the deck from above with a reciprocating saw fitted with a bi-metal blade. You will hit nails — a wood-only blade will bind and kick.
3. Stay inside the chalk lines. You can always trim more; you cannot put plywood back.
4. Have a helper below supporting the cutout section as you finish the last cut so it does not fall and damage the ceiling.
5. Inspect the exposed framing. Look for rot, insect damage, or compromised connections. In homes near the Fraser River — Agassiz, Rosedale, Harrison — moisture migration into attic framing is more common than you might expect.

Step 4: Frame the Opening (If Cutting a Rafter)

If your opening fits cleanly between existing rafters, skip ahead to Step 5. No structural work is needed.

1. Install double headers at the top and bottom of the opening. Use lumber the same dimension as the existing rafters (typically 2x8 in Fraser Valley stick-frame construction). Secure headers to the full-length rafters on each side with joist hangers and structural screws.
2. Cut the intercepted rafter only after both headers are locked in.
3. Install trimmer studs between the headers on both sides of the opening.
4. Verify zero deflection. Push and pull the framing — nothing should move or flex.

Step 5: Build and Install the Curb

The curb is the wooden frame that raises your skylight above the roof plane. It is the single most important element for keeping water out. Every millimetre of height creates drainage room, and in a climate where rain can fall sideways during winter storms blowing through the Fraser Canyon, that height matters.

1. Cut four pieces of 2x6 to match the skylight's base dimensions.
2. Miter the corners at 45 degrees for tight joints that resist water wicking.
3. Assemble the curb with construction adhesive and 3-inch screws at each corner.
4. Center the curb on the opening and fasten it to the deck and rafters with 3-inch screws every 8 inches.
5. Level the curb in all four directions. An out-of-level curb causes the skylight to bind (if venting) and creates uneven water channels.
6. Cap the curb with 3/4-inch plywood cut to match the skylight's mounting flange footprint.

Step 6: Waterproof the Curb

This is where Johnny and I see the most corners cut on failed skylight installs. The curb must be completely wrapped in ice and water shield membrane before any metal flashing goes on. No shortcuts.

1. Start at the bottom of the curb. Cut a strip of ice and water shield wide enough to cover the deck extension, the curb face, and fold over the plywood cap.
2. Work up the sides, overlapping each strip by at least 6 inches.
3. Double-layer the uphill side and all four corners. These are the highest-pressure points during driving rain.
4. Press the membrane firmly into every corner and surface. No exposed wood should remain anywhere on the curb.
5. Seal overlapping seams with roofing cement for belt-and-suspenders waterproofing.

Step 7: Install Base Flashing (Downhill Side)

1. Bend the base flashing so it covers the lower curb face and extends 8 inches onto the deck surface.
2. Seal the flashing to the curb with a continuous strip of butyl tape along the curb face.
3. Nail the deck flange along the top edge only — shingles will cover the lower portion.
4. Verify the bottom edge is straight and promotes clean water runoff downslope.

Step 8: Weave Step Flashing Up Both Sides

Step flashing is where skylight installations succeed or fail. In our experience across 500-plus roofs in the Fraser Valley, roughly 9 out of 10 skylight leaks trace back to step flashing that was improperly sequenced, under-sealed, or nailed in the wrong position.

1. Begin at the bottom corner of each side, right where the base flashing ends.
2. Place one step flashing piece per shingle course. Each piece should extend 5 inches onto the deck and 5 inches up the curb face.
3. Overlap consecutive pieces by 3 inches. The upper piece always goes over the lower piece — water flows down, never up under a flashing lap.
4. Nail each piece once, high on the deck flange where the next shingle will cover the nail head.
5. Seal every piece to the curb with butyl tape. Do not skip a single piece. In Fraser Valley rain, one unsealed step flashing joint will eventually admit water.

Step 9: Install Head Flashing (Uphill Side)

The head flashing is the most critical single piece in the entire assembly. It must go under the shingles above. If it goes over them, water running down the roof will slide behind the flashing and into the curb. We have repaired this exact mistake on homes in Agassiz, Chilliwack, and Harrison more times than we can count.

1. Bend the head flashing to cover the top curb face and extend at least 8 inches up the roof surface.
2. Slide the upper edge under the shingles above. This is non-negotiable.
3. Overlap the top of each side's step flashing by at least 3 inches.
4. Seal to the curb with butyl tape along the curb face.

Step 10: Reinstate Shingles Around the Skylight

1. Cut shingles to fit the skylight perimeter. Use a utility knife with a fresh blade for clean edges.
2. Maintain the original overlap pattern: shingles cover flashing at the sides and base.
3. At the top, slide shingles under the head flashing. This keeps the water flow consistent: roof surface to shingle to head flashing to curb.
4. Seal every cut shingle edge with a dab of roofing cement. Cut edges are exposed fibreglass mat, and they wick water in BC's sustained rain.
5. Nail above the flashing line, never through the flashing itself.

Step 11: Set the Skylight Unit and Final Seal

1. Run a continuous bead of butyl tape around the entire plywood curb cap perimeter.
2. Lower the skylight onto the curb and center it. Two people make this much safer, especially on steep pitches.
3. Drive screws through the mounting flange into the curb following the manufacturer's spacing — typically every 6 to 8 inches.
4. If the skylight vents, test the operator mechanism before buttoning up the interior trim. A binding operator is easier to diagnose now than after drywall is finished.
5. Inspect every flashing lap from top to bottom. Seal any visible gaps with polyurethane caulk. One gap is one future leak.
6. Clean all debris from the roof. Shingle granules and sawdust in flashing channels cause water dams during rain.

Interior Finishing

Once the skylight is sealed from outside, frame the interior light shaft with 2x4 studs from the roof opening down to the ceiling opening. Insulate the shaft walls with batt insulation and vapour barrier — this is critical in the Fraser Valley where interior humidity in winter can condense on cold skylight shaft walls and drip onto finishes. Finish with drywall, tape, and paint. Angle the shaft walls to spread light into the room rather than creating a narrow tunnel.

Five Mistakes That Cause Fraser Valley Skylight Failures

1. Step flashing installed over shingles instead of woven between courses

Each step flashing piece must sit between two shingle courses: over the one below, under the one above. Laying flashing on top of a finished shingle field is not step flashing — it is a leak waiting for the next atmospheric river.

2. Head flashing placed over the upslope shingles

This is the single most common professional-grade mistake we correct. The head flashing must tuck under the shingles above it. Water runs downhill and must always transition from shingle to flashing without any reverse lap.

3. Cutting a rafter without installing headers first

The rafter is holding up your roof. Cutting it before the headers are locked in transfers load to adjacent rafters instantly and unevenly. We have seen sagging ridgelines on homes in Chilliwack from exactly this sequence error.

4. Starting the cut without checking the 48-hour forecast

The Fraser Valley's weather can shift overnight. A clear morning forecast can turn into a rain warning by afternoon. Check Environment Canada, not just your phone app, and build in a full 48-hour dry window before making the first cut.

5. Skipping the ice and water shield on the curb

Butyl tape and metal flashing alone are not enough in our climate. The ice and water shield membrane is the last line of defence if a flashing seam eventually fails. Every skylight we install gets full curb wrapping, corners doubled. The membrane costs about $40 for a roll. The ceiling repair from a leaking skylight costs $2,000 or more.

When to Call a Professional

We believe in giving homeowners honest information, even when it means they might do the work themselves. But skylight installation is one of the few jobs where we genuinely recommend professional installation for most homeowners. The consequences of a flashing mistake are not visible until a heavy rain event, and by then the water has been traveling through your roof deck, insulation, and ceiling for hours.

If any of the following apply, we would encourage you to call us or another qualified roofer:

• The opening requires cutting through a rafter
• Your roof pitch is at or near the 3:12 minimum
• You do not have experience with step flashing sequences
• The skylight is on a second-storey roof with limited safe access
• You live in a high-rainfall area of the valley (Agassiz, Harrison, Hope)

At Dads Roofing, Johnny and I have installed skylights on homes across every community in the Fraser Valley. We are Red Seal certified tradespeople who transitioned from industrial boilermaking to residential roofing, and that precision background shows in our flashing work. We warranty every skylight installation we do, and we have never had a warranty callback for a skylight leak. If you want the job done once, done right, we are here.

Frequently Asked Questions

How much does skylight installation cost in the Fraser Valley?

Professional curb-mounted skylight installation typically runs $1,500 to $3,500 CAD including the unit and all flashing materials. The exact price depends on skylight size, whether rafters need to be cut and reframed, and the roofing material. DIY materials alone cost $500 to $1,200, but the risk of improper flashing in our rain-heavy climate makes professional installation the better value for most homeowners.

Can you install a skylight on a low-slope roof in BC?

Skylights require a minimum 3:12 roof pitch. Many rancher-style homes in Chilliwack and Abbotsford sit around 4:12, which works well. Anything below 3:12 creates pooling water around the curb and dramatically increases leak risk. If your roof is close to that minimum, a curb-mounted skylight with extra-tall framing helps shed water faster.

Why do skylights leak so often in BC?

The Fraser Valley receives 1,500 to 2,000 millimetres of rainfall annually, and sustained rain events put relentless pressure on every flashing seam. Skylights leak when step flashing is improperly woven with shingles, when head flashing is installed over instead of under shingles, or when butyl tape sealant deteriorates after prolonged UV exposure. Proper curb-mount installation with quality flashing eliminates most leak sources.

What is the best time of year to install a skylight in the Fraser Valley?

Late May through September gives the most reliable dry windows. You need at least 48 consecutive dry hours to safely cut the roof, frame, flash, and seal the skylight. We have installed skylights in shoulder seasons by watching forecasts closely and keeping tarps staged, but summer installations carry the least weather risk.

Should I choose a fixed or venting skylight?

Venting skylights are worth the upgrade in the Fraser Valley. Our humid summers create indoor moisture buildup, and a venting skylight helps exhaust warm, damp air from kitchens and bathrooms. Fixed skylights cost less and have fewer mechanical parts to maintain, making them a good choice for hallways and living rooms where ventilation is not the priority.

Ready for a skylight that never leaks? Call (778) 539-6917 or visit us in Agassiz for a free consultation.