Illinois Roofing License IDFPR #19HC00108700 · GAF Certified Contractor
Skylights add daylight, ventilation, and architectural character to a home – but they’re also the single most leak-prone roof penetration. When a skylight is installed correctly and the right product is selected, it can last 25-30 years. When it’s installed wrong, it starts leaking within years. This guide covers skylight types, when to replace vs reflash, what to specify, and how skylights integrate with a full roof replacement.
Skylight types – curb-mounted vs deck-mounted
Two main installation styles for residential skylights:
Curb-mounted skylights – a wood frame (“curb”) is built up from the roof deck, typically 4-6 inches tall. The skylight unit sits on top of the curb. The roofing material wraps up the sides of the curb and is flashed at the top edge.
- Pros: more weatherproof (skylight is elevated above the roof surface), easier to replace without disturbing roof shingles
- Cons: more visible profile, can look bulky from outside
- Best for: low-slope roofs, modern aesthetic, replacement projects
Deck-mounted skylights – the skylight unit mounts directly to the deck, flush with the roof surface. Roofing material flashes around the skylight frame.
- Pros: lower profile, more aesthetic on traditional roofs
- Cons: more vulnerable to wind-driven rain and snow accumulation, harder to replace without disturbing roofing
- Best for: steeper-pitched roofs, traditional aesthetics
Both types work when installed correctly. The choice is largely aesthetic and depends on roof pitch and existing architecture.
Why skylights leak – and how to prevent it
Common skylight leak causes:
- Failed flashing. The metal flashing kit around the skylight has multiple components (sill, step, head, apron). If any piece is missing, undersized, or not lapped correctly with the surrounding shingles, water enters.
- Failed sealant on the glazing. The glass-to-frame seal degrades over 15-25 years. New glazing seals are silicone or butyl; older skylights used less durable materials.
- Condensation, not a leak. About a quarter of “skylight leaks” we get called for are condensation from inadequate attic ventilation, not actual leaks. The fix is ventilation, not the skylight.
- Improper installation – the skylight wasn’t installed plumb, the curb is rotted, or the flashing was installed under the wrong shingle course.
The right install: factory flashing kit (matched to the skylight manufacturer) installed by someone who’s done at least a dozen skylights. Generic shingle-and-caulk installation always fails.
When to replace the skylight vs reflash
If you have an existing skylight that’s leaking or showing problems:
Reflash only (replace the metal flashing, keep the skylight):
- Skylight is less than 15 years old
- Glazing is intact (no fogging, no cracked glass, no failed seal between panes)
- Frame is sound
- Wood curb (if curb-mounted) is not rotted
- Cost: $400-$800 typically
Full replacement:
- Skylight is 15-20+ years old
- Glazing shows fogging or seal failure between panes
- Curb has rot or insect damage
- You’re already replacing the roof and the skylight is approaching end-of-life
- Cost: $1,200-$2,500 per skylight installed (varies by size and brand)
When in doubt: full replacement during a re-roof. The labor to remove and replace a skylight is much lower while the roof is already opened up. The marginal cost of replacing the unit vs reflashing it is just the unit price.
Brand recommendations
The skylight market is dominated by two brands:
Velux – the standard. We install Velux on most projects. They’re a Danish company with long warranties (typically 10-year glass, 10-year flashing) and reliable factory flashing kits. Models range from fixed (don’t open) at the low end to electric vented with rain sensors at the premium end. Pricing $400-$1,500 per unit.
Fakro – Polish, also reputable. Often less expensive than equivalent Velux. Quality is comparable; market share is smaller so flashing kits and parts can be harder to find years later.
Avoid the budget brands at the very bottom of the market – they’re cheaper for a reason. The flashing kits don’t hold up and the glazing seals fail early.
Solar tubes (tubular skylights)
An alternative to traditional skylights: solar tubes (also called tubular skylights). A reflective tube runs from a small dome on the roof down through the attic to a ceiling fixture below. Brand names: Solatube, Velux Sun Tunnel.
- Less leak risk (smaller penetration, simpler flashing)
- Lower cost ($800-$1,500 installed)
- Brings light deeper into the house (the tube can run 10+ feet through the attic)
- No ventilation or view – just light
For interior rooms that need natural light but don’t need a view, solar tubes are often a better choice than traditional skylights.
Schedule an assessment
If you have a leaking skylight, are considering adding one, or want to evaluate an existing skylight as part of a planned roof replacement, schedule a free Trill Roofing inspection at /free-inspection/. We’ll evaluate condition, recommend repair vs replacement, and quote the work as part of the broader roof scope.
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