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Skylight Retrofit on a Monsoon-Zone Roof — Cost + Leak Risk

Adding a skylight to your existing roof is the single highest-leak-risk roof modification you can make in NAZ.

By NorthernAZRoofing Team · 2 min read

Skylights are wonderful — until they leak. Retrofitted skylights

in NAZ leak at 3-5x the rate of factory-installed skylights.

Why? Two reasons:

  1. The original roof was designed without the penetration; flashing

has to be retrofitted, never as clean as original

  1. The roof material (often asphalt) wasn't sized to the skylight

brand — incompatible flashing kits

Cost to retrofit a skylight in NAZ (2026)

| Skylight type | Material | Install | Total |

|---------------|----------|---------|-------|

| Velux fixed (24"x36") | $400-$650 | $1,800-$2,400 | $2,200-$3,050 |

| Velux venting (24"x36") | $700-$950 | $2,200-$2,800 | $2,900-$3,750 |

| Solar-powered venting | $1,400-$1,800 | $2,800-$3,400 | $4,200-$5,200 |

| Custom shape | $1,200-$3,500 | $3,500-$6,000 | $4,700-$9,500 |

Add: $400-$800 for interior light shaft drywall + finish work.

Leak failure modes

  1. Flashing separation — most common. Sealant ages, gaps form.
  2. Curb-frame failure — wood curb rots from condensation.
  3. Flashing-to-shingle weave — incorrect installation lets

water under shingles uphill of the skylight.

  1. Glass-to-frame seal failure — typically 15-20 years.
  2. Operator mechanism failure (venting only).

The single most important install detail

The flashing kit MUST match the roof type:

  • Asphalt shingle: Velux EDL flashing (low-profile)
  • Tile: Velux EDM flashing (high-profile, weave through tile

ridges)

  • Metal standing-seam: custom-fabricated Z-flashing

~80% of NAZ retrofit-skylight leaks come from the wrong flashing

kit being used.

Best timing for retrofit

NEVER retrofit a skylight during monsoon. Best windows:

  • March-April — pre-monsoon, roof dry, low humidity
  • September-October — post-monsoon, roof has dried out

Avoid:

  • June-August — monsoon active; rain ruins fresh sealant
  • December-February — cold sealant doesn't bond properly

When NOT to retrofit

  1. Roof < 5 years old — wait until next re-roof, install

skylight as part of original install

  1. Roof > 15 years — re-roof first, install skylight during

re-roof

  1. Tile roof with mortar-bedded ridges — extreme leak risk;

specialized contractor required

The skylight-during-re-roof discount

If you're already planning a re-roof, adding a skylight is

significantly cheaper:

  • Material: same
  • Install labor: $400-$800 less (no separate setup)
  • Roof modification: $0 (vs $300-$500 retrofit-only)

Net: ~$700-$1,300 cheaper to do it during re-roof.

Match with a skylight-experienced contractor →

#skylight #retrofit #leak #monsoon #installation

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