During a roof replacement, homeowners often try to save money by leaving an old skylight in place and asking the roofer to “just re-flash it.” This is a high-risk gamble. The violent vibration of tearing off old shingles and hammering new ones frequently breaks the compromised thermal seals on 10+ year-old acrylic skylights. Reputable contractors will often explicitly void the roof warranty around a preserved skylight. While a new flashing kit costs roughly $350, a full replacement of a standard Velux unit runs $1,200 to $1,800. Replacing the unit during the roof installation is the only way to guarantee a waterproof envelope.
A skylight is a massive, intentional hole cut directly into the structural decking of your roof. It is subjected to extreme thermal expansion, expanding in the summer sun and contracting in the winter cold. Over time, this constant movement stresses the seal between the glass and the frame.
When you sign a contract for a new roof, you must decide what to do with the existing skylights. Choosing incorrectly will lead to severe drywall damage and a multi-thousand dollar interior repair bill.
The Liability of Forensic Vibration
If your current skylight is 12 years old and “not currently leaking,” it is surviving on borrowed time. The plastic or rubber gaskets holding the glass pane to the aluminum frame are baked dry by UV radiation.
When a roofing crew begins the tear-off process, they use heavy steel pitchforks to forcefully pry up thousands of old nails from the plywood deck. The entire roof structure physically vibrates. This violent, sustained vibration acts as the breaking point for brittle skylight seals. The glass may not visibly shatter, but the microscopic thermal seal will crack.
The Warranty Void: Because contractors know this, they will include a legal waiver in your contract stating: “Contractor is not responsible for leaks originating from existing skylights retained at the owner’s request.” If it leaks 6 months later, you will have to pay the roofer to tear up the brand new shingles around the unit to replace it, costing double what it would have cost during the initial installation.
Curb-Mounted vs. Deck-Mounted Skylights
The cost of your replacement or repair depends entirely on the architectural engineering of the skylight frame.
| Engineering Type | Structural Description | Replacement Process |
|---|---|---|
| Curb-Mounted | The skylight sits like a lid on top of a raised wooden box (the curb) built out of 2x4s protruding from the roof deck. | Easier. The roofer unscrews the “lid,” checks the wooden box for rot, flashes the box with new metal, and drops a new unit on top. |
| Deck-Mounted | The skylight is a single, integrated unit nailed directly flush to the plywood deck. It has a lower, sleeker profile. | Harder. The entire unit must be pried off the plywood. Often requires minor interior drywall/trim adjustments inside the house to fit the new modern dimensions. |
Skylight Action Estimator
Input the age of your current skylight and your desired scope of work to calculate the estimated financial surcharge per unit.
If you choose to keep an existing skylight, the contractor must still completely remove all the shingles around it. To properly integrate it into the new roof, they must purchase a new manufacturer-specific Step Flashing Kit (typically $150 to $250 for the metal alone). If a contractor’s bid says “Re-flash skylight – $50”, they are likely just going to smear a massive pile of black roofing tar around the base of the unit. This will crack and leak within 3 years. Demand to see the “Flashing Kit” listed explicitly on the estimate.
Eliminate Hidden Surprises
Do not wait for a mid-project change order to figure out you need a $1,500 skylight. Our 40-Factor Estimator allows you to input your exact number of skylights and specify “Re-Flash” or “Full Replacement” to guarantee absolute budget accuracy.
Launch the 40-Factor Estimator →Frequently Asked Questions
If I replace a deck-mounted skylight, will I have to paint the ceiling inside?
Highly likely. Modern skylights (like the Velux brand) have slightly different internal dimensions than older brands manufactured 20 years ago. When the new unit is dropped into the hole, there is usually a small gap between the new frame and your interior drywall that will require minor trim carpentry or spackle to finish.
Are acrylic domes better than flat glass?
No. Acrylic “bubble” domes were popular in the 1990s because they shed water easily, but they degrade under UV light, turn yellow/cloudy, and crack easily during hail storms. Modern flat glass skylights use tempered, Low-E argon-filled glass that provides vastly superior energy efficiency and impact resistance.
Engineering & Fenestration References
- International Residential Code (IRC): Section R308 – Glazing Requirements, detailing impact resistance mandates for sloped glazing (skylights) over occupied spaces.
- Velux Commercial / Residential: Manufacturer technical specifications regarding the mandatory integration of EDL/EDW step-flashing kits with standard architectural shingles to validate the “No Leak” warranty.