When did you last look at the skylight over your kitchen instead of through it? If a roof replacement is on your calendar this season, that unit deserves a few minutes of attention before the tear-off crew shows up with a dumpster.
Most homeowners file a skylight under "part of the house" rather than "part of the roof," and that filing decision is how a fifteen-year-old unit ends up sitting under a brand-new shingle field. The stain on the drywall appears two winters later, and by then the repair costs several times what the swap would have cost while the roof was open.
What "Curb-Mounted" Means And Why It Changes The Job
A curb-mounted skylight sits on a site-built box — typically 2x framing lumber built up off the roof deck — and the glazing unit drops over that curb the way a lid drops onto a shoebox. A deck-mounted unit, by contrast, has an integrated frame that fastens directly to the sheathing and sits lower against the shingle plane, with its flashing tucked into the unit's own perimeter.
The distinction matters at tear-off because on a curb-mounted assembly, the curb is the part that gets buried. Once new underlayment, step flashing, and shingle courses are woven around that box, everything about its condition — soft corners, insufficient height, a failed sealant joint at the deck — is locked in for the life of the roof.
Keep in mind that the skylight itself is the easy component to change later. The wood it sits on, and the flashing woven into the field around it, are not.
Why The Old Unit Usually Fails Before The New Roof Does
A modern architectural asphalt roof is commonly rated for 25 to 30 years, and metal or tile assemblies run considerably longer; the service-life differences between coverings are covered in architectural vs three-tab shingles. Skylight hardware does not keep that pace, and that mismatch is the entire reason the timing question exists.
The failure modes are predictable, and they cluster in the components that see the most thermal cycling and ultraviolet exposure. The most common include but are not limited to:
- Insulated glass seal failure. The sealant bonding the two panes of an insulated glass unit degrades under decades of expansion and contraction, letting humid air into the cavity. That is the permanent haze or fogging you see between the panes, and it cannot be cleaned, dried, or resealed in place.
- Gasket and glazing seal aging. The EPDM or silicone gaskets that hold glass in the frame harden and shrink with UV exposure. A shrunken gasket lets water past the glass edge and into drainage channels that were designed to handle condensation, not bulk water.
- Flashing and cladding fatigue. Aluminum cladding at the head and sides oxidizes and works loose at its fasteners over time. The sealant behind the head flashing is usually the first part of the assembly to fail outright, because it sits where the most water concentrates.
- Curb rot. Anything that gets past the flashing lands on the top plate and corners of a wooden curb. Rot there spreads inward toward the deck long before it announces itself on the interior drywall.
- Fastener movement. Twenty years of daily thermal cycling backs fasteners out of a frame by fractions of a millimeter at a time. The resulting gaps become a drainage path that nobody designed and nobody inspects.
All of these share a timeline. Manufacturers commonly warrant an insulated glass unit for ten to twenty years, and real-world service life for the glazing seal typically lands in the fifteen-to-twenty-five-year band — well short of the roof going on above it.
How To Judge Whether The Curb Itself Is Worth Keeping
The unit and the curb are two separate decisions, and the curb is the one with consequences you cannot revisit. Here is the inspection sequence to run, ideally with the roofer standing next to you before the bid is signed:
- Probe the top plate and all four corners. Push an awl or a screwdriver tip into the wood; anything that takes the point with little resistance, or that reads dark and spongy, is rot rather than weathering.
- Measure the curb height. Manufacturer instructions and most code adoptions expect the top of the curb to stand at least four inches above the finished roof surface, with more height required on low-slope roofs and in heavy-snow regions.
- Check the opening from the attic side. Staining on the shaft framing, compressed or discolored insulation, and rust tracks on nail points all say water has been moving through the assembly for a while.
- Inspect the deck around the opening. Sheathing within a foot or two of a leaking curb is often the first area a crew condemns, and roof decking replacement explains what that discovery adds to the job.
- Confirm the curb is square and flat. A racked curb or a cupped top plate will not seat a new unit's gasket evenly, and no amount of sealant compensates for a frame that only makes contact on three sides.
If the curb passes all five checks, keeping it is reasonable and rebuilding is optional. If it fails even one — particularly the probe test — the curb comes off with the shingles, because the alternative is framing a brand-new roof around wood you already know is bad.
Why The Old Flashing Kit Cannot Be Reused
A skylight flashing kit is a matched set of parts: an apron at the bottom, step or soaker pieces up the sides, a head flashing at the top, and cladding that covers the joint. Kits are sized to a specific unit and manufactured for a specific roof covering, and the versions for asphalt shingle, tile, standing-seam metal, and low-slope membrane are not interchangeable, because each one assumes a different way of lapping water down the slope.
The old kit comes off the roof bent, nailed, and sealed into shingle courses that no longer exist. Straightening and reinstalling those pieces produces a joint that depends on sealant instead of on laps, and sealant is a maintenance item rather than a waterproofing strategy — the same principle that governs every other transition covered in roof flashing.
There is a warranty dimension as well. Manufacturers commonly condition their no-leak and installation warranties on the use of their own matched kit installed per printed instructions, so a reused kit can quietly convert a covered assembly into an uncovered one.
The Cost Math: During The Tear-Off Versus Two Winters Later
The figures below are estimated ranges rather than quotes, and actual pricing varies with region, unit size, glazing package, roof pitch, and access. What does not vary is the shape of the comparison:
- Replacing during the tear-off. The unit itself is the dominant cost — roughly $300 to $1,000 for a fixed curb-mounted skylight in common sizes, and roughly $900 to $2,500 for venting or solar-powered venting models — plus a matched flashing kit in the $80 to $250 range and a modest labor add, often a few hundred dollars per opening, because the crew, staging, dumpster, and surrounding shingle courses are already accounted for.
- Replacing after the roof is finished. The same unit now carries a return trip, a minimum job charge, and the careful removal and re-weaving of shingles installed weeks or years earlier; installed pricing commonly lands in the estimated $800 to $2,000-plus range per unit, before any interior work.
- Replacing after a leak. Add shaft drywall, paint, and insulation, and add deck repair if the water sat long enough. This is the scenario where a $600 unit turns into a four-figure ceiling repair and a week of interior disruption.
- Rebuilding a rotted curb later. Rebuilding a curb under a finished roof means opening the shingle field on all four sides of the opening, which is the most expensive way ever devised to buy sixty dollars of framing lumber.
Read those four lines as a single argument. The unit costs about the same whenever you buy it, and what changes is how much roof has to be taken apart to install it — a tear-off hands you that access at no additional charge, which is worth reading alongside how much a roof replacement costs in 2026 to see how the surrounding line items are typically priced.
When Keeping The Existing Skylight Is Defensible
A blanket replace-everything rule would cost some homeowners money for no reason, and plenty of units have years left in them. Keeping the existing skylight is a defensible call when all of the following hold at once:
- The unit is genuinely young. Roughly eight years or less, ideally with a purchase record or a date stamp on the frame label rather than a previous owner's recollection.
- The glazing reads clean. No haze or moisture between the panes, no fogging that comes and goes with temperature, and gaskets that are still pliable rather than chalky and shrunken.
- The curb passed every check above. Sound wood, adequate height, square and flat, with no staining visible from the attic side.
- A matched flashing kit is still manufactured for it. Models get discontinued, and a kit for the new roof covering has to exist in the correct size before this plan works at all.
Even when all four conditions hold, budget for the new flashing kit anyway. Reusing an eight-year-old unit is a reasonable decision; reusing eight-year-old flashing that has already been nailed and sealed once is a different and much weaker one.
Put The Decision In The Contract, Not In The Driveway
Skylight scope is among the most common change-order surprises on a residential tear-off, because it is easy to leave vague at bid time and expensive to settle on a Tuesday morning with the deck already open. Your written scope should name the unit model and size, the flashing kit part number, whether the curb is being rebuilt or reused, and who pays if rot is discovered underneath.
Ask each bidder to price the skylight work as its own line item rather than folding it into a lump sum. That is the only way to compare proposals honestly, for the same reason that comparing roof estimates line by line beats comparing bottom-line numbers, and it belongs in the same document as the rest of your roof replacement contract scope.
Note that a rot-discovery clause is worth more to you than a slightly lower price. A unit price per sheet of sheathing and per linear foot of curb framing, agreed in advance and in writing, keeps a Tuesday discovery from becoming a Tuesday negotiation.
Ice, Condensation, And The Details That Decide Cold-Climate Skylights
In regions with a history of ice damming, the area around a skylight is a predictable trouble spot: a heated shaft, an interruption in the insulation plane, and a horizontal head flashing sitting directly in the path of meltwater running down the slope. Codes in those regions generally require an ice barrier membrane at the eaves, and good practice extends self-adhered membrane around the full perimeter of a skylight opening regardless of where the eave line falls — ice dams covers the underlying mechanism.
Ventilation belongs in the same conversation. A skylight shaft interrupts both insulation continuity and airflow, and a roof with marginal intake or exhaust tends to show the consequences at the skylight first, which is one more reason to read attic ventilation and roof lifespan before the new roof goes on.
One diagnostic note before you assume the worst about an older unit. Water at the interior trim in January is frequently condensation on cold glass rather than a roof leak, particularly above kitchens and bathrooms, and how to know if your roof is leaking walks through how to separate the two before anyone climbs on the roof.
The Decision Rule
Here it is in one line: if a curb-mounted skylight is more than about ten years old, it comes off with the shingles, and if it is younger than that, keep the unit and buy a new flashing kit. The exception runs in both directions and it is always the curb — rotted wood gets rebuilt at tear-off no matter how new the skylight above it happens to be.
Timing is the entire advantage here, and it is only available once per roof. If you are still working out when to schedule the replacement itself, roof replacement timing covers the seasonal and condition-based tradeoffs, and the skylight decision deserves to be made in that same sitting rather than after the crew is already on the roof.
Talk with a licensed roofing contractor in your area before materials are ordered, and ask specifically how each opening will be handled. A crew that has the answer ready — unit, kit, curb, rot clause — is telling you something useful about how the rest of the job will go.
This article is for informational purposes and is not contractor, engineering, or code-compliance advice. Verify requirements with your local building department and consult a licensed professional in your jurisdiction.