A wet spot beside a skylight does not prove that the skylight itself has failed. Water can enter at the head flashing, a side shingle, an exposed fastener or a roof opening several feet uphill. It can also form inside the house when warm, damp air reaches cold glass. Before you agree to replace the unit, the roofer should identify which path the water is actually taking.
Leak and repair
A roof skylight has several parts that can admit water. The glass and frame make up the visible unit. Many skylights sit on a raised curb, while others are made to mount directly to the roof deck. Flashing connects that assembly to the shingles. Underlayment provides another layer beneath the visible roofing. Interior trim and drywall hide most of the route between the opening and the stain.
The location of the first visible drip is only a starting point. Water entering above the skylight can run along the roof deck until it reaches the opening. It may then follow the skylight frame or a framing member and appear at one lower corner. That can make a sound skylight look responsible for a leak that began at a nail, shingle joint or vent farther upslope.
A useful inspection starts outside. The roofer should check the shingles above and beside the unit, the head flashing across the top, the step flashing along both sides and the lower apron. On a curb mounted unit, the curb itself should be checked for rot, open corners and improper height. Sealant may be present, but it should not be the only thing keeping water out.
Proper flashing directs water around the opening in layers. The upper pieces must overlap the lower pieces so gravity carries water toward the eave. A reverse lap can remain hidden under shingles and leak only during wind driven rain. St. Louis thunderstorms can push water across a roof in directions that a light vertical rain will not. A leak that appears only with wind from one direction is useful evidence.
Three problems that look alike indoors
- Flashing leakage: Water commonly appears during or shortly after rain. Staining may begin at a corner or on the downhill side, even when the opening is higher.
- Failure within the unit: Moisture may collect between panes, the frame may leak at a joint, or a gasket may deteriorate. Replacing roof flashing will not repair failed insulated glass.
- Condensation: Water forms on the room side of cold glass or metal, often during freezing weather. It may drip onto the same drywall that would be damaged by an exterior leak.
Condensation deserves a separate check because St. Louis regularly moves through freezing nights, warmer afternoons and rapid changes in humidity. A bathroom, kitchen or humidifier can add enough indoor moisture to wet a cold skylight. If the staining develops during cold dry weather without rain or melting snow, the roofer should not call it a flashing leak without more evidence.
Ice can complicate the diagnosis. Snow melting above a cold eave can refreeze lower on the roof and slow drainage. Water may back up around a skylight positioned near the eave, particularly if insulation and air sealing allow heat to escape unevenly through the roof. The repair might involve damaged flashing or underlayment, but the conditions that created the ice also need attention.
What a repair may involve
If the skylight unit is sound and the flashing is wrong, the repair usually requires removing shingles around the opening. The roofer can then inspect the deck, curb and underlayment instead of spreading roof cement over the exposed edges. Damaged wood is replaced as needed. New underlayment and compatible flashing are installed in the correct sequence, followed by shingles that tie the repair back into the existing roof.
A curb with soft wood or open joints should be rebuilt before it is covered. Fastening new metal to a rotten curb only conceals the weak part. The written scope should say whether the curb is being reused, repaired or replaced. It should also say whether interior drywall and paint are included, since roofing work commonly stops at the roof opening.
If the insulated glass seal has failed or the frame is cracked, replacing only the flashing may leave the original problem in place. The existing model, size and mounting method matter. A replacement unit may not fit the old opening without carpentry. That is why the dimensions and identification label should be recorded before materials are ordered.
The surrounding roof also affects the decision. Removing brittle shingles around an older skylight can break material beyond the intended repair area. A three tab roof near the end of its useful repair life may not accept a neat, durable patch, especially after years of hail, heat and freeze thaw movement. In that situation, the question is not merely whether the skylight can be flashed. It is whether the surrounding roof can be taken apart and put back together reliably.
What it costs
A skylight repair price should reflect the work required to expose the leak path. A surface sealant visit and a full flashing rebuild are different jobs. The main cost factors are roof pitch, access, the number of shingle courses that must be removed, the condition of the deck and curb, and whether matching Atlas or Malarkey shingles are available for the repair area.
Interior access matters too. A skylight over a tall stairwell or vaulted room may require equipment that a skylight over an unfinished attic does not. If drywall has to be opened to trace staining or inspect the shaft, ask who will close and finish it. That work may be priced separately from the exterior roof repair.
Unknown wood damage should not become an unlimited charge. The proposal can state a unit price for deck replacement and describe how additional curb carpentry will be approved. Photographs taken after the shingles and flashing are removed give you a record of why added work was needed.
Permit requirements depend on the municipality and the extent of the work. St. Louis County contains many separate permit desks, and individual cities may administer their own building rules. A simple flashing repair may be treated differently from changing the opening or replacing structural framing. Ask the contractor to identify the applicable permit office before work begins rather than assuming one countywide answer applies.
What to ask
- Where do you believe the water enters? The answer should identify a component and a path, not merely point to the ceiling stain.
- How did you rule out condensation? Weather timing, indoor moisture, glass condition and attic observations can help separate condensation from rain entry.
- Will shingles be removed? A flashing rebuild normally requires access to the layered materials around the opening.
- Is the skylight unit staying or being replaced? Make sure the scope separates the glass and frame from the curb, flashing, underlayment and shingles.
- What happens if the curb or deck is rotten? Get the approval process and pricing method in writing before the roof is opened.
- Are interior repairs included? Drywall, insulation, trim and paint should be named if they are part of the price.
- What photographs will I receive? Useful photographs show the suspected entry point, the opened assembly, any damaged wood and the completed flashing before every part is covered.
Be cautious if the proposed repair consists only of applying sealant around the visible frame. Sealant has legitimate uses at specified joints, but it cannot correct a reverse lap, missing step flashing, rotten curb or failed glass unit. It also makes the next inspection harder by covering edges that need to be seen.
Before scheduling the work, ask for one written sentence that names the diagnosed defect and one that names the repair. For example, the scope might state that the head flashing is improperly lapped and that shingles will be removed so the flashing and underlayment can be rebuilt. That is more useful than a line reading only "repair skylight leak." To arrange a roof inspection with Keys Roofing, call (314) 220-2333.