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The fastest way a small skylight problem turns into a pricey repair is simple: nobody looks at it until water is already dripping onto the floor below. Skylights rarely leak because the glazing itself fails. They leak because the curb around them does: sealant that has cracked and pulled away, counterflashing that has worked loose, or a drain that nobody cleared before the leaves piled up.
Why commercial skylight maintenance can’t wait
A leaking skylight rarely announces itself where the leak actually starts. Water follows the path of least resistance along framing members, insulation, and vapor barriers before it finally shows up as a stain on a ceiling tile, sometimes ten or fifteen feet from the curb itself. By the time anyone notices, wet insulation and a soaked deck have usually been sitting there for weeks.
That lag is exactly why a scheduled walk beats a reactive one. Catching a cracked sealant joint in September is going to be a lot better than in February, after a winter of freeze thaw cycling has widened the gap, tends to mean a wet ceiling, a business interruption, and a much bigger invoice. If you need professional help to fix or replace your leaky skylight, contact us today and we’ll be able to fix your issues ASAP!
Good to know
This article is general information, not professional advice. Roof conditions, flashing details, and manufacturer requirements vary by building and product, and they change over time. Confirm the specifics that apply to your roof with a qualified roofing contractor before you make a decision. Industrial Roofing Services Limited is not responsible for decisions made solely on the basis of this article.
Step 1: Start the inspection from inside
Before anyone gets on the roof, walk the building underneath every skylight. Look at the ceiling tiles, drywall, or exposed deck directly below each unit for staining, discoloration, or a soft spot. A ring shaped water stain almost always means an active or recent leak.
This step takes ten minutes and tells you exactly which skylights need the closest look. It’s also the easiest thing to skip when a facilities team is busy, which is exactly why it gets skipped, and why leaks get found late.
Step 2: Check the curb flashing and sealant
The curb, the raised frame the skylight sits on, is where almost every leak actually starts. Walk the perimeter of each unit and look for sealant that has gone chalky, cracked, or separated from either the curb or the skylight frame. Check that the counterflashing, the metal trim that laps over the membrane, is still snug and not loose.
Flashing is consistently identified as one of the most failure prone details on a low slope roof. The National Roofing Contractors Association’s guidance on roof flashing treats it as its own category of inspection for exactly this reason: it is a joint between two different materials, and joints move differently than the field of the roof around them.
Pro tip
Run a gloved hand along the sealant bead instead of just looking at it. Sealant that looks intact can still be soft, sticky, or crumbly to the touch, which is often the first sign it is starting to fail before a visible gap opens up.
Step 3: Clear the drainage path around every curb
Water that cannot drain away from a skylight curb has more time to find a way in. Clear leaves, granules, and any debris that has built up against the low side of the curb, and confirm the nearest roof drain or scupper is not blocked.
This is also the moment to look for ponding that sits well past the point where the roof should have drained. Standing water against a curb means that seal is under more pressure than it should be, for longer than it should be.
Step 4: Watch for movement from thermal cycling
Roof membranes and metal flashing expand and contract with temperature, and a skylight curb sits at the exact spot where several materials with different expansion rates all meet.That movement can make a sealant joint loose or pull counterflashing away from the fastener line, wearing down over time.
Look for hairline gaps, fasteners that have started to back out of the counterflashing, or a joint that looks slightly different from the same joint on another skylight about the same age. None of these need an emergency call on their own. Together, or left alone for another season, they add up.
Red flag
Daylight visible through a gap around the frame, a counterflashing panel that has come loose enough to move by hand, or a fresh water stain that grew since the last inspection all need immediate action.
Step 5: Build spring and fall walks into the schedule
Two inspections a year catches most of what matters. A spring walk tends to find whatever winter movement opened up. A fall walk confirms drains and curb bases are clear before snow and ice load the roof for months.
Both visits are also a chance to compare current photos against the last set. A joint that looked fine in the fall and looks different in the spring tells you something a single inspection never can: that something changed, and roughly when.
Step 6: Keep a written record, not a memory
A photo, a date, and a one line note for each skylight is enough. Six months from now someone can look at a joint and know if it looks the same, better, or worse than it did last time.
This habit pays off twice. It catches slow moving problems that a single visit would never see, and it gives a roofing contractor a head start.
Common mistakes that undo good maintenance
The most common mistake is not skipping maintenance entirely. It is doing a rooftop walk without ever checking underneath the skylights first, which means small leaks get missed until they show up somewhere else. The second most common mistake is treating a sealant touch up as a permanent fix rather than a stopgap, when the real issue is a flashing detail that needs to be redone properly.
A close third: assuming every skylight on a roof ages at the same rate. Orientation, shade, drainage, and foot traffic all differ from unit to unit, even on the same building. Two skylights installed on the same day can be in noticeably different condition five years later.
When it’s time to call a roofing contractor
A facilities team can handle the inspection routine above without any special tools. Sealant replacement, flashing repair, and curb re-detailing are a different category of work, and they are worth handing to a roofing contractor who does this daily, both for the workmanship and for the fall protection the job requires.
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Download the Skylight Maintenance Checklist (PDF)Frequently asked questions
How often should commercial skylights be inspected?
Twice a year is a reasonable baseline for most commercial buildings: once in spring after the freeze thaw season, and once in fall before drains and curbs get buried under leaves and debris. Buildings in exposed locations, or with older flashing details, may benefit from an additional mid-summer check. Your roofing contractor can help set a schedule based on the specific skylights and roof system on your building.
What are the first signs a skylight is starting to leak?
The earliest signs usually show up below the roofline rather than on it: a faint ring shaped stain on a ceiling tile, discoloration on drywall near the skylight opening, or a musty smell in the room underneath. On the roof itself, look for sealant that has gone chalky or cracked, and counterflashing that no longer sits tight against the curb.
Can facilities staff maintain skylights without a roofing contractor?
Routine visual inspection, checking for debris, and clearing drainage paths around the curb are tasks most facilities teams can handle safely with basic training and appropriate fall protection. Sealant replacement, flashing repair, and any work that involves cutting into or altering the roof membrane should go to a licensed roofing contractor, both for workmanship and for safety.
Does a small gap around a skylight always mean a leak?
Not necessarily, but it always means that joint is under more stress than a sealed one and worth watching closely. Movement from temperature swings can open small gaps that close again as materials contract, without any water getting through on that occasion. The safer approach is to treat any visible gap as something to document and monitor rather than something to ignore.
Who is responsible for skylight maintenance in a leased commercial building?
Responsibility typically depends on the lease agreement between landlord and tenant, and it varies from building to building. In most commercial leases, roof and building envelope maintenance, including skylights, falls to the property owner or property manager rather than the tenant. Check your specific lease terms, or ask your property manager directly, before assuming who is responsible for a repair.
Skylight and flat roof maintenance across Southern Ontario
Industrial Roofing Services Limited maintains, repairs, and inspects skylights and flat roof systems for commercial and institutional buildings throughout the GTA and Southern Ontario, including roofing crews serving Waterloo, Ontario and Fergus, Ontario. If it has been more than six months since anyone looked at your skylights from either side of the roof, get in touch with our team and we will build a maintenance visit around your building’s specific roof.
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