A metal roof that leaks at the ceiling is often not leaking through the metal itself. On an exposed-fastener roof, the panels are held down by screws that go straight through the metal and into the deck or purlins. Each screw has a rubber or neoprene washer under its head to keep the hole closed. When that washer dries out, splits, or gets crushed during installation, the screw becomes a channel, and water follows the threads down into the building. If you have a stain on a ceiling and a metal roof above it, the screw line is the first place to look.
Leak and repair
Why the washer goes first
The washer is the part of the roof most exposed to sun. In a St. Louis summer, the panel surface gets very hot on July afternoons, and the rubber cycles between that heat and the cold of winter nights. Over time it hardens, shrinks away from the screw shank, and cracks around its edge. The steel can stay sound for many years while the washer quietly stops sealing. That is why a roof with clean panels and no visible dents can still drip.
Installation causes the same failure sooner. A screw driven too deep crushes the washer and dimples the painted cap, and a screw driven too shallow stands proud and never seats the gasket. Either way the seal is wrong from the first day. Ask the roofer who installed the roof how the screws were set, because a cap that looks dished in the middle is a sign the gasket was compressed too hard.
Reading the stain
Water coming down a screw line usually shows on the ceiling as a short stripe or a small cluster of spots, often lined up with the framing below the roof. The spots may sit on or near a purlin, the horizontal member the panels rest on. Water running down the steel can travel along the purlin before it drops, so the stain may appear a few feet from the screw that is actually leaking. Start at the ceiling stain, then move upslope along the same framing member to find the screws, rather than assuming the leak is directly above the stain.
Condensation can mimic a screw leak, and the difference matters. On a cold, clear St. Louis morning, moisture can form on the underside of an uninsulated metal roof and drip along the purlins, even though it has not rained. A leak from a failed washer tends to appear after rain or snowmelt and to follow the same path each time. If the wet spots only show on cold mornings and dry up by midday, ask the roofer to check the attic and the underside of the deck for condensation before anyone starts replacing screws.
Hail matters here too. Hail on an exposed-fastener roof can crack the painted cap over a screw or lift the gasket edge, and the seal fails in the same spot where the dent sits. If the roof took hail, photograph each screw cluster that shows a crack or lifted cap before anyone touches it, so the photos show what the roof looked like before repair. Keys documents damage this way, with photos and measurements, and puts a written scope in the homeowner's hands. That file is yours to keep, and it is what you bring to your own insurer. Keys does not handle, file, or negotiate your insurance claim, because Missouri law (RSMo 407.725) bars a roofing contractor from representing or negotiating a homeowner's insurance claim, and the same statute bars a roofer from saying anything about paying, waiving, or covering a deductible.
What a proper repair looks like
A proper screw repair replaces the failed fastener, not just adds sealant on top of it. The crew removes the bad screw, checks the hole in the purlin or deck for stripping, and sets a new screw with a new sealing washer at the depth the fastener maker specifies. If the hole has enlarged, the crew moves to a larger fastener or a different fixing method rather than filling the hole with sealant. Sealant smeared over a cracked washer may hold for a season and then fail under the same cap, which is how a leak returns after a repair that looked tidy.
A single-screw leak is a small repair. A repair that is not always a single screw is different. If the washers in one run have all cracked at similar points, the problem is probably the batch of fasteners or the way the whole field was installed, and replacing a few screws will only move the leak to the next row. Ask for a count of the failing screws across the affected slope, not just the ones above the stain. Walking the field in dry weather is the only reliable way to get that count, because a wet metal panel is slippery and the crew should not be stepping on the ribs when it is damp.
What it costs
Screw-line repairs are usually priced by the number of fasteners, with labor to reach the run and any trip charge listed separately. A crew that has to set up a lift or a ladder on a steep section will need more time than a crew working from a flat walkway, so the same number of screws can cost differently depending on the roof. Ask whether the price covers replacing the fastener and its washer or only the cap and sealant. A lower line that only seals the caps is likely to come back.
Cost also depends on spread. A leak at one screw is a small job. A leak that shows at several purlins across one slope is a question about the condition of the whole field, and that is when a written scope listing each fastener checked is worth more than a single line that says repair leak. Ask whether a full field check is priced separately, and whether that charge is credited to the repair if you approve the work. Paying to look first is a reasonable choice when the stain runs across more than one row.
What to ask
- Which screws are being replaced, and does the line include new screws and new washers, or only sealant over the caps?
- How many failing fasteners did the crew find on the slope above the stain, and will you get the photos of each one?
- Is the field check priced separately, and is it credited to the repair if you approve the work?
- Who will photograph each screw before and after the repair, and will you receive the complete set?
- If the screws were overdriven at installation, will the crew say so in the written scope?
- Does the scope name the fastener size and washer type, so you can compare it with any later repair?
If you have a leak now, the first step is to document the stain and find the leaking screws while the water is still showing. Keys can be reached at (314) 220-2333. The crew will trace the water to the fastener it runs down and write up what it found, with photos and measurements, for you to keep.