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Why Is My Metal Roof Leaking If the Panels Look Fine?
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Because on a metal roof the panels are almost never where the water gets in. On an exposed-fastener roof, the most common answer by a wide margin is the screws: each one is a deliberate hole through the weather surface, sealed by a rubber washer under the head, and those washers harden, crack and stop sealing long before the metal shows anything at all. After that it is penetrations, laps and edge details. Arrowhead Roofing has chased leaks on northeast Oklahoma metal roofs since 1987, and a roof that looks perfect from the driveway is the normal starting point for this conversation.
Note: this is a general guide to where metal roofs commonly leak. Diagnosis on a specific roof needs somebody on it, because the point where water appears inside is frequently a long way from where it entered.
Five places, in the order we check them.
| Where | What has gone wrong | How obvious is it from the ground? |
|---|---|---|
| Fastener washers | Hardened, cracked, or the screw has backed out or been overdriven | Invisible. This is the most common cause |
| Penetrations | Pipe boots split, sealant failed at vents and stacks | Sometimes visible up close |
| Panel laps and end laps | Sealant tape aged out, or thermal movement has worked the joint | No |
| Edge and transition details | Ridge, eave, valley and wall flashings | Occasionally |
| The panel itself | Punctured, or corroded through at a detail | Yes, and it is the rarest of the five |
The Short Answer
A metal roof is a system of panels plus several thousand deliberate holes. The panels are excellent. The holes are the roof’s weak point and they always were.
This is why the concealed-fastener systems cost more. On a standing seam roof the clips sit under the seam and there are no fasteners through the weather surface at all, which removes this entire category of problem. On an exposed-fastener roof, the washers are doing a job that the metal is not.
What Actually Happens to a Fastener Washer
Worth understanding because it explains the timing, and the timing is what confuses people.
The washer is a rubber ring compressed between the screw head and the panel. It has to stay compressed and stay flexible through every thermal cycle the roof goes through, and a metal roof moves more than most.
Older roofs used neoprene. The IIBEC Interface article on problem panel roofs describes the failure directly: after a few weather cycles the neoprene gasket would start to dry and crack until the fastener became a potential source of leaks. The industry has largely moved to EPDM, and the US Department of Defense’s roofing criteria now specify EPDM rather than neoprene outright.
Two other ways the same joint fails and neither is about the rubber. Overdriving crushes the washer out from under the head, so it seals nothing from day one. Backing out happens as thermal movement works the screw loose over years, leaving the washer no longer compressed. Both are visible on the roof and invisible from the ground.
Why the Stain Is Not Above the Leak
The most useful thing to know before anybody goes looking.
Water entering at a fastener runs down the underside of the panel, along a purlin or a rafter, and drops wherever the structure stops carrying it. On a low slope it can travel a long way. The wet patch on the ceiling marks the end of the journey rather than the beginning.
So the honest method is to work uphill from the stain rather than to look directly above it, and to check every fastener and detail on that run. It is slow and it is the only thing that reliably works.
The Part That Is Genuinely Good News
Almost everything on this page is maintainable rather than terminal.
Fasteners can be replaced, usually with a larger diameter screw that bites fresh metal and carries a new washer. Pipe boots are replaceable. Lap sealant can be renewed. None of that requires a new roof, and all of it is cheaper than one.
That is the practical difference between a metal roof and an asphalt roof at the same point in life. An asphalt roof that has started to fail is generally replaced. A metal roof that has started to leak is generally repaired, and the panels carry on doing what they were doing.
What Changes the Answer
Three things move a metal roof leak from routine to serious.
How long it has been going on
A fastener leak is a small volume of water arriving repeatedly in the same place. Over years that reaches the deck, the insulation and the structure, and at that point the repair is no longer about a screw.
Whether the panel has been walked on
Metal panels deform underfoot, particularly between supports, and a deformed panel no longer sits flat against its washers or its laps. Walking a metal roof is a skill and doing it wrong creates the next leak.
Whether the roof is a repair or a replacement
If the fasteners are original, the washers are all the same age and fixing one is treating a symptom. That is a different conversation from a single failed boot, and it is the same repair-or-replace logic as anywhere else: should you repair or replace your roof?
Related Questions
How long should the roof last in the first place?
Longer than asphalt, and it depends entirely which metal system it is. How long does a metal roof last? covers what is published and what is not.
Could hail have caused this?
Possibly, and only certain damage counts on a claim. Will insurance pay for hail damage to a metal roof? covers dents against functional damage.
It is a commercial building and I am not sure it is the roof at all.
Frequently it is not, and there is a defined way to find out. My commercial roof is leaking, but is it actually the roof? covers the other routes water takes.
See Also
The two answers either side of this one are how long the system should last, and how to tell whether a leak is the roof at all.
Have the Fasteners Looked At Before the Deck Is Involved
We have chased leaks on northeast Oklahoma metal roofs since 1987, and most of them end at a screw rather than at a panel. Book a free roof inspection and we will work uphill from the stain until we find it.