Common problem
Most leaks start at the details, not in the middle of a sound sheet — at fasteners, laps, flashings, penetrations and gutters. Badly rusted sheets can also leak through holes. Find where it comes in first, then choose the repair that fits.
| Where | Why it happens | What you see |
|---|---|---|
| Screws and their washers | The rubber washers age, and heat cycling loosens the screws. Over- or under-tightening also lets water in. | Raised screws, cracked washers, rust or water stains around screws |
| Laps between sheets | The joints, not the sheets, are the weak point: gaps, broken sealant, and wind-driven rain pulled in. Dirt and moisture under the lap cause rust. | Gaps, shifted sheets, rust under the lap |
| Ridge and wall flashings | Flashings that cannot move with the heat work loose, and their sealant cracks in the sun. | Lifted flashings, broken sealant |
| Pipe and equipment penetrations | The joint between the roof and a pipe or equipment curb is weak, and rubber boots crack. | Cracked rubber, layer on layer of sealant |
| Gutters and box gutters | Leaves and debris block them and water overflows under the roof. Box gutters hold dirt and water and rust from the inside; if they are too small or too flat, heavy rain overflows into the building. | Overflow marks, rust around the gutter |
| Rust holes | Rust starts at scratches and cut edges and becomes a hole — often under laps and at the eaves. Humidity speeds it up. | Red rust, blistered paint, pinholes |
| Ponding water | A metal roof is made to shed water, not hold it. Too little slope or drainage leaves water standing, which shortens the roof's life and may void the warranty. | Water still standing after the rain |
We check screws, laps, flashings, penetrations, gutters and rust across the roof. Water that drips on dry, cool mornings may be condensation, not a leak.
On a dry day, water is run from the eaves upward, section by section, while someone inside marks where it drips. Where it drips is often not where it gets in.
Only once the cause is clear do we choose the repair — and after it, the roof is tested with water again.
These are examples of how leaks are traced. We choose the checks to suit the site.
These are the possible repairs. Which one fits is decided after we see the roof.
| Repair | When it fits | Keep in mind |
|---|---|---|
| Spot repair (replace screws, re-seal laps, fix flashings) | The leaks are in a few places and rust is light. | Sealant smeared over dirt fails first; repairs need compatible materials. |
| Coat the whole roof (silicone, liquid polyurethane)Silicone coating Details →Liquid polyurethane Details → | The sheets are still sound but ageing has spread across the roof. | A coating alone does not fix a leaking roof: screws and laps are fixed first, and laps are reinforced with fabric. The roof is cleaned, rust is treated and adhesion is tested, and it must be dry. |
| Lay a sheet over it (mechanically fixed PVC / TPO)Sheet membrane Details → | You want a new waterproof layer while keeping the old roof. | It is fixed through to the purlins, and the structure must be checked for the extra load. |
| Re-roof | Rust is heavy and the sheets themselves have failed. | It is usually the biggest job, so it is chosen when the sheets themselves have failed. |
| Also cut the heat (reflective coating, spray foam under the roof)Spray foam insulation Details → | The building is also hot under the metal roof. | Heat control is combined with the leak repair, not a substitute for it. |
This is one example. We decide the actual work after seeing the roof.
The roof area, how many places leak, whether it is a spot repair or the whole roof, how far the rust has gone, and the height and access. Send photos of the roof and the leaks on LINE.
Coatings cannot go on when rain or condensation is likely, so the work is planned around dry spells. Fast-curing resins such as PMMA resist rain about 30 minutes after application in good conditions; they still go on a dry surface, and full cure takes longer.
No. The sources of the leak — screws, laps, flashings — are fixed first, then the roof is coated. Badly rusted sheets need replacing.
Send photos of the roof and the leaks, and where it drips inside. We check the site and propose the repair that fits.
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