What causes a metal roof to leak?
Metal roofing comes in two broad families. Exposed-fastener panels, often called R-panel or corrugated, are screwed through the face of the metal into the purlins or deck, with a rubber washer under each screw head sealing the hole. Standing seam roofs hide the fasteners under raised seams that lock or snap together, so the panel face has no holes at all.
Either way, the panels themselves seldom wear out first. Leaks come from the parts that join, seal and finish the roof: thousands of screw washers, ridge caps, eave and rake trim, the flashing around vents and skylights, and the overlaps between panels. Each of those is a small seal doing a big job.
Metal roofs are a familiar sight on the mainland. The canal homes of Grand Cay Harbour on Moses Lake were built with metal roofs, and barns, shops and many houses across Hitchcock and Santa Fe use metal too. The way metal fails is predictable, which makes these leaks very repairable.
How a roofer fixes a metal roof leak
On exposed-fastener roofs, the most common repair is a fastener change. The roofer removes screws with cracked or flattened washers and drives new gasketed screws, using a slightly larger diameter where the old hole has wallowed out. On older roofs, a full re-screw of the field may make more sense than chasing individual leaks.
Laps and seams are cleaned and resealed with butyl tape or sealant designed for metal, and loose seams are re-fastened with stitch screws. Ridge caps and trim are pulled, the closure strips beneath them are replaced where they have deteriorated, and the pieces go back with fresh sealant and fasteners.
Around vents, the roofer often replaces a cracked pipe boot with a flexible metal-roof boot shaped to the panel profile, sealed and screwed to the ribs. Skylight curbs and wall transitions get new flashing.
Where rust has started, light surface rust is cleaned and coated. A section rusted through is cut out and a new panel installed. On standing seam roofs, damaged seams are re-crimped or the affected panel is replaced, which takes a crew familiar with that profile.
Signs of a leaking metal roof
- Drips or stains that line up with fastener rows
- Rust rings around screw heads
- Screws backed out or missing, visible from the ground
- Lifted or bent trim at the eaves and rakes
- Gaps or loose fasteners at ridge caps
- Water spots on ceilings after wind-driven rain
- Rust streaks running down from cut edges or overlaps
- Drips on cool, humid nights with no rain, a sign of condensation
Why metal roofs leak on the Gulf Coast
Heat movement comes first. A metal panel expands in the afternoon sun and shrinks after dark, every day of the year. Over time that motion works screws loose and stretches the holes around them, and the rubber washers crack from both the movement and the sun.
Salt in the air is the second factor. Homes close to Galveston Bay and Moses Lake breathe salty air, and salt accelerates corrosion wherever the protective coating is broken: cut panel edges, scratches from installation, and carbon steel screws that were not rated for coastal use.
Wind is third. Trim at the edges catches gusts, and once a rake trim lifts, rain blows straight into the opening. Storms also drive debris that dents and scratches panels.
Installation errors account for many early leaks: screws driven at an angle, screws placed in the panel flat instead of where the manufacturer specifies, missing closure strips under the ridge, or laps facing the wrong direction for the prevailing wind.
Last, condensation masquerades as a leak. On humid nights, warm air meets cool metal and drips form on the underside. Without proper underlayment or ventilation, that water soaks into insulation and ceilings and looks just like a roof leak.
Safe checks for metal roof owners
- Use binoculars from the yard to scan for backed-out screws, rust rings and lifted trim.
- Note whether drips happen only after rain or also on dry, humid mornings.
- In the attic or shop, look for daylight at screw holes and wet spots on the underlayment.
- Check gutters and the ground below the eaves for screws or trim pieces.
- Photograph each stain and where it sits relative to the panel ribs.
Metal roofs are slippery when wet, dusty or even lightly dewy, and panel edges are sharp. Leave walking the roof to a roofer with fall protection and soft-soled shoes.
The roofer's visit, step by step
- Identify the panel system. Exposed fastener or standing seam, and which profile, decides the parts needed.
- Inspect inside. Under-side staining, rusted screw tips and wet insulation narrow the area.
- Check fasteners and laps. The roofer looks at washers, seams and overlaps above the wet area.
- Check trim and penetrations. Ridge, eaves, rakes, boots and skylights are inspected.
- Rule out condensation. Underlayment and ventilation are checked if drips appear without rain.
- Scope and repair. You get photos and a written plan, then fasteners, sealant, trim or panels are replaced.
Factors that shape a metal roof repair
| Factor | Effect on the job |
|---|---|
| Panel type and profile | Matching panels and boots depends on the exact profile. |
| Fastener condition | A few bad screws versus a full re-screw of the roof. |
| Rust extent | Surface rust is coated; rust-through means new panels. |
| Trim and closures | Removing and refitting ridge and edge trim adds steps. |
| Building type | Houses, barns and shops differ in height, access and insulation. |
When to treat it as urgent
A storm that lifts or tears metal panels needs quick attention, since a loose panel acts like a sail and can damage the rest of the roof in the next gust. The same goes for steady drips over electrical equipment, a garage door opener or a panel in a shop building.
If loose metal is flapping, keep people and vehicles clear of the eave below, because pieces can come off in wind.
Repair, re-screw or replace?
Three paths come up on almost every metal roof call, and the right one depends on how widespread the wear is. A spot repair suits a roof where one area, such as a ridge cap or a single pipe boot, has failed while the fasteners elsewhere still hold tight with soft, intact washers.
A full re-screw suits an exposed-fastener roof that is otherwise sound but old enough that washers everywhere are hard and cracked. Replacing every screw at once stops the cycle of new drips appearing in a different row after each storm, and it is far less disruptive than new panels.
Replacement enters the conversation when panels are rusted through in several places, when the coating has worn off across large areas near the coast, or when storm damage has bent and torn many sheets. Even then, a roofer may suggest replacing only the worst slope if the rest of the roof is in good shape.
Whatever the path, ask what fasteners and sealants will be used. Near the bay, coastal-rated screws and sealants made for metal roofs hold up better than general hardware-store products, and that choice decides how long the repair lasts.
Metal roof questions
Why does my metal roof leak if the panels look fine?
Most metal roof leaks come from fasteners, trim and seams rather than the panels. Rubber washers under the screws dry out and crack, and flashing joints open as the metal moves with heat.
Can I just tighten the screws?
Overtightening crushes the washer and can make the leak worse. Worn screws are usually replaced with new gasketed fasteners, sometimes one size larger if the hole has stripped.
Is it a leak or condensation under the metal?
Condensation forms on the underside of the metal on cool, humid nights and drips even without rain. A leak shows after rain. Missing or torn underlayment makes condensation much worse.
Does salt air ruin metal roofs?
It speeds corrosion at cut edges, scratches and fasteners, especially on homes close to the water. Coated panels hold up well when cut edges and screws are maintained.
Can a rusted panel be patched?
Surface rust can be cleaned and coated. A panel rusted through is usually replaced, since patches on thin metal rarely last.
Do standing seam roofs leak?
Less often, since the fasteners are hidden, but seams can be damaged by wind or poor installation, and the trim and penetrations still need attention.
Related pages
Vent pipes and skylights through metal need their own seals, and the flashing and vent guide goes into those details. If panels were lifted in a storm, read the storm damage page before any permanent repair.
Metal barns and shop buildings are a big part of the calls from Hitchcock. Back on the home page, the leak tracer helps match the drip pattern to its source.