Metal Roof Leaks | Fastener, Seam and Rust Repairs for Commercial Buildings

Why Is My Metal Roof Leaking?

The good news is that most metal roof leaks are fixable without replacing the roof. Here’s how we diagnose and repair them on warehouses and metal buildings across commercial roofing in San Antonio.

Signs Your Metal Roof Needs Repair

Look for these before the next big rain. Most can be seen from a roof hatch or the ground with binoculars:

• Water stains under panel laps, skylights or along the eave inside the building
• Loose or backed-out screws, often in rows along purlin lines
• Rust streaks below screws, laps and cut edges
• Separated seams or sealant squeezing out of laps
• Wavy panels (oil canning) or panels bending between supports
• Cracked or yellowed skylight panels
• Dried-out sealant around pipes, vents and curbs

Leaking Fasteners and Failed Washers

Problem	Cause	Fix
Overdriven screw	Crushed washer bulges and lets water in	Replace with correctly seated fastener
Underdriven or angled screw	Washer never sealed	Replace and seat properly
Backed-out screw	Thermal movement loosens it over time	Replace with a larger-diameter screw
Rusted screw	Wrong coating or dissimilar metals	Replace with compatible, corrosion-resistant fastener
Aged washer	Rubber dries and cracks with age and UV	Replace fastener and washer

Replacement screws should be one size larger in diameter than the original so they cut fresh threads in the existing hole, for example moving from a #14 to a #17 screw. Reusing the same size can leave a loose connection.

Fastener guidance: SFS, How to Replace Metal Roof Screws.

Seam, Lap and Flashing Leaks

• Side and end laps where panels overlap lose their sealant tape over time and let wind-driven rain in.
• Ridge caps, trims and transitions pull loose with movement.
• Penetrations such as exhaust fans, skylights and pipe flashings crack or separate.
• Gutters and valleys clog and back water up under panels.

These are repaired by re-sealing laps with compatible sealant and, often, a reinforcing fabric and coating, plus replacing failed trim and penetration flashings.

How to Find the Leak on a Metal Roof

Water travels along panel ribs and purlins before it drips, so the leak is often uphill of the stain. Roofers trace it by:

1. Marking the drip location inside and measuring to a fixed point (wall or column)
2. Checking every fastener, lap and penetration upslope of that point
3. Looking for daylight from inside on a sunny day
4. Water-testing small sections, starting low and working up, so only one area is wet at a time

Why Is My Metal Roof Dripping When It’s Not Raining?

That’s usually condensation, not a leak. Warm, humid indoor air hits the cold underside of the panels, often on cool mornings, and drips like a leak. It’s common in metal buildings with little or no insulation.

• Signs it’s condensation: drips on clear days, droplets across large areas, worse on cool mornings
• Fixes: insulation with a sealed vapor retarder on the warm side, better ventilation, controlling indoor moisture sources, or an anti-condensation coating on the underside
• Long-term fix: a retrofit roof with continuous insulation between the old and new panels

Rust and Corrosion Repairs

1. Remove loose rust by wire brushing or grinding.
2. Treat remaining rust with a rust-inhibitive primer.
3. Seal or patch thinned areas; replace panels that are rusted through.
4. Coat the area or the whole roof to stop further corrosion.

Why Metal Roof Repairs Fail

Most repeat leaks come from repairs that didn’t account for how metal moves. Avoid these common mistakes:

Mistake	Why it fails	Better approach
Caulk smeared over a leaking screw	Seals for a season, then cracks with movement	Replace the screw with an oversized fastener
Rigid patches on laps	Metal expands and contracts daily	Flexible sealant plus reinforcing fabric and coating
Sealant over dirt or rust	Doesn’t bond	Clean, wire-brush and prime first
Wrong metal or fastener	Galvanic corrosion	Use compatible, coated fasteners and metals
Patching only the visible spot	Water entered elsewhere	Trace the full water path

Repair, Restore or Replace?

Choose	When
Repair	Roof under about 15 – 20 years old, a few isolated leaks
Restore (coating system)	Many fastener and lap leaks, surface rust, panels still solid
Replace or retrofit	Panels rusted through, structural damage, or you need new insulation

Spot Repair vs Full Restoration Coating

	Spot repair	Full restoration coating
Scope	Specific leaks, fasteners and laps	Whole roof: all fasteners addressed, laps sealed, rust treated, coating applied
Cost	Per item	About $1.50 – $4.50 / sq ft for silicone; acrylic $0.50 – $2.00
Best when	Roof is young and leaks are isolated	Roof is aging with many fastener and lap issues
Result	Stops current leaks	Adds 10 – 20 years and a new warranty

Coating cost: Roofr (2026).

See metal roof repair and restoration and commercial metal roofing in San Antonio.

Preventing Leaks | Metal Roof Maintenance Schedule

When	Task
Twice a year (spring and fall)	Check fasteners, laps, trims, penetrations and gutters
After hail or high wind	Inspect for damaged panels, loose trim and lifted fasteners
Every few years	Re-seal laps and penetrations as sealant ages
Around 20 years for screws	Plan fastener replacement or a restoration

 

FAQs | Metal Roof Leaks

How often should metal roof screws be replaced?

Plan on it around 20 years. Screws past that age are near the end of their service life, and most won’t last past 30. Inspect them twice a year and replace any that are loose, rusted or have cracked washers.

Can a rusted metal roof be saved?

Usually, if the rust is on the surface and panels aren’t rusted through. Rust is removed, primed and the roof is coated. Panels with holes are replaced or patched first.

Does coating stop metal roof leaks at screws?

A restoration coating system seals around fasteners, but only after loose or failed screws are replaced or tightened. Coating over bad fasteners just hides the problem for a while.

Why does my metal roof leak only in wind-driven rain?

Wind pushes water sideways into laps, trims and ridge caps that stay dry in normal rain. It usually points to failed lap sealant or loose trim.

What is oil canning, and does it cause leaks?

Oil canning is visible waviness in flat areas of metal panels. It’s usually cosmetic, but if it comes with loose fasteners or panel movement, have the attachment checked.

What sealant is best for a leaky metal roof?

Use sealants rated for metal roofing, such as butyl tape at laps and polyurethane or silicone sealants at trims and penetrations, matched to any coating you’ll apply later. Avoid asphalt-based roof cement, which cracks on metal.

Get a Metal Roof Repair Quote

We’ll inspect fasteners, laps, trim and rust, then quote spot repairs and a full restoration side by side.

• Free roof assessment for metal buildings across San Antonio and the I-35 corridor, including metal roof repair in Schertz, Converse and Helotes

Book your free roof inspection in San Antonio or see metal building (PEMB) roofing.