Metal Roof Maintenance: Fasteners, Sealant, Rust, and Scratches

Metal roof maintenance is a short list: the rubber washers on exposed screws, the sealant at laps and flashings, scratches that reach bare metal, and any spot where another metal touches or drains onto the panels. Each is where water or corrosion starts. You can watch for changes from the ground with binoculars or from a properly set ladder at the eave; a close check of screws, washers and coatings across the roof is work for the installer or a roofer.

Maintenance means watching those few places on a schedule and sending what you find to the installer before a small issue becomes a leak.

Where a Metal Roof Starts to Fail

A metal panel is a continuous sheet. Water gets in only where something interrupts it: a screw through the panel, a lap where two panels overlap, a flashing at the ridge, eave, wall or pipe, or a cut edge where the steel core is exposed. Corrosion starts in the same places, plus anywhere the protective coating has been scratched through.

Wind works on the attachment. FEMA’s Hurricane Ike Recovery Advisory on metal roof systems in high-wind regions (February 2009) recommends practices for designing and installing metal roofs where wind is severe. In that kind of wind, the panels, clips and fasteners are what hold the roof down. On an existing roof, that means a loose screw or a lifted seam is a wind problem as well as a leak problem.

Sealant is the other weak point, because it holds only as long as its bond does. Where a metal roof depends on sealant, the joint needs regular checks; what sealant can and cannot do explains the limits.

What to Inspect on Your Panel System

Your checks depend on how the panels are attached. Exposed-fastener panels are screwed through the face, so every screw is a potential leak point. Standing-seam panels are held by concealed clips or by fasteners through a flange that the next panel’s seam covers, so the seams and the trim matter more. If you are not sure which you have, the types of metal panel systems are described on the metal roofing page.

Do these checks twice a year. NRCA guidance points to that schedule for shingle damage: its consumer resources page says twice-yearly inspections “often can uncover cracked, warped or missing shingles,” and the same rhythm is a reasonable one for washers and laps; the seasonal maintenance routine puts both on a calendar. Add a look after any storm with high wind or hail.

Look hardest at the laps on a low-slope lapped-panel roof. International Residential Code (IRC) section R905.10.2, as printed in the 2021 Seattle Residential Code, Chapter 9 (your town’s edition may differ), sets a minimum slope of 3:12 for lapped, nonsoldered-seam metal roofs without applied lap sealant and allows 1/2:12 with it. On a lapped roof below 3:12, the sealant in those laps is part of what keeps water out, not a backup.

When you use a ladder, keep at least two ladder lengths of clear space between it and any overhead line, the spacing the CPSC gives in Ladders and Electricity Don’t Mix; the guide to setting and securing a ladder covers angle and footing. Do not walk on the panels. They are slippery, they dent, and a foot in the wrong place can bend a rib or crack the sealant in a lap. Skip eave checks while snow or ice sits on the roof, because it can slide off metal panels all at once.

Screws and Washers: Tighten, Replace or Upsize

On an exposed-fastener roof, the rubber washer under each screw head is what seals the hole. It works by being compressed just enough. A screw driven too hard squashes the washer until it splits; a screw left too loose never compresses it; a screw driven at an angle leaves a gap on one side. Sun and age harden the rubber over time, and a hardened washer stops sealing even if the screw is tight.

That gives the installer three choices at each problem screw:

• Retighten, when the screw has backed out slightly, the hole is sound and the washer is still soft. The screw is snugged until the washer is compressed, not crushed.
• Replace, when the washer is cracked, hardened or missing but the hole is sound. A new fastener with a new washer goes into the same hole.
• Upsize, when the hole is stripped or enlarged. The panel maker specifies what goes into a damaged hole, which may be a larger-diameter screw. Ask for the maker’s guidance rather than a screw picked off a store shelf.

The fastener itself matters as much as the washer. Use the type, size and coating the panel maker specifies, because a fastener of a different metal or coating can corrode where it meets the panel.

All three choices are made on the roof, so they belong to the installer. Your part is to spot backed-out screws and cracked washers with binoculars, photograph them, and send the photos.

Scratches, Cut Edges and Rust Spots

Painted steel roofing panels are protected in layers: a metallic coating on the steel, and a paint finish on top. A scratch through the paint alone is cosmetic. A scratch through both layers exposes bare steel, and that is where rust can start. Cut edges, at the eaves, around penetrations and wherever a panel was trimmed, expose the steel core by design, so look at them closely.

Touch-up is a judgment call for the installer or panel maker. The right product is a touch-up paint made for that panel’s coating system, applied only to the damaged spot as the maker instructs. Wire brushing or grinding around a scratch removes good coating along with the rust, and paint that does not match the coating system can peel. Ask the installer what the maker approves before anything is applied.

Separate surface rust from rust-through. A small orange spot at a scratch is an early warning. Flaking metal, holes, rust streaks running from a lap, or rust around a run of screws means the corrosion has gone further, and the installer needs to see it with the warranty in hand. If rust worries you as a reason to avoid metal in the first place, the evidence on metal roof rust addresses it.

Where Other Metals Touch or Drain Onto the Panels

Some corrosion comes from neighbors. The Oregon State University Extension page on controlling roof moss warns that zinc sulfate moss products should not be used on roofs with copper gutters, downspouts or flashing, because “zinc corrodes copper.” That is one documented case of one metal attacking another, and it is a good reason to keep moss products off a metal roof unless the panel maker allows them.

Ask the same question wherever another metal touches the panels or sends water onto them: copper flashing, a copper or galvanized gutter, an antenna mount, a satellite bracket, or fasteners left from earlier work. Ask the panel maker or installer whether each pairing is compatible with your panels’ coating. Keep wet debris and leaves from sitting against panels, flashing and fasteners, since standing moisture is what lets contact corrosion work.

Salt air adds a corrosion risk of its own. If you live near the coast, roofing choices for salt air covers the materials and details chosen for it.

What a Maintenance Log Shows Over Time

A single check tells you what the roof looks like today; a dated log tells you what is changing, and change is what the installer needs to see. The log below is invented, for an exposed-fastener roof checked from the ground and from a ladder at the eave.

A standing-seam log would track the rows from the table above instead: seams, closures and trim. Either way, the line that matters is the third column. A finding that repeats unchanged can be watched; a finding that grows, or a new one at a lap or flashing, goes to the installer with its photos.

Maintain It Yourself or Call the Installer?

Do the visual checks yourself: binoculars from the ground twice a year and after storms, a ladder at the eave for a closer look at laps and gutters, and a photo record of anything that changes. Call the installer for any loose or missing fastener, a cracked or hardened washer, a lap where sealant has opened, rust that has gone past a surface spot, a dent or lifted seam after a storm, or a leak inside.

This season, scan the screws and laps with binoculars, photograph any rust or backed-out screw, and send the photos to the installer together with the panel warranty.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• Metal Roof Systems in High-Wind Regions, Hurricane Ike Recovery Advisory, Federal Emergency Management Agency (via DOE Building America Solution Center)
• Resources (warranties, maintenance, weather events), National Roofing Contractors Association
• 2021 Seattle Residential Code, Chapter 9: Roof Assemblies, City of Seattle, Department of Construction and Inspections
• Ladders and Electricity Don’t Mix (Publication 5060), U.S. Consumer Product Safety Commission
• How to control roof moss and prevent long-term damage, Oregon State University Extension Service