Corrugated metal roof types: the main profiles and where leaks start
Most corrugated roofs leak at the fasteners and laps, not in the middle of the sheet. Here is how the types differ and what to look for from the yard.
Corrugated metal roof types come down to three choices: the profile of the ridges, the metal, and how the sheets are fastened. The last one matters most for leaks. Most trouble starts at screws and overlaps, not in the flat of the sheet.
The main profiles
The classic wave is the rounded corrugation. It is the old farm-shed look and still common. Next is the angular rib, often called R-panel, with flat pans between raised ribs. Then comes standing seam, where raised seams hide the fasteners.
Each sheds water the same way: along the channels, down to the eave. They differ in how many holes go through the metal.
Exposed fastener or hidden fastener
Wave and R-panel sheets are usually screwed straight through the face. Each screw has a small rubber washer. Those washers dry out and crack. Then water follows the screw into the deck.
Standing seam clips hold the panel from below, so the face has no holes. That removes the most common leak point. It also changes the job you ask a roofer to do, since the clips need to be installed correctly.
Steel, aluminum and coatings
Steel is the usual choice and carries a zinc or paint coating. When the coating wears through, rust starts at cut edges and scratches. Aluminum does not rust, but it dents more easily. Coating type and color affect how fast the panel ages in sun.
Where leaks start
- Screws with cracked or backed-out washers.
- Laps between sheets, especially on low slopes.
- Flashing at walls, chimneys and pipes.
- Ridge caps and closure strips with gaps.
- Cut edges and scratches that have started to rust.
What you can check from the ground
Use binoculars. Look for rust streaks below screw lines, panels that have lifted or waved, and gaps at the ridge. Check the gutter for grit from a wearing coating. In the attic, look for daylight, dark stains and condensation on the underside of the metal. Beads of moisture are not always a leak. Cold metal can drip from condensation, as our guide to attic condensation explains.
Why we do not walk it
Metal roofing is slippery, especially when damp or dusty, and walking can dent the ribs. Retightening screws is a job for someone trained to work at height. See working at height safely.
Repair, recoat or replace
If the sheets are sound and only the washers are tired, a roofer can often re-fasten and reseal. If rust has gone through the panel, the sheet needs replacing. See repair or replace for the questions that decide it, and metal roof lifespan for how long to expect.
Ask your roofer
- Are the screws or the washers the problem?
- Is the coating failing, or only the fasteners?
- Will you photograph the work?
We do not publish prices.
Frequently asked questions
What are the main corrugated metal roof types?
Rounded wave corrugation, angular R-panel ribs and standing seam. They differ in profile and in how the sheets are fastened.
Where does a corrugated metal roof usually leak?
At screws with worn washers, at overlaps between sheets, and at flashing around walls, chimneys and pipes.
Is standing seam better than exposed fastener?
It has no screw holes in the face, which removes the most common leak point. It still needs correct installation.
Can I walk on a metal roof to tighten screws?
We advise against it. Metal is slippery and ribs dent. Leave the work to a licensed roofer.
Why is my metal roof dripping inside with no hole?
It may be condensation on the cold underside of the metal, not a leak. Check the attic ventilation first.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NRCA. National Roofing Contractors Association
- US OSHA. 1926.501 — Duty to have fall protection (OSHA)