How to Hem, Fold and Bend Metal Roof Panel Ends: Drip Hems, End Dams and Notches

Step by Step

1. 1Step 1: Decide which fold the detail calls for

   A drip hem at the eave is a small fold, about 1/2 to 1 inch, turned back under the panel. An end dam at the ridge is an upward bend of about 1 inch, sometimes with a second return. A cut edge at a valley is hemmed about 1/2 to 1 inch. The manual gives the size and direction.

   Always fold on the side that hides the raw edge and leaves the finished face up.

2. 2Step 2: Mark the fold line and set up the support

   Use a square and measure the same distance from the end along the whole width. On a ribbed panel, mark each rib and each flat. A fold that wanders shows at the eave as a wavy line.

   Clamp the panel flat or support it on both sides of the fold line. Working on a bench or sawhorses is much easier than on the roof. Padded supports protect the finish.

3. 3Step 3: Notch the ribs so the flat can fold

   On ribbed and standing seam panels, the ribs stand in the way of a fold across the panel end. Cut a vertical notch at each side of a rib or seam leg, and cut the rib top back by the width of the fold. The flat between can then fold neatly. On standing seam, notch the seam leg to the marked line and avoid cutting into the flat.

   Make notch cuts square and stop exactly at the fold line. Overcutting leaves a hole that water can pass. Use offset snips for a tight fit in corners. A nibbler makes neat notches, and abrasive cutters should not be used. See cutting metal roof panels.

   Watch out: Do not cut past the fold line. A notch that is too deep opens a gap at the end dam where water and snow can enter.

4. 4Step 4: Start the bend with a seamer and work across the flat

   Put the jaws on the fold line with the edge of the panel inside them. A hand seamer is wide enough to make a short bend of 3 or 6 inches, so work from the centre of the flat toward each end, overlapping each bite by half. Keep the pressure steady so the bend is even.

   A quick single pass with too much force stretches the paint and can crack it along the fold. Start the bend slowly and in stages, and keep the tool square to the edge.

   Tip: Warm panels bend easier. On a cold morning, a few minutes in the sun reduces paint cracking at the fold.

5. 5Step 5: Close the fold to a hem or set the end dam angle

   For a hem, bend to about 90 degrees, then close to 180 degrees with the seamer, leaving a small rounded nose rather than a sharp crease. For an end dam, bend up to about 90 degrees and check the height against the gauge in the manual. Use a wood block and a rubber mallet to flatten, never a steel hammer directly on the panel.

   Check that the fold is straight along the whole width. A gap at one end means the bend angle is inconsistent. Pull it tighter with the seamer.

6. 6Step 6: Seal the notches and dress the ends

   Where ribs are notched, press a small piece of butyl tape into the corner, or dab sealant, so wind-driven rain does not find the gap. Keep the sealant small and neat, since it shows on the finished roof.

   File off burrs and touch up any exposed steel and any cracked paint with matched paint. Test-fit the end against the closure or trim before fastening.

7. 7Step 7: Dry fit before fastening

   A hem that is too wide will not slide into the trim, and an end dam that is too tall will foul the ridge cap. Adjust now, since after fastening it is difficult. Keep the first finished panel as a template for the rest in the run.

Why Paint Cracks When You Bend

Using a Brake for Wide Panels

Common Mistakes

• Bending too fast, which cracks the paint along the fold.
• Cutting notches past the fold line, leaving a hole.
• Uneven hems that wander across the panel width.
• Using a steel hammer directly on the panel, which dents and scars the finish.
• Hemming before dry-fitting, then finding the panel does not fit the closure.
• Folding on the wrong side, leaving the raw edge exposed.
• Skipping touch-up paint on cracked fold lines.