How to Install Metal Rake (Gable) Trim on a Metal Roof

Step by Step

1. 1Step 1: Check the gable edge and snap a reference line

   Rake boards are often wavy. Run a string along the edge and find high and low spots. Shim or pack the trim, or set the reference line on the roof instead of the board, so the panel line is true. The gap between the panel and the trim should be uniform along the whole rake.

   Replace any rotted rake board or barge board first. Metal trim over rot hides the damage and gives no holding power for screws.

2. 2Step 2: Run self-adhered membrane and underlayment correctly at the rake

   At the rake, water flows across and down the roof toward the eave, so the underlayment goes under the trim at the gable edge. That is the opposite of the eave, where the underlayment laps over the drip edge. Run membrane or underlayment right to the rake edge, then fasten the trim through it.

   Many details add a strip of self-adhered membrane over the trim's roof leg, or along the edge, to seal fasteners. Follow the panel manual. See metal roof underlayment.

3. 3Step 3: Fit the first section of trim from the eave up

   Set the trim with its vertical leg covering the face of the rake board and the roof leg flat on the deck. Start at the eave so that each upslope piece laps over the piece below it, as with shingles. Lap 2 to 4 inches, or the amount in the manual, with a bead of butyl tape between sections.

   Keep the trim straight and its bottom edge at the same distance from the fascia at both ends. Check with a string. A trim that drifts towards the roof at one end looks crooked from the ground.

4. 4Step 4: Fasten the trim at the right spacing and place

   Use trim screws with washers, placed on the flat part of the roof leg that the panel will cover, never on the vertical face. Fastener spacing is commonly 12 to 24 inches on centre, and the first few feet from the eave and ridge get closer spacing because wind loads are highest at the corners. Follow the engineering in the panel's manual.

   Also fasten the drip leg along the face at the listed spacing if the trim requires it, and use ring-shank nails or screws long enough to reach solid wood. See metal roof screws.

   Watch out: A rake is where screws pull out first in storm wind. Do not skimp on spacing or fasten into underlayment alone.

5. 5Step 5: Close the panel edge with closures, tape or channel

   Exposed-fastener panels are closed with foam closures cut to the rib profile, sitting under the last panel edge and against the trim. Standing seam and snap-lock panels engage a receiver or J-channel, or sit on a bed of tape, depending on the profile. The last panel is usually cut to width, so its edge stays straight and the cut edge is hidden by the trim.

   Do not block the panel's ability to expand and contract. Closures and channels must hold the edge without pinching it. See thermal movement in metal roofs.

6. 6Step 6: Finish the ends at the eave and ridge

   At the eave, the rake trim often ends over the eave trim with a cut and fold or an end cap. At the ridge, it runs up under the ridge cap or is capped with a matching piece. Bend the ends using a hand seamer and seal any open corners with sealant and a rivet or screw. See hemming and bending panel ends.

   Check the corner closely, since it is where eave trim, rake trim and panel all meet and where most gable leaks start.

Gable Overhangs and Wind

Rake Trim Versus Barge Board

Common Mistakes

• Laying the trim under the underlayment at the rake, which lets water run behind it. At the rake the trim goes on top.
• Wrong lap direction, which sends water into the joint instead of over it.
• Skimping on fastener spacing at the corners, where wind uplift is greatest.
• No closures or tape under the panel edge, allowing wind-driven rain to enter.
• Fixing trim to a rotten rake board, which gives no holding power.
• Leaving the ends at the eave and ridge open.