Wall Trim · Metal building trim guide
Metal Outside Corner Trim: What It Is, How to Measure and Install It
Outside corner trim caps the outside corners of metal wall panels, sealing raw edges and giving the walls a clean, square finish.
Also called: outside corner, corner trim, corner flashing, outside corner flashing, corner cap
Metal outside corner trim is the bent L-shaped piece that wraps the outside corners of a metal building. Where a sidewall meets an endwall, the panels stop short and leave raw edges and open ribs. The outside corner covers that joint so the building looks sharp and stays tight.
Every enclosed shop, garage, barn or shed with metal walls needs it. This guide covers what outside corner trim does, where it goes, how to measure it with a real worked example, and how to install it so it sheds water for years.
What is metal outside corner trim?
Outside corner trim (also called corner trim or corner flashing) is a long piece of sheet metal bent to 90 degrees. One leg lies on the sidewall panels. The other leg lies on the endwall panels. Most have a small hem on each edge for stiffness and safety.
It does four jobs. It keeps wind-driven rain out of the corner. It closes the gap so wasps, birds and rodents can't get in. It covers cut panel edges that would otherwise rust or snag. And it gives the walls a clean, finished line.
Where outside corner trim goes on a metal building
It runs vertically on every outside corner, from the bottom of the wall up to the eave. A plain box building has four outside corners. An L-shaped building has five outside corners and one inside corner.
On a gable building, the corner trim stops at the eave height on all four corners. The triangle above the eave on each end wall is finished by rake trim, not corner trim.
- Enclosed carport or garage: all four corners once the walls go full height.
- Partially enclosed barn or carport: anywhere a side wall and end wall panel meet.
- Shop with a lean-to: the outside corners of the lean-to walls too.
- Open carport with no wall panels: no corner trim needed.
Outside corner trim sizes, gauge, profile and colors
Most metal outside corner trim is 26 gauge steel, the same as R-panel and PBR wall panel. Lighter 29 gauge trim exists for lighter panel systems. Legs are commonly around 4 in. on each side, but sizes vary by building and by panel maker.
You can get it in bare Galvalume or in painted colors. Most people match the trim color, not the wall color, so the corners frame the building. Pieces are typically 10 ft long. Ask us about longer lengths or cut-to-length pieces so each corner can be one piece. Custom bends are available if your corner isn't a true 90 degrees or you need a special leg size.
How to measure outside corner trim and how many pieces to order
Formula: wall height at the corner x number of outside corners = total feet. Add about 10% for laps and waste, then divide by the piece length and round UP to whole pieces. Every joint between pieces eats about 2 to 4 in. of length.
Then check it corner by corner: one full piece plus one short piece at most, never three scraps.
Worked example: a 30 x 40 gable building with 12 ft walls and a 3:12 pitch. It has 4 outside corners, each 12 ft tall. 4 x 12 = 48 ft. Add 10%: 48 x 1.10 = 52.8 ft. With 10 ft pieces, 52.8 / 10 = 5.3, so order 6 pieces.
Corner check: each corner gets one full 10 ft piece plus a short piece of about 2 ft 3 in. (the 2 ft left over plus a 3 in. lap). Four short pieces cut easily from two more 10 ft pieces. 4 + 2 = 6 pieces. The math checks out. If you can get 12 ft or longer pieces, you can skip the joint entirely.
How to install outside corner trim
- Install the base trim and the wall panels on both walls first. The panels should end close enough to the corner that the trim legs cover the cut edges by at least an inch.
- Hold the first piece at the bottom of the corner. It should cover the end of the base trim and stop even with the base trim's bottom edge. Check it for plumb.
- Fasten it with color-matched #14 x 7/8 in. lap (stitch) screws into the panel, or #12 tek screws into the corner post or framing. Space them about 12 to 24 in. apart on each leg, staggered side to side.
- Set the next piece above so it laps OVER the lower piece by 2 to 4 in. This is shingle-style: water runs over the joint instead of into it. A strip of butyl tape in the lap adds extra protection.
- At the top, the eave trim and rake trim should lap over the top of the corner trim. If the roof trim is already on, slide the corner up under it or notch it so it tucks in.
- Brush off all metal shavings the same day. Steel filings rust and leave orange stains on painted trim.
Common outside corner trim mistakes to avoid
- Measuring the end-wall corners to the peak. Corner trim stops at the eave; the rake trim covers the gable.
- Lapping upside down (lower piece over the upper piece). That funnels water right into the joint.
- Ordering by total feet only and ending up with a corner pieced from three short scraps.
- Letting the panels stop too far from the corner, so the trim leg can't cover the gap.
- Forgetting a wainscot color line. Two-tone walls may need corner trim in two colors or one trim color top to bottom. Decide before you order.
- Leaving drill shavings on the paint.
What to order with outside corner trim
- Base trim (rat guard) at the bottom of the walls
- Eave trim and rake trim that lap over the top of the corners
- Inside corner trim if the building has an L-shape or a lean-to
- Color-matched lap screws and tek screws
- Butyl tape or sealant for the laps
- Inside foam closures for the base of the wall panels
- Touch-up paint in your trim color
Get metal outside corner trim in Houston from Ironrod Steel
Ironrod Steel rolls its own R-panel and PBR in-house and supplies matching metal outside corner trim, closures, screws and butyl tape. Send us your building size and a few photos and we'll help you build your full trim list. Pick up at 8122 Hillsboro St, Houston, TX 77029, or ask about delivery across Houston and Southeast Texas. Call or text (281) 902-7619.
Outside Corner Trim FAQ
How long is metal outside corner trim?
It typically comes in 10 ft pieces. Longer or cut-to-length pieces are often available, so ask. On walls taller than one piece, you lap two pieces with the upper one over the lower one.
Do I need corner trim on a carport?
Only if the carport has wall panels that meet at a corner. An open carport with just a roof doesn't need it. Once you add full or partial side and end walls, every outside corner needs trim.
What screws hold corner trim on?
Use color-matched #14 x 7/8 in. lap screws into the panels or #12 tek screws into the framing. Space them about 12 to 24 in. apart on each leg. Your panel maker's spacing guide always wins if it says different.
Should corner trim match the walls or the trim color?
Most people use the trim color so the corners match the eave, rake and door trim. That frames the building. Matching the wall color makes the corners blend in. Either works; it's your call.
What is the difference between outside and inside corner trim?
Outside corner trim wraps a corner that points out, like the four corners of a box. Inside corner trim fits a corner that points in, like where a lean-to wall meets the main building. They are bent differently and are not interchangeable.