Wall Trim · Metal building trim guide
Metal Building Head Trim (Drip Cap) for Doors and Windows
Head trim, also called header trim or drip cap, runs across the top of doors and windows and kicks rain away.
Also called: header trim, drip cap, door head trim, window head flashing, head flashing
Metal building head trim is the piece that sits across the top of every door and window. Its job is to catch the water running down the wall above and throw it clear of the opening. People also call it header trim or drip cap, and on a metal shop it's the difference between a dry door and a rusty, dripping one.
Rain in Houston comes sideways and comes hard. A head trim that's lapped right keeps that water out of your door frame and off your floor. This guide covers what head trim is, how to measure it with a real example, and the lap order that makes it work.
What is metal building head trim?
Head trim is sheet metal bent to fit across the top of an opening. A back leg tucks up behind the wall panel above. A face covers the header. A drip edge at the bottom kicks out so water falls clear of the door or window instead of running into it.
It sheds water, covers the cut edge of the panel above the opening, hides the header tube, and gives every opening a sharp, finished top line.
Where head trim goes on a metal building
Every opening should have a square-tube header across the top. That header is what the head trim fastens to. For roll-up doors, also check headroom: doors up to 10 x 10 ft generally need at least 12 in. above the opening for the coil, and larger doors need more. Confirm with your door supplier.
- Over every roll-up door, across the header at the top of the opening.
- Over walk doors (36 x 80 in. and similar).
- Over windows, such as 24 x 30 or 30 x 36 in. units.
- Over framed openings and frame-outs, even if no door is installed yet.
Head trim sizes, gauge, profile and colors
Most head trim is 26 gauge steel to match R-panel and PBR walls. 29 gauge versions exist for lighter systems. Face size, back leg height and drip kick vary by panel maker and by how deep your header and door frame are, so tell us what you're building.
It comes in Galvalume or painted colors, usually matching jamb and corner trim. Pieces are typically 10 ft long. Wide doors need longer pieces so there's no joint over the door, so ask us. Custom bends are available.
How to measure head trim and how many pieces to order
Formula: for each opening, head trim length = opening width + about 4 in. on each side so it laps over the jamb trim. Plan one piece per opening, then add up the pieces. Cross-check by adding 10% to the total feet and rounding UP.
Worked example: a 30 x 40 gable building with 12 ft walls and a 3:12 pitch, with one 10 x 10 ft roll-up door, one 3 x 7 ft walk door and two 30 x 36 in. windows (2.5 ft wide).
Roll-up: 10 ft + 8 in. = 10 ft 8 in. That's longer than a 10 ft piece, so order one 12 ft piece (or a custom length) to avoid a joint over the door. Walk door: 3 ft + 8 in. = 3 ft 8 in. Windows: 2.5 ft + 8 in. = 3 ft 2 in. each.
The three short heads total exactly 10 ft, with nothing left for cutting. So use two 10 ft pieces for them. Order: one 12 ft piece plus two 10 ft pieces. The 10% check agrees: about 20.7 ft x 1.10 = 22.7 ft, or three pieces.
How to install head trim
- Install the header tube and the jamb trim on both sides of the opening first.
- Cut the head trim to length. Notch and fold the ends down so they form small end dams and lap over the tops of the jamb trim.
- Set the head trim on the header with the drip edge out. Check it for level.
- Fasten the face or back leg into the header with color-matched #12 tek screws about 12 in. apart. Keep screws out of the drip edge.
- Run a strip of butyl tape along the back leg where the wall panel will lap over it.
- Many crews add an inside foam closure on the head trim so the ribs of the panel above are filled.
- Hang the panel above so it laps OVER the head trim's back leg. Water runs down the panel, onto the trim and off the drip edge. Brush off all shavings.
Common head trim mistakes to avoid
- Putting the head trim on top of the wall panel instead of tucking it behind. Water then runs behind the trim.
- Cutting it flush with the opening so it doesn't lap over the jamb trim.
- Splicing two short pieces over a wide door. Get one long piece.
- Leaving out the header tube, so the trim sags and has nothing to screw to.
- Forgetting roll-up door headroom when choosing wall height.
- Screwing through the drip edge, which leaves a leak right over the door.
What to order with head trim
- Jamb trim for the sides of each opening
- J-trim for window sills and cut edges
- Inside foam closures for the panel ribs above the opening
- Butyl tape or sealant
- Color-matched tek screws and lap screws
- Touch-up paint
Get metal building head trim in Houston from Ironrod Steel
Ironrod Steel rolls its own R-panel and PBR and supplies matching metal building head trim, jamb trim, J-trim, closures, screws and butyl tape. Send us your door and window sizes plus 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.
Head Trim (Header Trim / Drip Cap) FAQ
What is head trim on a metal building?
Head trim is the drip cap that runs across the top of a door or window. It tucks behind the wall panel above and kicks water away from the opening. It's also called header trim.
How long should head trim be?
Make it the opening width plus about 4 in. on each side, so it laps over the jamb trim. A 10 ft roll-up door needs about 10 ft 8 in., which means a 12 ft piece or a custom length.
Does head trim go over or under the wall panel?
Under. The back leg of the head trim goes behind the panel above, and the panel laps over it. That way water running down the wall lands on the trim and drips off.
Do roll-up doors need head trim?
Yes. The roll-up door mounts behind the opening, and the head trim covers the header and the cut panel edge across the top. Without it, water runs straight into the top of the door.
Can I use J-trim instead of head trim?
Some builders do. Head trim sheds water better because of its drip edge. If you use J-trim on top, lap it over the side pieces so water can drain.