How do you replace the trim around a garage door?

The four parts people call garage door trim

Four separate pieces sit around a garage door opening, and homeowners call all four of them trim. Sorting out which one you are looking at is most of the job, because two of them are an afternoon with hand tools and one of them holds the door up.

• Stop molding is the narrow strip inside the opening that the closed door presses against. It usually carries the rubber or vinyl weatherseal along its edge.
• Brickmold, also called casing, is the wider decorative trim on the outside wall that frames the opening.
• Header flashing is the metal above the opening, tucked behind the siding or the housewrap, that pushes water out past the trim below it.
• Jamb boards are the structural lumber behind all of it. The door's vertical track bolts to them.

Three quick tests sort them out. If you can see it standing in the driveway, it is brickmold or flashing. If the closed door touches it, it is stop molding. If a track bracket is lag-screwed into it, it is a jamb, and it is not trim at all.

Stop molding: the piece you will replace most often

Replace stop molding when the weatherseal is torn, the wood is soft at the bottom, or you can see daylight around the closed door from inside the garage. This is the most common garage door trim job and the easiest one to get right.

Stop molding is nailed to the face of each side jamb and across the header, then the door closes against it. Clopay's residential installation instructions put it plainly: "Door stop molding should be temporarily but securely nailed to edges of jambs and flush with inside framing." The same document notes that the rough opening is measured without it, since "Rough opening (framed opening without stop molding) = door size." The stop sits inside that opening and laps over the door face.

The closed door is your jig. Work in this order:

1. Close the door and disconnect nothing. You are not touching springs or track.
2. Pry the old stop off from the outside edge with a flat bar. It is face-nailed, so it comes off in one or two pieces.
3. Cut the new stock so the two side pieces run from the floor to the header, and the header piece runs across the top between them.
4. Hold each new piece against the closed door so the weatherseal just compresses against the door face. Snug, not squeezed.
5. Nail into the jamb roughly every 16 inches, then open and close the door once by hand before you drive the last nails.

The classic mistake is setting the stop too tight. A stop crowded against the door drags on every cycle, wears the seal early, and makes the opener work harder. Loose is easier to fix than tight, so err loose and adjust. Stop molding with the weatherseal already bonded to it is sold as a single unit, which Clopay lists as an option, and buying it that way gets the seal geometry right.

Brickmold and casing: the exterior trim you can replace yourself

Replace brickmold when the bottom several inches are soft enough to push a screwdriver into, when the paint film is the only thing holding the shape, or when the joints have opened far enough to hold standing water. It is a straight swap and it does not touch any door hardware.

Brickmold comes in standard milled profiles. The millwork manufacturer Metrie lists 2 inches as the most common face width, with 1-1/2 inch and 1-1/4 inch also widely sold. Measure the face width of what is on the house before you buy, because a mismatched width leaves a visible reveal line where the old paint stopped.

The work itself: cut the paint and caulk line with a utility knife so the siding does not tear, pry the old piece free, pull the nails through from the back rather than hammering them out the face, cut new pieces to length, prime every surface including the cut ends before installation, fasten with hot-dipped galvanized or stainless nails, then caulk the joint where the trim meets the door frame.

Two details decide whether the new trim lasts: prime the end grain, and keep the bottom end from sitting in water on the slab. An unsealed cut end is an open straw, and the slab is where wood trim fails first.

Header flashing: the piece above the opening that decides how long the trim lasts

Header flashing is required, not decorative, and it belongs behind the wall finish rather than on top of it. Section R703.4 of the International Residential Code requires approved corrosion-resistant flashing at exterior window and door openings, and also requires it "continuously above all exterior projecting wood trim." Brickmold is projecting wood trim, so the flashing goes above the brickmold, not stuck to it.

The code also sets where the water has to end up: "Flashing at exterior window and door openings shall extend to the surface of the exterior wall finish or to a listed water-resistive barrier." In plain terms, water running down the wall has to be handed off to the outside face of the siding or to the housewrap, and never behind the trim.

This is why some brickmold rots twice. If the flashing was left out, installed upside down, or lapped over the siding instead of under it, every rain sends water behind the trim and into the jamb. New brickmold on bad flashing is new brickmold that rots on the same schedule as the old one. If you pull the trim and find dark staining or crumbling sheathing behind it, the flashing is the actual repair, and that means opening the siding above the opening. That is a siding job, not a trim job.

Jamb boards: the one you should not touch

Do not treat a jamb board as trim. The vertical track bolts to the jamb, and the door hangs on the vertical track, so the jamb is carrying the door every second it is not resting on the slab.

DASMA Technical Data Sheet 156 lists what that framing has to hold: "the weight of the door, track and spring assemblies," "torque generated by the counterbalance system," "wind load forces," and "vibration caused by door operation." Clopay's manual is blunter about the consequence of getting it wrong: "Do not attach any brackets directly to drywall or sheetrock. All track brackets, flag brackets and spring brackets should only be attached directly to 2 inch by 6 inch wood jambs. Otherwise, brackets could pull out of the drywall with dangerous force."

The dimensions are specified, not improvised. TDS 156 recommends a minimum size of 2x6 where a separate wood jamb is installed for door attachment, requires the same 2x6 minimum for a torsion spring pad, and notes that "Vertical back jambs shall extend to within 1/2 inch (12.7 mm) of finished floor." Clopay's framing step says the inside of the opening should be framed with 2 inch by 6 inch lumber, plumb on the sides and level at the header.

The fasteners are engineered too. TDS 161 publishes separate connection schedules for 3/8 inch by 3 inch lag screws, 16d by 3-1/2 inch common wire nails, and several masonry anchors, with maximum spacing set by door width and by the wind load pushing on the door. DASMA adds that "professional engineering advice should be obtained when considering the attachment of garage door jambs to a structure."

So a rotted jamb is a real repair, and it is a door repair, done with the counterbalance unloaded and the track reset afterward. TDS 156's inspection list for an existing jamb is worth running yourself before you call: check the attachment to the building frame, whether the wood is solid, whether it is decayed, and whether it is plumb, level, square and flush.

Wood, PVC, or composite: why wood always fails at the bottom

Wood trim rots from the bottom up because that is where liquid water reaches it, and the moisture threshold for decay is well documented. The USDA Forest Products Laboratory's Wood Handbook states that "serious decay occurs only when the moisture content of the wood is above the fiber saturation point (average 30%)," and that the only way previously dried wood gets there is direct contact with rain, condensation, or wet ground. Fully air-dried wood usually sits at 20 percent moisture content or below, which the handbook calls "a reasonable margin of safety against fungal damage."

A garage door opening delivers all three of those wetting mechanisms at the bottom of the trim: splash-back off the driveway, snowmelt pooling against the slab, and end grain resting on concrete that stays damp long after the surface looks dry. The Forest Products Laboratory's standing recommendation for wood on a slab is that it "generally should be pressure treated and protected by installing a moisture-resistant membrane." That is why the top of a wood brickmold leg can look fine while the bottom 6 inches crumble.

Cellular PVC and composite trim do not have that failure mode, because there is no wood fiber for decay fungi to feed on. They are milled in the same standard brickmold and stop profiles, so they drop into the same openings. The honest trade-offs are cost per foot and the fact that PVC trim carries no structural load. It is a fine brickmold and a fine stop molding. It is not a jamb board, and it cannot be substituted for one.

If you stay with wood, two DASMA points cut the failure rate. Finish the material on all six sides before it goes up rather than painting it in place. And keep fasteners away from defects: TDS 179 specifies that "no splits or knots should be within 2 inches of any fastening into the wood."

What each job actually takes

Stop molding is a half day with a pry bar, a miter saw, exterior nails, and paint. Brickmold is a half to full day and adds caulk and a careful hand around the siding. Neither one puts you near a spring. Header flashing means opening siding above the door, which is siding work, and a jamb board means the door and its counterbalance come off first, which is door-technician work.

When the trim is done, close the door, kill the garage lights, and look at the perimeter from inside. A thin, even line of daylight at the floor is normal on many doors. Daylight up the sides or across the header means the stop is not set right, and it is easier to pull one nail now than to chase a draft all winter.