Most people notice the bottom seal first. It drags on the floor, it shreds, it lets in leaves and cold air. But the sides and top of a residential garage door leak just as much air and water, and they do it quietly. A 16-foot double door has roughly 40 linear feet of perimeter. The bottom takes 16. The other 24 feet are the jambs and header — and that is where the side and top weatherstripping lives.
If you can see daylight around the closed door, or feel a breeze when you stand inside with the door shut, the perimeter seal is either missing, worn, or installed wrong. Water staining on the drywall above the opening, rust on the track near the top corners, or a musty smell in the garage after rain — same diagnosis.
What the seal actually does
Side and top weatherstripping — often called stop molding or perimeter seal — is a vinyl or PVC molding with a flexible fin or bulb that presses against the face of the door sections when the door closes. It mounts to the wood jamb and header, not to the door itself. The door moves; the seal stays put.
The fin compresses against the steel or wood face of the door. That compression is the seal. No compression, no seal. If the molding sits proud of the door face by even a quarter inch, you have a gap. If it presses so hard it binds the door, you have a motor strain problem and premature roller wear.
Vinyl is standard. It handles UV and temperature swings better than the old rubber strips, and it does not rot. Some manufacturers sell a two-piece system: a rigid base that nails to the jamb, and a snap-in flexible insert you can replace without pulling nails. That is the better choice on wood frames that move with the seasons. On steel jambs, a one-piece vinyl molding with a nailing flange works fine.
Common failure modes
The fin takes a set. After a few winters, the vinyl remembers the compressed shape and stops springing back. You close the door and the fin barely kisses the panel. Air moves through.
Nails pull loose. The molding flexes every cycle. On a door that runs four times a day, that is nearly 1,500 cycles a year. Standard roofing nails back out. The molding bows away from the door at the top corners first — exactly where wind-driven rain hits hardest.
Caulk fails at the ends. The top piece butts into the side pieces. If the installer did not run a bead of exterior-grade polyurethane sealant at those joints, water tracks behind the molding and into the wall cavity.
The door shifts. Settling foundations, loose track brackets, or a bent vertical track can move the door panels away from the seal on one side while crushing it on the other. The seal looks intact but the gap is there.
Mice chew the corners. The bottom of the side pieces, where they meet the concrete, is a favorite entry point. Vinyl offers zero resistance to rodents.
How to check yours
Close the door. Turn off the lights inside the garage. Stand outside and look for light leaks at the sides and top. Even a hairline gap shows up.
Run your hand along the perimeter on a windy day. You will feel the draft before you see the gap.
Inspect the fin. It should look like a smooth, slightly curved lip. If it is flattened, cracked, brittle, or missing chunks, it is done.
Tug the molding gently. If it moves more than a millimeter, the fasteners have failed.
Look at the miters. The top corners should be tight. If you see daylight or old caulk cracking, water is getting in.
Replacing it — what the job looks like
This is a two-person job on a double door. The top piece is 16 feet long, floppy, and awkward solo.
Remove the old molding. A flat bar and a hammer. Work slowly so you do not damage the jamb or the door panels. Pull all old nails. Scrape off the old caulk.
Check the jamb. If the wood is soft, spongy, or rotted, cut it out and sister in new pressure-treated lumber before you mount anything. Sealing over rot traps moisture and guarantees a callback.
Dry-fit the new pieces. Cut the top piece first. Miter the ends at 45 degrees. Cut the side pieces long, then trim the bottoms to sit 1/8 inch above the concrete — not on it. Concrete wicks water. Vinyl sitting in water wicks it up into the molding and the jamb behind it.
Nail the side pieces first. Use 1 1/2-inch stainless or hot-dipped galvanized siding nails every 12 to 16 inches. Drive them through the nailing flange, not through the fin. Leave the heads slightly proud so the molding can still move a little with thermal expansion.
Nail the top piece. Push it tight to the side miters. Nail the same pattern.
Caulk the miters and the ends where the molding meets the wall. Use a quality polyurethane — not silicone, not latex. Tool it smooth with a wet finger.
Test the door. Run it up and down three times. Watch the fin. It should compress evenly along its full length. If it binds at one spot, the door is out of alignment or the molding is proud. Adjust the molding, not the door. If the door is out of alignment, that is a separate repair.
The bottom seal is a different animal
Do not confuse perimeter seal with the bottom astragal. The bottom seal mounts to the bottom section of the door — usually a U-channel retainer with a T-end rubber or vinyl insert that slides in. It wears faster because it drags on concrete, hits ice, and takes the full weight of the door. Replace it when it cracks, flattens, or lets light through at the corners. But do not skip the sides and top because the bottom looks new. They fail on different schedules.
When to call a pro
If the jamb is rotted, if the door binds or runs crooked, if the header is bowed, or if you simply do not want to wrestle a 16-foot piece of vinyl on a ladder — call a door company. The materials are cheap. The labor is where the cost lives, and the labor is what makes the seal last.
A proper perimeter seal job on a standard double door takes two techs about 90 minutes. The door runs quiet, the garage stays warmer, and the drywall above the opening stays dry. That is the whole point.
Call 778-873-7282 — Metro Vancouver.