Seals and insulation are the least visible parts of a garage door and usually the first thing a homeowner notices once they stop working. A split bottom rubber lets rain sheet in under the door, tired jamb seals whistle in a wind coming up the valley, and uninsulated panels stay cold all winter and drip condensation onto whatever is stored underneath them.
Where A Garage Door Leaks
- Bottom rubber, which flattens and hardens with age until it stops touching the slab
- Perimeter or jamb seals, which close the gap between the door edge and the frame
- The header seal at the top of the opening
- The threshold, where the slab meets the door, and an apron that drains back toward the opening instead of away from it
- The aluminium retainer and panel joints on a door that has been struck, has bowed or has rusted through along the bottom edge
Water Wicking Into The Bottom Section
The most expensive leak on a garage door is the one you cannot see. In a hard rain, water runs down the driveway, spreads across the apron and passes under the bottom rubber, where it sits against the door. The bottom section is a folded steel hem, two layers of metal pressed together, and water climbs into that fold by capillary action and stays there. It cannot evaporate from inside a closed hem, so rust begins on the inner surfaces, works along the fold and finally shows on the outside as a brown stain. By then the panel is thin, the bottom bracket and the lower hinges have rusted with it, and the fix is a panel rather than a seal. This is the failure we see most often on Seattle doors, and it is the reason we inspect the hem and the retainer on every sealing visit rather than just measuring the gap under the door.
What R-Value Actually Measures
R-value expresses resistance to heat flow: the higher the number, the more slowly heat moves through a panel. It is not a measure of how airtight a door is. An insulated door with a good R-value and a torn bottom seal will still leak water and air, and a perfectly sealed door with thin single-skin panels will still run with condensation all winter. The two belong together, which is why we inspect the seal and the panels on the same visit. In an unheated detached garage the panels sit close to the outside temperature from November to March, so warm damp air inside condenses on the inner face and drips onto tools, bikes and stored timber. Insulated panels with a polyurethane core lift that surface temperature, which is what stops the dripping, and they stiffen the door as well, reducing rattle and deflection. Insulation also cuts noise, which matters when the garage shares a wall with a bedroom or a home office.
Choosing Seal Material For A Wet Climate
Constant wet and cold are hard on rubber. Vinyl and EPDM hold up better than soft sponge rubber, which hardens, cracks and crumbles instead of compressing against the slab. On a slab that has settled or cracked, a thicker bulb or U-style seal tolerates the uneven surface far better than a thin T-style blade. Whatever the material, the seal has to be thick enough to close the gap once it has compressed, and it has to be fitted to a straight, clean bottom edge, because a bent bottom section will not seal no matter how good the rubber is. The retainer matters just as much: rust swelling inside an aluminium channel, or a bend where the door was backed into, will hold the seal open in the middle and let water straight through.
What Seal Replacement Involves
- Measuring the opening and the gap under the door with the door closed
- Removing the old seal and cleaning out the aluminium retainer, including any rust and grit packed into the channel
- Straightening or replacing a bent or rusted bottom section before the new seal goes on
- Fitting and trimming jamb and header seals so they compress evenly along their whole length
- Adjusting the door so it meets the slab squarely across its full width, and adding a threshold section where the apron drains toward the opening
Noise, Damp And Pests
A sealed opening is quieter, drier and harder for insects and rodents to enter, which matters in a city where a gap under the door is an open invitation to rats working along the alley. Most of the draught a homeowner feels in a room that adjoins the garage arrives through the garage opening, so sealing it often improves comfort in the house as well as in the garage, and it takes some of the load off a heating system that is otherwise warming the alley all winter.
Keeping Seals Alive Between Visits
- Sweep fir needles, moss and grit out of the seal channel instead of letting the door grind them into the rubber
- Check for tears and separation after the wet season, particularly at the ends where the seal meets the retainer
- Keep the track clear so the door does not drag the seal sideways as it travels
- Do not grease or oil the bottom rubber, because it attracts grit and degrades the material
Seals are inexpensive compared with the damage they prevent, and they are the fastest way to make an older door feel tighter, quieter and drier through a Pacific Northwest winter. Every bottom rubber, jamb seal and insulation upgrade F1 Garage Door fits carries a one-year parts and labour warranty.