This is a sore subject with me, for some stupid reason when I built my shop I felt I needed a big door in the front, 18x10 That is a whole `nuther story
It has just been a complete disaster trying to get it sealed up to what I feel is acceptable and so far only most attempts have been short term patches at best.
Initially it was ok when first installed...Then the temperature changed...You could throw a cat thru the gap at the top in the winter (expansion, contraction on inside/outside temps) well multiple trys from the original installer proved futile, finally called another company and they suggested Brush seals, I thought "OK" in theory this might work, and in all fairness it did help.
However as they have aged the last couple of years, the effectiveness has diminished a bunch. We have had a rather cold last 90 days and I have the electric bills to prove it.
I`m still trying to figure out a better idea as this is just a complete pain in the ***, The amount of bowing on this door with temperature changes is incredible and while one`s first thought is to pull it in tighter this time of year, the minute it warms up an opposite problem crops up, it goes the other way and catches at the header and won`t open (not a good thing with a jack shaft opener) Looking back now that big of door was a HUGE mistake, While it has it`s moments, they are few enough that the justification for it can`t be made and modifying for two smaller doors just isn`t feasible without completely tearing off that end of the building.
Rick