Over time, many garage doors will sag or shift and create a gap between the bottom of your door and the garage floor. These small cracks aren’t an immediate threat, but they can become larger and result in unwanted water, drafts and sometimes even security threats. Here’s how you can fix your garage door gap without an expensive new install.
A garage door sweep, or retainer, is a rubber gasket that mounts to the bottom of your garage door and creates a seal. Door sweeps vary in price, material and effectiveness, but most will help eliminate energy waste and other gap-related problems. Installing most seals is a DIY-able job, but always hire a pro if you’re unsure. You can purchase a garage door sweep at most hardware stores.
Comparing the Pros and Cons of an Attached and Detached Garage 
Protect Your Garage With Garage Door Insulation 
Garage Doors 
Garage Remodeling Prep Steps 
Carports 
Need maintenance on overhead residential garage door
https://www.homeadvisor.com/task.Garage-Door-Repair.40064.html