The simplest and fastest way to cool the garage is to add radiant barrier to a garage door. If your roll up door is catching direct sunlight, then you definitely should add a radiant barrier to the door and/or any other walls that are catching direct sunlight from the exterior.
For roll up doors we recommend the foil only radiant barrier or the BlueTex™ 2mm Pro product. Both of these materials are thin enough to install and not interrupt the mechanism that rolls the door up. You can use an adhesive to permanently attach it directly to the metal or you can use flat magnets to attach it, fitting the magnets into the valleys of the corrugations so the profile remains flat for ease of rolling up.
Either way, the foil side of the product MUST face an air gap to work so the foil surface ALWAYS has to face in, toward the inside of the garage/shop.
If you have questions about how to install BlueTex™ products on your roll up door, please contact us.