How can i fix sweating Duct work in my unconditioned garage?
Air seal with air duct sealant (a gray goo that hardens after it's brushed on or applied with a putty knife), not duct tape, and insulate, preferably a LOT better than R8 (your heating/cooling cost is hugely affected by poorly insulated &amp; leaky ducts in unconditioned space.)
You can reinforce the duct sealant by embedding fiberglass mesh drywall tape in it. I don't suggest using duct tape because it has a habit of falling off after a few years.