The original post: /r/diy by /u/BloomenOnion on 2024-12-26 17:07:36.

I’m needing to insulate my crawlspace ductwork, but uncertain about code requirements. Back story, years back I redid the ductwork because the old ductwork was falling apart and I felt the best bet was to diy cause I had little money. Pretty proud of what i did, 14” main run for the return and supply, with 10” branches and 6” supplies to registers. I have a return register in every room, so its a significant amount of ductwork. I bought a few roles of foil faced bubble insulation( r-8 with spacer). I never insulated as I encapsulated the crawlspace, so condensation was never an issue, and frankly I got burnt out on spending time in crawlspace after those two projects.

Flash forward a few years, and the package unit is looking like it will give out. To permit the job, the ductwork insulation needs completed. The problem now is I am unable to find the same R-8 insulation, and don’t think I bought enough to event complete the supply. The best foil faced bubble wrap I can find, outside duct insulation sleeves, is R-6 with spacer. I am taken back by the coat of the duct sleeves, as I think I will be looking at 1k-1.5k to purchase what i need from HD.

Kinda pinballing around, but here are my current questions regarding Residential Code in NC. Is foil faced bubble wrap insulation acceptable? What is the minimum duct R-Value in a crawlspace? (Seeing R8 but also seeing that outside attic it can be R6).