I recently inspected a house that I am rating and discovered the HVAC contractor used Big 8 bubble wrap on the metal main duct in a vented attic in Climate zone 5. I spoke to the contractor about this at the rough inspection and duct testing and told him he needed to add more insulation to the nice wrap job he had done. My experience has been that a materiel that thin + a thin air space can not be classified as a R-8. I found a few articles from some pretty knowledgeable building science guys to confirm my thoughts. The contractor however is insistent that this is a suitable method of insulating duct work. He sent me the manufacturers claims and I looked up a ESR -report. (ESR-1236). First I must say I do not work on really any new buildings with duct work outside the thermal boundary and advised agaisnt it!
What is the industry accepted method for crediting duct work wrapped with a radiant barrier and a airspace.?The ducts did pass a total leakage test, but they still leaked so, it is not in a vacuum either. I could not find any official language by RESNET or IECC on this.
Thanks for your Thoughts in advance!