Duct Insulation R Value Requirements

The following information applies to combined heating and cooling ducts in zone 4 areas.

Duct insulation r value requirements.

Specific insulation requirements of section c402 2 thermal requirements of either. R value of r 6 is required for exterior ductwork or ducts installed in a ventilated attic or an unvented attic above a. R value of 3 5 is required for buried ductwork and ducts installed in an unvented attic. Add insulation to attic.

Existing 3 4 inches of insulation. R value based method of section c402 1 3 u c and f factor based method of section c402 1 4. Allison bailes of decatur georgia is a speaker writer building science consultant and the author of the energy vanguard blog. You can follow him on twitter at energyvanguard.

The international code council icc is a non profit organization dedicated to developing model codes and standards used in the design build and compliance process. Recommended insulation levels for retrofitting existing wood framed buildings. Insulation r value to match the supply duct. Ashrae 90 1and the ieccboth require r 6 insulation for ducts in unconditioned spaces and r 8 or r 12 depending on the climate zone for ducts installed outside the building.

If the lesser r value most likely the duct r value is chosen the envelope of the building must be shown to comply with a performance based option. Or component performance alternative of section c402 1 5 roof solar reflectance and thermal emittance fenestration in building envelope. And that means it s time to deal with duct insulation in a more meaningful way than just increasing the required r value to 8 for ducts in attics. For example if you have a type of insulation that has an r value of r 5 per inch of thickness you will need a depth of 6 inches of this insulation installed your attic to reach r 30 if you live in zones 2 or 3.

These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation.