# N1103.3 Duct insulation



## Inspector 102 (Nov 2, 2010)

In reviewing this section, I am having trouble grasping the requirements of "R-8 insulation applied between the duct and that portion of the assemby furthest from the conditioned space." Is this stating that all duct work that might be running through an exterior wall space needs R-8 applied on the backside of the duct work to create a theraml barrier to the exterior wall? If someone has a picture showing the intent, it would be greatly appeciated.


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## globe trekker (Nov 2, 2010)

Inspector 102,

Can you please list your applicale code book that you are using?

Also, please verify the code section you are asking about. From

the 2006 IRC, Section N1103.3 is for Mechanical system piping

isulation.

Thanks!

.


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## Inspector 102 (Nov 2, 2010)

Currently we are using the 2003 IRC, sorry about that. It sounds to me that if there is a duct running along an exterior wall, that there needs to be a minimum of R-8 provided on the cold side of the duct and that this can be accomplished with duct wrap or sheathing material as long as R-8 is achieved. This would provide the thermal break to eliminate or reduce any chance of condensation and other nasty things from occuring. I think I am reading this section correctly. Thanks.


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## Jobsaver (Nov 2, 2010)

2003 IRC

N1103.3 Duct insulation.

All portions of the air distribution system shall be installed in accordance with Section M1601 and be insulated to an installed R-5 when system components are located within the building but outside of conditioned space, and R-8 when located outside of the building. When located within a building envelope assembly, at least R-8 shall be applied between the duct and that portion of the assembly furthest from conditioned space.

Exception: Exhaust air ducts and portions of the air distribution system within appliances or equipment.


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## Jobsaver (Nov 2, 2010)

102: I read it to mean that if the duct is located within a wall, or within rafter spaces, or within some other assembly comprising the building envelope, that R-8 is required between the duct and the exterior portion of the building envelope assembly. In other words, this applies when the duct is located between the outermost and innermost layers of the building envelope assembly.


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## Inspector 102 (Nov 2, 2010)

The last sentence is the part that is throwing me for the loop. When stating "applied between the duct and that portion of the assembly furthest from the conditioned space" tells me that the entire duct does not need insulated, only the "cold side" to create the thermal break. Am I still reading this incorrectly and does the entire duct need an insulating wrap?


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## Jobsaver (Nov 2, 2010)

It is already established that the duct must be insulated only to a minimum R5 if it is located in an unconditioned space. For unconditioned spaces, inside of the outermost portion of the building envelope, R5 is all that is required.

The last sentence applies to the circumstance of a duct being installed within the building envelope that encloses a conditioned space.


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## Jobsaver (Nov 2, 2010)

So long as R8 is established between the duct and the outermost postion of the building envelope, the duct does not need to be wrapped.


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## Inspector 102 (Nov 3, 2010)

Jobsaver - Thanks for the replies and guidance


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## Paul Sweet (Nov 3, 2010)

I'd still recommend at least minimum duct wrap, in case they don't do a good job of insulating the enclosure.


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## Jobsaver (Nov 3, 2010)

Yes. I also recommend the entire duct be wrapped, though the 2003 IRC section mentioned does not require it.

Interestingly, the 2003 Mechanical Code addresses condensation on ducts in this vague manner:

*603.12 Condensation. *Provisions shall be made to prevent the formation of condensation on the exterior of any duct.


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