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Duct insulation

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ndtolearn

Member
Joined
Feb 5, 2010
Messages
11
I'm just wondering what everyone out there is accepting for duct insulation. We have a contractor building a slab on grade home with the duct work located in the attic. To insulate the main trunk line they have simply blown insulation in the attic and covered the duct up. While in the attic during the final inspection I could see where people have disturbed the insulation and left the main trunk line exposed to whatever temperature the attic is. Is this an acceptable way to insulate ducts or should they be individually insulated.

We are in a cold climate and the state has amended the IRC to require ducts in unconditioned spaced to be insulated to R-4.2. Typically our ducts are located in conditioned basements or crawlspaces. What are everyones thoughts on this? Thanks in advance for all replies.

ndtolearn
 
Re: Duct insulation

IRC section M1601.2.1 Addresses duct insulation materials. I would require the ductwork to be insulated separately
 
Re: Duct insulation

Admitedlly I have never seen this done. Maybe if the manufacturer has some instructions for installing the blown-in insulation on a duct. Do they provide inch markers?

My initial reaction is no, I would not allow it, unless they had some manufacturer's instructions.

Code: 
N1101.3 Materials and equipment. Materials and equipmentshall be identified in a manner that will allow a determination oftheir compliance with the provisions of this chapter. Materialsand equipment used to conform to the applicable provisions ofthis chapter shall be installed in accordance with the manufac-turer's installation instructions.

Tim
 
Re: Duct insulation

Needs a vapor barrier if there is cooling

M1601.3.4 Duct insulation.

Duct insulation shall be installed in accordance with the following requirements:

1. A vapor retarder having a maximum permeance of 0.05 perm [(2.87 ng/(s m2 Pa)] in accordance with ASTM E 96, or aluminum foil with a minimum thickness of 2 mils (0.05 mm), shall be installed on the exterior of insulation on cooling supply ducts that pass through nonconditioned spaces conducive to condensation.2. Exterior duct systems shall be protected against the elements.

3. Duct coverings shall not penetrate a fireblocked wall or floor.
 
Re: Duct insulation

ndtolearn,

Welcome to the codes forum!

I also agree with mtlogcabin! The duct is required to be insulated separately from the ' blown in ' type

of thermal insulation covering the ceiling.

 
Re: Duct insulation

Thanks for the replies. It's always good to have people to bounce things off when questioned by contractors. We're from a small community (7,000 people) and the contractors here seem to have a hard time dealing with change. It's always "now when did this start?" Thanks again.
 
Re: Duct insulation

ndtolearn said:
Thanks for the replies. It's always good to have people to bounce things off when questioned by contractors. We're from a small community (7,000 people) and the contractors here seem to have a hard time dealing with change. It's always "now when did this start?" Thanks again.
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I feel your pain.
 
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