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Duct Insulation

Duct Insulation

Duct Insulation

(OP)
I have observed uni-stut support installed in contact with mechanical duct and the insulation was installed on the outside of the uni-strut with the exception of the outside ends 6". This condition in my opinion will transfer heat / cold and cause sweating. I believe a barrier should be installed between the duct and the unistut when the ends are exposed to unconditioned space.

I have searched codes and have been unable to find any documentation that requires a barrier between the duct and the unistrut or require the contractor to wrap the exposed uni-strut. Does anyone know where I may force the contractor to protect this area? See picture attached below.



RE: Duct Insulation

You're the Engineer, write it in the spec.

RE: Duct Insulation

(OP)
I am a QA/QC for the owner. The EOR states he has no issue with it however I think as a QA it will be an issue.

RE: Duct Insulation

Your job as QA/QC is to inspect for compliance to the approved design.

If you believe the design is flawed then inform the owner so that the owner can initiate a change order.

RE: Duct Insulation

While your perceived problem of sweating is a possibility in some circumstances, it is actually rarely a problem in reality.

RE: Duct Insulation

(OP)
Thanks for the responses.
A code official has provided me with the two following code sections per the IMC 2015:

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

Commentary: Condensation can form on a duct when the temperature
of the air in the duct is near the dewpoint of the
air around the duct. The application of insulation with
a vapor barrier covering prevents the duct from
“sweating” by preventing moisture vapor from penetrating
the insulation and reaching the duct surface.
Duct sweating (condensation formation) is typically a
problem for cooling ducts that pass through unconditioned
areas where the humidity is not controlled.
Condensation can cause insulation damage, corrosion
or duct failure, and the accumulated water can
cause damage to the building.

604.9 Thermal continuity. Where a duct liner has been
interrupted, a duct covering of equal thermal performance
shall be installed.
Commentary: To maintain energy efficiency, a covering of equal
thermal resistance must be installed where a duct
liner has been interrupted. This is intended to prevent
gaps or weak links in the required thermal performance
of ducts.

RE: Duct Insulation

Riffing on MintJulep's point, if the design/construction team have approved plans showing duct support as shown you may have just landed your client with a large CO which the AHJ may give them no option on, now that you've brought them into the discussion.
You may get some blowback on this.

RE: Duct Insulation

(OP)
You make a good point however the EOR specifications only state to support in compliance with IMC and MSS 58. The contractor as usual did not submit anything for approval. I am a 3rd party QC/QA for State projects no local AHJ is involved. The client who I represent is the AHJ. It becomes difficult when the EOR specifications / drawings is very vague such as support to meet code. The contract documents require the contractor to meet code therefore no CO is expected by my client.

Thanks to all.

RE: Duct Insulation

Over a few years of being a commissioning guy (also a 3rd party type) I’ve had to pick and choose my battles. The project specs are important but don’t typically define every aspect of installation. Based on your description and photo, this is a battle that is either worth fighting for or punting:

Fighting for: the mechanical space in which this photo is taken is cooled only by draw-through ventilation and it is in a climate where outdoor dew point can be very high (e.g., often over 65F). This pretty much includes all of the continental US.

Punting: the mechanical space is conditioned by FCUs or AHUs that can bring the dew point below 60-65F, or, it is north of Montreal.

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