# DWV in Return Air Ducts



## jar546 (Aug 15, 2019)

Such as this.  What is your opinion?


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## ICE (Aug 16, 2019)

Fluid dynamics is a complicated subject.  Sometimes it comes down to which way the wind is blowing.


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## steveray (Aug 16, 2019)

What's my opinion? or what code section would I use to deny that crap?

307.6 Piping materials exposed within plenums. Piping
materials exposed within plenums shall comply with the provisions
of the International Mechanical Code.

308.3 Materials. Hangers, anchors and supports shall support
the piping and the contents of the piping. Hangers and strapping
material shall be of approved material that will not promote
galvanic action.
308.4 Structural attachment. Hangers and anchors shall be
attached to the building construction in an approved manner.


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## mtlogcabin (Aug 16, 2019)

I assume this is a SFR and since the IRC is silent on this I will use the IPC and IMC. 

2012 IPC
307.6 Piping materials exposed within plenums.
All piping materials exposed within plenums shall comply with the provisions of the International Mechanical Code.

602.2.1 Materials within plenums.
Except as required by sections 602.2.1.1 through 602.2.1.5, materials within plenums shall be noncombustible or shall be listed and labeled as having a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E 84 or UL 723.
*Exceptions:*
1.    Rigid and flexible ducts and connectors shall conform to Section 603.
2.    Duct coverings, linings, tape and connectors shall conform to Sections 603 and 604.
3.    This section shall not apply to materials exposed within plenums in one- and two-family dwellings.


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## HForester (Aug 16, 2019)

"I assume this is a SFR and since the IRC is silent on this, I will use the IPC and IMC."

The IRC is intended to be an all encompassing bible for SFRs. Everything that one needs to build SFRs is in that book. The IRC covers ductwork/return air chases ("plenum") and DWV piping. The IRC does have not a prohibition of PVC piping in a plenum.   Cherry picking regulations from other I-Codes to apply to an SFR is standing on shaky ground.


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## classicT (Aug 16, 2019)

HForester said:


> The IRC is intended to be an all encompassing bible for SFRs. Everything that one needs to build SFRs is in that book. The IRC covers ductwork/return air chases ("plenum") and DWV piping. The IRC does have not a prohibition of PVC piping in a plenum. Cherry picking regulations from other I-Codes to apply to an SFR is standing on shaky ground.


Since when?

It is the exact opposite. The IRC is intended to represent the most common and typical configurations and construction methods and is not intended to be all encompassing. Where not covered by the IRC, more expansive codes such as the IBC/IPC/IMC/etc. are to be used.

*R104.11 Alternative Materials, Design and Methods of Construction and Equipment*
The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been _approved_. An alternative material, design or method of construction shall be _approved_ where the _building official_ finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, not less than the equivalent of that prescribed in this code. Compliance with the specific performance-based provisions of the International Codes shall be an alternative to the specific requirements of this code. Where the alternative material, design or method of construction is not _approved_, the _building official_ shall respond in writing, stating the reasons why the alternative was not _approved_.
​IRC is the prescriptive "conventional/typical" playbook, whereas the other codes (IMC, IPC, etc.) allow for performance based "non-conventional/atypical" methods where supported by quantitative testing.


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## mtlogcabin (Aug 16, 2019)

HForester said:


> The IRC does have not a prohibition of PVC piping in a plenum. Cherry picking regulations from other I-Codes to apply to an SFR is standing on shaky ground.


You missed the point of the code path that I outlined

It was to verify that since the IRC was silent on this installation and the mechanical code has an exception for materials in a plenum in a one and two family dwelling that the installation in the photo is not a violation of the IRC and therefore allowed.
Inspectors will sometimes call out things that just don't look right. As a building official I have to make the final determination if it is not specifically addressed in the code. Finding an answer in the IMC for a IRC building and basing my decision on another adopted code is not "shaking ground".


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## Pcinspector1 (Aug 16, 2019)

Seams are taped and the tape meets UL 181, nonmetallic insulated duct board meets a Class 1 rating, though I hardly see information on the duct material.


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## HForester (Aug 21, 2019)

You have missed my point.  Here's a simple example: The IPC requires a 3 inch drain when the fixture drain from an ACW combines with another drain.  The IRC does not have that requirement. Should you apply the IPC requirement to the IRC building?  No, because the IRC has everything you need to know about drainage piping for ACW standpipes and branch drain sizing. On the other hand, if someone installs a urinal in an IRC building, what do you do because the IRC doesn't cover urinals. That's when you go to the IPC for guidance on urinals.  

There will always be questions as to how far you go in enforcing the requirements of another code (over the IRC) and does the IRC "sufficiently address" the general subject matter such that those who are developing the code, didn't see fit to make the IRC anymore complex and ultimately, more expensive to build homes. "Cherry picking" requirements out of other codes for construction of an IRC building could be viewed as arbitrary, depending on the situation. If it comes down to deposition time, what code section are you going to cite in the IRC that says that the arrangement is prohibited? This is why I used the "shaky ground" point. How are you going to look in front of a lawyer or in court when you try to support your grounds for making the installer do something that is not in the IRC.


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## classicT (Aug 21, 2019)

HForester said:


> You have missed my point.  Here's a simple example: The IPC requires a 3 inch drain when the fixture drain from an ACW combines with another drain.  The IRC does not have that requirement. Should you apply the IPC requirement to the IRC building?  No, because the IRC has everything you need to know about drainage piping for ACW standpipes and branch drain sizing. On the other hand, if someone installs a urinal in an IRC building, what do you do because the IRC doesn't cover urinals. That's when you go to the IPC for guidance on urinals.
> 
> There will always be questions as to how far you go in enforcing the requirements of another code (over the IRC) and does the IRC "sufficiently address" the general subject matter such that those who are developing the code, didn't see fit to make the IRC anymore complex and ultimately, more expensive to build homes. "Cherry picking" requirements out of other codes for construction of an IRC building could be viewed as arbitrary, depending on the situation. If it comes down to deposition time, what code section are you going to cite in the IRC that says that the arrangement is prohibited? This is why I used the "shaky ground" point. How are you going to look in front of a lawyer or in court when you try to support your grounds for making the installer do something that is not in the IRC.


Well, fortunately for me, WA state does not adopt the plumbing sections of the IRC, but adopts the UPC for both residential and commercial.

As for your point, I still disagree. The IRC is a conventional cookbook; if provisions for the desired system are not covered by the IRC, the code directs that the performance-based codes (IMC, IPC, etc.) be used.


Ty J. said:


> R104.11 Alternative Materials, Design and Methods of Construction and Equipment
> ...Compliance with the specific performance-based provisions of the International Codes shall be an alternative to the specific requirements of this code. ...


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## mtlogcabin (Aug 21, 2019)

M1301.1 Scope.
The provisions of this chapter shall govern the installation of mechanical systems not specifically covered in other chapters applicable to mechanical systems. Installations of mechanical appliances, equipment and systems not addressed by this code shall comply with the applicable provisions of the International Mechanical Code and the International Fuel Gas Code.


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## jar546 (May 5, 2021)

So PVC does not meet the flame and smoke rating to be in plenum spaces........................


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## rogerpa (May 5, 2021)

HForester said:


> You have missed my point.  Here's a simple example: The IPC requires a 3 inch drain when the fixture drain from an ACW combines with another drain.  The IRC does not have that requirement. Should you apply the IPC requirement to the IRC building?  No, because the IRC has everything you need to know about drainage piping for ACW standpipes and branch drain sizing. On the other hand, if someone installs a urinal in an IRC building, what do you do because the IRC doesn't cover urinals. That's when you go to the IPC for guidance on urinals.
> 
> There will always be questions as to how far you go in enforcing the requirements of another code (over the IRC) and does the IRC "sufficiently address" the general subject matter such that those who are developing the code, didn't see fit to make the IRC anymore complex and ultimately, more expensive to build homes. "Cherry picking" requirements out of other codes for construction of an IRC building could be viewed as arbitrary, depending on the situation. If it comes down to deposition time, what code section are you going to cite in the IRC that says that the arrangement is prohibited? This is why I used the "shaky ground" point. How are you going to look in front of a lawyer or in court when you try to support your grounds for making the installer do something that is not in the IRC.


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## Sifu (May 12, 2021)

Interesting discussion.  We had a similar debate a few days back concerning a service pit in an IRC regulated home.  I contend that if service pits were addressed in any way in the IRC then we are bound by them.  But if not addressed, other codes can be used.  In this case, the subject is covered so IMHO we are bound by the content of the IRC in this matter.

I always thought one could _choose_ to build a house using the provisions of the "commercial" codes if so desired, and that the IRC was created as a prescriptive cookbook so one could use it instead.  The IBC expressly states either can be used.  Unfortunately, the IMC, IPC, IFGC don't provide the option.  Is this an oversight?  Probably.  Can you get to those books by reference through the IBC?  Probably.  Is the intent to allow either?  Probably.  In fact , the very exception cited by MT seems to validate this.  Why have that exception if you aren't allowed to use that book to begin with?  But, with all the hard work and great minds that develop these things, I would think such an oversight would have been identified, so I am left with a little doubt.


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## steveray (May 12, 2021)

You could also fail it on improper duct sealing in the IRC per 1601.4.1....And if you really want to fail it, insulation requirements....


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## Paul Sweet (May 13, 2021)

Code writers can't think of and address all the stupid things that can be done.  If they could, the code book would be a foot or more thick and too heavy to carry!


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## klarenbeek (May 13, 2021)

mtlogcabin said:


> I assume this is a SFR and since the IRC is silent on this I will use the IPC and IMC.
> 
> 2012 IPC
> 307.6 Piping materials exposed within plenums.
> ...


Even if you DO apply the IMC, PVC in plenums in SFR is still allowed^


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