# Dryer Duct in Multi-Family Wood Apartment Project Questions



## ETThompson1 (Mar 6, 2019)

Hi

I've looked at several dryer exhaust threads but still not quite clear on the two issues I have on my project.  Multifamily apartment/mixed-use, VB, 12.5k sf, full sprinkler.  Ohio Building Code 2017, based on 2015 IBC.

1.  Can the dryer exhaust penetrate a rated wall?  The walls are required to be rated for two reasons, either fire separation distance less than 10' (which means they are 1-hour rated from exterior as well as interior) or because some of them are part of an egress court.  I know that the mechanical code (IMC) 504.2 says you cannot unless the duct is constructed of the right material (which we can do) and in compliance with the building code.

IBC 705.10 tells me ducts in exterior FRR walls required to have opening protections shall comply with section 717.  But the reference there (717.5.6) is circular, referring back to 705.10.  But my reading anyway is I don't have to have opening protectives per 705.8 - we're under the percentage of required openings for that wall.  Is that correct?

2.  Secondly, we had planned to run our dryer duct through the floor assembly (L528), based on input from our mechanical engineer.  We are using a 14" depth, so we can't have dampers anyway (L528 requires 18" depth for using approved dampers).  The concept was that since the dryer duct did not (and cannot) have dampers, this should be allowable.  The dryer duct starts at a non-rated wall, turns vertically up into it, penetrates the top of the non-rated partition, and turns from vertical to horizontal laterally to head out (in a straight run) to the exterior facade.  Am I right in thinking this should work, and without modifying the 14" depth?

Thanks


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## cda (Mar 6, 2019)

Not an expert

But I would say yes to both questions


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## IJHumberson (Mar 6, 2019)

With respect to Question #1, so long as your openings are less than 10% of the wall area (which they easily should be), it looks like you'd comply.

With respect to Question #2, in the UL L528 Floor/Ceiling Assembly, the references are only to ceiling dampers (which is not what you'd have in a continuous duct), and it limits the use of such to the 18-inch deep assembly. Correct me if I'm wrong, but I'm not seeing any exemption in IBC or in the UL L528 listing criteria that would allow the unprotected penetration of a rated floor/ceiling assembly by a dryer exhaust duct, just because the floor/ceiling assembly is less than 18 inches in depth.


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## ETThompson1 (Mar 6, 2019)

Thanks for the response.  Looking back at the reviewer's comments, I think I'm seeing the issue.  She cites 717.6.1 and 717.6.3 which deal with through or membrane penetrations of a FRR floor/ceiling assembly.  So maybe the issue isn't that we can't have the 14" depth (which would be prevented by having a damper, which we're not allowed anyway), but because we can't penetrate the membrane (or go through the assembly) without a damper.  I thought, based on comments from my mech engineer, that there was an exception if we were coming up through the top of a partition wall (and therefore not penetrating the membrane?), but I'm not finding it.  

If not, could we use one of these methods?  http://www.ncdoi.com/OSFM/Engineeri...Duct Rated Assembly Membrane Penetrations.pdf


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## ETThompson1 (Mar 6, 2019)

Update:  spoke to my mechanical engineer, he apparently negotiated the approach to the dryer exhaust with the building official directly.  It was not clear this is based on any code exception, but the concept is as I noted above - because the penetration comes through the top of the partition wall, she apparently does not consider it a membrane penetration, and therefore is good.  My fingers are crossed that he is correct and there has not been a miscommunication...


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## steveray (Mar 7, 2019)

Penetrating rated structure is probably not an issue (exterior wall)....Penetrating some sort of rated separation gets a little more sticky (floor/ceiling assembly).....


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## ETThompson1 (Mar 7, 2019)

Thanks - that's the conclusion I've come to.  I hope the MEP is right and the floor/ceiling penetration works...


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## cda (Mar 7, 2019)

Not sure if this thread helps you any



https://www.thebuildingcodeforum.com/forum/threads/multi-family-dryer-venting.23566/


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## Yikes (Mar 7, 2019)

ETThompson1 said:


> If not, could we use one of these methods?  http://www.ncdoi.com/OSFM/Engineering_and_Codes/Documents/Interpretations4/2012 Building/0716.6.2 - Dryer Duct Rated Assembly Membrane Penetrations.pdf



We use method B as a standard detail on most of our apartments.


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## ADAguy (Mar 13, 2019)

You mention two (2) horizontal transitions from vertical, both become collection points for lint. 
Does the vent have a blower to suck the lint out?


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## ETThompson1 (Mar 13, 2019)

Not sure...I think so but will check w mechanical.  But the bends factor into the limited length, so I think that already may be taken into account by the code...


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## mtlogcabin (Mar 13, 2019)

2012 IMC
504.3 Cleanout.
Each vertical riser shall be provided with a means for cleanout.


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## ADAguy (Mar 13, 2019)

Cleanout/outs must therefore be accessible?


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## mtlogcabin (Mar 13, 2019)

No they do not have to be accessible to the handicapped. It can be simply moving the dryer out of the way and disconnecting the transition duct or an elbow where it changes from horizontal to vertical.


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## steveray (Mar 14, 2019)

We don't really define "riser" in the IMC......would you use the IPC "one full story" guideline?


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## ADAguy (Mar 14, 2019)

Wouldn't that be defined as any vertical element between direction transitions?
If so and as previously noted above that there are multiple transitions then each vertical riser would require access to it, no?


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## mtlogcabin (Mar 14, 2019)

steveray said:


> We don't really define "riser" in the IMC......would you use the IPC "one full story" guideline?



No I would not. The term "riser" in the mechanical code is used 5 times to refer to grease and dryer ducts that "rise" either vertically or by offsets. The only time a distance is specified is a return air duct that serves two or more stories.


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## ETThompson1 (Mar 15, 2019)

I would hope my engineer knows this, but I will check.  Thanks!


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## rgrace (Mar 15, 2019)

ETThompson1 said:


> Update:  spoke to my mechanical engineer, he apparently negotiated the approach to the dryer exhaust with the building official directly.  It was not clear this is based on any code exception, but the concept is as I noted above - because the penetration comes through the top of the partition wall, she apparently does not consider it a membrane penetration, and therefore is good.  My fingers are crossed that he is correct and there has not been a miscommunication...



I believe the reference you are looking for is (2015) IBC 714.4.2 exception 7.



ETThompson1 said:


> If not, could we use one of these methods? http://www.ncdoi.com/OSFM/Engineering_and_Codes/Documents/Interpretations4/2012 Building/0716.6.2 - Dryer Duct Rated Assembly Membrane Penetrations.pdf



Item 1 - I'm pretty certain there are no duct wraps out there that are listed for the combination of (1) clothes dryer exhaust duct and (2) use in lieu of a ceiling radiation damper
Item 2 - Pretty much the same as item 1. Good luck with that too.
Item 3 - Looks like a reasonable approach.


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## mtlogcabin (Mar 15, 2019)

There is a dryer/residential kitchen exhaust wrap product 
http://www.morganfireprotection.com/media/2180/7-14-241_dryerwrap_032016_website-file.pdf


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## rgrace (Mar 18, 2019)

mtlogcabin said:


> There is a dryer/residential kitchen exhaust wrap product
> http://www.morganfireprotection.com/media/2180/7-14-241_dryerwrap_032016_website-file.pdf



Yes, there is ....... and to address a couple of points ....

1- The product description on page one states the application is intended for dryer vent ductwork in multi-unit housing. This corresponds with the second figure on page two.
(2015) IBC 714.4.2 exception 7 permits this without using the duct wrap. This IBC section is applicable to, at minimum, clothes dryer exhaust ducts, toilet exhaust ducts, even residential kitchen hood exhaust systems provided all are within the cavity of the wall and penetrate the double top plates. This would be different if one chose to route a kitchen exhaust duct through a top cabinet and penetrate the ceiling membrane. In this case, a ceiling radiation damper would be required, and the duct wrap could not be substituted. The general purpose of ISO 6944 is to measure the ability to resist the spread of fire from one fire compartment to another without the aid of *fire dampers. *Ceiling radiation dampers serve a completely different purpose and are tested and listed differently than fire dampers.

2- The listed systems in this publication, ISO 6944, HNLJ.V-29 and FRD 28 reference ventilation air ducts. Is a clothes dryer exhaust duct considered a ventilation air duct? IMC definition says no. These duct systems convey two completely different products, one of which is highly combustible.

Many duct wrap products are _approved_ (italicized for IBC definition) for specific installations based on engineering judgements and unofficial applications of IBC 104.10.


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