2018 IBC - STC at an exterior corridor

[MAGB]

We are working on a courtyard style multi-family project. Our plan reviewer is requesting we provide an STC 50 wall at the exterior of the building where it is adjacent to an exterior corridor/egress balcony. I spoke with an acoustical consultant who basically said the wall rating would be negligible due to the openings door/windows and this is not a viable request. I reread IBC 1206 which notes that it covers room-to-room sound transmission. The scoping section also notes the section shall apply to interior walls, partitions and floor ceiling assemblies...

I do not think this section is intended to be applied to exterior wall conditions and there are no STC requirements in the exterior wall section of the IBC. I am preparing to make my case to the reviewer and was wondering if anyone else has come across this issue.

This is 2018 IBC, R-2 Occupancy.

 

[RLGA]

Although it does say the STC is limited between units, it also says it is limited between units and public or service areas. It does not require that these public or service areas be enclosed, plus it does say walls--not interior walls--so, it could be interpreted to include exterior walls of courts, which could also be interpreted as "public areas."

Now, with that said, it does only refer to "walls" and not "wall assemblies," so openings and penetrations (except those listed) are excluded. Thus, windows are not prohibited and should not be considered when determining the STC rating of the "wall," much like the entrance doors that are excluded.

 

[MAGB]

Although it does say the STC is limited between units, it also says it is limited between units and public or service areas. It does not require that these public or service areas be enclosed, plus it does say walls--not interior walls--so, it could be interpreted to include exterior walls of courts, which could also be interpreted as "public areas."

Now, with that said, it does only refer to "walls" and not "wall assemblies," so openings and penetrations (except those listed) are excluded. Thus, windows are not prohibited and should not be considered when determining the STC rating of the "wall," much like the entrance doors that are excluded.

I see that interpretation; and initially I was scrambling to find a wall type with such a rating, but then looked back to 1201.1 Scope after speaking with the acoustical consultant. In this section it states "This section shall apply to common interior walls, partitions and floor ceiling assemblies(...)." To me this defines the scope of all that follows to be limited to interior elements.

The acoustician also stated due to the openings an STC 100 wall would only perform negligibly different from and STC 35 wall. The modified wall assembly would add a great deal of cost with imperceptible benefit.

 

[RLGA]

What edition of the IBC is applicable? If it's any of the more recent editions (2012 and later--I didn't look back any further), then they include yards and courts "associated" with interior spaces. I could not find the quote you provided unless it was an older edition of the IBC or a local amendment.

 

[MAGB]

2018 IBC Section 1206 Sound Transmission 1201.1 Scope

 

[RLGA]

I think you meant 1206.1--that's what was throwing me off. It still says "adjacent public areas such as..." The list that follows is not all-inclusive. The building official has the authority to interpret the code and there's nothing that I could find that would prohibit the interpretation they are making.

I agree with your acoustician that an exterior wall, including all of the openings, would not actually provide an overall STC of 50; however, the code is not requiring that all of the openings provide the minimum STC...just the wall portion. Provide an exterior wall that would provide an STC of 50 (insulation, resilient channels, etc.) and install normal windows and doors that comply with the energy requirements. In my opinion, that would comply with the letter of the code as they interpret it.

 

[MAGB]

Ugh, you are correct on my typo. Thank you for your responses and interpretation.