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R2 over S2 parking garage in wood frame type VA

S

Scott_R

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Apr 27, 2011
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Chicago, IL
Sorry, I posted this under the wrong section, should be here.

Building design using 2006 IBC:

A Mixed-use 4-story R2 apartments over S2 below grade plane basement for private enclosed parking.

Type VA construction, fully sprinklered to increase the 3 stories to 4 (as per table 503 and section 504.2).

Question: can the horizontal separation between the basement/first floor be built in wood frame floor trusses assuming the proper fire rating between the R2 and S2 uses is met? I seem to recall this was allowed (wood floor truss) in previous BOCA code versions, but am unsure in 2006 IBC (section 509.2 and 509.4).

Thanks in advance,

Scott
 
The garage will be type I, so no wood structural members.

So your question is if the separation between the garage and residential is considered a roof or a floor?

If it is a roof, 603.1.1.1.1.3 might apply, allowing wood., trusses, framing, etc.

Even if it is like a roof to the garage, it is still a floor to the R use and the building as a whole. I'd say the separation is a floor and therefore no wood because of the type I construction.
 
509.2 considers the parking garage to be a separate building. Part 1 of the Exception to Item 2 in 509.2 infers that the IBC anticipates that the horizontal assembly will be of Type I construction.

509.4 specifically states, "The floor assembly between the parking garage and the Group R above shall comply with the type of construction required for the parking garage..."

Therefore, it appears that the code anticipates the horizontal separation to be as a Type I floor assembly.
 
509.2 is the code section you need to follow for your project since the parking garage is enclosed and below grade. The garage needs to be Type I with a 3-hour separation from the R. If you took an area increase you'll need a NFPA 13 sprinkler system throughout. With no area increase you could use a NFPA 13R system in the R.
 
Not knowing the areas of the R2 occupancy or the S2 occupancy and if you are evaluating the building as a separated or non-separated mixed use, I will be conservative in my approach. First, section 509.2 need only be used if the S2 basement exceeds the permissible area for a one story building (Section 506.1.1). Assuming the building is a non-separated mixed use, with the R2 occupancy being the control, the basement is permitted to be 36,000sf for Type V-A construction. The 36,000sf area was derived using the sprinkler increase only and no frontage increase. The permitted area may increase if the building is evaluated as a non-separated mixed use occupancy. If the area of the S2 parking garage is within the permissible limits of section 506.1.1 it could be constructed of any material permitted for Type V-A construction (yes, wood) and would require a one hour assembly from the R occupancy above (Sections 406.2.7, 508.3 and Table 508.3.3).
 
Correction to my previous post. The one hour separation would be required by Table 601 NOTSections 406.2.7, 508.3 and Table 508.3.3 (unless separated mixed use is used).
 
The sprinkler increase for area requires a NFPA 13 sprinkler system throughout.
 
My footprint is approximately 15,000 sf. Is it true that I do not need to separate the S2 from the R2 which would make distinct separate buildings per section 509.2 and just apply restrictions for R2 to whole structure as non-separated uses? If their is a choice - why is that? Major difference from type 1A separation at 3 hour versus wood floor and 1 hour rated if non-separated.
 
So, you want to build a 5 story (1 parking, 4 residential) R-2 building, as VA construction?

As R2, the height increase for sprinklers only gets you to 4 stories total. You'll need to provide the separation, or drop a story.

And reading through section 509, I don't see an exception to some sort of separation when you have parking below residential. 509.7.1 might let you do a 2 hour wood separation, if it is an open parking structure and you meet all the height and area restrictions.
 
The parking is located in a basement, not a story, so 4 stories over a basement. VA allows it with sprinklers (3 story + 1). My question is what determines whether section 509.2 applies or if I do a non-separated mixed use and use R2 as dominate use allowing wood frame between basement (parking) and R2 above.

The larger question I have is what are the determining factor(s) between separated and non-separated as it pertains to this design?
 
Sorry, I missed the below grade.

Section 509 is still a problem. Applies to parking under other uses, including and particularly R uses (509.4). Some separation will be required.

Doesn't seem to allow VA above without IA and 3 hour separation below.

509.7 still might allow for a 2 hour wood construction separation IFF there is open parking below.

So...is your basement parking open or enclosed?
 
Last edited by a moderator:
Scott_R said:
The parking is located in a basement, not a story, so 4 stories over a basement. VA allows it with sprinklers (3 story + 1). My question is what determines whether section 509.2 applies or if I do a non-separated mixed use and use R2 as dominate use allowing wood frame between basement (parking) and R2 above. The larger question I have is what are the determining factor(s) between separated and non-separated as it pertains to this design?
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Hi Scott, Have you talked with an architect about this? Ben
 
iggentleman said:
Sorry, I missed the below grade.Section 509 is still a problem. Applies to parking under other uses, including and particularly R uses (509.4). Some separation will be required.

Doesn't seem to allow VA above without IA and 3 hour separation below.

509.7 still might allow for a 2 hour wood construction separation IFF there is open parking below.

So...is your basement parking open or enclosed?
Click to expand...
Basement parking in enclosed. I have had conflicting interpretations by AHJ. One says in a non-separated mixed use applying the R2 use group to the whole structure with sprinklers allows me to use 1 hour (most everywhere). Another says that 509.2 applies and Type 1A is required and VA above for the R2 is acceptable.

This is the same building being built in two different municipalities! Major construction $ implications.
 
brudgers said:
Hi Scott, Have you talked with an architect about this? Ben
Click to expand...
Hi Ben, I am an architect. As I mentioned in a previous post - I have the same building being interpreted two different ways in two different municipalities.
 
Scott_R said:
Hi Ben, I am an architect. As I mentioned in a previous post - I have the same building being interpreted two different ways in two different municipalities.
Click to expand...
Why are you interpreting it two different ways?
 
brudgers said:
Why are you interpreting it two different ways?
Click to expand...
The AHJ is interpreting it one way in one town and a different AHJ in another town the other way. (Same design is being built in two different municipalities).
 
Scott_R said:
The AHJ is interpreting it one way in one town and a different AHJ in another town the other way. (Same design is being built in two different municipalities).
Click to expand...
Why would that affect your code analysis?
 
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