R2 over S2 parking garage in wood frame type VA

[Scott555]

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

[Jerry Peck - Codeman]

[Scott555]

Thanks....although I am getting a lot of resistance because of section 509.2. Doesn't this section require type 1 construction making the ceiling/floor construction require steel or concrete only? Or am I missing something?

[Jerry Peck - Codeman]

[Scott555]

Jerry, sorry for the long delayed reply...

My footprint is approximately 15,000 sf. So you are suggesting 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?

[Jerry Peck - Codeman]

[Scott555]

Ok, although I am a bit confused on why there is a choice between separated (Type IA construction) and non-separated (using only one or two hour with wood combustible construction). Why is it a "choice" and not a requirement one way or another? Very misleading and subjective for such a huge issue...

[Jerry Peck - Codeman]

You have a single building with mixed use and occupancy, and in going over the code sections and taking the various paths available for various options, I have not found a section which I believe precisely addresses your description, not even section 509 Special Provisions.

None of the specific sections in 509 address your description, and the sections do not state that they are required, those sub-section appear to only be allowances, i.e., if-this-is-done, this-is-allowed. In fact 509.1 says:
- 509.1 General. The provisions in this section shall permit the use of special conditions that are exempt from, or modify, the specific requirements of this chapter regarding the allowable heights and areas of buildings based on the occupancy classification and type of construction, provided the special condition complies with the provisions specified in this section for such condition and other applicable requirements of this code.

Your description does not fit the combinations listed in 509, therefore 509 does not apply. I suspect that the AHJ is trying to apply 509.2 as your requirement as it closely fits what you described them as saying. However, one must keep in mind that 509.1 may be used to "permit" the use of the special conditions which follow, this does not state that the section is a requirement instead of other applicable code sections.

The code does not, cannot, specifically address every conceivable configuration, that is where the AHJ can apply this:
- 104.11 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, at least the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability and safety.

Meaning it comes down to the AHJ being able to allow what you are proposing. Likewise, the AHJ also has the authority to not approve what you are proposing. An often repeated answer to a code question is: "It depends.", and with questions like this one, "it depends" to a large degree on what the AHJ will or will not approve.

Scott, I see you are reading this as I am correcting some of my wording, please make sure to re-read it again for the final working. Jerry

[Scott555]

So the short answer is I can do type VA over basement garage in all wood frame and 1 hour separation between garage and first floor using sprinklers.

The only reason one would consider doing a separated mixed use and applying 509.2 and using type 1A construction would be for square footage of footprint limitations. In other words, if the building was so large it couldn't qualify for Type VA area requirements (with all the increases added) THEN 509.2 would apply and type 1A would be required. Correct?

[Jerry Peck - Codeman]

As correct as I can determine by the code.

Your AHJ may state otherwise, and if they apply 509.1, you should point out that 509 says that it "shall permit the use of" the special conditions and that you are not applying any of those special conditions.