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Building height and horizontal separation

B

bwswede

Member
Joined
Dec 3, 2013
Messages
9
Location
United States
Long time lurker here...I think this is my first post.

I have a client who wishes for me to design him a 5 story wood building. The ground floor would be an A-2 or a B, and the 4 floors above would be R-2.

When I read Section 508.4.3 it states that the occupancies heights are to be limited by 503.1 and are based on Type of Construction. 508.4.4 states that occupancies are to be separated in accordance with Table 508.4 (1-HR with NFPA 13 sprinklers). 508.4.4.1 goes on to say how the horizontal separations are to be constructed per 712.

Table 503 states I can have a A-2 on the ground floor of up to 2 stories. It also states I can have an R-2 of up to 3 stories when constructed per V-A standards. If I install NFPA 13 sprinklers I can bump the R-2 (built with V-A construction) up to 4 stories, to get my 5 stories in the building?

What confuses me is that the above sections reference "height" and not "stories". Am I incorrectly making a jump from "height" to "stories"? If so, what good is all the height that is allowed ((50 + 20' )+ (50 + 20') =140') if you can't also add stories? It doesn't make any sense to have 28' stories in a mostly residential building? Am I missing something here? Do I have to meet the provisions of 509 to add stories (without changing type of construction)?

Thanks in advance,

BWSwede
 
504.2 Automatic sprinkler system increase. Where a building is equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.1, the value specified in Table 503 for maximum building height is increased by 20 feet (6096 mm) and the maximum number of stories is increased by one. These increases are permitted in addition to the building area increase in accordance with Sections 506.2 and 506.3.

**************** For Group R buildings equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.2, the value specified in Table 503 for maximum building height is increased by 20 feet (6096 mm) and the maximum number of stories is increased by one, but shall not exceed 60 feet (18 288 mm) or four stories, respectively. ****************

Yes you would have to meet 509....and then there are the structural concerns...
 
Thank you for your reply.

Are you saying that if I construct the ground floor A-2 with Type V-A and construct a 1 hour horizontal separation above it that by sprinklering the entire structure to NFPA 13 I can add 1 more R-2 Type V-A floor to the 3 already allowed for a total of 5 floors in the building?

In other words this all makes sense as long as the 1-Hr horizontal separation between the occupancies allows me to add the number of allowable floors per occupancies together.

Would the second statement not apply in this case? I was told by a plan reviewer in the past that I could not install NFPA 13R sprinklers in the non-residential portion of a building. Or are you suggesting that the A-2 portion would not need to be sprinklered and that we could get away with NFPA 13R sprinklers in the R-2 portion which would allow us to stack 4 floors of R-2 on top of the horizontal separation above a non-sprinklered A-2.

Thanks again,

BWSwede
 
Good luck designing a 5 story wood structure unless you are using cross-laminated timbers http://www.smartlam.com/

2304.3.3 Shrinkage.

Wood walls and bearing partitions shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure or any plumbing, electrical or mechanical systems, or other equipment installed therein due to excessive shrinkage or differential movements caused by shrinkage. The analysis shall also show that the roof drainage system and the foregoing systems or equipment will not be adversely affected or, as an alternate, such systems shall be designed to accommodate the differential shrinkage or movements.

I believe at the very least you will have steel columns throughout the design
 
Thanks Fatboy.

mtlogcabin-Thanks for pointing out that section. I already spoke with my structural engineer and he did a 5 story wood building a few years ago. He of course did not address the plumbing/mechanical sections but he did say they developed a system of long hold-down rods that are spring loaded at each floor to take into account the floor to floor shrinkage. It was built in the same county as my project but in a different city. I'll need to run this by the local AHJ to make sure they are fine with it what is being proposed.

Thanks again,

BWSwede
 
4 stories "above grade plane" for R....Period...Is the A2 above grade plane? ..............I looked quickly for that section MT and couldn't find it thanks!
 
Thanks Steveray.

Upon further investigation I figured that. I know understand that for me to get an A-2 at the ground with 4 stories of R-2 above it I need to go to Type III-B w/NFPA 13 sprinklers for the extra R-2 story.

Thanks again,

BWSwede
 
bwswede said:
I see I have a typo or two in the post I just made. Is there a post edit feature in this forum?BWSwede
Click to expand...
There is...but you have to pay to play...Or as I see it, for the wealth of knowledge that I get access to...
 
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