multi-story wood framed apartment building

[BayPointArchitect]

Given:

Type VA fully sprinkled apartment building (R2)

with a base allowable area of 12,000 S.F. and base allowable height of 3 stories.

Fourth story afforded by 13R sprinkler system.

2009 IBC 506.4.1(2) the allowable area per floor is multiplied by 3 to determine the total allowable area for the entire building with a full 13 sprinkler.

The full 13 sprinkler system is thought to be superior to the 13R system - am I correct in my thinking?

So is there a mistake in the code that uses a multiplier of 4 (for a four story building) to determine the total allowable area for the same apartment building if we use the inferior 13R sprinkler system rather than the thorough coverage (attic area) provided by the full 13? See exception #2 under IBC 506.4.1

This does not make sense to me that my multiplier would be 4 rather than 3.

Thanks again everyone.

ICC Certified Plan Reviewer

NFPA Certified Fire Plan Examiner

 

[tmurray]

The full 13 sprinkler system is thought to be superior to the 13R system - am I correct in my thinking?

No, 13 only tries to protect property. 13R and 13D protect lives and property. The basic difference is that 13R and 13D heads are more sensitive and will operate faster than than 13 which meams they can keep the fire at a smaller size longer or extinguish quicker.

 

[kilitact]

Given:Type VA fully sprinkled apartment building (R2)

with a base allowable area of 12,000 S.F. and base allowable height of 3 stories.

Fourth story afforded by 13R sprinkler system.

2009 IBC 506.4.1(2) the allowable area per floor is multiplied by 3 to determine the total allowable area for the entire building with a full 13 sprinkler.

The full 13 sprinkler system is thought to be superior to the 13R system - am I correct in my thinking?

So is there a mistake in the code that uses a multiplier of 4 (for a four story building) to determine the total allowable area for the same apartment building if we use the inferior 13R sprinkler system rather than the thorough coverage (attic area) provided by the full 13? See exception #2 under IBC 506.4.1

This does not make sense to me that my multiplier would be 4 rather than 3.

Thanks again everyone.

ICC Certified Plan Reviewer

NFPA Certified Fire Plan Examiner

Where is the code section that allows an area increase of 4 for a four story?

"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 building area limitation in Table 503 is permitted to be increased by an additional 200 percent (Is = 2) for buildings with more than one story above grade plane and an additional 300 percent (Is = 3) for buildings with no more than one story above grade plane. These increases are permitted in addition to the height and story increases in accordance with Section 504.2. "

 

[BayPointArchitect]

Section 506

Building Area Modifications

506.4 Single occupancy buildings with more than one story.

Exceptions:

2. The maximum area of a building equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.2 [13R sprinklers] shall be determined by multiplying the allowable area per story (Aa), as determined in Section 506.1, by the number of stories above grade plane.

 

[Francis Vineyard]

Perhaps this commentary may provide the answer your question. You can get an increase due to frontage in accordance with 506.1

"Exception 2 is an increase allowed for residential sprinkler systems installed in accordance with NFPA 13R. The area increases allowed by Section 506.3 are only applicable when the building is to be equipped with a sprinkler system in accordance with NFPA 13—not NFPA 13R. The three-story multiplier limit or "three-story cap" was initially evaluated based upon use of area increases resulting from the installation of an NFPA 13 system. Since buildings equipped with an NFPA 13R system are not allowed an area increase, it was determined that the "three-story cap" had an unintentional detrimental impact on residential buildings. Specifically, for a four-story residential building with an NFPA 13R sprinkler system, the provisions of Section 506.4.1 would reduce the area per story and the total building area. Given that the maximum height of buildings with NFPA 13R systems is four stories, this application of an increase in allowable area was determined to be warranted."

http://publicecodes.cyberregs.com/icod/ibc/2009f2cc/icod_ibc_2009f2cc_5_sec006.htm

 

[Paul Sweet]

IBC 903.3.2 requires Quick-response or Residential sprinklers in R occupancies.