NFPA 13R System for 4-Story with 2-Levels Below?

5/25/2022

I have a Type V-A Group R-2 apartment building whose code summary indicates as having four stories atop two levels of basement, all of the same construction and occupancy, and requiring a 13R system type.

I’m no expert in the building code, but it's my understanding that in order to have a building taller than four stories and still use 13R, a 3-hour horizontal assembly would be required having Type I construction below such assembly and up to four stories above; this building looks to be Type V throughout six levels with no horizontal assembly.

The large building is vertically separated into four individual buildings by 2-hour fire walls but I see no horizontal separation.

Is there a way this proposed 13R sprinkler system can be code compliant (IBC 2015)?

Thanks in advance.

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5 Comments

Alex

5/25/2022 06:23:44 am

Hi,

IBC (2015) Table 504.4 outlines the allowable number of stories above grade plane. The short definition of a grade plane is a “reference plane representing the average of finished ground level adjoining the building at exterior walls”. (IBC Chapter 2) For Type V-A Construction, with a NPFA 13R sprinkler system, you are permitted 4 stories above the grade plane, with a maximum allowable building height of 60 feet above grade plane.

Are the basements truly located below the grade plane? If so, are you still under the maximum allowable area including all stories?

Buildings with a horizontal separation are called podium structures. Podium construction is really all you see in and around Boston these days.

Thanks,
Alex

Todd E Wyatt

5/25/2022 08:26:35 am

Per 2021 IBC, a "BASEMENT" is defined as "a story that is not a story above grade plane."

A "STORY ABOVE GRADE PLANE" is defined as "any story having its finished floor surface entirely above grade plane, or in which the finished surface of the floor next above is:

More than 6 feet (1829 mm) above grade plane; or
More than 12 feet (3658 mm) above the finished ground level at any point."

If these (2) "stories below the grade plane" do not meet these prescribed requirements, they are classified as BASEMENTS and this building would be classified as a (4) story building + (2) basement levels.

Basements are not required to be included in the evaluation of Building Height and Number of Stories per 2021 IBC Section 504. The BUILDING HEIGHT is defined as the "vertical distance from grade plane to the average height of the highest roof surface."

The GRADE PLANE is defined as "a reference plane representing the average of finished ground level adjoining the building at exterior walls. Where the finished ground level slopes away from the exterior walls, the reference plane shall be established by the lowest points within the area between the building and the lot line or, where the lot line is more than 6 feet (1829 mm) from the building, between the building and a point 6 feet (1829 mm) from the building."

Lastly, while basements are not required to be included in the evaluation of the maximum BUILDING AREA, the total area of such basements cannot "exceed the area permitted for a one-story above grade plane building" per 506.1.3. For a Type VA Group S-2, the allowable area per Table 506.2 (S-1) would be 36,000 sf for each basement (Parking Garage) level.

Todd E Wyatt

5/25/2022 08:33:18 am

The prescribed requirements for utilizing an automatic sprinkler system in Group R occupancies per 2021 IBC is as follows :

"903.3.1.2 NFPA 13R Sprinkler Systems

Automatic sprinkler systems in Group R occupancies shall be permitted to be installed throughout in accordance with NFPA 13R where the Group R occupancy meets all of the following conditions:

1. Four stories or fewer above grade plane.

2. The floor level of the highest story is 30 feet (9144 mm) or less above the lowest level of fire department vehicle access.

3. The floor level of the lowest story is 30 feet (9144 mm) or less below the lowest level of fire department vehicle access.

The number of stories of Group R occupancies constructed in accordance with Sections 510.2 and 510.4 shall be measured from grade plane."

While this project meets #1 (4 stories or fewer), the submitted info does not address #2.

Lastly, the basement Group S-2 parking garages would not be permitted to be protected by a NFPA 13R automatic sprinkler system.

Dan Wilder

5/25/2022 08:15:21 am

It also really depends on what allowances the Architect took, floor area increases, fire rating decreases.

The NFSA did a big write up on this recently, see below:

https://nfsa.org/2020/11/17/nfpa-13-vs-nfpa-13r-in-podium-and-mixed-use-construction/

Another resource:
https://nfsa.org/wp-content/uploads/2018/03/Fire-Sprinkler-Guide-IBC-2015.pdf

Greg

5/25/2022 03:55:58 pm

I read the NFSA's explanation and looked at the picture of the residential and business use areas. I was left with the question about the depiction of the roof as 13R...

Is the roof of the building a Residential Roof or a Business Roof ?

A bit of Chicken and the Egg question but when you look at the materials used for the roof is it really residential OR is it business / mercantile ?

Possibly NFPA 13 R should either require the attic sprinkler protection or simply identify it as an area requiring protection under NFPA 13

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NFPA 13R System for 4-Story with 2-Levels Below?

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