Maximum Height for Non-Protected Plenum?

2/13/2019

Is there a maximum height that's permitted between the main roof and a suspended ceiling in order to still omit sprinklers above the ceiling?

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6 Comments

Wayne Ammons

2/13/2019 07:52:33 am

If I am understanding your question correctly, you are describing a concealed space above a suspended ceiling. The omission of sprinklers will depend on there being access to the space and the amount of combustibles within the space (also considering construction type). If there is limited or no access and minimal combustibles are present, sprinklers can be omitted regardless of the distance between the suspended ceiling and main roof deck.

MIGUEL ANGEL D ADARIO

2/13/2019 04:03:56 pm

Dear Wayne
I would like to invert the question
What is the minimum height to which a sprinkler is effective in concealed space of combustible construction?

Wayne Ammons

2/14/2019 07:37:35 am

Unfortunately, there are a number of exceptions of varying scenarios where sprinklers may be omitted. I have copied the section from NFPA 13, 2019 edition concerning concealed spaces below. Hopefully one of these exceptions explain your particular situation:

5-13 Special Situations.
5-13.1 Concealed Spaces.
5-13.1.1*All concealed spaces enclosed wholly or partly by exposed combustible construction shall be protected by sprinklers.

Exception No. 1: Concealed spaces formed by studs or joists with less than 6 in. (152 mm) between the inside or near edges of the studs or joists. (See Figure 5-6.4.1.4.)
Exception No. 2: Concealed spaces formed by bar joists with less than 6 in. (152 mm) between the roof or floor deck and ceiling.
Exception No. 3: Concealed spaces formed by ceilings attached directly to or within 6 in. (152 mm) of wood joist construction.
Exception No. 4: Concealed spaces formed by ceilings attached directly to the underside of composite wood joist construction, provided the joist channels are firestopped into volumes each not exceeding 160 ft
3(4.53 m3) using materials equivalent to the web construction.
Exception No. 5: Concealed spaces entirely filled with noncombustible insulation.
Exception No. 6: Concealed spaces within wood joist construction and composite wood joist construction having noncombustible insulation filling the space from the ceiling up to the bottom edge of the joist of the roof or floor deck, provided that in composite wood joist construction the joist channels are firestopped into volumes each not exceeding 160 ft3 (4.53 m3) to the full depth of the joist with material equivalent to the web construction.
Exception No. 7: Concealed spaces over isolated small rooms not exceeding 55 ft2 (4.6 m2) in area.
Exception No. 8: Where rigid materials are used and the exposed surfaces have a flame spread rating of 25 or less and the materials have
been demonstrated not to propagate fire in the form in which they are
installed in the space.
Exception No. 9: Concealed spaces in which the exposed materials are constructed entirely of fire-retardant treated wood as defined by NFPA 703, Standard for Fire Retardant Impregnated Wood and Fire Retardant Coatings for Building Materials.
Exception No. 10: Noncombustible concealed spaces having exposed combustible insulation where the heat content of the facing and substrate of the insulation material does not exceed 1000 Btu/ft2 (11,356 kJ/m2).
Exception No. 11: Sprinklers shall not be required in the space below insulation that is laid directly on top of or within the ceiling joists in an otherwise sprinklered attic.
Exception No. 12: Pipe chases under 10 ft2(0.93 m2) formed by studs or wood joists, provided that in multifloor buildings the chases are firestopped at each floor using materials equivalent to the floor construction. Such pipe chases shall contain no sources of ignition, piping shall be noncombustible, and pipe penetrations at each floor shall be properly sealed

Wayne Ammons

2/14/2019 07:55:41 am

I realized I copied sections from the entirely wrong edition. Please disregard my previous response and I will follow-up shortly.

Wayne Ammons

2/14/2019 08:29:08 am

Below is from the 2016 edition of NFPA 13, I am having trouble pulling from the 2019 edition:

8.15 Special Situations.
8.15.1 Concealed Spaces.
8.15.1.1 Concealed Spaces Requiring Sprinkler Protection.
Concealed spaces of exposed combustible construction shall be protected by sprinklers except in concealed spaces where sprinklers are not required to be installed by 8.15.1.2.1 through 8.15.1.2.18 and 8.15.6.

8.15.1.2* Concealed Spaces Not Requiring Sprinkler Protection.
8.15.1.2.1*Concealed spaces of noncombustible and limited combustible construction with minimal combustible loading having no access shall not require sprinkler protection.
8.15.1.2.1.1 The space shall be considered a concealed space even with small openings such as those used as return air for a plenum.
8.15.1.2.1.2 Small openings with a combined total area of not more than 20 percent of the ceiling, construction feature, or plane used to determine the boundaries of the concealed space shall be permitted where length greater than 4 ft (1.2 m) shall not have a width greater than 8 in. (200 mm).
8.15.1.2.1.3 The space above cloud ceilings meeting the requirements in 8.15.24.1 and having openings with a combined total area of not more than 20 percent of the ceiling, construction feature, or plane used to determine the boundaries of the concealed space shall be permitted.
8.15.1.2.2 Concealed spaces of noncombustible and limited combustible construction with limited access and not permitting occupancy or storage of combustibles shall not require
sprinkler protection.
8.15.1.2.2.1 The space shall be considered a concealed space even with small openings such as those used as return air for a plenum.
8.15.1.2.3 Concealed spaces formed by studs or joists with less than 6 in. (150 mm) between the inside or near edges of the studs or joists shall not require sprinkler protection. (See Figure 8.6.4.1.5.1.)
8.15.1.2.4 Concealed spaces formed by bar joists with less than 6 in. (150 mm) between the roof or floor deck and ceiling shall not require sprinkler protection.
8.15.1.2.5*Concealed spaces formed by ceilings attached directly to or within 6 in. (150 mm) of wood joist or similar solid member construction shall not require sprinkler protection.
8.15.1.2.6*Concealed spaces formed by ceilings attached to composite wood joist construction either directly or onto metal channels not exceeding 1 in. (25 mm) in depth, provided the joist channels are firestopped into volumes each not exceeding 160 ft3 (4.5 m3) using materials equivalent to the web construction and at least 3 1⁄2in. (90 mm) of batt insulation is installed at the bottom of the joist channels when the ceiling is attached utilizing metal channels, shall not require sprinkler protection.
8.15.1.2.7 Concealed spaces filled with noncombustible insulation shall not require sprinkler protection.
8.15.1.2.7.1 A maximum 2 in. (50 mm) air gap at the top of the space shall be permitted.
8.15.1.2.8 Concealed spaces within wood joist construction and composite wood joist construction having noncombustible insulation filling the space from the ceiling up to the bottom edge of the joist of the roof or floor deck, provided that in composite wood joist construction the joist channels separated into volumes each not exceeding 160 ft3 (4.5 m3) to the full depth of the composite wood joist with material equivalent to the web construction, shall not require sprinkler protection.
8.15.1.2.9 Concealed spaces over isolated small compartments not exceeding 55 ft2 (5.1 m2) in area shall not require sprinkler protection.
8.15.1.2.10 Concealed spaces where rigid materials are used and the exposed surfaces have a flame spread index of 25 or less, and the materials have been demonstrated not to propagate fire more than 10.5 ft (3.2 m) when tested in accordance with ASTM E84,Standard Test Method of Surface Burning Characteristics of Building Materials, or ANSI/UL 723, Standard for Test for Surface Burning Characteristics of Building Materials, extended for an additional 20 minutes in the form in which they are installed, shall not require sprinkler protection.
8.15.1.2.11*Concealed spaces in which the exposed materials are constructed entirely of fire retardant–treated wood as defined by NFPA 703 shall not require sprinkler protection.
8.15.1.2.12 Noncombustible concealed spaces having exposed combustible insulation where the heat content of the facing and substrate of the insulation material does not exceed 1000 Btu/ft2 (11,400 kJ/m2) shall not require sprinkler protection.
8.15.1.2.13 Concealed spaces below insulation that is laid directly on top of or within wood joists or composite wood joists used as ceiling joists in an otherwise sprinklered concealed space, with the ceiling attached directly to the bottom of the joists, shall not require sprinkler protection.
8.15.1.2.14 Vertical pipe chases under 10 ft2 (0.9 m2), where provided in multifloor buildings where the chases are firestopped at each floor using

Franck Orset

2/19/2019 11:15:57 am

Dear Wayne

NFPA 13 2019 Edition is a nightmare for those who used NFPA 13 for ages...

The information you provided, is now in chapter 9 (Sprinkler location requirements)
The main § is now 9.2.1* Concealed Spaces Not Requiring Sprinkler Protection.
All the § you mentioned above are the same, but with "9.2.1" instead of "8.15.1.2".

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