How Tall is Storage Above & Below Mezzanine?

5/12/2023

So I've run into this a couple of places and I'm curious where other professionals land. You have a warehouse that has a mezzanine. Say the warehouse is 20'-0" tall and the height of the mezzanine is an even 10'-0".

You have 8'-0" of shelf storage underneath the mezzanine. You have 8'-0" of shelf storage on the mezzanine.

You are protecting under the mezzanine separately, but the mezzanine does not make up the full floor area of the entire warehouse. So there are open areas where you only have 8'-0" of storage to a taller 20'-0" building.

Does the storage over the mezzanine bring your storage up to 18'-0" or is it 8'-0" of storage?

It's 18'-0" over the floor, but 8'-0" over the floor of the mezzanine.

And there is protection beneath the mezzanine, but the storage under the mezzanine extends beyond the outline of the mezzanine. It's still only 8'-0" high, but now the ceiling height is different.

Anyway, any input or thoughts would be great. Code references always appreciated.

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10 Comments

Anthony

5/12/2023 07:37:20 am

Depends how wide the mezzanine is. If it's under 15' then you have to cover it as if it was the adjacent hazard anyway so the area above the mezzanine is protected at 20' height requirements.

Generally speaking, if the spacing is similar and the calc's work them I'm going to let it stay as a single hazard covered at the higher rating. The field productivity will probably not be worth the material cost differences.

The area under the mezz should be treated as a lower(pun intended) hazard with the exception of heat transfer to adjacent rack storage. If the aisle is very narrow, then some judgment is needed to either change the storage configuration or add additional protection.

Dewayne Martinez

5/12/2023 08:33:30 am

I would treat it the same as Anthony.

Glenn Berger

5/12/2023 08:21:06 am

Looks like you have three different issues here:

System 1 is designed for the storage that occurs below the mezzanine. System 2 is designed for the storage on the mezzanine. System 3 is designed for the storage that occurs where there is no mezzanine.

Is the mezzanine floor solid construction or is the floor a grated material?

Dan Wilder

5/12/2023 08:44:41 am

They are considered separate areas.

Storage height from finished 1st floor = 8'
Ceiling height from finished 1st floor = 10' (below mezz)
Ceiling height from finished 1st floor = 20' (below roof deck)

Storage height from finished mezz floor = 8'
Ceiling height from finished mezz floor = 10' (below roof deck)

To confirm, no shelf/rack is taller than 8' in this scenario, just it's location.

Now the deciding factor is the mezzanine construction. If it is a solid mezz (pan deck/concrete/wood) this finalizes the separation and in either case, you have 8' of storage.

In the case of some (specifically auto parts stores are great at this) mezzanines that have open metal grating, that would trigger a total higher storage height of 18', especially if the shelving aligns above and below (and I have even seen the mezzanine have cutouts for those racks).

This creates a huge issue with shelf storage over 15' tall and I have been successful in using the lower protection as a level of in-rack protection splitting the storage. The owner did agree to place sheet metal below or plywood above to further separate the upper and lower storage areas.

Only other consideration is which NFPA 13 is being referenced as to where the square footage is assigned, but that was not your question.

Todd E Wyatt

5/12/2023 09:14:57 am

SUMMARY
2021 NFPA 13 references “MEZZANINE” (12) times but none include prescriptive requirements in determining the height of “storage above & below” a MEZZANINE.

EXPLANATION
The first step would be to verify that the MEZZANINE meets the definition and requirements (Area Limitations, Openness, Clear Height Above & Below) per the scoping Code (e.g. 2021 IBC, Section 505 MEZZANINES and Equipment Platforms). See REFERENCES below.

Assuming that the MEZZANINE meets the definition and requirements, the next step is to review the scoping Code (2021 IBC) references to “RACK STORAGE” & “HIGH-PILED (COMBUSTIBLE) STORAGE” to determine WHICH is applicable to your condition.

As it relates to “Fire Protection and Life Safety Systems”, 2021 IBC Chapter 9 Fire Protection and Life Safety Systems directs us to the 2021 International Fire Code (IFC) for additional requirements for “HIGH-PILED COMBUSTIBLE STORAGE.”

The 2021 IFC includes an entire chapter (32) on HIGH-PILED COMBUSTIBLE STORAGE ... “storage of combustible materials in closely packed piles or on pallets, in racks or on shelves where the top of storage is greater than 12 feet in height, or 6 feet for high-hazard commodities”.

Based on the referenced “8’-0” of storage”, we will assume that it is “RACK STORAGE” and not “HIGH-PILED (COMBUSTIBLE) STORAGE”

The 2021 IFC references RACK STORAGE in Chapter 32, 51, and 57 but none of these reference “MEZZANINES.”

Todd E Wyatt

5/12/2023 09:15:16 am

REFERENCES

2022 NFPA 13
Chapter 4 General Requirements
4.4 System Protection Area Limitations.
4.4.2
The floor area occupied by MEZZANINEs shall comply with 4.4.2.1, 4.4.2.2, or 4.4.2.3.
ENHANCED CONTENT
Subsection 4.4.2 clarifies where a MEZZANINE area needs to be tabulated as part of the floor area limitations specified in 4.4.1 and where it does not. Prior to these clarifications being added in the 2019 edition, it could have been interpreted that a system riser protecting a 52,000 ft² (4380 m²) area could also protect a MEZZANINE of unlimited size.
4.4.2.1
In a building with only one sprinkler system, the floor area occupied by MEZZANINEs shall not be included in the area limits of 4.4.1.
ENHANCED CONTENT
FAQ When determining the area limitations for a single floor, is the additional area occupied by MEZZANINEs required to be added to the floor area?
Paragraph 4.4.2.1 does not require the additional area occupied by the MEZZANINE to be counted against the area limitation. Exhibit 4.7 shows an example of the intent of this requirement. For high-piled storage, the area protected by one system riser cannot exceed 40,000 ft2 (3720 m2). When the area is being determined, the MEZZANINE area does not need to be added to the actual floor area.
4.4.2.2
In a building with more than one sprinkler system, if a MEZZANINE is located entirely within the same sprinkler system boundary as the sprinklers protecting the ceiling above, the floor area occupied by MEZZANINE(s) shall not be included in the area limits of 4.4.1.
4.4.2.3
In a building with more than one sprinkler system, if any portion of the MEZZANINE floor area is located outside the system boundary of the riser supplying the sprinklers under the MEZZANINE, the area of the MEZZANINE outside the boundary of the overhead system shall be added to the system area from which it is supplied, and the total system area shall meet the limits of 4.4.1.
ENHANCED CONTENT
For the 2019 edition of NFPA 13, new system protection area limitation requirements were added where MEZZANINEs are present. Prior to the 2019 edition, there was nothing to prevent an overhead sprinkler system from being installed to the area limitations of 4.4.1 and then supplying the underside of a MEZZANINE whose area far exceeded the overhead system’s boundary. For example, there was nothing to prevent a sprinkler system in a 1,000,000 ft2 (92,903 m2) building supplying a 52,000 ft2 (4830 m2) area at the roof from also supplying a 300,000 ft2 (27,870 m2) MEZZANINE. Now, with the new requirements, any MEZZANINE area that is outside the overhead system boundary must be added to the system protection area limitations and not exceed the limitations of 4.4.1. See Exhibit 4.8 for clarification of the requirements of 4.4.2.

Chapter 28 Plans and Calculations
28.5 Pipe Schedules.
28.5.1.5 Slatted Floors, Large Floor Openings, Mezzanines, and Large Platforms.
Buildings having slatted floors or large unprotected floor openings without approved stops shall be treated as one area with reference to pipe sizes, and the feed mains or risers shall be of the size required for the total number of sprinklers.
ENHANCED CONTENT
Fire spreads readily through grated or slatted floors. Therefore, an area with such divisions must be treated as a single fire area for sizing pipe.

Todd E Wyatt

5/12/2023 09:15:59 am

REFERENCES

2021 IBC
Chapter 5 General Building Heights and Areas
User note:
About this chapter: Chapter 5 establishes the limits to which a building can be built. Building height, number of stories and building area are specified in this chapter. Chapter 5 must be used in conjunction with the occupancies established in Chapter 3 and the types of construction established in Chapter 6. This chapter also specifies the impact that MEZZANINES, accessory occupancies and mixed occupancies have on the overall size of a building.

Section 505 MEZZANINES and Equipment Platforms
505.1 General
MEZZANINES shall comply with Section 505.2. Equipment platforms shall comply with Section 505.3.
505.2 MEZZANINES
A MEZZANINE or MEZZANINES in compliance with Section 505.2 shall be considered a portion of the story below. Such MEZZANINES shall not contribute to either the building area or number of stories as regulated by Section 503.1. The area of the MEZZANINE shall be included in determining the fire area. The clear height above and below the MEZZANINE floor construction shall be not less than 7 feet (2134 mm).
505.2.1 Area Limitation
The aggregate area of a MEZZANINE or MEZZANINES within a room shall be not greater than one-third of the floor area of that room or space in which they are located. The enclosed portion of a room shall not be included in a determination of the floor area of the room in which the MEZZANINE is located. In determining the allowable MEZZANINE area, the area of the MEZZANINE shall not be included in the floor area of the room.
Exceptions:
1. The aggregate area of MEZZANINES in buildings and structures of Type I or II construction for special industrial occupancies in accordance with Section 503.1.1 shall be not greater than two-thirds of the floor area of the room.
2. The aggregate area of MEZZANINES in buildings and structures of Type I or II construction shall be not greater than one-half of the floor area of the room in buildings and structures equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.1 and an approved emergency voice/alarm communication system in accordance with Section 907.5.2.2.
3. The aggregate area of a MEZZANINE within a dwelling unit that is located in a building equipped throughout with an approved automatic sprinkler system in accordance with Section 903.3.1.1 or 903.3.1.2 shall not be greater than one-half of the floor area of the room, provided that:
3.1. Except for enclosed closets and bathrooms, the MEZZANINE shall be open to the room in which such MEZZANINE is located;
3.2. The opening to the room shall be unobstructed except for walls not more than 42 inches (1067 mm) in height, columns and posts; and
3.3. Exceptions to Section 505.2.3 shall not be permitted.
505.2.1.1 Aggregate Area of MEZZANINES and Equipment Platforms
Where a room contains both a MEZZANINE and an equipment platform, the aggregate area of the two raised floor levels shall be not greater than two-thirds of the floor area of that room or space in which they are located. The area of the MEZZANINE shall not exceed the area determined in accordance with Section 505.2.1.
505.2.2 Means of Egress
The means of egress for MEZZANINES shall comply with the applicable provisions of Chapter 10.
505.2.3 Openness
A MEZZANINE shall be open and unobstructed to the room in which such MEZZANINE is located except for walls not more than 42 inches (1067 mm) in height, columns and posts.
Exceptions:
1. MEZZANINES or portions thereof are not required to be open to the room in which the MEZZANINES are located, provided that the occupant load of the aggregate area of the enclosed space is not greater than 10.
2. A MEZZANINE having two or more exits or access to exits is not required to be open to the room in which the MEZZANINE is located.
3. MEZZANINES or portions thereof are not required to be open to the room in which the MEZZANINES are located, provided that the aggregate floor area of the enclosed space is not greater than 10 percent of the MEZZANINE area.
4. In industrial facilities, MEZZANINES used for control equipment are permitted to be glazed on all sides.
5. In occupancies other than Groups H and I, which are no more than two stories above grade plane and equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, a MEZZANINE having two or more exits or access to exits shall not be required to be open to the room in which the MEZZANINE is located.

Todd E Wyatt

5/12/2023 09:16:49 am

REFERENCES

2021 IBC

Chapter 9 Fire Protection and Life Safety Systems
Section 903 Automatic Sprinkler Systems
903.1 General
Automatic sprinkler systems shall comply with this section.
903.1.1 Alternative Protection
Alternative automatic fire-extinguishing systems complying with Section 904 shall be permitted instead of automatic sprinkler system protection where recognized by the applicable standard and approved by the fire code official.
903.2 Where Required
Approved automatic sprinkler systems in new buildings and structures shall be provided in the locations described in Sections 903.2.1 through 903.2.12.
Exception: Spaces or areas in telecommunications buildings used exclusively for telecommunications equipment, associated electrical power distribution equipment, batteries and standby engines, provided that those spaces or areas are equipped throughout with an automatic smoke detection system in accordance with Section 907.2 and are separated from the remainder of the building by not less than 1-hour fire barriers constructed in accordance with Section 707 or not less than 2-hour horizontal assemblies constructed in accordance with Section 711, or both.
903.2.7 Group M
903.2.7.1 HIGH-PILED STORAGE
An automatic sprinkler system shall be provided in accordance with the International Fire Code in all buildings of Group M where storage of merchandise is in HIGH-PILED or RACK STORAGE arrays.

Section 905 Standpipe Systems
905.1 General
Standpipe systems shall be provided in new buildings and structures in accordance with Sections 905.2 through 905.11. In buildings used for HIGH-PILED COMBUSTIBLE STORAGE, fire protection shall be in accordance with the International Fire Code.

Section 907 Fire Alarm and Detection Systems
907.1 General
This section covers the application, installation, performance and maintenance of fire alarm systems and their components.
907.2.15 HIGH-PILED COMBUSTIBLE STORAGE Areas
An automatic smoke detection system shall be installed throughout HIGH-PILED COMBUSTIBLE STORAGE areas where required by Section 3206.5 of the International Fire Code.

Section 910 Smoke and Heat Removal
910.2.2 HIGH-PILED COMBUSTIBLE STORAGE
Smoke and heat removal required by Table 3206.2 of the International Fire Code for buildings and portions thereof containing HIGH-PILED COMBUSTIBLE STORAGE shall be installed in accordance with Section 910.3 in unsprinklered buildings. In buildings and portions thereof containing HIGH-PILED COMBUSTIBLE STORAGE equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, a smoke and heat removal system shall be installed in accordance with Section 910.3 or 910.4. In occupied portions of a building equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, where the upper surface of the story is not a roof assembly, a mechanical smoke removal system in accordance with Section 910.4 shall be installed.

Todd E Wyatt

5/12/2023 09:17:30 am

REFERENCES

2021 IFC
Chapter 32 HIGH-PILED COMBUSTIBLE STORAGE
User note:
About this chapter: Chapter 32 provides guidance for reasonable protection of life from hazards associated with the storage of combustible materials in closely packed piles or on pallets, in racks or on shelves where the top of storage is greater than 12 feet in height, or 6 feet for high-hazard commodities. It provides requirements for identifying various classes of commodities; and general fire and life safety features including storage arrangements, smoke and heat venting, fire department access and housekeeping and maintenance. This chapter attempts to define the potential fire severity and, in turn, determine fire and life safety protection measures needed to control and in some cases suppress a potential fire. This chapter does not cover miscellaneous combustible material storage as regulated in Section 315.

Section 3201 General
3201.1 Scope
HIGH-PILED COMBUSTIBLE STORAGE shall be in accordance with this chapter. In addition to the requirements of this chapter, the following material-specific requirements shall apply:
1. Aerosols shall be in accordance with Chapter 51.
2. Flammable and combustible liquids shall be in accordance with Chapter 57.
3. Hazardous materials shall be in accordance with Chapter 50.
4. Storage of combustible paper records shall be in accordance with NFPA 13.
5. Storage of combustible fibers shall be in accordance with Chapter 37.
6. General storage of combustible material shall be in accordance with Chapter 3.

3201.3 Construction Documents
10. Type of fire protection systems.
14. Additional information regarding required design features, commodities, storage arrangement and fire protection features within the high-piled storage area shall be provided at the time of permit, where required by the fire code official.

Section 3206 General Fire Protection and Life Safety Features
3206.1 General
Fire protection and life safety features for high-piled storage areas shall be in accordance with Sections 3206.2 through 3206.11.

Section 3208 Rack Storage
3208.1 General
Rack storage shall be in accordance with Section 3206 and this section. Bin boxes exceeding 5 feet (1524 mm) in any dimension shall be regulated as rack storage.
3208.1.1 Storage Racks
The design and installation of storage racks shall be in accordance with the International Building Code.
3208.2 Fire Protection
Where automatic sprinklers are required by Table 3206.2, an approved automatic sprinkler system shall be installed throughout the building or to 1-hour fire barriers constructed in accordance with Section 707 of the International Building Code. Openings in such fire barriers shall be protected by opening protectives having a 1-hour fire protection rating. The design and installation of the automatic sprinkler system and other applicable fire protection shall be in accordance with Section 903.3.1.1 and the International Building Code.
3208.2.1 Plastic Shelves
Storage on plastic shelves shall be protected by approved specially engineered fire protection systems.
3208.2.2 Racks With Solid Shelving
Racks with solid shelving having an area greater than 20 square feet (1.9 m2), measured between approved flue spaces at all four edges of the shelf, shall be in accordance with this section.
Exceptions:
1. Racks with mesh, grated, slatted or similar shelves having uniform openings not more than 6 inches (152 mm) apart, comprising not less than 50 percent of the overall shelf area, and with approved flue spaces are allowed to be treated as racks without solid shelves.
2. Racks used for the storage of combustible paper records, with solid shelving, shall be in accordance with NFPA 13.
3208.2.2.1 Fire Protection
Fire protection for racks with solid shelving shall be in accordance with NFPA 13.

Franck

5/12/2023 09:23:17 am

Answer is in NFPA 13

If you have open steel gratings, you have to consider the mezzanine floor as walkways.

26.9 Special Design for Palletized, Solid-Piled, Bin Box, or Shelf Storage of Class I Through Class IV Commodities.
26.9.1 Bin Box and Shelf Storage.
26.9.1.1 Bin box and shelf storage that is over 12 ft (3.7 m) but not in excess of the height limits of 21.2.1 and that is provided with walkways at vertical intervals of not over 12 ft (3.7 m) shall be protected with automatic sprinklers under the walkway(s).

26.9.1.2 Protection shall be as follows:

(1) Ceiling design density shall be based on the total height of storage within the building as provided in Chapter 21.

(2) Automatic sprinklers under walkways shall be designed to maintain a minimum discharge pressure of 15 psi (1.0 bar) for the most hydraulically demanding six sprinklers on each level. Walkway sprinkler demand shall not be required to be added to the ceiling sprinkler demand. Sprinklers under walkways shall not be spaced more than 8 ft (2.4 m) apart horizontally.

This means that in your case, you need a design for a 18 ft storage height in the mezzanine area (at the ceiling level) + sprinklers between the shelves underneath the mezzanine, designed as indicated above.

The remaining of the building is fine for a storage up to 8 ft. But I would recommend, in that case, to protect the entire building for an 18 ft high storage, just in case they want to extend the mezzanine later on.

Sprinklers installed under open gratings should be of the intermediate level/rack storage type or otherwise shielded from the discharge of overhead sprinklers.
The shielding is required to prevent cold soldering of the thermal element from the discharge of the overhead sprinkler, resulting in a delay in operation of the sprinkler.

The purpose of the sprinklers underneath the walkway is to accomplish the following:
• Reduce the likelihood of horizontal fire spread under the walkway
• Protect any storage in the walkway
• Help control the fire in the shelves

If the mezzanine is solid floor (no open shelves), then you need to protect the ceiling level for a storage up to 8 ft, and underneath the mezzanine for a storage up to 8 ft.
In that case, a minimum free space of 18 in. (45 cm) should be maintained between the top of storage and the sprinkler deflector position (ceiling level as well as under the mezzanine).

You can also check:
NFPA Research Foundation – Impact of elevated walkways in storage on sprinkler protection – Phase 1 – March 2020.

How Tall is Storage Above & Below Mezzanine?

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