Construction Type of Air-Supported Structure?

6/16/2023

We have a project with an air supported dome structure. It's serving around 430,000+ sqft of indoor sports.

However, I am a bit confused with the type of construction this would be clasified as.

As per NFPA 5000 and IBC, an air-supported structure can be Type II-B (000), but wouldn't we be limited on allowable floor area restrictions for the site of the building?

Are there any exceptions to sprinkler protection for a building like this?

I would really appreciate your point of view, thanks in advance.

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8 Comments

Pete H

6/16/2023 07:03:05 am

I don't know of an exception personally. Because I agree with you, by IBC standards (2020 edition), this is an A-4 occupancy (indoor sporting arena). It's assumedly to be sprinklered (you're asking this question on a fire protection forum), so I'd look at Table 506.2 in the IBC. Based on what I'm seeing: The allowable area for a sprinklered A-4 occupancy built out of type II-B construction is 38,000 sq. ft. Type I would be unlimited.

Take with a grain of salt, I didn't check NFPA 5000 or look into air supported structures specifically, just type II-B construction for the occupancy.

Dan Wilder

6/16/2023 08:09:05 am

NFPA 102 Section 9.5 would likely be helpful to allow some omission of sprinklers when over the field area (pending roof height) and over seating areas.

Glenn Berger

6/16/2023 08:16:02 am

The area over the stadium itself cannot be physically sprinklered. Most indoor (or covered) sports stadiums do not contain fire sprinkler systems in the arena area.

Sprinklers are provided all areas where physically possible.

With that said - Automatic smoke exhaust (or smoke management) systems are provided to ensure safe egress. Extra egress paths are provided.

You need to work with the AHJs and other safety professionals to ensure that an adequate level of fire safety is provided. You may want to research major sports arenas to obtain back-up information.

Jesse

6/16/2023 08:24:19 am

I'm going to reiterate what Glenn is saying. Its not feasible to protect over the playing field, and most sports facilities are like this.As an insurance guy I did assessments on several NBA arenas and they are, but more to protect the cat-walks and scoreboard / jumbo-tron things

Todd E Wyatt

6/16/2023 08:58:31 am

SUMMARY
This “membrane structure” (e.g. air-supported, air-inflated, membrane-covered cable, membrane-covered frame and tensile membrane structures) would be classified as a A-3/A-4 Occupancy Classification and requires to be protected by an automatic sprinkler system (ASPS). Based on the anticipated Building Area (BA) of +430,000 SF, only Type IA and Type IB (both “Unlimited” UL) would be compliant.

This “membrane structure” is required to also meet the applicable Code (e.g. 2021 IBC Chapter 31 Special Construction, Section 3102 Membrane Structures) which states in 3102.3 Type of Construction
That “Noncombustible membrane structures shall be classified as Type IIB construction. Noncombustible frame or cable-supported structures covered by an approved membrane in accordance with Section 3102.3.1 shall be classified as Type IIB construction. Heavy timber frame-supported structures covered by an approved membrane in accordance with Section 3102.3.1 shall be classified as Type IV-HT construction. Other membrane structures shall be classified as Type V construction.” Because the Building Area (BA) surpasses Type IIB’s allowable BA of 62,000 SF, this Type of Construction is not compliant.

EXPLANATION
The requirement for a building to be protected by an automatic sprinkler system (ASPS) is based on the scoping Code (e.g. 2021 IBC). Chapter 9 Fire Protection and Life Safety Systems, Section 903 Automatic Sprinkler Systems, 903.2 Where Required identifies the ASPS requirements based on the building’s Occupancy Classification (OC). Based on your description, this building would be classified as Group A Assembly (see 303.1), either as an A-3 (gymnasiums w/o spectator seating) and/or A-4 (indoor sporting events and activities with spectator seating). It does not meet the intent of A-5 (assembly uses intended for participation in or viewing outdoor activities).

Assuming it is A-3 and/or A-4, we review 903.2.1 Group A and find that an ASPS is required for A-3 and/or A-4 if any one of the following parameters are met :
1. The fire area exceeds 12,000 square feet (1115 m2).
2. The fire area has an occupant load of 300 or more.
3. The fire area is located on a floor other than a level of exit discharge serving such occupancies.

Since this building meets all parameters, an ASPS is required.

Once we know the OCs and if an ASPS is required, we can then evaluate the “allowables” (Building Area, Number of Stories, and Building Height) per Chapter 5 General Building Heights and Areas to determine the compliant Types of Construction (TC) per Chapter 6 Types of Construction. The Building Area (BA) of +430,000 SF will be the deciding factor. Based on TABLE 506.2 ALLOWABLE AREA FACTOR, only Type IA and Type IB, both “Unlimited” (UL) would be compliant :

A-3 & A-4 (S1 : Single Story)
Type IA UL
Type IB UL
Type IIA 62,000
Type IIB 38,000
Type VA 46,000
Type VB 24,000

Per 2021 IBC, “Sections 3102.1 through 3102.8 shall apply to air-supported, air-inflated, membrane-covered cable, membrane-covered frame and tensile membrane structures, collectively known as membrane structures, erected for a period of 180 days or longer.”
Per 2021 IBC, a “NONCOMBUSTIBLE MEMBRANE STRUCTURE” is defined as “A membrane structure in which the membrane and all component parts of the structure are noncombustible.” A “TENSILE MEMBRANE STRUCTURE” is defined as “A membrane structure having a shape that is determined by tension in the membrane and the geometry of the support structure. Typically, the structure consists of both flexible elements (e.g., membrane and cables), nonflexible elements (e.g., struts, masts, beams and arches) and the anchorage (e.g., supports and foundations). This includes frame-supported tensile membrane structures.”

Todd E Wyatt

6/16/2023 08:59:15 am

REFERENCES
2021 IBC
303.4 Assembly Group A-3
Group A-3 occupancy includes assembly uses intended for worship, recreation or amusement and other assembly uses not classified elsewhere in Group A including, but not limited to:
Gymnasiums (without spectator seating)
Indoor swimming pools (without spectator seating)
Indoor tennis courts (without spectator seating)
303.5 Assembly Group A-4
Group A-4 occupancy includes assembly uses intended for viewing of indoor sporting events and activities with spectator seating including, but not limited to:
Arenas
Skating rinks
Swimming pools
Tennis courts
303.6 Assembly Group A-5
Group A-5 occupancy includes assembly uses intended for participation in or viewing outdoor activities including, but not limited to:
Amusement park structures
Bleachers
Grandstands
Stadiums

Chapter 4 Special Detailed Requirements Based on Occupancy and Use

Chapter 5 General Building Heights and Areas
Section 503 General Building Height and Area Limitations
503.1 General
Unless otherwise specifically modified in Chapter 4 and this chapter, building height, number of stories and building area shall not exceed the limits specified in Sections 504 and 506 based on the type of construction as determined by Section 602 and the occupancies as determined by Section 302 except as modified hereafter. Building height, number of stories and building area provisions shall be applied independently. For the purposes of determining area limitations, height limitations and type of construction, each portion of a building separated by one or more fire walls complying with Section 706 shall be considered to be a separate building.
Section 503 General Building Height and Area Limitations
503.1 General
Unless otherwise specifically modified in Chapter 4 and this chapter, building height, number of stories and building area shall not exceed the limits specified in Sections 504 and 506 based on the type of construction as determined by Section 602 and the occupancies as determined by Section 302 except as modified hereafter. Building height, number of stories and building area provisions shall be applied independently. For the purposes of determining area limitations, height limitations and type of construction, each portion of a building separated by one or more fire walls complying with Section 706 shall be considered to be a separate building.
506.1 General
The floor area of a building shall be determined based on the type of construction, occupancy classification, whether there is an automatic sprinkler system installed throughout the building and the amount of building frontage on public way or open space.

A-3 & A-4 (S1 : Single Story)
Type IA UL
Type IB UL
Type IIA 62,000
Type IIB 38,000
Type VA 46,000
Type VB 24,000

Chapter 6 Types of Construction
602.2 Types I and II
Types I and II construction are those types of construction in which the building elements specified in Table 601 are of noncombustible materials, except as permitted in Section 603 and elsewhere in this code.
602.3 Type III
Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.
602.4 Type IV
Type IV construction is that type of construction in which the building elements are mass timber or noncombustible materials and have fire-resistance ratings in accordance with Table 601.
602.5 Type V
Type V construction is that type of construction in which the structural elements, exterior walls and interior walls are of any materials permitted by this code.

Chapter 9 Fire Protection and Life Safety Systems
Section 903 Automatic Sprinkler Systems
903.1 General
Automatic sprinkler systems shall comply with this section.
903.2 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.
903.2.1 Group A
An automatic sprinkler system shall be provided throughout buildings and portions thereof used as Group A occupancies as provided in this section.
903.2.1.3 Group A-3
An automatic sprinkler system shall be provided throughout stories containing Group A-3 occupancies and throughout all stories from the Group A-3 occupancy to and including the levels of exit discharge serving that occupancy where one of the following conditions exists:
1. The fire area exceeds 12,000 square feet (1115 m2).
2. The fire area has an occupant load of 300 or more.
3. The fire area is located on a floor other than a level of exit discharge serving such occupancies.
903.2.1.4 Group A-4
An automatic sprinkler system shall be provided throughout stories containing Group A-4 occupancies and throughout all stories from the Group A-4 occupancy to and including the levels of exit discharge servin

Todd E Wyatt

6/16/2023 09:00:15 am

REFERENCES continued ...
2021 IBC

903.2.1.4 Group A-4
An automatic sprinkler system shall be provided throughout stories containing Group A-4 occupancies and throughout all stories from the Group A-4 occupancy to and including the levels of exit discharge serving that occupancy where one of the following conditions exists:
1. The fire area exceeds 12,000 square feet (1115 m2).
2. The fire area has an occupant load of 300 or more.
3. The fire area is located on a floor other than a level of exit discharge serving such occupancies.

Chapter 31 Special Construction
Section 3102 Membrane Structures
3102.1 General
The provisions of Sections 3102.1 through 3102.8 shall apply to air-supported, air-inflated, membrane-covered cable, membrane-covered frame and tensile membrane structures, collectively known as membrane structures, erected for a period of 180 days or longer. Those erected for a shorter period of time shall comply with the International Fire Code. Membrane structures covering water storage facilities, water clarifiers, water treatment plants, sewage treatment plants, greenhouses and similar facilities not used for human occupancy are required to meet only the requirements of Sections 3102.3.1 and 3102.7. Membrane structures erected on a building, balcony, deck or other structure for any period of time shall comply with this section.
3102.2 Tensile Membrane Structures and Air-Supported Structures
Tensile membrane structures and air-supported structures, including permanent and temporary structures, shall be designed and constructed in accordance with ASCE 55. The provisions in Sections 3102.3 through 3102.6 shall apply.
3102.3 Type of Construction
Noncombustible membrane structures shall be classified as Type IIB construction. Noncombustible frame or cable-supported structures covered by an approved membrane in accordance with Section 3102.3.1 shall be classified as Type IIB construction. Heavy timber frame-supported structures covered by an approved membrane in accordance with Section 3102.3.1 shall be classified as Type IV-HT construction. Other membrane structures shall be classified as Type V construction.
Exception: Plastic less than 30 feet (9144 mm) above any floor used in greenhouses, where occupancy by the general public is not authorized, and for aquaculture pond covers is not required to meet the fire propagation performance criteria of Test Method 1 or Test Method 2, as appropriate, of NFPA 701.
3102.3.1 Membrane and Interior Liner Material
Membranes and interior liners shall be either noncombustible as set forth in Section 703.3 or meet the fire propagation performance criteria of Test Method 1 or Test Method 2, as appropriate, of NFPA 701 and the manufacturer's test protocol.
Exception: Plastic less than 20 mil (0.5 mm) in thickness used in greenhouses, where occupancy by the general public is not authorized, and for aquaculture pond covers is not required to meet the fire propagation performance criteria of Test Method 1 or Test Method 2, as appropriate, of NFPA 701.
3102.4 Allowable Floor Areas
The area of a membrane structure shall not exceed the limitations specified in Section 506.
3102.5 Maximum Height
Membrane structures shall not exceed one story nor shall such structures exceed the height limitations in feet specified in Section 504.3.
Exception: Noncombustible membrane structures serving as roofs only.
3102.6 Mixed Construction
Membrane structures shall be permitted to be utilized as specified in this section as a portion of buildings of other types of construction. Height and area limits shall be as specified for the type of construction and occupancy of the building.
3102.6.1 Noncombustible Membrane
A noncombustible membrane shall be permitted for use as the roof or as a skylight of any building or atrium of a building of any type of construction provided that the membrane is not less than 20 feet (6096 mm) above any floor, balcony or gallery.
3102.6.1.1 Membrane
A membrane meeting the fire propagation performance criteria of Test Method 1 or Test Method 2, as appropriate, of NFPA 701 shall be permitted to be used as the roof or as a skylight on buildings of Type IIB, III, IV-HT and V construction, provided that the membrane is not less than 20 feet (6096 mm) above any floor, balcony or gallery.
3102.7 Engineering Design
The structure shall be designed and constructed to sustain dead loads; loads due to tension or inflation; live loads including wind, snow or flood and seismic loads and in accordance with Chapter 16.
3102.7.1 Lateral Restraint
For membrane-covered frame structures, the membrane shall not be considered to provide lateral restraint in the calculation of the capacities of the frame members.
3102.8 Inflation Systems
Air-supported and air-inflated structures shall be provided with primary and auxiliary inflation systems to meet the minimum requirements of Sections 3102.8.1 through 3102.8.3.
3102.8.1 Equipment Requirements
The inflation system shall consist of one o

Ben Hoffmann

1/9/2024 03:44:28 pm

Check IBC Section 507 Unlimited Area Buildings, specifically Section 507.4, Sprinklered, one-story buildings, Exception 2 where automatic sprinkler system shall not be required in areas occupied for indoor participant sports provided you have direct egress to the outside, have a fire alarm system, and have sprinklers in the ancillary / non-sport areas (storage, locker rooms, etc.)

Construction Type of Air-Supported Structure?

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