TOC (ASCE/SEI 55-16)
Provisions
CommentaryAREA LIMITS AND STRUCTURE CLASSIFICATIONS
This appendix is provided as a supplement to the legally adopted building code. The following standards are referred to in this appendix:
NFPA 10. “Portable fire extinguishers”
NFPA 13. “Installation of sprinkler systems”
NFPA 14. “Installation of standpipe and hose systems”
NFPA 72. “National fire alarm code”
The purpose of this appendix is to provide requirements for membrane structure sizes to be used in conjunction with the legally adopted building code or when such provisions do not exist in a legally adopted building code. These provisions are based on a combination of factors, including occupancy types, separation from other buildings, and availability of sprinkler systems. Building use and occupancy classifications are based on the 2012 International Building Code.
Table A-1 shall be used for structures constructed using Class I membranes or noncombustible frame or cable-supported structures covered by a Class II membrane. Table A-2 shall be used for all other membrane structures, including air-supported structures using a Class II membrane.
| Base Area, ft2 (m2) | Width 30 ft(9,144 mm) Open Space on All Sides | With Sprinklers | Width 30 ft(9,144 mm) Open Space on All Sides + Sprinklers | Width 60 ft(18,288 mm) Open Space on All Sides | Width 60 ft(18,288 mm) Open Space on All Sides + Sprinklers | ||
|---|---|---|---|---|---|---|---|
| Assembly | |||||||
| A-1 | Assembly uses, usually with fixed seating, intended for the production and viewing of performing arts (theaters and studios) | 25,500 (2,369) | 44,625 (4,146) | 76,500 (7,107) | 95,625 (8,884) | 63,750 (5,923) | 114,750 (10,661) |
| A-2 | Food and drink consumption | 28,500 (2,648) | 49,875 (4,634) | 85,500 (7,943) | 106,875 (9,929) | 71,250 (6,619) | 128,250 (11,915) |
| A-3 | Worship, recreation amusement, library | 28,500 (2,648) | 49,875 (4,634) | 85,500 (7,943) | 106,875 (9,929) | 71,250 (6,619) | 128,250 (11,915) |
| A-4 | Indoor sporting events | 28,500 (2,648) | 49,875 (4,634) | 85,500 (7,943) | 106,875 (9,929) | 71,250 (6,619) | 128,250 (11,915) |
| A-5 | Participation in or viewing outdoor activities | UL | UL | UL | UL | UL | UL |
| Business | |||||||
| B | Offices, professional services, outpatient clinics | 69,000 (6,410) | 120,750 (11,218) | 207,000 (19,231) | 258,750 (24,039) | 172,500 (16,026) | 310,500 (28,846) |
| Educational | |||||||
| E | A building or structure for use by six or more people at any one time for educational purposes through the 12th grade | 43,500 (4,041) | 76,125 (7,072) | 130,500 (12,124) | 163,125 (15,155) | 108,750 (10,103) | 195,750 (18,186) |
| Factory/Industrial | |||||||
| F-1 | Moderate hazard (not low hazard) | 46,500 (4,320) | 81,375 (7,560) | 139,500 (12,960) | 174,375 (16,200) | 116,250 (10,800) | 209,250 (19,440) |
| F-2 | Low hazard (involves manufacturing of noncombustible materials) | 69,000 (6,410) | 120,750 (11,218) | 207,000 (19,231) | 258,750 (24,039) | 172,500 (16,026) | 310,500 (28,846) |
| Hazardous | |||||||
| H-1 | Buildings or structures that contain materials, which present a detonation hazard: explosives | 7,000 (650) | 12,250 (1,138) | 21,000 (1,951) | 26,250 (2,439) | 17,500 (1,626) | 31,500 (2,926) |
| H-2 | Buildings or structures that contain materials, which present a deflagration hazard or a hazard from accelerated burning: flammable or combustible liquids | 21,000 (1,951) | 36,750 (3,414) | 63,000 (5,853) | 78,750 (7,316) | 52,500 (4,877) | 94,500 (8,779) |
| H-3 | Buildings or structures that contain material, which support combustion or present a physical hazard: aerosols, combustible fibers, and flammable solids | 42,000 (3,902) | 73,500 (6,828) | 126,000 (11,706) | 157,500 (14,632) | 105,000 (9,755) | 189,000 (17,559) |
| H-4 | Buildings or structures that contain materials, which are health hazards: corrosives, highly toxic materials, and radioactive materials | 52,500 (4,877) | 91,875 (8,535) | 157,500 (14,632) | 196,875 (18,290) | 131,250 (12,193) | 236,250 (21,948) |
| H-5 | Semiconductor fabrication facilities and comparable research and development areas in which hazardous production materials are used (exceeding specified quantities) | 69,000 (6,410) | 120,750 (11,218) | 207,000 (19,231) | 258,750 (24,039) | 172,500 (16,026) | 310,500 (28,846) |
| Institutional | |||||||
| I-1 | Supervised residential care facility with more than 16 people in 24 h | 30,000 (2,787) | 52,500 (4,877) | 90,000 (8,361) | 112,500 (10,451) | 75,000 (6,968) | 135,000 (12,542) |
| I-2 | Medical or custodial care with more than five people in 24 h, not capable of self-preservation | 33,000 (3,066) | 57,750 (5,365) | 99,000 (9,197) | 123,750 (11,497) | 82,500 (7,665) | 148,500 (13,796) |
| I-3 | More than five people not capable of self-preservation because of security measures | 30,000 (2,787) | 52,500 (4,877) | 90,000 (8,361) | 112,500 (10,452) | 75,000 (6,968) | 135,000 (12,542) |
| I-4 | Daycare facilities | 39,000 (3,623) | 68,250 (6,341) | 117,000 (10,870) | 146,250 (13,587) | 97,500 (9,058) | 175,500 (16,304) |
| Mercantile | |||||||
| M | A building or structure for the display and sale of merchandise and accessible to the public | 37,500 (3,484) | 65,625 (6,097) | 112,500 (10,451) | 140,625 (13,064) | 93,750 (8,710) | 168,750 (15,677) |
| Residential | |||||||
| R-1 | Transient (hotels and boarding houses) | 48,000 (4,459) | 84,000 (7,804) | 144,000 (13,378) | 180,000 (16,723) | 120,000 (11,148) | 216,000 (20,067) |
| R-2 | More than two dwelling units (apartments and dormitories) | 48,000 (4,459) | 84,000 (7,804) | 144,000 (13,378) | 180,000 (16,723) | 120,000 (11,148) | 216,000 (20,067) |
| R-3 | One- to two-family dwellings | UL | UL | UL | UL | UL | UL |
| R-4 | Assisted living facilities with fewer than 16 people | 48,000 (4,459) | 84,000 (7,804) | 144,000 (13,378) | 180,000 (16,723) | 120,000 (11,148) | 216,000 (20,067) |
| Storage | |||||||
| S-1 | Moderate hazard storage | 52,500 (4,877) | 91,875 (8,535) | 157,500 (14,632) | 196,875 (18,290) | 131,250 (12,193) | 236,250 (21,948) |
| S-2 | Low hazard storage of noncombustible materials, may be on wood pallets or in cardboard | 78,000 (7,246) | 136,500 (12,681) | 234,000 (21,739) | 292,500 (27,174) | 195,000 (18,116) | 351,000 (32,609) |
| Miscellaneous | |||||||
| U | Private garages, carports, sheds, and agricultural buildings | 25,500 (2,369) | 44,625 (4,146) | 76,500 (7,107) | 95,625 (8,884) | 63,750 (5,923) | 114,750 (10,661) |
Note: UL indicates unlimited.
| Base Area, ft2 (m2) | Width 30 ft(9,144 mm) Open Space on All Sides | With Sprinklers | Width 30 ft(9,144 mm) Open Space on All Sides + Sprinklers | Width 60 ft(18,288 mm) Open Space on All Sides | Width 60 ft(18,288 mm) Open Space on All Sides and Sprinklers | ||
|---|---|---|---|---|---|---|---|
| Assembly | |||||||
| A-1 | Assembly uses, usually with fixed seating, intended for the production and viewing of performing arts (theaters and studios) | 16,500 (1,533) | 28,875 (2,683) | 49,500 (4,599) | 61,875 (5,748) | 41,250 (3,832) | 74,250 (6,898) |
| A-2 | Food and drink consumption | 18,000 (1,672) | 31,500 (2,926) | 54,000 (5,017) | 67,500 (6,271) | 45,000 (4,181) | 81,000 (7,525) |
| A-3 | Worship, recreation amusement, library | 18,000 (1,672) | 31,500 (2,926) | 54,000 (5,017) | 67,500 (6,271) | 45,000 (4,181) | 81,000 (7,525) |
| A-4 | Indoor sporting events | 18,000 (1,672) | 31,500 (2,926) | 54,000 (5,017) | 67,500 (6,271) | 45,000 (4,181) | 81,000 (7,525) |
| A-5 | Participation in or viewing outdoor activities | UL | UL | UL | UL | UL | UL |
| Business | |||||||
| B | Offices, professional services, outpatient clinics | 27,000 (2,508) | 47,250 (4,390) | 81,000 (7,525) | 101,250 (9,406) | 67,500 (6,271) | 121,500 (11,288) |
| Educational | |||||||
| E | A building or structure, for use by six or more people at any one time for educational purposes through the 12th grade. | 28,500 (2,648) | 49,875 (4,634) | 85,500 (7,943) | 106,875 (9,929) | 71,250 (6,619) | 128,250 (11,915) |
| Factory/Industrial | |||||||
| F-1 | Moderate hazard (not low hazard) | 25,500 (2,369) | 44,625 (4,146) | 76,500 (7,107) | 95,625 (8,884) | 63,750 (5,923) | 114,750 (10,661) |
| F-2 | Low hazard (involves manufacturing of noncombustible materials) | 39,000 (3,623) | 68,250 (6,341) | 117,000 (10,870) | 146,250 (13,587) | 97,500 (9,058) | 175,500 (16,304) |
| Hazardous | |||||||
| H-1 | Buildings or structures that contain materials, which present a detonation hazard: explosives | 7,000 (650) | 12,250 (1,138) | 21,000 (1,951) | 26,250 (2,439) | 17,500 (1,626) | 31,500 (2,926) |
| H-2 | Buildings or structures that contain materials, which present a deflagration hazard or a hazard from accelerated burning: flammable or combustible liquids | 9,000 (836) | 15,750 (1,463) | 27,000 (2,508) | 33,750 (3,135) | 22,500 (2,090) | 40,500 (3,763) |
| H-3 | Buildings or structures that contain materials, which readily support combustion or present a physical hazard: aerosols, combustible fibers, and flammable solids | 15,000 (1,394) | 26,250 (2,439) | 45,000 (4,181) | 56,250 (5,226) | 37,500 (3,484) | 67,500 (6,271) |
| H-4 | Buildings or structures that contain materials, which are health hazards: corrosives, highly toxic materials, and radioactive materials | 19,500 (1,812) | 34,125 (3,170) | 58,500 (5,435) | 73,125 (6,794) | 48,750 (4,529) | 87,750 (8,152) |
| H-5 | Semiconductor fabrication facilities and comparable research and development areas in which hazardous production materials are used (exceeding specified quantities) | 27,000 (2,508) | 47,250 (4,390) | 81,000 (7,525) | 101,250 (9,406) | 67,500 (6,271) | 121,500 (11,288) |
| Institutional | |||||||
| I-1 | Supervised residential care facility with more than 16 people in 24 h | 13,500 (1,254) | 23,625 (2,195) | 40,500 (3,763) | 50,625 (4,703) | 33,750 (3,135) | 60,750 (5,644) |
| I-2 | Medical or custodial care with more than five people 24 h, not capable of self-preservation | NP | NP | NP | NP | NP | NP |
| I-3 | More than five people not capable of self-preservation because of security measures | 15,000 (1,394) | 26,250 (2,439) | 45,000 (4,181) | 56,250 (5,226) | 37,500 (3,484) | 67,500 (6,271) |
| I-4 | Daycare facilities | 27,000 (2,508) | 47,250 (4,390) | 81,000 (7,525) | 101,250 (9,406) | 67,500 (6,271) | 121,500 (11,288) |
| Mercantile | |||||||
| M | A building or structure for the display and sale of merchandise and accessible to the public | 27,000 (2,508) | 47,250 (4,390) | 81,000 (7,525) | 101,250 (9,406) | 67,500 (6,271) | 121,500 (11,288) |
| Residential | |||||||
| R-1 | Transient (hotels and boarding houses) | 21,000 (1,951) | 36,750 (3,414) | 63,000 (5,853) | 78,750 (7,316) | 52,500 (4,877) | 94,500 (8,779) |
| R-2 | More than two dwelling units (apartments and dormitories) | 21,000 (1,951) | 36,750 (3,414) | 63,000 (5,853) | 78,750 (7,316) | 52,500 (4,877) | 94,500 (8,779) |
| R-3 | One- to two-family dwellings | UL | UL | UL | UL | UL | UL |
| R-4 | Assisted living facilities with fewer than 16 people | 21,000 (1,951) | 36,750 (3,414) | 63,000 (5,853) | 78,750 (7,316) | 52,500 (4,877) | 94,500 (8,779) |
| Storage | |||||||
| S-1 | Moderate hazard storage | 27,000 (2,508) | 47,250 (4,390) | 81,000 (7,525) | 101,250 (9,406) | 67,500 (6,271) | 121,500 (11,288) |
| S-2 | Low hazard storage of noncombustible materials, may be on wood pallets or in cardboard | 40,500 (3,763) | 70,875 (6,585) | 121,500 (11,288) | 151,875 (14,110) | 101,250 (9,406) | 182,250 (16,932) |
| Miscellaneous | |||||||
| U | Private garages, carports, sheds, and agricultural buildings | 16,500 (1,533) | 28,875 (2,683) | 49,500 (4,599) | 61,875 (5,748) | 41,250 (3,832) | 74,250 (6,898) |
Note: UL indicates unlimited. NP indicates not permitted.
The areas in Tables A-1 and A-2 shall be permitted to be further increased by the authority having jurisdiction by performance-based approval, on the basis of the structure design having appropriate levels of safety in terms of exiting provisions, sprinkler systems, fire alarms, standpipes, and internal and external fire separations. Use and occupancy classification in Table A-1 is based on those as outlined in Chapter 3 of the International Building Code.
The base areas shown in Tables shall be increased based on frontage () and automatic sprinkler system protection in accordance with the following:
allowable area per floor (in sq. ft.)
base area per floor (in sq. ft.)
area increase due to frontage (percent) as calculated in accordance with Eq. A-2
area increase due to sprinkler protection (percent) as calculated in accordance with Eqs. (A-2) and (A-2.si)
Where a building has more than 25% of its perimeter on a public way or open space at least 20 ft(6,096 mm) wide, the frontage shall be determined as follows:
Area increase due to frontage
Building perimeter that fronts on a public way or open space having 20-ft(6,096-mm) open minimum width (ft or mm)
Perimeter of the entire building (ft or mm)
Width of the public way or open space (ft or mm),
Such open space shall be either on the same lot or dedicated for public use and shall be accessed from a street or approved fire lane.
Where a building is protected throughout with an approved automatic sprinkler system in accordance with NFPA 13, the area limitation in Tables shall be increased by an additional 300% () for buildings no more than one story above grade and 200% () for buildings with more than one story above grade.
Membrane structures using Class III membranes shall be limited to uses where occupancy by the general public is not authorized, such as greenhouses and aquaculture pond covers. Such structures shall have at least 20 ft(6,096 mm) of open space on all sides. The allowable area is unlimited.
Fire protection shall meet the following requirements and shall conform to the building code or the requirements of Appendix A, if Appendix A is accepted by the authority having jurisdiction.
Sprinkler systems shall be provided as required by the authority having jurisdiction and shall comply with NFPA 13. Fire protection of the membrane and liner shall not be required for that portion of the structure that is more than 25 ft(7,620 mm) above a combustible surface.
In areas where overhead sprinkler systems cannot be supported from the membrane structure, an alternate fire protection system shall be allowed as long as the system meets the standards for equivalent protection as allowed by the authority having jurisdiction.
Commentary
SPECIAL PROVISIONS
SPECIAL PROVISIONS
The history of tensile membrane structure regulation dates back to efforts to control circus tent flammability as a result of the circus fire in Hartford, Connecticut, in 1944, in which 168 lives were lost. These regulations focused on requiring that the tent fabric be flame resistant, that there be adequate exiting from the grandstands and from the tent, and that there be sufficient cleared space around the tent to control ignition sources there and to permit rapid emergency exiting.
When membrane structures first came into common use, their primary applications were as temporary, seasonal covers for outdoor areas, such as swimming pools and tennis courts. These covers would be put up during the winter and taken down for the summer. They were, therefore, classified as temporary structures, which today generally is defined as being in place for fewer than 180 consecutive calendar days. The requirements for such structures were essentially the same as for tents.
Large, permanent tensile membrane structures began to see significant use in the United States in the early 1960s. At that time, no provisions in any of the building codes defined and accepted such a structure. In the late 1960s, as a result of the erection of several major architectural fabric buildings and roof structures in California, an effort was begun to develop new provisions in the Uniform Building Code published by the International Conference of Building Officials. That effort, however, specifically addressed the PTFE-coated glass fiber membrane that was being used on those projects and, therefore, the provisions were written around that material. The provisions as written effectively banned the use of any of the other membranes, even though they had been used for many years in more traditional fabric structure applications.
The code permits allowable floor area to be increased when the perimeter of the building is more accessible to the local fire department. No increase is allowed until at least 25% of the building perimeter is accessible. It also mandates that the open space be at least 20 ft(6,096 mm) wide before area increases are allowed. The equations shown provide the method for calculating the amount of increase. Table A-1 and Table A-2 show the allowable increase when the entire perimeter of the building is accessible and when the open space width is at least 30 ft(9,144 mm). For conditions where the open perimeter is more than 25% less than 100%, or the open space width is more than 20 ft(6,096 mm) but less than 30 ft (9,144 mm), it is necessary to use the equations to determine the allowable area increase.
Class III materials are limited to occupancies that are intended to be well away from adjacent exposures and to be occupied only by those few who use them in the course of their work. Examples would include agricultural buildings, such as greenhouses.
TABLE A-1 AND TABLE A-2 MAXIMUM FOOTPRINT AREAS
Allowable floor areas for membrane structures were established by adding a multiplication factor of three to the formulas in the International Building Code for Type II B and Type V B construction. All other allowable area increases are then added, such as side yards and sprinkler systems, using the formulas in Section A.1.2.
This increase is based on the following:
An internal fire source may generate sufficient heat to damage the membrane, which allows for the venting of smoke and heat.
Conventional sprinkler and fire alarm systems can be designed and installed to activate if and when a fire occurs away from the structure membrane. Other fire suppression systems are on the market, such as foam deluge and water cannons, which can be incorporated.
Membrane structures can be set back from existing buildings and vegetation to prevent the spread of a fire from external sources.
Membrane structures can be penetrated easily by fire-fighting personnel. Firefighters can fight the fire from the perimeter of the structure.
The risk of flashover also is greatly minimized because of early heat and smoke venting.
Because of the high vaulted ceilings in a membrane structure, it has been found that smoke and heat have a tendency to collect in the high roof areas, leaving the floor clear of smoke and making it easier for the public to safely exit the building and for firefighters to locate and extinguish the fire.
Emergency exits with panic hardware can be easily installed into a membrane structure. Exit distances can be reduced or increased based on occupancy, exit distances, width, and quantity.
Roof monitors with dampers can be installed to remove smoke as it collects in the high roof (smoke reservoir) areas.
In the case of air-supported structures, the fact that the building is a positive pressure space will further aid in smoke removal through built-in vents or an opening caused by a fire.
High Hazard Group H1 buildings or structures contain materials that present a detonation hazard – explosives. The allowable area for this use and occupancy is the same in both Tables A-1 and A-2, because when an explosive event occurs, the membrane for both structures will react similarly by opening up and providing an area for venting of smoke and heat.