Welcome to Chapter 3. In this chapter we will explore general building heights and areas. This chapter includes some definitions that are applied to this code. The purpose of definitions is to keep you updated on words that may take on different meanings in the International Building Code world. I am going to introduce you to a few more groups and their classifications and the codes that these groups must follow.
The following words and definitions applied to this chapter and used in other places in this code have the meanings as described below:
Area, building: The area included within surrounding exterior walls (or exterior walls and fire walls) exclusive of vent shafts and courts. Areas of the building not provided with surrounding walls must be included in the building area if these areas are included within the horizontal projection of the roof or floor above.
Basement: The portions of buildings that are partly or completely below grade plane. A basement must be considered as a story above grade plane where the finished surface of the floor above the basement is more than 6 feet above grade plane or more than 12 feet above the finished ground level at any point.
Equipment platform: An unoccupied, elevated platform used exclusively for mechanical systems or industrial process equipment, including the associated elevated walkways, stairs, and ladders necessary to access the platform.
Grade plane: 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 must 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 from the building, between the building and a point 6 feet from the building.
Height, building: The vertical distance from grade plane to the average height of the highest roof surface.
Height, story: The vertical distance from top to top of two successive finished floor surfaces; and, to the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters.
Mezzanine: An intermediate level or levels between the floor and ceiling of any story and in accordance with this chapter.
The height and area for buildings of different construction types will be ruled by the intended use of the building and cannot go over the limits except as modified from now on. Each part of a building included within the inside and outside walls and fire walls, where present, will be allowed to be a separate building. Buildings and structures that are designed to accommodate special industrial processes that require large areas and unusual heights to contain cranes or special machinery and equipment are exempt from the height restrictions, such as:
Rolling mills
Structural metal fabrication shops and foundries
The production and distribution of electricity
The production and distribution of gas or steam power.
There are situations when two or more buildings are on the same building lot. When this happens, they are to be regulated as separate buildings or they will be considered as parts of one building if the height of each building and the total area of the buildings are within the limits of Table 4.4 as modified by this code. The requirements of this code that are valid to the total building will be appropriate to each building. Buildings that are Type I construction are allowed to be unlimited level heights and areas are not required to stick to the special requirements that allow unlimited area buildings, unlimited height, or increased height and areas for other types of construction in this chapter.
The height that is allowed by code will be increased in agreement with this section with the exception that the height of one-story aircraft hangars, aircraft paint hangers, and buildings used for the manufacturing of aircraft will not be limited if the building is provided with an automatic fire-extinguishing system and is entirely surrounded by public ways or yards no less in width than one and one-half times the height of the building.
Mezzanines that conform to this section can be considered a portion of the story. They cannot, however, be counted as either the building area or the number of stories as regulated by this section. The area of the mezzanine must be included in determining the fire area. The clear floor height of your mezzanine cannot be less than 7 feet.
CODE UPDATE |
A basement is a story that is not a story above the grade plane. |
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Height includes roof structures. Towers, steeples, and other roof structures must be constructed of materials that are consistent with the required type of construction except where other construction is allowed by Chapter 15. These structures cannot be used for living space or storage. If roof structures, such as towers and steeples, are made of noncombustible materials then their height is unlimited, but they cannot extend more than 20 feet above the allowable height if the structure is not made of noncombustible materials. Chapter 15 has additional information regarding these requirements. |
The total area of a mezzanine within a room is not allowed to be over one-third of the floor area of the room or the space that they are in. You also cannot include the enclosed part of the room to determine the floor area where the mezzanine is located. When determining the allowable mezzanine area, the area of the mezzanine cannot be included in the floor area except for the following:
The total area of mezzanines in buildings and structures that are Type I or II for special industrial occupancies in accordance with this chapter cannot be more than two-thirds of the area in the room.
The total area of mezzanines in buildings and structures that are Type I or II cannot be more than one-half of the area of the room in buildings and structures that have an approved sprinkler system throughout. The sprinkler system has to be in accordance with code requirements and an approved emergency voice/alarm communication system.
Mezzanines are no different when talking about exits and exit routes. Each occupant of a mezzanine must have access to at least two exits where the common path of exit travel is over the limits of Chapter 10. If the exit from your mezzanine is a stairway, the maximum travel distance must include the distance traveled on the stairway measured in the plane of the tread nosing. Accessible means of exits must be provided, as well as a single means of exit. If a building or structure has a mezzanine it has to be open and no obstructions are allowed in the room where the mezzanine is located, except for walls that are not more than 42 inches high, columns, and posts.
There are five exceptions to this code, and they are as follows:
Mezzanines or portions that are of concern are not required to be open, provided that the occupant load does not go over 10 persons.
Mezzanines or portions that are of concern are not required to be open to the room if at least one of the exits provides direct access to an exit from the mezzanine level.
Mezzanines are not required to be open to the room, provided that the total floor area of the enclosed space does not go over 10 percent of the area.
In industrial facilities, mezzanines used for control equipment are allowed to be glazed on all sides.
In Groups H and I occupancies that are no more than two stories in height above grade plane and equipped with an automatic sprinkler, a mezzanine having two or more exits is not required to be open to the room in which the mezzanine is located.
Equipment platforms in buildings cannot be considered as a portion of the floor below and must not contribute to either the building area or the number of stories as regulated by this chapter. You may also not use the area of the equipment platform to determine the fire area. Equipment platforms cannot be part of any mezzanine and these platforms and walkways, stairs, and ladders that provide access to an equipment platform cannot be used as an exit from the building either. There are some area limitations that you must be aware of.
The total area of all equipment platforms within a room cannot be larger than two-thirds of the area of the room which they are in. If the equipment platform is located in the same room as a mezzanine, the area of the mezzanine must be determined by this chapter and the combined total area of the equipment platforms and mezzanines cannot be more than two-thirds of the room that they are in. If a mezzanine is in a building that is required to have an automatic sprinkler system, equipment platforms must be fully protected by these sprinklers above and below the platform.
You know that this code limits the areas that are permitted to be increased with the proper automatic sprinkler system in place. There is an equation that must be applied when increasing these areas in accordance with Equation 3.1.
Aa = Allowable area per story in square feet.
At = Tabular area per story in accordance with Table 4.4 in square feet.
If = Area increase factor due to frontage as calculated in accordance with this chapter.
Is = Area increase factor due to sprinkler system protection as calculated in accordance with this chapter.
A single basement that is not a story above plane does need to be included in the total allowable area if it is not bigger than the area that is allowed for a building with no more than one story above grade plane.
Each building must connect or have access to a public way to receive an area increase for frontage. Where a building has more than 25 percent of its outside on a public way or open space that has a minimum width of 20 feet, the frontage increase must be determined in accordance with Equation 3.2.
If = Area increase due to frontage.
F = Building perimeter that fronts on a public way or open space having 20 feet open minimum width.
P = Perimeter of entire building in feet.
W = Width of public way or open space (feet) in accordance with this chapter.
Width must be at least 20 feet. Where the value of width varies along the perimeter of the building, the calculation performed in accordance with Equation 5.1 must be based on the weighted average of each part of the exterior wall and open space where the value of “W” is greater than or equal to 20 feet. When “W” is more than 30 feet, a value of 30 feet must be used in calculating the weighted average, regardless of the actual width of the open space. The exception being that the quantity of “W” divided by 30 must be permitted to be a maximum of two when the building meets all requirements of this chapter except for compliance with the 60-foot public way or yard requirement, if applicable. These open spaces must be either on the same lot or dedicated for public use and must be accessed from a street or approved fire lane.
If a building is equipped with an approved automatic sprinkler throughout the building, the area is allowed to be increased by an additional 200 percent (Is = 2) for buildings with more than one story above grade plane and an additional 300 percent (Is = 3) for buildings with no more than one story above grade plane. These increases are permitted in addition to the height and story increases. The following list contains exceptions that must be made to this:
The automatic sprinkler system increase cannot apply to buildings with an occupancy in Group H-1.
The automatic sprinkler system increase must not apply to the floor area of occupancy in Group H-2 or H-3. For mixed-use buildings containing these occupancies, the allowable area must be calculated in accordance with this book, with the sprinkler increase applying only to the portions of the buildings not classified as Group H-2 or H-3.
CODE UPDATE |
Two or more buildings on the same lot shall be regulated as separate buildings or shall be considered as portions of one building, if the building height of each building and the aggregate building area of the buildings are within code limitations. |
Fire-resistance rating substitution in accordance with code allowances.
The maximum area of a building with more than one story above grade plane must be determined by multiplying the allowable area of the first story (Aa), as determined in the above section, by the number of stories above grade plane as listed below:
For buildings with three or more stories above grade plane, multiply by three.
For buildings with two stories above grade plane, multiply by two.
No story can be larger than the allowable area per story (Aa), as determined in the above section, for the occupancies on that story.
Unlimited area buildings in accordance with this chapter and the maximum area of the building equipped throughout with an automatic sprinkler system determined by multiplying the allowable area per story (Aa), as determined in this chapter, by the number of stories above grade plane are two exceptions to area determination.
In buildings with mixed occupancies, the allowable area must be based on the most restrictive provision for each occupancy when the mixed occupancies are treated in accordance with this chapter. When the occupancies are treated according to this chapter, as separate occupancies, the maximum total building area must be the ratios for each area on all floors as calculated according to this chapter and not go over two for two-story buildings and three for buildings three stories or higher.
The area of buildings and occupancies and configurations of this section will not be limited. The area of a one-story, non-sprinkler Group F-2 or S-2 building must not be limited when the building is surrounded and attached by public ways or yards not less than 60 feet in width. If the area of a one-story, Group B, F, M, or S building or a one-story Group A-4 building, of other than Type V construction, must not be limited when the building is equipped with an automatic sprinkler system throughout, provided it is in accordance with code requirements and it must be surrounded and attached by public ways or yards not less than 60 feet in width. Exceptions:
The area of a Group F-2 or S-2 building that is no more than one story in height shall not be limited when the building is surrounded and adjoined by public ways or yards that are not less than 60 feet in width. |
Buildings and structures of Type I and II construction for rack storage facilities that do not have access by the public must not be limited in height, provided that these buildings conform to the requirements of this code and to NFPA 230.
The automatic sprinkler system is not required to be in an area occupied for indoor participant sports, such as tennis, skating, swimming, and equestrian activities in occupancies in Group-A, if the exit doors to the outside are provided and the building is equipped with a sprinkler system.
Group A-1 and A-2 occupancies other than Type V construction must be permitted, provided that all assembly occupancies are separate from other spaces as required with no reduction allowed in the fire-resistance rating and each Group A occupancy cannot be larger than the maximum allowance and all required exits lead directly outdoors.
If a two-story building that is Group B, F, M, or S, and is equipped with an automatic sprinkler system, the area will not be limited. It must, however, be surrounded and adjoined by public ways or yards no less than 60 feet in width. The permanent open space of 60 feet required in this chapter will be permitted to be reduced to no less than 40 feet, if the following requirements are met:
The reduced open space is not allowed for more than 75 percent of the perimeter of the building.
The exterior wall facing the reduced open space must have a minimum fire-resistance rating of three hours.
Openings in the exterior wall facing the reduced open space must have opening protectives with a minimum fire protection rating of three hours.
The area of a one-story, Group A-3 building used as one of the following:
A place of religious worship
Community hall
Dance hall
Exhibition hall
Gymnasium
Lecture hall
Indoor swimming pool
Tennis court.
These group uses that must be of Type II construction are not limited when the building does not have a stage other than a platform, if the building is equipped throughout with an automatic sprinkler system, the assembly floor is located at or within 21 inches of street or grade level; all exits provided with ramps and buildings not surrounded and adjoined by public ways or yards no less than 60 feet in width.
Group H occupancies to include H-2, H-3, and H-4 occupancies will be permitted in unlimited area buildings containing Group F and S occupancies, in accordance with this chapter and the limitations of this section. The total floor area of the Group H occupancies that are located at the outside of the unlimited area building cannot be more than 10 percent of the area of the building or the area limitations for Group H occupancies that are specified in the code as modified by this chapter that are based upon the percentage of the perimeter of each Group H fire area that looks onto on a street or other unoccupied space. Also, the total floor area of Group H occupancies not located at the outside of the building cannot be more than 25 percent of the area limitations for the Group H occupancies. For two-story unlimited area buildings, the Group H fire areas cannot be located above the first story unless permitted by the allowable height in stories and feet as described in this code based on the type of construction of the unlimited area building.
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The area of a one-story, Group H-2 aircraft paint hangar will not be limited when it complies with the provisions of this code and is totally surrounded by public ways or yards no less in width than one and one-half times the height of the building. |
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Covered mall buildings and anchor stores having an area of no more than three stories in height that comply with this code will not be limited. |
Group E buildings of Type II, IIIA, or IV construction will not be limited when the following criteria are met:
Each classroom must have no less than two means of exits, with one of those exits being a direct exit to the outside of the building.
The building is equipped throughout with an automatic sprinkler system.
The building is surrounded by and joined by public ways or yards no less than 60 feet (18,288 mm) in width.
Buildings or parts of buildings that contain two or more occupancies or uses are classified as mixed use. This section applies to mixed use occupancy and the buildings that they occupy. The first subject of this section cover incidental uses that must comply with this section, the only exceptions are incidental use areas that serve as a dwelling or living space that do not have to comply with this section. An incidental use area must be classified in accordance with the occupancy of that portion of the building in which it is located or the building must be classified as a mixed occupancy and will comply with this section.
With some exceptions, no separation is required between accessory occupancies and the main occupancy. |
Where the code allows an automatic fire-extinguishing system without a fire barrier, the incidental use area must be separated from the rest of the building by construction that is capable of resisting smoke from passing through the building. The partitions must extend from the floor to the underneath of the fire-resistance-rated floor/ceiling assembly or fire-resistance-rated roof/ceiling assembly above or to the bottom of the floor or roof sheathing or sub deck above. Doors must be self-closing or automatic closing when the detection of smoke is made. Doors also must not have any air transfer openings and cannot be undercut in excess of the clearance that is permitted in accordance of NFPA 80.
Where an automatic fire-extinguishing system or automatic sprinkler system is provided, only the incidental use areas need to be equipped with this system.
We are now ready to investigate Chapter 4 to learn more of the meat of the code.
