Building Heights and Areas PDF

5 Building Heights and Areas As noted in Chapter 3, building designers almost invariably start a project with a given occupancy. After a building’s occupancy classification is determined, the code analysis task becomes one of determining what heights and areas are allowable for the occupancy classi...

5 Building Heights and Areas As noted in Chapter 3, building designers almost invariably start a project with a given occupancy. After a building’s occupancy classification is determined, the code analysis task becomes one of determining what heights and areas are allowable for the occupancy classification, given various types of construction. Criteria for allowable building heights and areas are set forth in Chapter 5 of the IBC. Economics and utility generally dictate that buildings be built using the least costly and complicated type of construction that will meet the criteria set forth in the code. Two types of design choices typically impact the use of Chapter 5 for determining allowable heights and areas. The first is when the design of a given occupancy must provide enough area to contain the known uses. The second comes into play in speculative buildings built for economic gain. The goal in these facilities, such as office buildings or retail uses, is to maximize the allowable height and area using the most economical construction type. When addressing the question of maximizing the economically viable building size, the designer must use an iterative process to maximize the space for a given building. One must make assumptions regarding construction type and analyze the relative cost and return for various construction types before the owner can make a decision. This iterative process may also be used to maximize the economic efficiency of a building where the program size requirements are the primary consideration. In either case, the goal is to achieve the maximum area with the minimum investment in construction materials while still meeting or exceeding the code-mandated requirements to protect public health, safety, and welfare. The descriptions for the allowable heights and areas for buildings that are contained in Chapter 5 were completely reorganized in an earlier code cycle from the way they were presented in previous editions of the code. For those readers still familiar with the old table and methods presented in prior code editions, it is important to remember that this reorganization was NOT intended to make any substantive revisions to the heights or areas that would have been determined under prior codes. The reorganization was undertaken only to clarify and make more consistent how allowable heights and area are interpreted by code users and authorities having jurisdiction. There are no changes in the new code edition that alter the fact that using older height and area analysis methods will yield the same results as the newer methods for the same construction types. The organization of Chapter 5 in the code is based on a set of basic criteria that are then modified by mitigating factors to allow increases or trade-offs between heights, areas, construction types, fire protection, and life safety systems. Upon first reading, the tables in Chapter 5 may seem very restrictive, but they contain modifications that give the designer greater flexibility. In summary: 1. The designer usually knows the occupancy classification of the building. 2. The program area is usually set either by program needs or by budget. 3. A construction type will usually be determined during schematic design. 4. Note that, as described in Chapter 2 regarding fire extinguishing systems, code requirements for fire sprinkler systems from Chapter 9 must be determined at this time to fully understand how to use the provisions of Chapter 5. 5. Since almost any building has a mix of incidental and accessory occupancies, and perhaps a mixture of occupancy classifications as described in Chapter 3, the provisions of § 508 must be carefully examined. DEFINITIONS As for other chapters, all definitions occur only in Chapter 2. Definitions applicable to this chapter are discussed below. The definitions have very specific code-related criteria that may differ from the colloquial meanings of the terms. They should be studied carefully for applicability when determining allowable heights and areas. • Building area is “the area included within surrounding exterior walls.” This is generally interpreted as meaning the inside face of exterior walls. See the commentary at left for a description of a more conservative approach to calculating building areas. Height limitations for buildings contained in planning and zoning regulations do not necessarily use the same definitions or criteria for determining heights. The definitions in the code are developed to facilitate uniform application of regulations. Read the documents that pertain to the regulations in question. Never apply building-code criteria to planning issues, or vice versa. Building area is usually considered to exclude the thickness of the exterior walls of a building. This is based on the language describing gross floor area as “the area included within surrounding exterior walls.” The wording seems to imply the wall is not a part of the area to be considered. Therefore, the building area is the area enclosed within the building and the area begins at the inside face of the exterior wall. Another real-estate term often used for building area is “gross building area,” which is typically calculated to the exterior side of the exterior walls. The most conservative way to calculate building area is to measure from outside face of wall to outside face of wall. This generates the most building area when nearing the upper limit of allowable area, which should never be challenged by the Authorities Having Jurisdiction. The definitions of “basement,” “grade plane,” and “building height” are correlated and based on the relationship of building parts below or above the grade plane as it is defined. Note that building height, as measured in feet, takes roof profiles into account. Building heights are measured to the average height of the highest roof, thus allowing for pitched roofs, varying parapet heights, and rooftop equipment enclosures. The height is calculated using different criteria than those used to determine the height of a building in stories. “Story” is intended to mean occupiable or usable space located inside the building contained by a floor below and a plane (next story or roof) above. Thus, this would exclude such unoccupied spaces as depressed loading docks. This definition is found with other definitions in Chapter 2. 52 / BUILDING CODES ILLUSTRATED—THE BASICS • Vent shafts and courts are excluded from building area, taking into account both the shaft’s wall thickness and the area inside the shaft as part of the excluded area. • Areas included within the horizontal projection of a floor or roof above, even if not enclosed by surrounding walls, are included in building area at full value. Thus, roof overhangs can matter in area calculations. • Basement is defined as what it is not. It is a story, but one that is “not a story above grade plane,” which term is defined in § 202. (See facing page for an explanation of grade plane.) • If the finished surface of the floor above the lower level is more than 6’ (1829) above the grade plane or if it is more than 12' (3658) above grade at any point, then that level is considered to be “a story above grade plane,” as defined in Chapter 2 of the IBC. DEFINITIONS • Building height is “the vertical distance from the grade plane to the average height of the highest roof surface.” • The story height for the topmost floor takes into account the volume of the upper floor, but not projections above the roof. Thus, it is measured: • to the top of sloping roof rafters or • to the top of ceiling joists. • Note that parapets are excluded from the height definition, but pitched rafters are included. • Story height is measured as the vertical distance from the top of one finished floor to the top of the next successive finished floor. • This is a “story above grade plane” if the finished floor surface is entirely above the grade plane. • For sloping sites, the grade plane is based on the lowest points within the area between the building and the lot line, or between the building and a point 6' (1829) from the building, whichever is smaller. • Grade plane is a reference plane representing the average grade levels along the exterior walls of the building. • Basement (if it does not meet the definition of a story above grade plane): To be a basement, the relationship between the lower floor shown and the floor above it must fail either of the following tests: 1. Be more than 6' (1829) above grade plane, or 2. Be more than 12' (3658) above the finished ground level at any point. • When an intermediate floor meets the criteria of § 505 and is considered to be a “mezzanine,” the floor level is not considered to be a “story” and it does not contribute to the floor area. Egress from mezzanines must comply with the applicable exit access provisions of Chapter 10. • Mezzanine is an intermediate floor level inserted between larger floor plates. The area of a mezzanine is limited to one-third of the floor area of the space where the mezzanine is located. Floor areas greater than one-third of the space containing them will be considered as creating another story. Note that the definition language allows multiple levels of mezzanines. • The mezzanine section calls out mezzanines and equipment platforms separately. § 505.3.1 limits the aggregate area of mezzanines and equipment platforms to be no more than twothirds of the area of the room or space where both of these elements are co-located. BUILDING HEIGHTS AND AREAS / 53 EXCEPTIONS TO BUILDING HEIGHT AND AREA LIMITATIONS § 503.1.1 exempts low-hazard, high-bay spaces, such as mills or foundries, from the height and building area limitations in § 504 and § 506. This recognizes the special-process requirements for such uses as well as their limited occupant loads with little or no public access. 1 2 3 § 503.1.3 states that Type I buildings, permitted to be of unlimited height and area per § 504 and § 506, do not require the mitigations for unlimited-area building imposed on other construction types by other sections of this chapter. § 503.1.4 regarding “occupied roofs” is included in the code to recognize the increased use of building roofs for open space in urban areas. The occupancy classification of the roof is to be per the uses allowed for the story immediately below the roof unless the building is fully sprinklered and an occupant notification alarm system is provided at the roof. The area of an occupied roof is not added to the area of the building as long as there is no roof above the uses or the elements enclosing the occupied roof area are less than 48" (1219) high and penthouses or other enclosed roof structures comply with § 1511. • § 503.1 allows one or more “fire walls” (defined and regulated by the provisions of Chapter 7) to divide a single structure into a number of “separate” buildings, determining area limitations, height limitations, and type of construction. • § 503.1.2 states that multiple buildings on a single site may be considered as separate buildings (see also § 705.3 regarding assumption of an imaginary line between them), or as a single building for determining building areas. A C B • For a group of buildings to be considered as a single building, the group must meet the aggregate area limitations based on the most restrictive occupancy. Means of egress must also be carefully examined when multiple buildings are treated as one. When multiple buildings are treated as one, the walls between them (facing area C) do not have to conform to the requirements for exterior-wall fire separation and opening protection per § 705. • E.g., Areas of A + B must not exceed the single building area of the more restrictive occupancy. If Area C is open to the sky, it does not contribute to the building area. If Area C were to be covered, it would be assigned an area and the building area would thus be A + B + C. • Penthouse or other structures per § 1511 • Occupied roof • Enclosure less than 48" (1219) high 54 / BUILDING CODES ILLUSTRATED—THE BASICS BUILDING HEIGHT AND AREA LIMITATIONS The provisions for determining allowable heights and areas are based on several factors. The first question to be determined is the type of occupancy (or multiple types in mixed-occupancy buildings) present in the proposed building. The second is whether the building is to be sprinklered or not. Next come determinations or assumptions about what construction type is desired or required for the proposed occupancies. The new organization of Chapter 5 uses the following abbreviations for conditions: • NS: Buildings not equipped throughout with an automatic sprinkler system • S = Buildings equipped throughout with an automatic sprinkler system installed in accordance with § 903.3.1.1 (NFPA 13) • S1 = Buildings a maximum of one story above grade plane and equipped throughout with an automatic sprinkler system installed in accordance with § 903.3.1.1 (NFPA 13) • SM = Buildings two or more stories above grade plane equipped throughout with an automatic sprinkler system installed in accordance with § 903.3.1.1 (NFPA 13) • S13R = Buildings equipped throughout with an automatic sprinkler system installed in accordance with § 903.3.1.2 [NFPA 13R sprinkler systems in Group R occupancies up to and including four stories in buildings not exceeding 30' (9144) in height above or below fire vehicle access. Note that the code overrides the 60' (18 288) limit of the NFPA standard.] • S13D is rarely used, so it is not anlyzed here. There are tables in the code that address heights in § 504 and areas in § 506. They are organized around occupancies and construction types, and the tables are separated to address only one aspect of height and area allowances in each table. The construction types are based on those described in Chapter 6, ranging from Type I fire-protected construction to Type V unrated construction. As in Table 601, “A” denotes construction that is “protected” with increased fire resistance and “B” denotes construction not provided with fire resistance protection or with a reduced amount of protection. BUILDING HEIGHTS AND AREAS / 55 BUILDING HEIGHT AND AREA LIMITATIONS We will first discuss the standards in the tables as general limitations. We will then examine in detail the allowable modifications contained in the tables. There are now sets of mass timber wood construction types included in the IBC. These are additional subdivisions of Type IV construction. The detailed descriptions of these types—IV-A, IV-B, and IV-C—are found in Chapter 6 and there are added height and area columns for these types in the tables in Chapter 5. Table 504.3—Height in Feet above Grade Plane Table 504.4—Height in Number of Stories above Grade Plane Construction Type (see Chapter 6) Type I Type II Type III Type IV Type V A B A B A B A B C HT A B • • • • • • • • * * * * * See Chapter 6 for a discussion of the distinctions between categories of Type IV construction. Classification (Occupancy) • A (Assembly) • B (Business) • E (Educational) NS (Nonsprinklered) S (Sprinklered) • F (Factory) • H (Hazardous) • I (Institutional) • M (Mercantile) • R (Residential) • S (Storage) • U (Utility) 55' (16 764)/2 75' (22 860)/3 56 / BUILDING CODES ILLUSTRATED—THE BASICS • Allowable building height and building area, defined in Chapter 2, are determined by the intersection of occupancy group and construction type. • As occupancy is usually determined before heights and areas, the table will typically be entered by reading down the list of occupancy groups to find the occupancy that fits the building design. • Then, reading across leads to the allowable building heights based on type of construction and whether or not the building is sprinklered. • Note that the distinction between A and B categories of construction types is the level of fire resistance as described in Table 601. Category A is of higher fire resistance, thus Type A buildings of any construction type have higher allowable heights and areas than Type B buildings. Using the principle of classifying occupancies by degree of hazard and building types by fire resistance, the higher the level of fire and life safety, the larger and taller a building can be. • Heights are expressed in two ways, both of which refer to defined terms. The first, in Table 504.3, is height in feet above the grade plane and is generally tied to fire resistance rather than occupancy. The second, in Table 504.4, is height in stories and is tied to occupancy. For discussion purposes, the values from Tables 504.3 and 504.4 are combined here. Both sets of criteria apply to any analysis. That is to avoid having high floor-to-floor heights between stories that could generate a building complying with the allowable number of stories but exceeding the height limit in feet above grade plane if heights were not also tabulated. • The illustrations starting on the facing page are taken from Table 504.3 to show the relationship of occupancy and construction type to allowable building heights in feet. The examples are chosen from building types typically encountered by designers with the construction types chosen to highlight the differences as one proceeds from Type I fire-protected construction to Type V unrated construction. Entries in the table represent allowable heights in feet, as adjusted for inclusion of fire sprinklers or not. ALLOWABLE BUILDING HEIGHTS § 504 pertains to the determination of allowable building heights in feet and stories above the grade plane. As with building areas, building heights in feet and in stories are dependent on the occupancies to be included in the building and on the building’s construction type. The inclusion of automatic sprinklers in the building also results in increases in allowable heights in feet and stories. Heights are described in two tables. The first, Table 504.3, shows allowable building heights in feet only, based on occupancy type, construction type, and sprinkler conditions. The second, Table 504.4, shows allowable building heights in terms of the number of stories, also based on occupancy type, construction type, and sprinkler conditions. The tables include all of the criteria necessary to determine allowable values for these variables. One looks in the tables under the chosen construction type, then reads down the chosen column to the occupancy in question and then makes a selection based on whether the building is sprinklered or not. The intersection of those variables in the tables gives the code user the allowable values for height in feet (Table 504.3) or height in stories (Table 504.4). There are not any adjustments necessary to the values in the tables for provision of sprinklers; those determinations are built into the two tables. Shown below is a graphic example of how Table 504.3 applies to various construction types for a representative range of occupancies. This is only an abbreviated list. Table 504.3 Allowable Building Heights in Feet above Grade Plane (based on construction type, occupancy, and sprinklers) Occupancy Classification Sprinklers Type I Type II Type III Type IV Type V A B A B A B A B UL 160' (48.8 m) 65' (19.8 m) 55' (16.8 m) 65' (19.8 m) 55' 50' (16.8 m) (15.2 m) 40' (12.2 m UL 180' (54.9 m) 85' (25.9 m) 75' (22.9 m) 85' (25.9 m) 75' 70' (22.9 m) (21.3 m) 60' (18.3 m) NS A, B, E, F, M, S, U S See expanded Table 504.3 for Type IV construction on page 59. BUILDING HEIGHTS AND AREAS / 57 ALLOWABLE BUILDING HEIGHTS Table 504.3 (cont’d) Allowable Building Heights in Feet above Grade Plane (based on construction type, occupancy, and sprinklers) Occupancy Classification Sprinklers Type I A Type II B A Type III B A Type IV Type V B A B NS1,2 UL 160' (48.8 m) 65' (19.8 m) 55' (16.8 m) 65' (19.8 m) 55' (16.8 m) 50' (15.2 m) 40' (12.2 m) S13D 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 50' (15.2 m) 40' (12.2 m) S13R 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) 60' (18.3 m) UL 180' (54.9 m) 85' (25.9 m) 75' (22.9 m) 85' (25.9 m) 75' (22.9m) 70' (21.3 m) 60' (18.3 m) R S Footnotes: 1. Nonsprinklered occupancies included only for evaluation of existing building height per the IEBC. 2. All R occupancies must be sprinklered. 58 / BUILDING CODES ILLUSTRATED—THE BASICS See expanded Table 504.3 for Type IV construction on page 59. ALLOWABLE BUILDING HEIGHTS Table 504.3 (cont’d) Allowable Building Heights in Feet above Grade Plane for Type IV Construction Occupancy Classification Sprinklers A B C HT 65' (19.8 m) 65' (19.8 m) 65' (19.8 m) 65' (19.8 m) 270' (82.3 m) 180' (54.9 m) 85' (54.9 m) 85' (54.9 m) 65’ (19.8 m) 65’ (19.8 m) 65’ (19.8 m) 65’ (19.8 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 60’ (18.3 m) 270’ (82.3 m) 180’ (54.9 m) 85’ (25.9 m) 85’ (25.9 m) NS A, B, E, F, M, S, U S NS1,2 S13D R S13R S Footnotes: 1. Nonsprinklered occupancies included only for evaluation of existing building height per the IEBC. 2. All R occupancies must be sprinklered. BUILDING HEIGHTS AND AREAS / 59 MEZZANINES AND EQUIPMENT PLATFORMS Mezzanines and Equipment Platforms § 505 considers mezzanines that meet the definition in Chapter 2 to be part of the story below them. If they meet the criteria limiting their area to one-third of the floor below, then they are not considered part of the overall building area, or as an additional story. However, the area must be counted toward the overall “Fire Area” as defined in Chapter 2. Room Area 1/3 Room Area • Equipment platforms are not considered as a portion of the floor below. Equipment platforms do not contribute to either the building area or the number of stories. Where a room contains both a mezzanine and an equipment platform, the aggregate area of the two raised floor levels may not be greater than two-thirds of the floor area of that room or space in which they are located. The area of the mezzanine may not exceed the area determined in accordance with § 505.2.1. • Mezzanines are limited by the definition in Chapter 2, which in turn refers to § 505, to one-third of the area of the space in which they are located. Such a mezzanine is not only excluded from the overall area but also from the total floor-area calculation for the room containing the mezzanine. Thus, a 1,000 sf (93 m 2 ) floor space can typically have a 333 sf (31 m 2 ) mezzanine. • Type I and II buildings housing special industrial occupancies get a bonus allowing the mezzanine to be up to two-thirds of the room floor area. • Type I and II buildings with sprinklers and voice/alarm systems may have mezzanines of up to one-half the area of the room floor area. This increase is also allowable in sprinklered residential units. • Mezzanines must be of habitable height, having a minimum of 7' (2134) clear headroom at the mezzanine level as well as in the floor area under the mezzanine. Mezzanines are conceived of by the code as open areas set above other spaces in a room. The code makes an absolute-sounding statement that all mezzanines shall be open and unobstructed to the room in which they are located, except for a railing-height wall at the edge. The statement is then followed by numerous exceptions. The basic idea is that if the mezzanine is small in area or occupant load, is furnished with a clearly defined separate exit path, or has two means of egress, it may be enclosed. 60 / BUILDING CODES ILLUSTRATED—THE BASICS • Enclosed portions of a room are not included when determining the size of the room in which a mezzanine is located. • Mezzanines are required to have means of egress per the requirements of Chapter 10 of the code. Where the common path of travel or the occupant load exceeds the limits in Table 1006.2.1, two means of egress will be required. ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Areas per Table 506.2 As discussed, in code editions prior to 2015, Table 503 combined allowable building heights in feet and stories with basic allowable areas. Each of the sets of tabular values for heights and areas were then adjusted for sprinkler conditions and location on property. The code now breaks apart height in feet, height in number of stories, and allowable areas per level into three tables. It also includes modifications inside of each table based on whether the buildings are sprinklered or not. The allowable areas are determined per Table 506.2. This table shows allowable building areas based on occupancy type and construction type. It also shows areas based on whether the building is nonsprinklered or is a sprinklered single-story or multiple-story building. It is very important to realize that under the increase formulas, the “NS” (nonsprinklered) values in this table will be used in area-increase calculations, even for sprinklered buildings. When doing a code analysis for a proposed building, it is important to note the allowable area values for nonsprinklered buildings based on anticipated occupancies and proposed construction types, so that you are able to insert them into the formulas from § 506.2 as described below. Combined Table 504.4 and Table 506.2 The tables below and on the following pages show graphically the allowable areas taken from Table 506.2, based, as for heights, on the building’s construction type, occupancy, and whether or not it is sprinklered. This table also graphically combines the number of allowable stories from Table 504.4 to represent the comparative heights and areas for the various combinations of the variables in the tables. This is a graphic tool to convey the use and implications of the choices for construction types for the various occupancies that may occur in a building. The intent of the code is that the determinations of the values from each table are made independently and then combined into a set of code criteria for design of the building. The following tables are only a sampling of the various combinations for different occupancy groups and cosntruction types. Allowable Building Heights in Stories above Grade Plane and Graphic Allowable Areas (based on construction type, occupancy, and sprinklers, and on values taken from Tables 504.4 and 506.2) Sprinklers Type I Type II Type III Type V A B A B A UL/UL 11/UL 3/15,500 2/9,500 3/14,000 2/9,500 2/11,500 1/6,000 1/UL 1/UL 1/62,000 1/38,000 1/56,000 1/38,000 1/46,000 1/24,000 UL/UL 12/UL 4/46,500 3/28,500 4/42,000 3/28,500 3/34,500 2/18,000 NS A-2, A-3, A-4 Type IV S1 SM B A See expanded Tables 504.4 and 506.2 for Type IV construction on pages 65–68. Occupancy Classification B BUILDING HEIGHTS AND AREAS / 61 ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) (based on construction type, occupancy, and sprinklers) (cont’d) Sprinklers Type I Type II Type III Type V A B A B A UL/UL 11/UL 5/37,500 3/23,000 5/28,500 1/UL 1/UL 1/150,000 1/92,000 1/114,000 1/76,000 1/72,000 1/36,000 UL/UL 12/UL 6/112,500 4/69,000 6/85,500 4/57,000 4/54,000 3/27,000 UL/UL 5/UL 3/26,500 2/14,500 3/23,500 2/14,500 1/18,500 1/UL 1/UL 1/106,000 1/58,000 1/94,000 1/58,000 1/74,000 1/38,000 UL/UL 6/UL 4/79,500 4/70,500 3/43,500 2/55,500 2/28,500 NS B Type IV S1 SM B A See expanded Tables 504.4 and 506.2 for Type IV construction on pages 65–68. Occupancy Classification 3/19,000 3/18,000 B 2/9,000 NS E 1/9,500 S1 SM 62 / BUILDING CODES ILLUSTRATED—THE BASICS 3/43,500 ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) (based on construction type, occupancy, and sprinklers) (cont’d) Sprinklers See footnotes Type I Type II Type III Type V A B A B A UL/UL 11/UL 4/24,000 4/16,000 4/24,000 4/16,000 3/12,000 2/7,000 4/UL 4/UL 4/24,000 4/16,000 4/24,000 4/16,000 4/12,000 3/7,000 1/UL 1/UL 1/96,000 1/64,000 1/96,000 1/64,000 1/48,000 1/28,000 UL/UL 12/UL 5/72,000 5/48,000 5/72,000 5/48,000 4/36,000 3/21,000 UL/UL 11/UL 4/24,000 4/16,000 4/24,000 4/16,000 3/12,000 2/7,000 4/UL 4/UL 4/24,000 4/16,000 4/24,000 4/16,000 4/12,000 3/7,000 1/UL 1/UL 1/96,000 1/64,000 1/96,000 1/64,000 1/48,000 1/28,000 UL/UL 12/UL 5/72,000 5/48,000 5/72,000 5/48,000 4/36,000 3/21,000 NS1,2 S13R R-1 Type IV S1 SM B A See expanded Tables 504.4 and 506.2 for Type IV construction on pages 65–68. Occupancy Classification B NS1,2 S13R R-2 S1 SM BUILDING HEIGHTS AND AREAS / 63 ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) (based on construction type, occupancy, and sprinklers) (cont’d) Sprinklers Type I A Type II B A Type III B A 3/26,000 4/39,000 NS S-2 Type IV See expanded Tables 504.4 and 506.2 for Type IV construction on pages 65–68. Occupancy Classification Type V B A UL/UL 11/79,000 5/39,000 1/UL 1/316,000 1/156,000 1/104,000 1/156,000 1/104,000 1/84,000 1/54,000 UL/UL 12/237,000 6/117,000 4/78,000 5/117,000 5/63,000 3/40,500 S1 SM Footnotes: 1. Nonsprinklered occupancies are included only for evaluation of existing building height per the IEBC. 2. All R occupancies must be sprinklered. 64 / BUILDING CODES ILLUSTRATED—THE BASICS 3/26,000 B 4/78,000 4/21,000 2/13,500 ALLOWABLE BUILDING HEIGHTS AND AREAS The following are expanded Tables 504.4 and 506.2 for Types IV-A, IV-B, IV-C, and IV-HT construction. Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) for Type IV Construction Occupancy Classification Sprinklers A B C HT NS A-2, A-3, A-4 3/45,000 3/30,000 3/18,750 3/15,000 1/180,000 1/120,000 1/75,000 1/60,000 18/135,000 12/90,000 6/56,250 4/45,000 5/108,000 5/72,000 5/45,000 5/36,000 1/432,000 1/288,000 1/180,000 1/144,000 18/324,000 12/216,000 9/135,000 6/108,000 S1 SM NS B S1 SM BUILDING HEIGHTS AND AREAS / 65 ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) for Type IV Construction (cont’d) Occupancy Classification Sprinklers (See footnotes.) A B C HT NS E 3/76,500 3/51,000 3/31,875 3/25,500 1/306,000 1/204,000 1/127,500 1/102,000 9/229,500 6/153,000 4/95,625 4/76,500 4/61,500 4/41,000 4/25,625 4/20,500 4/61,500 4/41,000 4/25,625 4/20,500 1/246,000 1/164,000 1/102,500 1/82,000 18/184,500 12/123,000 8/76,875 5/61,500 S1 SM NS1,2 S13R R-1 S1 SM 66 / BUILDING CODES ILLUSTRATED—THE BASICS ALLOWABLE BUILDING HEIGHTS AND AREAS Allowable Building Heights in Stories above Grade Plane (Table 504.4) and Graphic Allowable Areas (Table 506.2) for Type IV Construction (cont’d) Occupancy Classification Sprinklers (See footnotes.) A B C HT NS1.2 4/61,500 4/41,000 4/25,625 4/20,500 4/61,500 4/41,000 4/25,625 4/20,500 1/246,000 1/164,000 1/102,500 1/82,000 18/184,500 12/123,000 8/76,875 5/61,500 4/115,500 4/77,000 4/48,125 5/38,500 1/462,000 1/308,000 1/192,500 1/154,000 12/346,500 8/231,000 5/144,375 6/115,500 S13R R-2 S1 SM NS S-2 S1 SM Footnotes: 1. Nonsprinklered occupancies are included only for evaluation of existing building height per the IEBC. 2. All R occupancies must be sprinklered. BUILDING HEIGHTS AND AREAS / 67 50' (15 240) 68 / BUILDING CODES ILLUSTRATED—THE BASICS 10' (3048) 15' (4572) 75' (22 860) 25' (7620) 25' (7620) 50' (15 240) 50' (15 240) 25' (7620) 50' (15 240) The code allows for increases in allowable area when buildings front on steets and when there is separation distance from adjacent buildings or from property lines. The code uses two terms for describing the relationship of buildings to the open space around them. One term is “frontage,” which is undefined in Chapter 2. Every building must adjoin or have access to a public way to receive an area factor increase based on frontage. The frontage is also related to the overall perimeter of the building. The term “W” still appears in the code. W is related to a now-deleted equation but is intended to refer to the width of a public way or open space (feet) per § 506.3.2. 50' (15 240) In the 2021 IBC, the calculation for frontage increases has also changed as described below. Frontage Increases § 506 specifies that the areas set by Table 506.2 may be modified based on how much open space adjoins the building, including streets and open space. This is known as “frontage.” As in prior editions of the code, the equation numbering in Chapter 5 is somewhat misleading. The values for frontage increase (If) are determined by using new Table 506.3.3 and then used in Equations 5-1, 5-2, and 5-3. 40' • Every building must adjoin or have (12 192) access to a public way in order to receive an area increase. When a building has 25% or more of its perimeter opening onto a public way or open space at least 20' (6096) wide, the building’s area may be increased based on the added width (W) of the public way(s) and/ or open space(s) and the extent of the building perimeter surrounded by them. 50' (15 240) 55' (16 764) • Public way per Chapter 2 with a minimum width of 20' (6096). 75' (22 860) Allowable Building Area Determination The allowable area of a building is to be determined in accordance with the applicable provisions of § 506.2.1, § 506.2.2, and § 506.3, using the values from Table 506.2. The calculations for area increase changed dramatically from the way area increases were done under editions of the IBC prior to 2015. As noted, the increases for heights in feet and stories based on sprinklers and construction type are now built into the tables in § 504. For those code users familiar with the old calculation methods, it is very important to remember that the new methods are intended to yield the same results in terms of allowable building areas, and heights as well, as were allowed under previous editions of the IBC. Experienced code users may want to verify their calculations for allowable heights and areas using the new formulas against determinations for the allowances using formulas from the prior version of the IBC. This will help familiarize experienced users with the new methods while minimizing calculation errors. We have presented here only the new formulas to avoid confusing new code users for whom such comparisons would not be helpful. This will also familiarize experienced code users with the procedures found in the new edition of the code. 40' (12 192) ALLOWABLE BUILDING HEIGHTS AND AREAS Perimeter meeting criteria for frontage increase • The allowable increases were calculated as weighted averages in prior codes. With the 2021 edition Table 506.3.3 is introduced, showing how increases relate to the open space around the building. • If = area increase due to frontage = 0.50 from Table 506.3.3, based on 50% of building perimeter fronting onto open space that is 30' (9144) or greater in width. AREA MODIFICATIONS § 506.3.2 Minimum Frontage Distances To qualify for an area factor increase based on frontage, the public way or open space adjacent to the building perimeter must have a minimum distance (W) of 20' (6096) measured at right angles from the building face to any of the following: • Frontage • Property line • Public way lf = 0 lf = 0.17 < 20' < 20' ≥ 30' 25'– < 30' 25'– < 30' 20'– < 25' lf = 0.33 lf = 0.42 lf = 0.50 ≥ 30' 25'– < 30' ≥ 30' lf = 0.63 lf = 0.75 < 20' 20'– < 25' < 20' 25'– < 30' < 20' 25'– < 30' ≥ 30' ≥ 30' ≥ 30' 20'– < 25' 25'– < 30' < 20' 75% to < 100% “open” lf = 0.50 25'– < 30' lf = 0 ≥ 30' 25'– < 30' < 20' < 20' ≥ 30' lf = 0.25 20'– < 25' Allowable lf percent increase lf = 0 lf = 0 lf = 0.21 20'– < 25' 50% to < 75% “open” 30' or greater ≥ 30' lf = 0 < 20' 25% to < 50% “open” lf = 0 20'– < 25' lf = 0 < 20' 0% to < 25% “open” Open Space 20' to < 25' 25' to < 30' ≥ 30' Percentage of Building Perimeter 0 to < 20' 25'– < 30' 20' (6096) 25'– < 30' Example building 40' (12 192) Table 506.3.3 40' (12 192) 1. The closest interior lot line. 2. The entire width of a street, alley, or public way. 3. The exterior face of an adjacent building on the same property. 20' (6096) The frontage increase is to be based on the smallest public way or open space that is 20' (6096) or greater, and the percentage of building perimeter having a minimum 20' (6096) public way or open space. In past editions, the code had a complex set of calculations of weighted averages for determining frontage increases when distances from buildings to adjacent elements were in the 20' to 30' (6096 to 9144) range. This has been replaced with a new table giving step values for separations in those ranges. When there is a range of values based on varying distances, the lowest value is the one to be used. See the example following the table. Note that interpolation is allowed when using Table 506.3.3. For buildings where more detailed calculations may yield a larger area increase factor, calculations based on the methods used in prior code editions should be considered to be proper interpolation methods. BUILDING HEIGHTS AND AREAS / 69 AREA MODIFICATIONS Example using Table 506.3.3 From Table 506.3.3: Line Perimeter Frontage Length Length L1 L2 L3 L4 L5 L6 80' 20' 30' 75' 110' 95' 0 20' 30' 75' 110' 95' “W” Table Value for Frontage Increase 0 >30' = 0.75 >30' = 0.75 >30' = 0.75 25' = 0.63 [smallest distance >20'] >30' = 0.75 • W is measured perpendicular from the face of the building to the nearest property line. • Where W is > 30' (9144), use value of 0.75 in calculating frontage increase factor. • Where W is < 20' (6096), its value is zero in calculations. W4 = 40' (12 192) Legend W2 = 30' (9144) • L1 not included in F since W1 is < 20' (6096) • Because W1 is < 20' (6096), its value is zero per Table 506.3.3. Lot line W5 = 25' (7620) L6 = 95' (28 956) W6 = 60' (18 288) L1 = 80' (24 384) L2 = 20' (6096) W1 = 10' (3048) Perimeter where W is ≥ 20' (6096), to be used in sum of perimeter for determining frontage increase factors from Table 506.3.3. L4 = 75' (22 860) L5 = 110' (35 528) L3 = 30' (9144) W3 = 60' (18 288) Lf = 0.63 Centerline of public way 70 / BUILDING CODES ILLUSTRATED—THE BASICS • In this example, the frontage increase factor = 0.63 per Table 506.3.3. This is the value for If that is to be used for frontage increases. This is based on the language in § 506.3.2 that states: “The frontage increase shall be based on the smallest public way or open space that is 20 feet (6096 mm) or greater, and the percentage of building perimeter having a minimum 20 feet (6096 mm) public way or open space.” AREA MODIFICATIONS The first formula is Equation 5-1 from § 506.2.1, which is for single-occupancy buildings. This formula also applies to the area per story for multiple-story, single-occupancy buildings up to three stories in height. The basic tabular area is taken from Table 506.2 and is based on the construction type and sprinkler status of the building in question. 10' (3048) • Open space less than 20' (6096) not considered “frontage” but sides are part of the perimeter. • Open space more than 20' (6096) is considered “frontage.” Perimeter meeting criteria for frontage increase per Table 506.3.3 • Equation 5-1: For our example we have assumed a sprinklered B occupancy building of Type IIIA construction. The tabular area is thus for a sprinklered, single-occupancy, single-story building with added increase for frontage based on location on property. Aa = At + (NS × If) • Grade plane • Tabular area per Table 506.2 48' (14 640) 75' (22 860) 50' (15 240) 50' (15 240) 15' (4572) § 506.2 contains three formulas for calculating area modifications. The formulas make use of the frontage increase allowable per Table 506.3.3. It is very important to keep in mind that while part of the area determination is based on whether the building is to have sprinklers, the “NS” value is to be used as well, regardless of whether the building is sprinklered. Be sure that for sprinklered buildings you do not duplicate the tabular values for sprinklered buildings; instead, use the NS values in the appropriate location in the equations. • Additional area for frontage increase where: Aa = Allowable area (square feet). At = Tabular allowable area factor (NS, S1, or S13R value, as applicable) in accordance with Table 506.2. NS = Tabular allowable area factor in accordance with Table 506.2 for nonsprinklered buildings (regardless of whether the building is sprinklered). If = Area factor increase due to frontage (percent) as calculated in accordance with § 506.3. [Table 506.3.3] • Frontage Increase per § 506.3 (using Table 506.3.3) 98/196 = 0.50 Percent of building perimeter = 50% Open space > 30' = 0.50 If per Table 506.3.3 • Per Equation 5-1: Aa = At + (NS × If) Aa = 114,000 sf [10,591 m2] + ( 28,500sf [2648 m2] × 0.50) = 128,250 sf [11,914 m2] BUILDING HEIGHTS AND AREAS / 71 AREA MODIFICATIONS The second formula is Equation 5-2, which is used for determining the total area for multistory buildings with more than three stories above grade plane and containing a single occupancy group. This takes the allowable areas for shorter buildings and adds a factor for stories greater than three. Note that for this calculation, the area per Equation 5-2 is total area, not area per story. For this example, we assume a four-story, B occupancy, Type IIIA building with sprinklers and a frontage increase of 25% per Table 506.3.3. • Equation 5-2: Aa = At + (NS × If) × Sa where: Aa = Allowable area (square feet). At = Tabular allowable area factor (NS, S13R, S13D, or SM value, as applicable) in accordance with Table 506.2. NS = Tabular allowable area factor in accordance with Table 506.2 for nonsprinklered buildings (regardless of whether the building is sprinklered). If = Area factor increase due to frontage (percent) as calculated in accordance with § 506.3. [Table 506.3.3] Sa = 3 where the actual number of stories above grade plane exceeds three, or Sa = 4 where the building is equipped throughout with an automatic sprinkler system complying with § 903.3.1.2. • Frontage Increase per § 506.3 [Table 506.3.3] If = 0.25 per Table 506.3.3 (assumed for example) • Tabular area per Table 506.2 • Additional area for • Included sprinkler frontage increase increase in Table 506.2 • Per Equation 5-2: Aa = Aa = = = At + (NS × If) × Sa 85,500 sf [7943 m2] + (28,500sf [2648 m2] × 0.25) 92,625 sf [8605 m2] × 3 277,875 sf [25,815 m2] • Grade plane • Single basement, no larger than the allowable area (Aa) for a building with no more than one story above the grade plane. This could result in a code-compliant basement that is larger than the floors above. 72 / BUILDING CODES ILLUSTRATED—THE BASICS BUILDING HEIGHT AND AREA CALCULATION PROCEDURE The height and area calculation procedure we suggest is as follows: • Step 1: Read charging language at § 503.1. • Determine the height and area of the proposed building and whether multiple buildings on a single lot are to be treated as a single building or as multiple buildings with assumed lines between them. • Step 2: Read charging language at § 504.1. • The height, in feet, and the number of stories of a building shall be determined based on the type of construction, occupancy classification, and whether there is an automatic sprinkler system installed throughout the building. • Step 3: Read § 504.1 through § 504.3 and determine allowable building height in feet. From Table 504.3 Occupancy Classification Sprinklers • Determine the height in feet of the proposed building using Table 504.3. Type III A B 65' (19.8 m) 55' (16.8 m) 85' (25.9 m) 75' (22.9 m) NS A, B, E, F, M, S, U S BUILDING HEIGHTS AND AREAS / 73 BUILDING HEIGHT AND AREA CALCULATION PROCEDURE • Step 4: Read § 504.4 and determine allowable building height in stories. From Table 504.4 Occupancy Classification Sprinklers • Determine the height in stories of the proposed building using Table 504.4. Type III See footnotes A B 5/28,500 3/19,000 NS B S1 1/114,000 1/76,000 SM 6/85,500 75' (22 860) Perimeter meeting criteria for frontage increase per Table 506.3.3 50' (15 240) 10' (3048) 50' (15 240) 50' (15 240) 74 / BUILDING CODES ILLUSTRATED—THE BASICS • Determine what frontage increases are available for the proposed building based on its location on property. 15' (4572) • Step 5: Read § 506.1 through § 506.2.3 and determine the values required for determining maximum building floor area in Equation 5-1 or 5-2. If need be, go to § 506.3. (See Step 6.) 4/57,000 BUILDING HEIGHT AND AREA CALCULATION PROCEDURE 50' (15 240) 25' (7620) 25' (7620) 25' (7620) 50' (15 240) Perimeter meeting criteria for frontage increase per Table 506.3.2. • Determine if the increase in frontage is allowable per Table 506.3.3. 75' (22 860) 50' (15 240) 50' (15 240) 10' (3048) 15' (4572) • Step 6: Read § 506.3 and determine applicable allowable area frontage increase from Equations 5-1, 5-2, and 5-3. • Step 7: Using values obtained in Steps 5 and 6, determine the maximum building floor area using Equation 5-1, 5-2, or 5-3. • Insert values from Table 506.3.3 into Equations 5-1, 5-2, or 5-3, depending on configuration of the building. • Step 8: Determine maximum allowable area per story for the building using Equation 5-1, 5-2, or 5-3. • Multiply allowable area by number of stories based on allowable increases for unsprinklered or sprinklered buildings. + + = • Finished. BUILDING HEIGHTS AND AREAS / 75 MIXED USE AND OCCUPANCY § 508 Mixed Use and Occupancy This section addresses four concepts that involve having more than one occupancy in a single building. They are: • Accessory Occupancies (§ 508.2) • Nonseparated Occupancies (§ 508.3) • Separated Occupancies (§ 508.4) • Live/Work Units (§ 508.5) Per exceptions to § 508.1, the following are not considered mixed occupancies for the purposes of applying § 508: occupancies separated per § 510 and hazardous materials in separate buildings when required by Table 415.6.5. • Uses incidental to the basic or main occupancy must be separated or protected per § 509. • Accessory occupancies are still to be classified by their uses in accordance with Chapter 3 of the code. • Accessory occupancy areas need not be separated from the primary occupancy if they meet the criteria of § 508.2.3 as described at left on this page. Incinerator Room Accessory Occupancies When the occupancy contains a distinctly different ancillary use to the main occupancy of a building, and aggregate accessory occupancies do not occupy more than 10% of the floor area of the story in which they are located and do not exceed the area allowed for various nonsprinklered occupancies in Table 506.2, the accessory use need not be separated from the primary occupancy. Exceptions exist for hazardous uses or when required as an “incidental use” for dwelling units and sleeping units per § 420. It should be noted that “incidental uses” are regulated by § 509 and viewed as being part of the occupancy where it is located and not as a mixed occupancy. • The allowable building area and height is to be based on the main occupancy. B Occupancy • Separations are required for the following accessory occupancies: • Group H-2, H-3, H-4, and H-5 accessory occupancies are to be separated per § 508.4. R-1 H-2 R-1 76 / BUILDING CODES ILLUSTRATED—THE BASICS • Dwelling units and sleeping units in I-1, R-1, R-2, and R-3 occupancies are to be separated from each other and from contiguous occupancies per § 420. MIXED USE AND OCCUPANCY Mixed Occupancies When a building has a mix of occupancies that are each distinct or extensive enough to be considered as separate uses, each use is considered a separate and distinct occupancy. The mix of occupancies is addressed in several ways instead of being treated as accessory occupancies: • When using nonseparated occupancy criteria per § 508.3, uses need not be separated from one another or from the remainder of the building, but the allowable height, area, and construction type for the entire building is governed by the most restrictive criteria for each of the unseparated uses. H-2 1. Nonseparated Occupancies For nonseparated occupancies, the entire building is regulated according to the most restrictive of the height, area, and fire-protection requirements for each of the multiple occupancies under consideration. H-2 I-2 Condition 2 There are some limitations on how nonseparated occupancy rules can be applied. • Per § 508.3.1.1, where nonseparated occupancies occur in a high-rise building, the most restrictive requirements of § 403 are to apply throughout the high-rise building. • Per § 503.3.1.2, where one of the nonseparated occupancies is Group I-2, Condition 2, the most restrictive requirements of § 407, § 509, and § 712 are to apply throughout the fire area containing the Group I-2 occupancy. Per exceptions to § 508.3.3: • H-2, H-3, H-4, and H-5 occupancies must be separated, even in nonseparated occupancies. • Also, I-1, R-1, R-2, and R-3 dwelling and sleeping units must be separated from each other and from contiguous occupancies per § 420. • When using separated occupancy criteria per § 508.4, different uses may need to be separated from each other with a fire barrier, but the allowable height area and construction types for the building as a whole are determined by the requirements for each separate area. 2. Separated Occupancies Separated occupancies may require that an occupancy separation with a fire-resistance rating as defined by Table 508.4 be provided between the occupancies. Allowable Building Height and Building Area for Nonseparated Occupancies with M and A-2 Occupancies Occupancy 1 Occupancy 2 + M Occupancy (Retail) 50' (15 240)/ 3 stories/ 14,000 sf (1300 m2) = A-2 Occupancy (Restaurant) 50' (15 240)/ 2 stories/ 11,500 sf (1068 m2) 50' (15 240)/ 2 stories/ 11,500 sf (1068 m2) Example of the allowable height and area determination for a nonseparated occupancy: • Assume Type VA construction, unsprinklered (for the purposes of this example), basic allowable heights and areas per Tables 504.4 and 506.2. BUILDING HEIGHTS AND AREAS / 77 MIXED USE AND OCCUPANCY Example for a separated-occupancy height and area determination. Assume the same construction type and occupancies as on preceding page: Type V-A construction, unsprinklered, M-Occupancy (Retail/ 10,000 sf/929 m2), and A-2 Occupancy (Restaurant/ 3,000 sf/279 m2), located on the first floor. Criteria A-2 Occupancy M Occupancy Allowable Proposed Allowable Proposed (Chapter 5) (Chapter 5) Area Height (feet) Area Height (stories) Floor Area/Story (sf/m2) 50' (15 240) 2 stories 11,500/1068 m2 < 50' (15 240) On first floor 3000/279 m2 50' (15 240) 3 stories 14,000/1300 m2 < 50' (15 240) 3 stories 10,000/929 m2 Calculation for the first floor per the example and § 508.4.2: A-2 Actual area + M Actual area Allowable area Allowable area • No A-2 occupancy on third floor = 3,000 sf + 10,000 sf = 0.26 + 0.71 = 0.98 < 1.00…OK 11,500 sf 14,000 sf M-1 M-2 M-3 • The M occupancy area may be three stories in height and M uses may be located on any of the three floor levels since Table 504.4 allows the M occupancy to be three stories in height. • A-2 occupancy is to be completely separated from M occupancy by 2-hour fire barriers per § 707 and horizontal assemblies per § 711. • Potential A-2 occupancy on second floor in a sprinklered building. [Example calculations would change.] 78 / BUILDING CODES ILLUSTRATED—THE BASICS • Each occupancy area is to comply with the height and area restrictions contained in § 503. • The A-2 occupancy cannot be located above the second floor since an A-2 occupancy can only be two stories in height per Table 504.4. A-2 Per § 508.4.4.1 and § 509.4.1.1, mass timber serving as fire barriers in occupancy separations or incidental use separations in Type IV-B or IV-C construction shall be separated from building interiors by thermal barriers of gypsum board that is not less than 1/2" (12.7 mm) in thickness or a material that is tested in accordance with both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275. < 1.00 • 1/2" (12.7 mm) Gypsum board or equivalent, each side • Cross-Laminated-Timber (CLT) Type IV-B or Type IV-C mass timber framing Occupancy 1 Occupancy 2 MIXED USE AND OCCUPANCY Live/Work Units Criteria for the special class of R-2 occupancies known as “live/work units,” which used to be found in § 419, have been moved to § 508.5 since they are now considered to be a type of mixed-use occupancy. There are no technical changes to the requirements for these uses; this is just a reorganization of the code. • Storage for nonresidential portion is limited to 10% of the nonresidential portion’s area. • Live/work unit; 3,000 sf (279 m 2 ) maximum. • Unit requires sprinklers per § 903.2.8 and where required, an alarm system per § 907.2.9. Residential Area • Maximum of 5 employees Nonresidential Area • Egress per Chapter 10 for the function served by the means of egress element. • Nonresidential function areas may only occur on the first or main floor of the unit. • Nonresidential portion may be up to 50% maximum of total area. • Spiral stairs are permitted, as are vertical openings inside unit. • No separations are required inside live/ work unit, but separations between live/ work units are to be per § 420. BUILDING HEIGHTS AND AREAS / 79 MIXED USE AND OCCUPANCY Incidental Uses Uses or occupancies that are incidental to the main occupancy are not considered to have enough impact to warrant their classification as an occupancy. The structure or portion thereof must be one of the uses listed in Table 509.1. These uses are typically considered to have a higher level of fire or safety risk than the occupancies within which they occur and Table 509.1 requires additional protection or isolation from the areas within which they occur. When the occupancy of a building contains one or more incidental uses as defined in Table 509.1, the areas are considered part of the main occupancy but require fire-resistance-rated separations from the rest of the occupancy according to the requirements listed in the table. These are seldom required due to the widespread prevalence of sprinklers in buildings. Note that separation requirements for incidental uses are not applicable to dwelling units. Designation of incidental use areas is limited to those uses listed in Table 509.1. Note that incidental uses do not change the occupancy group of the area where they occur. That is why they are called “incidental.” • The code notes in § 509.4.2 that even where Table 509.1 allows just the use of a sprinkler system to protect an incidental use, barriers (including openings) around the use must be smoke-resistant. • The code states in § 509.4.2.1 that “only the space occupied by the incidental use need be equipped with such a system.” This is less than the full sprinkler provisions of NFPA 13, but based on the code conflict resolution provisions in § 102.4.1, the code allows for a very limited system instead of requiring the sprinklers throughout the building or in surrounding spaces. 80 / BUILDING CODES ILLUSTRATED—THE BASICS • The incidental uses listed in Table 509.1 include those that carry an inherent risk of fire, such as boilers, furnace rooms, and certain types and sizes of storage areas. • Fire barriers per § 707 or horizontal assemblies per § 711 should extend from the floor to the underside of the fire-resistance-rated floor/ceiling or roof/ceiling assembly. • In some cases, an automatic sprinkler system may be substituted for the firerated separation, in which case the separation must still be able to resist the passage of smoke. The code states that where an automatic sprinkler system is provided to meet the requirements of Table 509.1, it need only be provided in the incidental-use room or area. • Because § 509.4.2.1 only requires the sprinkler system within the incidental use area, such a limited sprinkler system will not qualify a building for such things as area increases that are granted for provision of sprinkler systems throughout the building. MIXED USE AND OCCUPANCY The layout of the code places Table 509.1 after the text for that section. Do not confuse Table 508.4 regarding occupancy separations with the incidental-use Table 509.1. As examples we have highlighted the incidental uses most likely to be encountered in building design: • Furnace room with equipment with > 400,000 BTUH input 1-hour separation or provide automatic sprinkler system. 1-hour separation or provide automatic sprinkler system. • Boiler room with equipment > 15 psi and 10 hp 1-hour separation or provide automatic sprinkler system. • Refrigerant machinery room 2-hour separation and provide automatic sprinkler system. • Incinerator room • Paint shops not classified as an H occupancy, in occupancies other than F • Labs not classified as an H occupancy in Groups E, I-2, or ambulatory care facilities • Laundry rooms > 100 sf (9.29 m2) 2-hour separation or provide 1-hour separation and automatic sprinkler system. 1-hour separation or provide automatic sprinkler system for Group E occupancy or ambulatory care. 1-hour separation and sprinklers for Group I-2. 1-hour separation or provide automatic sprinkler system. In I-2 laundry rooms >100 sf (9.29 m2) provide 1-hour separation. • Storage rooms > 100 sf (9.29 m2) in ambulatory care facilities or Group I-2 occupancies 1-hour separation. • In other than ambulatory care facilities and Group I-2 occupancies, waste and linen collection rooms > 100 sf (9.29 m2) 1-hour separation or provide automatic sprinkler system. • Electrical installations and transformers See § 110.26 through § 110.34 and § 450.8 through § 450.48 of NFPA 70 for protection and separation requirements. BUILDING HEIGHTS AND AREAS / 81 SPECIAL PROVISIONS § 510 is devoted to exceptions to the provisions of Tables 504.3, 504.4, and 506.2, and the other sections in Chapter 5. These exceptions apply only when all of the conditions in the subsections are met. These conditions are based on specific combinations of occupancy groups and construction types. These special provisions were code responses developed over time to meet construction conditions found in the jurisdictions of the model codes that preceded the IBC. These special provisions will usually give t