Code structure: the IBC and local adoption

Kostyshyn begins the second week by stacking books on the table, one on top of another, until the pile is nearly as tall as Joon-ho's elbow. The International Building Code. The International Residential Code. The International Fire Code. The International Energy Conservation Code and the ASHRAE energy standard. The Minnesota Rules chapters that adopt and amend them. The city's zoning code. Then the standards the codes refer to: sprinklers, fire alarms, the electrical code, accessibility, concrete, steel, wood, glass. She looks at the students. 'Nobody reads all of this. Your job is to know which book answers which question, and how the books fit together. That is what today is about.'

Model codes and adopted codes

The United States has a layered system. At the national level, the International Code Council develops a family of model codes: the International Building Code, the International Residential Code for one- and two-family dwellings and townhouses, the International Fire Code, the International Energy Conservation Code, the International Mechanical, Plumbing and Fuel Gas codes, and the International Existing Building Code, among others. The model codes have no force until a state or local government adopts them. Under the Constitution, building regulation belongs to the states, which either adopt a code statewide or leave adoption to cities and counties. Some states adopt the model codes word for word; most adopt them with amendments that reflect local conditions or policies. A few large cities, such as New York and Chicago, write their own codes.

Minnesota has a single State Building Code that applies throughout the state. The Department of Labor and Industry adopts the model codes by rule, with Minnesota amendments, in a series of chapters of the Minnesota Rules: chapter 1300 for administration, chapter 1305 for the building code, chapter 1309 for the residential code, chapter 1341 for accessibility, chapters 1322 and 1323 for residential and commercial energy, and others for mechanical, plumbing and fire. The current State Building Code, adopted in 2020, is based on the 2018 International Building Code. The department began rulemaking in January 2025 to adopt the 2024 edition, and until that rule takes effect, the 2018-based code remains the law. The commercial energy code was updated separately and since January 2024 has been based on ASHRAE Standard 90.1-2019. Cities such as Minneapolis enforce the state code and cannot adopt stricter technical requirements of their own, although they may adopt certain optional chapters, such as additional sprinkler requirements.

Kostyshyn insists on one habit: on the first sheet of every permit set, the code analysis must name the edition of the code that applies. A drawing that says it complies with the IBC without saying which edition, and without naming the Minnesota State Building Code, is not a code analysis. Requirements change between editions, sometimes significantly, and the edition in force is the one the permit will be judged against. Many of the textbooks, websites and manufacturers' guides that students consult refer to editions that are not in force where they are working.

How the code is organized

The International Building Code is organized in chapters. Chapter 1 covers scope and administration, Chapter 2 definitions, Chapter 3 occupancy classification and Chapter 4 special requirements for particular uses such as atriums, high-rise buildings, parking garages and assembly spaces. Chapter 5 sets allowable building heights and areas, Chapter 6 types of construction, Chapter 7 fire and smoke protection features such as fire walls, fire barriers and opening protectives, Chapter 8 interior finishes, and Chapter 9 fire protection and life safety systems such as sprinklers and fire alarms. Chapter 10 covers means of egress, Chapter 11 accessibility and Chapter 12 the interior environment, including light, ventilation and sound. The later chapters cover the envelope, structure, materials, building services by reference to the other codes, and safeguards during construction. Chapter 35 lists the referenced standards.

Requirements in the IBC are numbered by chapter and section, so that Section 1005.3 is in Chapter 10, and tables carry the number of the section in which they appear: Table 504.3 sets building heights in feet, Table 504.4 heights in stories, and Table 506.2 allowable areas. Exceptions follow many sections and are as important as the rules they modify; a large share of the arguments between designers and building officials turn on whether an exception applies. The code also uses defined terms, printed in italics in the official text and defined in Chapter 2. 'Building area', 'fire separation distance', 'story above grade plane' and 'occupant load' have precise meanings that are not always the everyday ones.

Referenced standards

A building code does not contain everything it requires. It refers to hundreds of standards written by other organizations and makes them part of the code by reference. When the code says that sprinklers must be designed and installed in accordance with NFPA 13, the whole of that standard, as listed in the code's table of referenced documents and in the edition listed there, becomes part of the code for the project. The same is true of the standards for fire alarms, for concrete, steel and wood design, for glass, for accessibility, for the fire testing of assemblies and for dozens of other subjects.

The International Building Code refers to standards from the National Fire Protection Association, ASTM International, Underwriters Laboratories and many other organizations. Important examples for architects include ASTM E119 and UL 263 for fire tests of building assemblies, ASTM E84 for surface flame spread, NFPA 13, 13R and 13D for sprinklers, NFPA 72 for fire alarms, NFPA 70, the National Electrical Code, ASCE 7 for structural loads, and ICC A117.1 for accessible design. The referenced edition is the one listed in Chapter 35, which may be older than the newest edition the publisher sells.

Other laws also apply to buildings, and some of them are not building codes at all. The Americans with Disabilities Act of 1990 is a civil rights law, enforced by the Department of Justice and through lawsuits, and its 2010 Standards for Accessible Design apply to public accommodations and government buildings regardless of what the building code says. The Fair Housing Act requires accessible design in most new multifamily housing. Fire safety in occupied buildings is governed by the fire code. Workplace safety rules, heritage designations, environmental regulations and the zoning code each impose their own requirements. A building that satisfies the building code may still break one of these other laws, and the architect must know which apply.

Which code applies to which building

The most important first decision in the United States is whether a building falls under the International Residential Code or the International Building Code. The IRC applies to detached one- and two-family dwellings and to townhouses not more than three stories above grade plane, each with its own separate means of egress, and to their accessory structures. Every other building, including apartment buildings of any size, falls under the IBC. The distinction matters because the IRC is simpler and largely prescriptive, while the IBC requires more analysis and almost always the involvement of architects and engineers.

Kostyshyn gives the students a list of buildings from their earlier studios and asks them to sort them. The script below does the sorting with the rules just described. Its most surprising result is the warming hut at Kestrel Point. It is small, one story and built of wood, but it is a place of public assembly, and assembly buildings are treated as the more demanding kind, however small they are.

# IRC or IBC? (scope of the International Residential Code)
def which(kind, stories, own_exit):
    if kind in ("one-family", "two-family") and stories <= 3:
        return "IRC"
    if kind == "townhouse" and stories <= 3 and own_exit:
        return "IRC"
    return "IBC"

projects = [
    ("Kestrel Point warming hut", "assembly", 1, True),
    ("Detached house on Marlow Street", "one-family", 2, True),
    ("Corner store with two flats above", "mixed", 3, False),
    ("Greenway Homes, 49 homes", "apartments", 4, False),
    ("Row of six townhouses, 3 stories", "townhouse", 3, True),
    ("Community hub with daycare and library", "assembly", 2, False),
]
for name, kind, n, own in projects:
    print(f"{name:<40} {kind:<11} stories {n}  -> {which(kind, n, own)}")

Kestrel Point warming hut                assembly    stories 1  -> IBC
Detached house on Marlow Street          one-family  stories 2  -> IRC
Corner store with two flats above        mixed       stories 3  -> IBC
Greenway Homes, 49 homes                 apartments  stories 4  -> IBC
Row of six townhouses, 3 stories         townhouse   stories 3  -> IRC
Community hub with daycare and library   assembly    stories 2  -> IBC

The results show how quickly a project leaves the IRC. Greenway Homes is residential, but apartments are always in the IBC. The stacked townhouses at Greenway, which share a floor between homes and a common corridor, are not IRC townhouses. The warming hut, with its wood stove and its benches for twenty skaters, is an assembly building and falls under the IBC, although many IBC requirements will be easy to meet in a building so small.

Existing buildings, change of use and the fire code

The building code applies mainly to new construction. When an existing building is repaired, altered, enlarged or given a new use, the International Existing Building Code sets out how much of the building must be brought up to current standards. It offers several compliance methods, from prescriptive rules for small alterations to a performance method that scores the existing building's safety features. A change of occupancy is especially important: converting a warehouse into apartments, or a house into a daycare, may change the occupancy classification and bring requirements that the old building never had to meet. Once a building is occupied, the fire code governs its maintenance: keeping exits clear, testing fire alarms, inspecting sprinklers and limiting what may be stored where.

Kostyshyn tells the students about the hardest permit she ever reviewed: the conversion of an old brick warehouse into lofts. The warehouse had wide floor plates, heavy timber floors, a single stair and no sprinklers. As apartments it needed a second exit, sprinklers, fire separations between suites, accessible entrances and new energy performance for the parts being rebuilt. The architect who succeeded was the one who began by reading the code for existing buildings, met the examiner before drawing anything, and proposed a package of improvements that gave the old building a level of safety close to a new one without destroying the timber and brick that made it worth saving.

Exercise 2: code structure

• Prepare a one-page map of the codes and standards that apply to the Greenway Homes project, from the model code to the referenced standards, with the edition of each.
• Find the scope rule for the IRC in the code in force and explain it in your own words with three examples of your own.
• Choose one referenced standard and find which edition the code refers to and whether a newer edition exists.
• Find one Minnesota amendment to the model code and explain why you think it was made.

Self-check

• Can I name the code, the edition and the amendments that apply to my project?
• Do I know when a building moves from the simpler residential rules to the full building code?
• Do I know that referenced standards are part of the code, in the edition the code lists?