10.1 IRC 2018 & IBC 2018 Fundamentals

What the IRC Governs

The International Residential Code (IRC), published by the International Code Council (ICC), is a comprehensive model code covering the construction of one- and two-family dwellings and townhouses not more than three stories above grade plane. It bundles structural, mechanical, fuel gas, plumbing, and electrical provisions for these residential occupancies into a single document, which is why the AZ ROC designates the 2018 IRC as the open-book reference for the residential B trade exam.

Scope of the IRC

• Buildings covered: detached one- and two-family houses, townhouses with a separate means of egress
• Height limit: three stories above grade plane
• Included disciplines: foundations, framing, roof, interior finish, residential mechanical/plumbing/electrical
• Not covered: commercial buildings, multi-family (R-2 occupancies with more than two units), institutional occupancies — these fall under the IBC

What the IBC Governs

The International Building Code (IBC) is the ICC's flagship model code for all buildings not covered by the IRC — essentially everything commercial, industrial, institutional, and multi-family residential above two units. The 2018 IBC is the open-book reference for the B-1 and B-2 (General Commercial) trade exams, and it also appears in the NASCLA Commercial General Building exam.

Scope of the IBC

• Occupancy classifications: A (assembly), B (business), E (educational), F (factory), H (high-hazard), I (institutional), M (mercantile), R (residential), S (storage), U (utility)
• Type of construction: Type I through Type V, with subtypes based on fire-resistance ratings
• Key areas: structural design, fire-resistive construction, means of egress, accessibility, interior finishes, foundations, special inspections

The ICC Model Code Family

The IRC and IBC are two volumes in the broader International Code Council (ICC) family of model codes, known collectively as the I-Codes. Other volumes include the International Fire Code (IFC), International Mechanical Code (IMC), International Plumbing Code (IPC), International Fuel Gas Code (IFGC), and the International Energy Conservation Code (IECC). The IRC bundles residential mechanical, plumbing, and fuel gas provisions directly within its covers; the IBC, by contrast, references the IMC, IPC, and IFGC as separate companion documents. On the B-1/B-2 open-book exam, only the 2018 IBC is provided — the companion mechanical, plumbing, and energy codes are not in your exam reference set, so questions that depend on those volumes are limited to the general provisions found inside the IBC itself or to the ACI concrete standards referenced for structural work.

Code Adoption by Arizona Jurisdictions

Arizona does not impose a single uniform statewide building code. Instead, cities, towns, and counties adopt model codes locally through ordinance. A jurisdiction may adopt the 2018 IRC and IBC, an earlier or later edition, or local amendments that modify specific provisions. Before bidding or pulling a permit, verify the adopted code edition and amendments with the local building department — what applies in Phoenix may differ from what applies in an unincorporated Pima County area.

How to Navigate the IRC and IBC

Both codes follow a similar chapter structure. Knowing the layout saves time during the open-book exam.

IRC Chapter Map

IBC Chapter Map

Using Tables and Exceptions

• Tables condense numeric requirements (span tables, egress distances, fire-resistance ratings). Always read the table header and footnotes — footnotes often modify or restrict the values in the body.
• Exceptions appear beneath a code section as indented paragraphs and narrow or exclude the general rule. On the exam, an exception is often the key to the correct answer.
• Referenced standards (ACI 318 for concrete, AISC 360 for steel, NDS for wood) are incorporated by reference and are legally part of the code. For the B exam, the IRC's prescriptive tables usually suffice; for B-1/B-2, the IBC may send you to ACI or AISC for structural details.

Quick Answer: During the open-book trade exam, use the index or table of contents to find the chapter, then scan for the specific section and any applicable exception — do not read the code cover-to-cover.