Orientation · General Building (B) · Core Trades

Core Trades: Seven Trades, One Section

About 13 minutes · 6 sections

What this guide covers

Most builders come up strong in two or three of these trades and hire out the rest. This section spans all seven — plumbing, electrical, HVAC, concrete, earthwork, insulation and weatherproofing, roofing — and it is nearly a third of the test, the biggest share of any section. What it rewards is a supervisor's grasp of each trade's SYSTEMS: what each one is made of, what it is doing when it works, how it fails, and what an inspector wants to see. You will not be an expert in all seven, and you do not need to be. Skim past the trades you run every day and spend your time where your experience is thin — the vocabulary and confusions below are organized trade by trade so you can do exactly that. The one habit to unlearn: on the job you look it up; in the exam room, nothing goes in with you.

Key terms

Title 24
The California Building Standards Code — the family of California code books (building, residential, electrical, plumbing, mechanical, and others) that govern construction in this state. Each book is a numbered "part" of Title 24.
Grade plane
The code's defined reference level, set by the finished ground around the building, from which stories and building height are measured. The exact definition lives in the code's definitions chapter.

The rules the exam tests

  1. Core Trades is roughly 30 percent of the General Building (B) exam and covers seven trades.

    Core Trades covers plumbing, electrical, HVAC, concrete, earthwork and surveying, insulation, acoustical, and weatherproofing, and roofing. The guide's own footnote says its percentages, including the 30 percent for Core Trades, are approximate.

    On the job

    Seven trades share one section — the weight tells you to spread your study across all of them rather than going deep on the ones you already know.

    Exact wording

    The Core Trades section is approximately 30 percent of the General Building (B) examination — the guide's own footnote says the percentages are approximate — and covers plumbing, electrical, HVAC, concrete, earthwork and surveying, insulation, acoustical, and weatherproofing, and roofing.

    CSLB General Building (B) Examination Study Guide — s03-core-trades

  2. You take the examination closed-book. Nothing you would look up on the job comes in.

    Closed-book means no reference materials of any kind may be used during the examination: no code book, no notes, no printed tables. Everything you need has to be in your head before you walk in.

    On the job

    On the job the code book is always within reach; in the exam room it is not. What you would normally look up, you have to carry in.

    Exact wording

    The examination is closed-book: no reference materials may be used during the examination.

    CSLB General Building (B) Examination Study Guide — test-policy

  3. Each multiple-choice question has four choices and one best answer.

    Some questions require mathematical computation, so a calculator is provided for the examination. More than one of the four choices can be partly right, so you pick the single best answer rather than the first one that sounds correct.

    On the job

    BEST answer means more than one choice can be partly right — and the computation questions (areas, volumes, material quantities) are worked with the provided calculator, not from memory.

    Exact wording

    The examination is multiple-choice with four choices per question, written to provide only one BEST answer; some questions require mathematical computation, and a calculator is provided.

    CSLB General Building (B) Examination Study Guide — test-strategy

  4. The California Residential Code governs one- and two-family dwellings and townhouses up to three stories.

    The California Residential Code is Part 2.5 of Title 24, based on the 2024 International Residential Code. Its scope section covers detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate , plus their accessory structures not more than three stories above grade plane in height — and that same scope section carries a short list of its own exceptions permitting certain sprinklered occupancies to be built under this code.

    On the job

    Which book governs a job is the first routing question — and the scope section, exceptions included, is where that question gets answered, not from memory.

    Exact wording

    The California Residential Code is Part 2.5 of Title 24, based on the 2024 International Residential Code. Its scope section covers detached one- and two-family dwellings and townhouses not more than three stories above grade plane in height with a separate means of egress, and their accessory structures not more than three stories above grade plane in height — and it carries a short list of its own exceptions permitting certain sprinklered occupancies to be built under this code.

    Title 24 codes (2025 editions) — crc

  5. Build your hallways at least 36 inches wide under the California Residential Code.

    The California Residential Code states it as "not less than 3 feet," which is the same as 36 inches. That is a floor, not a target: a wider hallway passes, and anything narrower than 36 inches does not comply.

    On the job

    CSLB's own study guide uses this exact question — the minimum allowable width of a residential hallway, answered 36 inches — as its sample of what the examination asks: a specific code minimum, recalled closed-book.

    Exact wording

    Under the California Residential Code, the width of a hallway must be not less than 3 feet — 36 inches.

    Residential Code § r318.6

  6. every plumbing fixture separately unless the code lists a shared-trap combination.

    Under the California Plumbing Code, each fixture's trap must be an approved type of liquid seal trap. Fixtures with integral traps are exempt. A laundry-sink trap may also take the waste of a clothes washer set next to it. One trap may serve up to three single-compartment sinks or laundry sinks of the same depth, or three lavatories, immediately adjacent in the same room, with waste outlets not more than 30 inches apart and the trap centrally located where three compartments are installed.

    On the job

    The trap is what stands between the building and the sewer. Per-fixture is the default; the shared-trap arrangements are the code's own and narrow — recognize them as exceptions, not the norm.

    Exact wording

    Under the California Plumbing Code, each plumbing fixture must be separately trapped by an approved type of liquid seal trap — subject to the section's own exceptions: it does not apply to fixtures with integral traps, a laundry-sink trap may also receive the waste of a clothes washer set adjacent to it, and one trap may serve a set of up to three single-compartment sinks or laundry sinks of the same depth, or three lavatories, immediately adjacent in the same room with waste outlets not more than 30 inches apart and the trap centrally located where three compartments are installed.

    Plumbing Code § 1001.2

  7. A feeder runs from the power source to the final branch-circuit overcurrent device.

    In the California Electrical Code, a feeder starts at service equipment, at the source of a separately derived system, or at another power supply source. All the circuit conductors from there to the final branch-circuit overcurrent device are the feeder.

    On the job

    Feeder versus decides which sizing and protection rules apply — the definitions article is where the electrical code settles what its other rules mean.

    Exact wording

    In the California Electrical Code, a feeder is all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

    Electrical Code § 100

  8. Plumbing work in California follows the California Plumbing Code.

    The California Plumbing Code is Part 5 of Title 24, and the state publishes it with IAPMO. So when a job question or an exam question is about drains, , traps, or fixtures, Part 5 is the book to open.

    On the job

    Knowing which book owns which trade is what lets you find a rule — and tells you which code an exam question is really asking about.

    Exact wording

    Plumbing work in California runs under the California Plumbing Code, which is Part 5 of Title 24, published with IAPMO.

    Title 24 codes (2025 editions) — cpc

  9. Electrical work in California runs under the California Electrical Code.

    The California Electrical Code is Part 3 of Title 24. Your wiring, services, feeders, branch circuits, and devices fall under that part.

    On the job

    The electrical book stands apart even in how you reach it — a different publisher than every other core-trades part, and the one code whose free online reading requires an account.

    Exact wording

    Electrical work in California runs under the California Electrical Code, which is Part 3 of Title 24.

    Title 24 codes (2025 editions) — cec

  10. The California Mechanical Code covers your heating, ventilation, and air conditioning work.

    The California Mechanical Code is Part 4 of Title 24, published with IAPMO. Heating, ventilation, and air conditioning all run under it, so HVAC questions go to that code, not the California Building Code.

    On the job

    HVAC questions route to the Mechanical Code, not the Building Code — the same publisher and format as the Plumbing Code, one part number apart.

    Exact wording

    Mechanical work — heating, ventilation, and air conditioning — runs under the California Mechanical Code, which is Part 4 of Title 24, published with IAPMO.

    Title 24 codes (2025 editions) — cmc

  11. The California Building Code is Part 2 of Title 24, from the 2024 International Building Code.

    Title 24 is organized into numbered parts, and the California Building Code sits at Part 2. The model code behind it is the 2024 International Building Code.

    On the job

    This is the book for buildings the Residential Code does not reach — the scope line of the neighbouring rule is what decides which of the two you are in.

    Exact wording

    The California Building Code is Part 2 of Title 24, based on the 2024 International Building Code.

    Title 24 codes (2025 editions) — cbc

  12. The California Building Code applies to every building and structure in California.

    The California Building Code covers construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition, plus any appurtenances connected or attached to a building or structure. It is Part 2 of Title 24's thirteen parts and incorporates the 2024 International Building Code with California amendments.

    On the job

    The Building Code's scope is every building; the Residential Code carves one narrow class out of it. If a job is not inside the Residential Code's scope line, it is here.

    Exact wording

    The California Building Code applies to the construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition of every building or structure, or any appurtenances connected or attached to them, throughout the State of California. Its title section names it Part 2 of the thirteen parts of Title 24 and says it incorporates the 2024 International Building Code with California amendments.

    Building Code § 1.1.3

  13. The California Plumbing Code applies to every building and structure in California.

    The California Plumbing Code covers construction, alteration, movement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition throughout the state, plus any appurtenances connected or attached to a building or structure. Its title section names it Part 5 of the thirteen parts of Title 24 and says it incorporates the 2024 Uniform Plumbing Code of the International Association of Plumbing and Mechanical Officials with California amendments.

    On the job

    Same every-building scope as the Building Code, one trade deep: the plumbing book reaches every structure in the state, and its model code is IAPMO's Uniform Plumbing Code, not an ICC code.

    Exact wording

    The California Plumbing Code applies to the construction, alteration, movement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition of every building or structure, or any appurtenances connected or attached to them, throughout the State of California. Its title section names it Part 5 of the thirteen parts of Title 24 and says it incorporates the 2024 Uniform Plumbing Code of the International Association of Plumbing and Mechanical Officials with California amendments.

    Plumbing Code § 1.1.3

  14. The California Mechanical Code applies to every building or structure in California.

    The California Mechanical Code covers construction, alteration, movement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition of every building or structure in California, plus any appurtenances connected or attached to them. Its title section names it Part 4 of Title 24's thirteen parts, incorporating the 2024 Uniform Mechanical Code of the International Association of Plumbing and Mechanical Officials with California amendments.

    On the job

    The mechanical book is the plumbing book's twin: same publisher, same every-building scope, one part number apart. An HVAC question routes here, not to the Building Code.

    Exact wording

    The California Mechanical Code applies to the construction, alteration, movement, replacement, repair, equipment, use and occupancy, location, maintenance, removal, and demolition of every building or structure, or any appurtenances connected or attached to them, throughout the State of California. Its title section names it Part 4 of the thirteen parts of Title 24 and says it incorporates the 2024 Uniform Mechanical Code of the International Association of Plumbing and Mechanical Officials with California amendments.

    Mechanical Code § 1.1.3

  15. The National Fire Protection Association has published the California Electrical Code since the 2019 edition.

    The California Electrical Code is Part 3 of Title 24. Three publishers cover the current edition's parts: the International Code Council publishes Parts 1, 2, 2.5, 6, 7, 8, 9, 10, 11, and 12, and the International Association of Plumbing and Mechanical Officials publishes Parts 4 and 5. The National Fire Protection Association has published Part 3 from the 2019 edition onward, and its free online resource requires creating a user login and shows the California-specific amendments only. The Building Standards Commission also lists BNi Building News as the source for the 2016 Part 3.

    On the job

    Knowing the publisher tells you where a book lives online and why the electrical book looks different on the shelf: it is the one part not from ICC or IAPMO, and the one you cannot read free without an account.

    Exact wording

    For the current edition of Title 24, three publishers cover its parts: the International Code Council publishes Parts 1, 2, 2.5, 6, 7, 8, 9, 10, 11, and 12; the International Association of Plumbing and Mechanical Officials publishes Parts 4 and 5; and the National Fire Protection Association publishes Part 3, the California Electrical Code, for the 2019 edition onward — its free online resource requires creating a user login and shows the California-specific amendments only. The Building Standards Commission also lists BNi Building News as the source for the 2016 Part 3.

    Building Standards Commission — Title 24 codes page ↗

Take away

Which book: the five core-trades parts of Title 24

Where people go wrong

Where to look it up

Plumbing — fixtures, DWV, water supply, traps and vents
2025 California Plumbing Code (Title 24, Part 5) — readable free in IAPMO's online viewer at epubs.iapmo.org
Electrical — circuits, conductors, overcurrent protection, GFCI locations
2025 California Electrical Code (Title 24, Part 3) — free to read via NFPA's online access (a free NFPA login is required); the state's code page at dgs.ca.gov/bsc links every part
HVAC — ducts, venting, combustion air, equipment installation
2025 California Mechanical Code (Title 24, Part 4) — readable free in IAPMO's online viewer at epubs.iapmo.org
One- and two-family dwellings and townhouses within the Residential Code's scope — framing, egress, room dimensions, roofing
2025 California Residential Code (Title 24, Part 2.5) — readable free in ICC's online viewer at codes.iccsafe.org
Buildings beyond the Residential Code's scope
2025 California Building Code (Title 24, Part 2) — readable free in ICC's online viewer at codes.iccsafe.org
Concrete, earthwork, insulation, and roofing practice — mix, placement, compaction, installation
Trade practice references the study guide lists (Fundamentals of Building Construction; Modern Carpentry; Olin's), plus the Building and Residential Codes for what is code-required
The exact definition of a code term — grade plane, means of egress, plenum, and the rest
Chapter 2 of the Building, Residential, Plumbing, and Mechanical Codes; the Electrical Code keeps its definitions in Article 100 instead
The official statement of what this section covers
CSLB's Study Guide for the General Building (B) Examination, section 3 — cslb.ca.gov

Glossary

Every term this guide defines, in one place. Each is also defined where it first appears.

Ampacity
How much current a conductor can safely carry — set by the electrical code's tables for each size and condition of wire.
Benchmark
A known, fixed elevation reference that grading and surveying measurements are taken from.
Branch circuit
The wiring past the final overcurrent device — the breaker or fuse — out to the outlets and equipment it serves. Feeders end where branch circuits begin.
Cleanout
An accessible fitting for rodding out a blockage in a drain line.
Combustion air
The air a fuel-burning appliance needs in order to burn safely — a supply the mechanical code addresses in detail.
Compaction
Mechanically densifying soil or fill so it can carry load without settling. Poor compaction under a slab or footing shows up later as cracks.
Cure
Concrete gains strength by hydration while it cures — keeping it moist and at a workable temperature — not by drying out.
DWV
Drain, waste, and vent — the half of a plumbing system that carries water and sewage out and lets air in so the drains flow and the traps keep their seal.
Flashing
Material installed at joints, openings, and penetrations — roof edges, chimneys, windows — to direct water back out. Sheet metal is the classic form; the codes also recognize self-adhered membranes and liquid-applied flashing systems.
GFCI
Ground-fault circuit interrupter — a device that cuts power when it senses current leaking outside the circuit, such as through a person. Required in the wet and outdoor locations the electrical code lists.
Means of egress
The code's term for the way out of a building — the exit path an occupant travels. Defined precisely in the code's definitions chapter.
Plenum
An air compartment or chamber that ducts connect to — the box where supply or return air is gathered and distributed.
R-value
A measure of a material's resistance to heat flow. Higher R means better insulation.
Rough-in
The stage when pipes, wires, and ducts are installed in the open framing, before insulation and drywall close the walls.
Slump
A field measure of the consistency and workability of fresh concrete. Adding extra water raises slump — and raising the water-cement ratio above the design mix weakens the cured concrete.
Trap
The bend of pipe below a fixture that holds standing water, sealing sewer gas out of the building.
Underlayment
The water-resistant layer installed on the roof deck beneath the roof covering.
Vapor retarder
A material that slows water vapor moving through a wall, floor, or ceiling assembly — moisture control, a different job from insulation's heat control.
Vent (plumbing)
The pipe that lets air into the drainage system behind flowing waste, so drains flow freely and trap seals stay put.

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