Core Trades: seven trades, 30% of the exam
The heaviest section on the B exam. It asks a general contractor to know enough about each trade on the job to check the work, not to do it.
Core Trades covers plumbing, electrical, HVAC, concrete, earthwork and surveying, insulation, acoustical and weatherproofing, and roofing. Seven trades in 30% means no single trade is huge, but together they are the largest block on the exam. Most B candidates are strong in two or three of them and have always subcontracted the rest. The rest is where the points are.
The numbers that get asked
| Rule | Number |
|---|---|
| Footings extend into undisturbed ground CRC, Grass Valley 2025 general notes | 12 in min |
| Concrete slab on grade, thickness CRC, San Diego County PDS 081; Clovis 2025 list | 3½ in min |
| Footing reinforcement CRC, San Diego County PDS 081 | two No. 4 bars, top and bottom |
| Rebar cover, concrete cast against earth UFGS 03 30 00 | 3 in |
| Portland cement for high early strength / high sulfate resistance Portland Cement Association (ASTM C150) | Type III / Type V |
| Grade away from the foundation CRC, City of Burbank 2025 list | 6 in in 10 ft |
| GFCI trips when current differs by as little as CPSC GFCI fact sheet | 0.006 A |
| Wall insulation, 2025 Energy Code: 2×4 / 2×6 wood framing Title 24 Part 6, §150.0(c) | R-15 / R-21 |
| Asphalt shingles, minimum slope; two layers of underlayment below CRC, Covina re-roof handout 2026 | 2:12; 4:12 |
| Asphalt shingle layers allowed in total (one overlay) CRC, Covina re-roof handout 2026 | 2 |
CRC = California Residential Code, as restated by the local building departments named. Checked 29 September 2026.
Where people lose points
- Depth is not thickness. Footings go at least 12 inches into undisturbed soil. A slab is at least 3½ inches thick. Questions pair these with each other's numbers.
- Leveling runs one direction. Height of instrument = known elevation + backsight. Elevation of the new point = height of instrument − foresight. A backsight is always taken on a point of known elevation (USDA field manual, chapter 1).
- Ohm's law versus power. Volts = amps × ohms (E = IR). Watts = amps × volts (P = IE), so amps = watts ÷ volts. A 1,500-watt heater on 120 volts draws 12.5 amps (DOE electrical science handbook).
- A GFCI is not a breaker. It protects people from shock by comparing outgoing and returning current. It does not protect the wire from overload.
- The 2025 insulation numbers moved. Mandatory wall insulation in 2×4 wood framing is now R-15 and in 2×6 R-21. Study material written for earlier code editions shows lower values.
- 2:12 and 4:12 are both right, for different things. Asphalt shingles need at least 2:12. From 2:12 up to 4:12 they need two layers of underlayment; above 4:12, one.
How the questions tend to read
A reading, a rating or a slope, and a rule or calculation to apply. Two examples of our own (not actual exam questions):
A bench mark is at elevation 100.00 ft. You read 4.25 ft on it (backsight), then 6.10 ft on the top of a footing form (foresight). What is the elevation of the form?
98.15 ft. Height of instrument = 100.00 + 4.25 = 104.25. Form = 104.25 − 6.10 = 98.15. The trap answer, 101.85, adds the foresight and subtracts the backsight.
You are re-roofing a 3:12 roof with asphalt shingles. What underlayment is required?
Two layers. Shingles are allowed at 2:12 and steeper, but from 2:12 up to 4:12 the underlayment is doubled. At 5:12 one layer would do.
How to study it
- Rank the seven trades by how often you have subcontracted them. Start with the ones you never touch.
- Learn each trade's inspection checklist. A general contractor is asked what to check, not how to bend conduit. City plan-check lists and inspection handouts are short and written exactly that way.
- Keep formulas on one card. E = IR, P = IE, HI = elevation + BS, elevation = HI − FS, cubic yards = cubic feet ÷ 27.
- Check the 2025 Energy Code changes. The Energy Commission publishes a short “what's new” summary for single-family homes.
- Budget. The largest block in our B study plan: about 4½ hours in two weeks, 7½ in four.
Common questions
What trades are in the Core Trades section of the B exam?
Plumbing, electrical, HVAC, concrete, earthwork and surveying, insulation, acoustical and weatherproofing, and roofing: about 30% of the exam together.
Which code edition does the B exam use?
The study guide (03-2026) lists the 2025 California codes (Title 24) for exams on or after 1 January 2025.
Last reviewed 29 September 2026 against the CSLB General Building (B) study guide 13E-B (03-2026); California Residential Code values as restated by the City of Grass Valley (2025 general notes), San Diego County (PDS 081), the City of Clovis (2025 plan check list), the City of Burbank (2025 plan check list) and the City of Covina (re-roof handout, 2026); 2025 Title 24 Part 6 §150.0 and the Energy Commission's 2025 single-family summary; UFGS 03 30 00; the Portland Cement Association; the USDA engineering field manual (surveys); DOE-HDBK-1011; and CPSC's GFCI fact sheet. Confirm with your building department. We are not affiliated with CSLB or PSI.