C-2 Insulation and Acoustical exam questions, with answers
10 practice questions for the CSLB Insulation and Acoustical trade exam, each with the answer, a plain explanation and the source it rests on.
These are not real exam questions. CSLB does not release its test questions or answer keys, and nobody else has them. We write our own questions from the C-2 outline and the codes, standards and references CSLB lists for the exam. Each answer names its source so you can check it.
The C-2 exam has 4 sections. The questions below are grouped by section, with the share of the exam each one carries. Read the question, pick an answer, then open “Show the answer”. The other questions of the free test, scored section by section, are in the free 25-question C-2 test.
Planning and Estimating · 29% of the exam
Review plans and specifications; evaluate job sites; estimate material quantities and costs.
1. The specification for a new office ceiling cites 2025 CBC Section 808 for the lay-in acoustical panels. Under 2025 CBC 808.1.1, the acoustical materials must comply with the requirements of which section, and how are they installed?
- Section 1206 sound rules; installed per the architect's own details
- Section 803 interior finish rules; installed per the maker's recommendations
- Section 2603 foam plastic rules; installed per the architect's own details
- Section 720 insulation rules; installed per the maker's recommendations
Show the answer
Answer: B. 2025 CBC 808.1.1 says acoustical materials that comply with the interior finish requirements of Section 803 are installed per the manufacturer's recommendations and the rules for applying interior finish. Section 720 covers thermal and sound insulating materials, not the ceiling panels. Section 1206 sets sound transmission ratings, and Section 2603 covers foam plastic insulation.
2. You are reviewing the specification for a new nonresidential office in California that includes mineral wool batts and lay-in acoustical ceiling panels. Under 2025 CALGreen 5.504.4.7 and 5.504.4.8, what must both products meet?
- The ASTM E84 Class A flame spread limits, with documentation
- The CDPH emissions test (California Specification 01350), with documentation
- The SCAQMD Rule 1168 VOC limits for adhesives, with documentation
- The ARB formaldehyde limits for composite wood, with documentation
Show the answer
Answer: B. CALGreen 5.504.4.7 and 5.504.4.8 require thermal insulation and acoustical ceilings and wall panels in nonresidential buildings to meet the CDPH emissions test (Standard Method v1.2, California Specification 01350), with documentation. SCAQMD Rule 1168 sets VOC limits for adhesives and sealants, and the ARB formaldehyde limits apply to composite wood such as particleboard and MDF. Flame spread limits come from the building code, not these CALGreen sections.
3. You are evaluating the site of a new apartment building next to a freeway before bidding its sound insulation. Under 2025 CBC 1206.4, what is the highest interior noise level from exterior sources allowed in any habitable room (Ldn or CNEL)?
- 45 dB
- 50 dB
- 55 dB
- 60 dB
Show the answer
Answer: A. 2025 CBC 1206.4 limits interior noise from exterior sources to 45 dB in any habitable room, using Ldn or CNEL as set by the noise element of the local general plan. 50 is the STC and IIC minimum for walls and floors in 1206.2 and 1206.3, not an interior noise level. A site next to a freeway needs walls, windows and roof-ceilings that keep the rooms at 45 dB or less.
Source: 2025 CBC 1206.4, 2025 California Building Code (Title 24, Part 2), Section 1206 Sound Transmission
Acoustical · 16% of the exam
Ceiling grids; acoustical tile and wall panels; seismic requirements.
4. On a DSA school job, your crew is adding slack safety wires to the light fixtures in a new lay-in ceiling. Under DSA IR 25-2 (2022 CBC), how are these slack safety wires treated for installation and testing?
- As fixture parts, installed and tested only per the fixture maker
- As hanger wires for installation, but left out of the field testing
- As bracing wires, with four tight turns and the bracing-wire tests
- The same as hanger wires, for both installation and field testing
Show the answer
Answer: D. Section 1.6.3 of DSA IR 25-2 says slack safety wires shall be considered hanger wires for installation and testing requirements. So they get the hanger-wire attachment (at least three tight turns in 3 in, Section 1.4.1) and are part of the hanger-wire testing. They are not bracing wires, and the fixture maker's instructions do not replace the IR.
5. The specification for a new apartment building says the party walls your crew insulates will be field tested after construction instead of relying on a lab rating. Under 2025 CBC 1206.2, what minimum airborne sound rating must the field test (ASTM E336) show?
- NNIC 45
- STC 55
- NNIC 50
- STC 50
Show the answer
Answer: A. 2025 CBC 1206.2 requires walls between dwelling units to have an STC of at least 50 when lab tested to ASTM E90, or a Normalized Noise Isolation Class (NNIC) of at least 45 when field tested to ASTM E336. STC 50 is the lab rating, not the field-test rating. Penetrations for pipes, boxes and ducts must also be sealed, lined or insulated to keep the rating.
Source: 2025 CBC 1206.2, 2025 California Building Code (Title 24, Part 2), Section 1206 Sound Transmission
Insulation · 28% of the exam
Site preparation and blown-in applications; insulation preparation; insulation installation.
6. During attic prep on an existing home with soffit vents, you see the old loose-fill pushed back from the eaves, leaving bare drywall along the exterior walls. Per the DOE Building America Solution Center, what is the likely cause and fix?
- Wind washing; close off the soffit vents with blocks of rigid foam board
- Settling; staple netting over the loose-fill along the eaves to hold it
- Settling; blow extra loose-fill along the eaves and leave out the baffles
- Wind washing; install a baffle in each rafter bay that has a soffit vent
Show the answer
Answer: D. The DOE guide describes wind washing: wind blowing in through soffit vents pushes attic insulation back from the edges of the ceiling. The fix is a baffle in each rafter bay with a soffit vent, which directs air above the insulation and acts as a dam. Blocking the vents defeats attic ventilation, and extra loose-fill or netting does not stop the wind that moved it.
7. Supply ducts in a vented attic in a dry climate will be laid on the ceiling and buried in blown insulation. Per the DOE Building America Solution Center guide on buried ducts, what minimum duct insulation should they have before you blow?
- R-4.2 minimum duct insulation, with no vapor barrier cover
- R-8 minimum duct insulation, with no vapor barrier cover
- R-8 minimum duct insulation, with a vapor barrier cover
- R-6 minimum duct insulation, with a vapor barrier cover
Show the answer
Answer: C. The DOE guide says buried ducts should be covered with R-8 or higher duct insulation that includes a vapor barrier cover, with all connections mechanically fastened and mastic-sealed, before the loose-fill is blown over them. R-4.2 and R-6 appear in the guide only as levels in its effective R-value table, and dropping the vapor barrier cover misses the guide's other condition. In humid or marine climates it also calls for spray foam encapsulation first.
Source: DOE Building America Solution Center, Ducts Buried in Attic Insulation guide
8. Your crew is stapling a single-sided foil radiant barrier to the underside of the rafters in an existing vented attic. Per the DOE Building America Solution Center guide on attic radiant barriers, which way should the foil face?
- Foil side down, toward the attic floor
- Foil side up, toward the roof deck
- Foil side up, with a 1-in air space above it
- Either side, as long as an air space is above it
Show the answer
Answer: A. The DOE guide says single-sided radiant barrier in attics should be installed with the foil side facing down. It may be stapled to the rafters, the truss top chords or the underside of the roof deck. The guide adds that the air space above the barrier is not critical, so attaching it right under the decking is acceptable.
Source: DOE Building America Solution Center, Attic Radiant Barriers guide
Safety · 27% of the exam
Personnel safety; job site safety.
9. Your crew will spray foam on the walls of a warehouse while other trades work elsewhere in the building. Per U.S. EPA's checklist for professional spray polyurethane foam (SPF) insulation contractors, how should the spray area be set up?
- As an open area, with a spotter who warns people walking near the sprayer
- As an open area, with the other trades told about it at the morning meeting
- As a safe work zone with warning and PPE signs and barriers around it
- As a safe work zone marked only on the site plan kept in the job trailer
Show the answer
Answer: C. EPA's checklist says to establish a safe work zone around the SPF application to isolate the work area, post warning signage including signs for the proper PPE, and set up barriers. The zone's size depends on the size and layout of the job. Only protected workers should be inside during application, curing and cleanup, so a spotter, a site-plan note or a meeting announcement is not enough.
Source: U.S. EPA, Checklist for Professional SPF Insulation Contractors
10. Your blowing machine plugs into a temporary 120-volt, 20-ampere receptacle on a construction site; it is not part of the building's permanent wiring. Under 8 CCR 2405.4, how must the employees using it be protected?
- GFCI protection, but only on circuits that feed cords longer than 100 ft
- An assured grounding program, but only on jobs that last more than 30 days
- GFCI protection, or an assured equipment grounding conductor program
- A grounding-type plug and cord only, with no added device for 20-A outlets
Show the answer
Answer: C. 8 CCR 2405.4 requires employers on construction sites to use ground-fault circuit interrupters (GFCIs), an assured equipment grounding conductor program, or both. Temporary 120-volt, single-phase, 15- and 20-ampere receptacles in use by employees must have GFCIs for personnel protection unless the assured program is used. The rule has no cord-length or job-length cutoff.
Source: 8 CCR 2405.4, 8 CCR 2405.4, Ground-Fault Circuit Protection - Construction Site
Where to go from here
How the license works, from experience to fees: how to get a C-2 license. Everything about the course: the C-2 exam page.
Questions from our free C-2 test, written from CSLB License Examination Study Guide, Insulation and Acoustical (C-2), form 13E-2 (03-2026), for examinations scheduled on or after August 1, 2023. CSLB notes that the percentages are approximate. Reviewed 14 October 2026. Study guidance only; we are not affiliated with CSLB or PSI.