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Practice and exam technique

Practice: thermal and moisture

Compiled by the Sitonce editorial team from the PSI Candidate Information Bulletin, NASCLA's own published material and the federal standards named belowUpdated 2 min readFacts verified 4 September 2026
The short answer

Thermal and Moisture Protection carries 6 questions. Most of them test sequence and detailing - shingle lapping, flashing order, vapor barrier placement - rather than product specifications.

Six questions, and the theme running through them is water going downhill.

Four questions

Question 1

Roofing and siding materials are installed in a shingle lap. What does that mean?

  1. Each course is sealed to the one below
  2. Each upper course overlaps the one below so water sheds outward
  3. Courses are staggered for appearance
  4. Courses are mechanically locked
Answer: B. Shingle lap means upper over lower, so water running down the surface stays on the outside. Reversing it at any single point sends water behind the assembly, and most envelope failures are one reversed lap rather than a bad product.
Question 2

Where is a vapor retarder generally installed in a heating-dominated climate?

  1. On the exterior side of the insulation
  2. On the warm side of the insulation
  3. Directly beneath the roof covering
  4. It is not required in insulated assemblies
Answer: B. On the warm side, so moisture in warm interior air is stopped before it reaches a surface cold enough to condense. Placing it on the cold side traps moisture within the assembly, which is the failure the rule exists to prevent.
Question 3

What is the primary purpose of step flashing at a roof-to-wall intersection?

  1. To secure the roofing to the wall
  2. To carry water from the roof surface out over the roofing at each course
  3. To provide an expansion joint
  4. To close a ventilation gap
Answer: B. Step flashing is installed course by course, each piece lapped so water is directed out onto the roofing rather than down behind it. A continuous piece instead of stepped pieces is a recognized defect.
Question 4

Continuous insulation on the exterior of a wall assembly primarily addresses which problem?

  1. Air leakage at penetrations
  2. Thermal bridging through framing members
  3. Water intrusion at windows
  4. Sound transmission
Answer: B. Framing conducts heat far better than the insulation between it, so a wall insulated only in the cavities performs worse than the cavity R-value suggests. Continuous insulation covers the framing and interrupts that path.
Sequence is the category

Almost every question here can be answered by asking which way water runs and which layer goes on first. That is a reasoning route, not a memorized one, and it works when the lookup does not.

What to have tabbed

  • Flashing details at walls, valleys and penetrations
  • Vapor retarder placement by climate
  • Underlayment requirements
  • Roof slope minimums by covering type

Common questions

How many thermal and moisture questions are on the exam?

Six of 125.

What is a shingle lap?

Each upper course overlaps the one below so water sheds outward. Reversing it once sends water behind the assembly.

Where does a vapor retarder go?

On the warm side of the insulation in a heating-dominated climate.

What does step flashing do?

Carries water out over the roofing at each course, rather than letting it run down behind.

What does continuous insulation address?

Thermal bridging through framing members.

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