Air Sealing and Insulation
Two jobs, two materials
Air sealing stops the movement of air; insulation slows conductive heat flow. Candidates must explain why both are required: a well-insulated wall with a leaky top plate still underperforms because wind washing and convective loops bypass the insulation. Know that the air barrier should be continuous and aligned with, or near, the thermal boundary, and that it must be sealed at every penetration, rim joist, and top plate.
Priority air-sealing locations
The classic list: attic floor penetrations (chimney, flue, wiring, plumbing, top plates), rim joists and sill plates, recessed lights and attic hatches, knee walls, band joists, and the boundary between conditioned and unconditioned space. Traps appear around recessed can lights (older units are not airtight and cannot be buried in insulation unless rated IC and airtight) and around attic stairs and whole-house fans that need insulated, gasketed covers.
Installation quality
Know the difference between nominal and installed performance: compression of batts, gaps around framing, and misalignment all reduce R-value. Blown insulation depth must be verified with a depth marker; the coverage chart on the bag gives bags per area for a target R. Dense-pack in walls and attics requires the right density to control convection. Also know that duct sealing and duct insulation belong to this domain: leaky ducts in unconditioned space are a major energy and pressure problem.
Worked example
A 1,200 square-foot attic needs R-49 with blown fiberglass at about R-2.5 per inch, so target depth is roughly 20 inches. If the crew stops at 14 inches, the delivered R is about 35, so the job is short roughly 14 R, or about 29% of the target. Verify depth at several points, not one.