Windows and Doors
Performance ratings
Candidates must read NFRC labels: U-factor (heat loss), solar heat gain coefficient (SHGC, solar gain), visible transmittance (light), and air leakage. Lower U is better. SHGC choice depends on climate: lower SHGC reduces cooling loads in hot climates, while higher SHGC can be beneficial for heating in cold climates. Traps include confusing U-factor with R-value (U = 1/R), and assuming low-e always means low SHGC, which is not necessarily true.
Frame, glazing, and installation
Know the difference between frame types (wood, vinyl, aluminum, fiberglass, clad) and glazing features (double vs triple, argon or krypton fill, warm-edge spacers, low-e coatings). Installation matters as much as the product: flashing, sill pans, backer rod and sealant, and proper shimming. A common exam trap is treating the window flange as the primary water barrier rather than integrating it with the water-resistive barrier in shingle fashion.
Doors and air leakage
Know that doors leak at the perimeter, threshold, and frame, and that weatherstripping, sweeps, and adjustable thresholds reduce leakage. Exterior doors should be sealed and insulated where appropriate. Storm doors add a dead-air space and reduce air and heat transfer.
Worked example
A window is labeled U-0.30. Its R-value is 1/0.30 = about R-3.3, comparable to a single pane plus a bit more. A solid wall at R-13 is roughly four times as resistant. That is why windows dominate comfort complaints even when they meet code.
Rule of thumb
Specify by climate: cold climates favor low U and moderate-to-high SHGC on south glazing; hot climates favor low SHGC and low U.