HERS Building Science Principles Questions and Answers

Question 1

Which of the following best describes the 'house-as-a-system' concept in building science?

Accepted Answer

The idea that the building envelope, mechanical systems, occupants, and environment are interconnected, and a change in one can affect the performance of the others.

Answer

The 'house-as-a-system' approach is a core principle in building science. It emphasizes that a home's various components—such as the building shell (walls, roof, windows), mechanical equipment (HVAC, water heater), the occupants' behavior, and the surrounding environment—all interact and influence each other's performance. Altering one component, like adding insulation without considering ventilation, can have unintended consequences on moisture levels and indoor air quality.

Question 2

During a winter energy audit, a HERS Rater observes significant frost on the nails in the attic sheathing. This is most likely an indicator of what building science phenomenon?

Accepted Answer

Air leakage from the conditioned space carrying warm, moist air into the cold attic, where it condenses and freezes on cold surfaces.

Answer

The frost on the nails indicates that warm, moisture-laden air from the living space below is leaking into the cold attic. The nails, being metal, are excellent conductors of heat and become very cold, acting as thermal bridges. When the moist air comes into contact with these cold nail tips, the water vapor condenses and then freezes, creating frost. This is a classic sign of air leakage and insufficient attic insulation/sealing.

Question 3

A two-story home in a cold climate experiences drafts near the floor on the first level and feels stuffy on the second level during the winter. This condition is most likely caused by:

Accepted Answer

Stack effect

Answer

The stack effect describes the movement of air into and out of buildings due to temperature differences. In winter, the warm, buoyant air inside the house rises and escapes through openings in the upper levels (exfiltration). This creates a negative pressure at the lower levels, which pulls cold outside air in through cracks and leaks (infiltration), causing drafts. The accumulation of warm air on the second floor can lead to a stuffy feeling.

Question 4

What are the three primary mechanisms of heat transfer that a HERS Rater must consider when evaluating a building's thermal envelope?

Accepted Answer

Conduction, Convection, and Radiation

Answer

Building science fundamentals dictate that heat moves in three ways. Conduction is heat transfer through direct contact (e.g., through a window pane). Convection is heat transfer through the movement of fluids like air or water (e.g., warm air rising). Radiation is heat transfer via electromagnetic waves (e.g., heat from the sun). A HERS Rater analyzes how the building's thermal envelope controls all three of these mechanisms.

Question 5

A homeowner in a hot, humid climate decides to add a polyethylene vapor barrier to the interior side of their insulated walls during a remodel. What is the most likely outcome of this decision?

Accepted Answer

Trapping moisture within the wall cavity, leading to potential mold and rot.

Answer

In hot, humid climates, the primary direction of vapor drive is from the warm, moist exterior to the cooler, air-conditioned interior. Placing an impermeable vapor barrier on the interior side of the wall assembly will trap moisture that diffuses or leaks into the wall from the outside. This trapped moisture cannot dry to the inside and can lead to condensation, mold growth, and structural rot.

(HERS) Certified Home Energy Rating System Rater Practice Test

(HERS) Certified Home Energy Rating System Rater Practice Test

HERS Building Science Principles Questions and Answers