Building Science Principles Flashcards

Which phenomenon causes warm, moist air to condense on a cold surface inside a wall assembly?

Answer: Dew point condensation

When air cools to its dew point temperature at a cold surface, water vapor condenses into liquid moisture.

In a hot-humid climate, where should the vapor retarder be placed in a wall assembly?

Answer: On the exterior side, toward the hot exterior

In hot-humid climates, the dominant moisture drive is inward from the hot exterior, so the vapor retarder belongs on the exterior side.

What does the term 'thermal mass' refer to in building science?

Answer: A material's ability to store and slowly release heat

Thermal mass describes a material's capacity to absorb, store, and release heat energy, moderating interior temperature swings.

Which heat transfer mechanism does low-emissivity (low-e) window coating primarily reduce?

Answer: Radiation across the air gap

Low-e coatings reflect infrared radiation, reducing the radiative heat transfer between the glass panes.

A HERS rater measures attic ventilation to ensure balance between intake and exhaust. What is the recommended ratio of net free area to attic floor area when using balanced ventilation?

Answer: 1:150

The standard building code ratio for balanced attic ventilation (50% intake, 50% exhaust) is 1:150 net free area to floor area.

What is the primary purpose of an air barrier in a building enclosure?

Answer: To resist convective air movement through the building shell

An air barrier controls convective airflow (infiltration and exfiltration) through the building envelope, not diffusion.

Which condition best describes a 'negative pressure' house?

Answer: Interior air pressure is lower than exterior pressure

A negative pressure building has interior pressure below outdoor pressure, causing outdoor air to be drawn inward through any gaps.

How does wind-driven rain most commonly enter a wall assembly in a climate with high wind exposure?

Answer: Forced water entry through gaps and cracks under pressure

Wind pressure forces liquid water through gaps, cracks, and penetrations in the cladding and air barrier under positive pressure.

What is 'interstitial condensation' in a building assembly?

Answer: Condensation forming within the layers of a wall, roof, or floor assembly

Interstitial condensation occurs inside the building assembly layers when vapor migrates to a surface that is at or below the dew point.

A building with tight construction and mechanical ventilation exemplifies which principle from ASHRAE 62.2?

Answer: Build tight, ventilate right

ASHRAE 62.2 embraces the 'build tight, ventilate right' approach, using controlled mechanical ventilation instead of uncontrolled air leakage.

Which type of foundation is most susceptible to ground moisture intrusion by capillary action?

Answer: Slab-on-grade without capillary break

Concrete slabs placed directly on soil without a capillary break (gravel layer or poly film) allow moisture to wick upward continuously.

In whole-building energy modeling, what does the term 'internal gains' refer to?

Answer: Heat generated inside the building by occupants, lighting, and appliances

Internal gains are heat sources within the conditioned space—occupants, lights, cooking, and plug loads—that contribute to the cooling load.

What is the function of a 'drain plane' or 'drainage plane' in a wall assembly?

Answer: To channel any water that gets past the cladding back out of the assembly

A drainage plane (housewrap, building paper, or similar) sheds water that penetrates the cladding and directs it out of the wall system.

Which metric is used to quantify the airtightness of a building in a blower door test?

Answer: CFM50 or ACH50

Blower door results are reported as CFM50 (cubic feet per minute at 50 Pa) or ACH50 (air changes per hour at 50 Pa depressurization.

What is a 'thermal bridge' and how does it affect wall performance?

Answer: A highly conductive element like a metal stud that bypasses insulation and increases heat flow

A thermal bridge is a conductive path—such as a metal stud—that bypasses insulation and significantly increases heat transfer through the assembly.

During summer in a cooling-dominated climate, which solar orientation typically receives the highest heat gain through unshaded windows?

Answer: East- and west-facing windows

East and west windows receive direct low-angle sun in the morning and afternoon, causing high solar heat gain that is difficult to shade externally.

What does 'sensible heat' describe in HVAC and building science?

Answer: Heat that changes the temperature of a substance without changing its phase

Sensible heat is thermal energy that causes a measurable temperature change in a substance, measured with a thermometer.

In a vented crawlspace, which condition creates the most risk of moisture damage to floor framing?

Answer: Warm, humid outdoor air entering a cool crawlspace in summer

When warm, humid outdoor air enters a cool crawlspace in summer, it cools to its dew point and condenses on framing and insulation.

What is the purpose of the 'Solar Heat Gain Coefficient' (SHGC) of a window?

Answer: It quantifies how much solar radiation passes through the window into the building

SHGC is a dimensionless number (0–1) indicating the fraction of incident solar radiation transmitted through a window as heat gain.

Which insulation material is classified as an air barrier when installed properly at the correct thickness?

Answer: Closed-cell spray polyurethane foam (ccSPF)

Closed-cell spray foam is both an insulator and a Class II vapor retarder and air barrier when applied at sufficient thickness (typically 2 inches or more).