Building Science Fundamentals Flashcards
7 cards from real HERS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Building Science Fundamentals flashcards as text
What does 'effective R-value' account for that 'clear-field R-value' does not?
Answer: Thermal bridging through framing and other conductive elements in the assembly
Effective (or whole-assembly) R-value accounts for thermal bridging through studs, plates, and other framing, which can significantly reduce the performance below the cavity R-value.
In hot-humid climates, which vapor control strategy is generally recommended for wall assemblies?
Answer: Use vapor-open assemblies on both sides that allow drying to the interior and exterior
In hot-humid climates, walls should be able to dry to either the interior or exterior; trapping moisture with vapor retarders on either side causes problems.
What is the primary purpose of a 'rainscreen' wall assembly?
Answer: To create an air gap behind the cladding that equalizes pressure and promotes drainage and drying
A rainscreen creates a vented cavity behind cladding that equalizes pressure (reducing rain penetration), allows drainage, and promotes drying of any moisture that enters.
Which psychrometric property describes the actual moisture content of air independent of its temperature?
Answer: Specific humidity (humidity ratio)
Specific humidity (humidity ratio) expresses the mass of water vapor per unit mass of dry air (grains/lb or g/kg), independent of temperature — unlike relative humidity.
A HERS rater finds that a vented crawl space has significantly higher moisture levels than the soil beneath it. What is the most likely cause?
Answer: Warm humid outdoor air entering through foundation vents and condensing on cooler crawl space surfaces
In warm weather, humid outdoor air entering crawl space vents can condense on cooler soil, joists, and pipes — often making vented crawl spaces more humid than unvented ones.
What is the building science significance of the 'neutral pressure plane' in a multistory building?
Answer: The elevation where indoor and outdoor pressures are equal, with infiltration below and exfiltration above
The neutral pressure plane is where stack-effect-driven indoor and outdoor pressures equalize; air infiltrates below it and exfiltrates above it in heating conditions.
Which material property makes extruded polystyrene (XPS) better suited than expanded polystyrene (EPS) for below-grade applications?
Answer: XPS has a much lower water vapor permeance, making it more resistant to moisture absorption
XPS has a perm rating of approximately 0.6–1.0, much lower than EPS (2–5 perms), making it more resistant to vapor diffusion in wet below-grade environments.