Building Science & Radon Entry Flashcards

What is the primary pathway through which radon enters most U.S. residential buildings?

Answer: Through cracks and openings in the foundation and slab

Radon, a soil gas, enters buildings primarily through cracks in foundation walls, floor-wall joints, sump pits, and other openings in the lowest structural level in contact with soil.

What is the stack effect and how does it relate to radon entry?

Answer: Warm air rising creates negative pressure at lower levels, drawing in soil gases

The stack effect occurs when heated indoor air rises and exits through upper levels, creating negative pressure at lower levels that draws soil gases, including radon, into the building.

What is the EPA recommended action level for radon in the United States?

Answer: 4 pCi/L (picocuries per liter)

The EPA recommends that homeowners take action to reduce radon levels at or above 4 pCi/L, while also noting that reducing levels below 2 pCi/L is difficult to achieve.

What role does soil permeability play in radon mitigation system design?

Answer: Higher permeability allows better sub-slab communication and more effective depressurization

Soil permeability affects how well suction from a mitigation point extends beneath the slab. Highly permeable soils allow better communication, while tight soils may require multiple suction points.

What is a sub-membrane depressurization system?

Answer: A radon system for crawlspaces using a sealed membrane over soil with suction beneath

Sub-membrane depressurization seals a polyethylene membrane over exposed crawlspace soil, then applies suction beneath the membrane to capture radon before it enters the living space.

What is the difference between passive and active radon mitigation systems?

Answer: Passive relies on natural airflow; active uses a fan to create suction

Passive systems rely on thermal stack effect to draw radon through a vent pipe naturally, while active systems use a continuously running fan to create mechanical suction, achieving much greater radon reduction.