The LEED for Homes rating system references ASHRAE Standard 62.2, "Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings," for ventilation requirements. Under this standard, local mechanical exhaust for bathrooms must meet a minimum airflow rate. For intermittent systems (i.e., those controlled by a switch or timer), the required rate is 50 cfm. This requirement is a fixed value for all bathrooms and is not dependent on the size of the dwelling unit, the number of bedrooms, or the square footage of the bathroom itself.

A. 25 cfm is incorrect. The minimum rate for continuous bathroom exhaust is 20 cfm, but the question specifies an intermittent system.

C. The requirement is a fixed airflow rate (cfm), not a variable rate based on the bathroom's floor area (cfm per ft²).

D. The requirement is a fixed airflow rate (cfm), not a variable rate based on the bathroom's floor area (cfm per ft²).

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1. U.S. Green Building Council. (2021). LEED v4.1 Homes and Multifamily Reference Guide. Washington, DC: U.S. Green Building Council. Page 288, EQ Prerequisite: Minimum Indoor Air Quality Performance, Step-by-Step Guidance, Option 1, which requires compliance with ASHRAE 62.2-2016.

2. ASHRAE. (2016). ANSI/ASHRAE Standard 62.2-2016: Ventilation and Acceptable Indoor Air Quality in Residential Buildings. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers. Section 5.3, Local Mechanical Exhaust, and Table 5.1, "Minimum Local Exhaust Airflow Rates," which explicitly lists "Bathrooms - Intermittent" as requiring 50 cfm.

3. Sherman, M. H. (2005). ASHRAE Standard 62.2-2004: A Standard for Residential Mechanical Ventilation. Lawrence Berkeley National Laboratory. LBNL-58132. Page 5, Table 2, "Local Ventilation Exhaust Airflow Rates." (This earlier version, foundational to later editions, also specifies 50 cfm for intermittent bathroom exhaust). DOI: https://doi.org/10.2172/885111