Navigating Single Family Ventilation – Related Building Codes

The ventilation requirements for most all single-family homes begin with what is called “spot” or “local” ventilation. This type of ventilation is meant to take care of events such as showering and cooking that can generate excess moisture and other pollutants in bathrooms and kitchens. The requirements for these are fairly uniform across all recent International Residential Code (IRC) model code versions (the model codes are updated every three years and states or municipalities decide which versions to adopt). They require intermittent (occupant-controlled) exhaust ventilation of 50 cfm for bathrooms and 100 cfm for kitchens. Note that these airflow requirements must be met after the product is installed. A bath fan that is rated for only 50 cfm on the box for example will likely not deliver 50 cfm after being installed and ducted as the duct system static pressure is likely higher than what the certified airflow was based on.

The more complex type of ventilation that is now required in the majority of new residential dwellings is 24-hour continuous, whole-house ventilation. Even if the local bathroom and kitchen ventilation is done well, today’s tighter building envelopes can trap stale, unhealthy air inside. This type is sometimes also referred to as dwelling unit ventilation (DUV). The requirements and incentives for DUV usually depend on the version of the International Energy Conservation Code (IECC) that a given jurisdiction has adopted and any amendments they may have made. Note that the compliance path chosen (prescriptive, performance or Energy Rating Index) can also factor in.

Below is a list of typical DUV-related requirements by IECC version.

• IECC 2012, 2015, 2018
  • Require basic 24-Hour Continuous “Dwelling Unit Ventilation” (DUV)
• IECC 2021
  • Same basic requirements as above
  • All airflows must be field verified
  • Exhaust and supply DUV fans must meet current ENERGY STAR efficiency levels (cfm/watt)
  • Heat recovery ventilators (HRVs) or Energy Recovery Ventilators (ERVs) are required in climate zones 7 and 8 (some parts of MN, ND, ME, WY and CO).  See climate zone map below.
• IECC 2024
  • Same basic requirements as IECC 2021 except
    • HRVs/ERVs also required in climate zone 6

In some cases, the requirement for DUV may depend on the result of an optional building envelope leakage (blower door) test.
Again, your state/municipality may have amended the basic model code language so it is always best to confirm requirements with your local building official/authority having jurisdiction (AHJ).
Below are some example websites that track state-level code adoptions. Again, always check with your local code official as there may have been recent updates not captured on these sites.
https://www.iccsafe.org/adoptions/code-adoption-map/IBC
https://www.iccsafe.org/adoptions/
https://www.energycodes.gov/state-portal

Note that HUD recently announced that any homes financed with FHA mortgages must comply with IECC 2021 by May 28^th, 2026.  HUD also now includes an Alternative Compliance Path for some above-code programs such as ENERGY STAR-certified homes, etc.  Also, states whose IECC code version is judged to be equivalent to IECC 2021 even though some have made amendments will automatically meet the requirement.  Those states currently are WA, CA, IL, VT, MA, NJ and FL.