Council asked for more study after staff outline safety and code differences for park‑model RVs and manufactured homes as ADUs

Mesa staff told the council Thursday that the different building standards and fire‑safety features for park‑model recreational vehicles, manufactured homes and conventional construction create technical issues that require further study before the city changes its code to allow park‑model RVs as accessory dwelling units (ADUs).

Rachel Phillips, assistant planning director, said the city already permits conventional (site‑built) ADUs and factory‑built dwellings that meet the International Residential Code or HUD manufactured‑home standards. The staff presentation asked whether park‑model RVs — factory‑built units built to American National Standards Institute (ANSI) recreational‑vehicle standards and titled through the state motor‑vehicle department — should also qualify as ADUs.

Fire Marshal Sean Alexander said his office reviewed national standards and literature and did not find large‑scale laboratory testing directly comparing park‑model RVs and HUD‑certified manufactured homes. He said the primary regulatory distinction is that park‑model RVs are designed for temporary or seasonal occupancy and are engineered to a lighter construction standard so they can be transported: that leads to different smoke‑alarm, exit and surface‑material requirements in RV ANSI codes compared with HUD rules or the residential code.

Alexander described some differences: ANSI RV standards typically require fewer smoke alarms (one per vehicle rather than alarms outside every sleeping area), permit different exit configurations (roof hatches or windows may qualify as exits), and rely on lighter interior finishes to meet vehicle weight and transport requirements. He said manufacturers must provide a written notice at sale that ANSI park‑model RVs are designed for recreational — not permanent — occupancy; that notice is part of the federal HUD/ANSI regulatory framework that permits RVs to remain outside HUD manufactured‑home standards.

Because some park‑model RVs use propane or other fuel systems with different venting and clearance requirements, Alexander said permanent residential use of those units raises questions about ventilation, egress and fire‑safety performance that the RV standards do not address at the same level as HUD or the residential code. He said he had not found authoritative laboratory studies showing that one construction type is definitively more hazardous in typical residential usage but recommended city staff research and legal review before adopting code changes.

Council members asked for more time and for the city to consult members not present at the study session; several council members also said they wanted staff to provide comparisons of actual construction materials, examples of permitted uses in other jurisdictions, the practical experience of local parks and subdivisions where park‑model units are currently used, and an explicit legal assessment of municipal liability if the city permits park‑model RVs as ADUs.

City staff said they would return with additional analysis and that, because two council members were absent, more deliberation would be scheduled before any code change is proposed.

Speakers quoted or referenced in this article are: Rachel Phillips, assistant planning director; Sean Alexander, fire marshal; and John Scheffer, deputy director of development services and chief building official.