School Portables

Portables are Classrooms

The requirements for siting, planning, and using K-12 instruction spaces in the Board of Health’s School Rule (Chapter 246-366 WAC) also apply to portables. See our guide on Ventilation and Air Quality for Reducing Transmission of Airborne Illnesses (PDF). This guide highlights key Environmental Protection Agency (EPA) and DOH recommendations. For support on inspections or measurements, contact your local health jurisdiction or our School Environmental Health and Safety Program.

EPA Guidance: The EPA provides checklists for specification, commissioning, and maintenance of portables. See
Maintain Portable Classrooms, Part of Indoor Air Quality Design Tools for Schools.

Ventilation and Environmental Quality

  • Portables can be "stuffy" due to poorly functioning HVAC systems that provide minimal ventilation with outside air.(1,2) Run the ventilation fan continuously – not on "auto." Supply at least 15 cubic feet per minute (CFM) per person or 5 air changes per hour (ACH)(3) of outside air when in use.
  • Ensure that portables are equipped with outdoor air intakes by the manufacturer or by adding a kit.
  • Ensure that the outdoor air damper is providing outdoor air (unless outdoor air is very polluted). The intake should be located away from pollutant sources, such as parking lots.
  • Upgrade filters to MERV 13 if possible. Visually inspect filters monthly and change as needed.
  • Portable HEPA air filters can supplement the ventilation system. See Ventilation and Air Quality for Reducing Transmission of Airborne Illnesses (PDF) for guidance on selection. You can also build a DIY box fan filter, keeping sound levels in mind. See Research on DIY Air Cleaners, EPA.
  • Plan and train for HVAC system maintenance and use.
  • Loud ventilation systems are a common problem with portables.(2) Ensure that background noise, including the ventilation system and any portable air cleaners, is below 45 dBA (WAC 246-366-110). Measure informally using a mobile application or officially using a commercial instrument.
  • Provide natural light. Intensities must meet WAC 236-366-120. Maintain lights, including in restrooms.
  • Monitor carbon dioxide (CO2) levels over time with the goal of keeping levels below 800 ppm.(3)
  • Monitor temperature (T) and relative humidity (RH) and aim for ASHRAE’s Standard 55 on thermal comfort: at RH of 60%, T 68-74.5°F in winter or 74.5-79°F in summer; at RH of 40%, T 69-75.5°F in winter or 74.5-81°F in summer. The temperature must be at least 65° F (WAC 246-366-090).
  • Clean carpet regularly. Put walk-off mats at the doorway to reduce tracking dirt into the portable.
  • Scented products can cause reactions for people with sensitive respiratory or immune systems. As in all classrooms, avoid using fragranced items, such as cleaning products, essential oils, or plug-ins. Store cleaning supplies in a separate space.
  • Establish and implement an Integrated Pest Management plan.
  • Inspect the crawl-space regularly and remove any standing water, mold, debris, or critters. Make sure ventilation openings are covered with ¼ inch hardware cloth screening.
  • Freezing and burst pipes may be a concern in some areas. Follow local building and plumbing codes.
  • Avoid water entry and mold growth by maintaining the roof, flashing, and gutters.

Siting and Plan Review

Local Health Jurisdictions are required to do site approval and plan review for portables (WAC 246-366-030 and 040).

  • Portables need a mechanical ventilation system. They cannot rely on natural ventilation. Keeping windows open to meet the requirements for outside air is not always practical.
  • Consider not using portable classrooms for specialized instruction that could generate airborne contaminants, such as a wood shop, auto shop, art room, or laboratory.
  • Site portables away from parking lots, loading areas, equipment, and solvent/fuel storage to provide for safe travel to the school and playground and to distance from classroom pollutants.
  • Conduct a site sound level survey to address traffic or other noise sources in the surrounding area.
  • The American Disabilities Act (ADA) must be considered. Ramps must be ADA accessible, non-slip, equipped with drainage for ice buildup, and maintained. There should be a paved pathway to the school.
  • If a portable has no restrooms, locate it close to a school entrance and restroom. For younger students, include a restroom in the portable. Follow local building code requirements. Do not link the bathroom exhaust fan to the lighting. The exhaust fan needs to operate continuously.
  • Potable water for drinking and sufficient hand-washing can be provided using bottles or tanks. Hot water tanks must be checked for a maximum of 120°F (WAC 246-366-060) and sized to provide sufficient hot water for handwashing needs. Handwashing water temperature should be adjusted to 95-105oF if the user can not mix hot and cold water. 
  • Portables can be built with materials that off-gas volatile organic compounds (VOCs) and are often rapidly occupied after construction.(4) Look for low-VOC building materials and ventilate portables prior to use.
  • Remove vinyl flooring installed below a carpet to allow the building to breathe. Avoid carpet in entryways.


  1. Report to the California Legislature: Environmental Health Conditions in California’s Portable Classrooms, California Air Resources Board and California Department of Health Services, November 2004 (PDF)
  2. Indoor Air Quality in Schools: Maintain Portable Classrooms, Part of Indoor Air Quality Design Tools for Schools, US EPA.
  3. Ventilation in Buildings, CDC 
  4. Air concentrations of VOCs in portable and traditional classrooms: Results of a pilot study in Los Angeles County, Journal of Exposure Science & Environmental Epidemiology, January 2004