Cal Iaq

California Interagency Working Group on Indoor Air Quality

Indoor Air Quality Info Sheet


This document summarizes the indoor environmental quality (IEQ) considerations regarding the purchase/lease of relocatable classrooms (or "portables") and the contracting for renovation of existing space. It is provided to advise school facility managers how to minimize potential health impacts from IEQ problems with cost-effective practices. The key IEQ concerns address design, construction/installation, first-use, and maintenance; some of the issues apply both to "portables" and renovated classrooms. Related documents where further technical details may be found are also listed.


The State Department of General Services (DGS) issues specifications on "Building, Classroom, Prefabricated, Relocatable General Requirements", which outlines the DGS requirements for the State Portable Classroom Program. The demand generated by the Class Size Reduction Program exhausted the available inventory of state lease program relocatable classrooms. Many school districts will instead obtain relocatable classrooms directly from manufacturers. Although all classroom units manufactured for California must conform to the Building Standards Code (Title 24), these standards are not specific for "portables". Hence, these relocatable units may not adhere to the DGS specifications, and their design and quality can vary.

Ventilation and Outdoor Air

For the design of heating, ventilation, and air conditioning (HVAC) systems, the ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) Standard 62- Ventilation for Acceptable Indoor Air Quality recommends 15 cubic feet per minute (cfm) per person of outdoor air for school classrooms. This value has been incorporated into the California Energy-Efficiency Building Standards. The DGS bid specifications for Relocatable Classrooms require that HVAC systems deliver a minimum of 480 cfm of total outdoor air. To achieve the ASHRAE Standard, this supply of outdoor air limits classroom occupancy in relocatable classrooms to no more than 32 persons.

When specifying a new relocatable classroom, ensure that the HVAC system can: (a) provide the minimum outdoor air stated above; and (b) heat and cool this outdoor air at design outdoor temperatures for the specific geographic location where each classroom is installed. Some manufacturers of relocatable units do not include outdoor air intakes in their standard classroom models. It is important that an additional "outdoor air kit" be ordered for this purpose. Further, installation of an outdoor intake must be specified as part of the exhaust system. Lack of an exhaust in an HVAC system with an outdoor air intake will result in room pressurization, reduced outdoor air flow rates, and lower efficiency of removal of pollutants from the room.

Outdoor air must be supplied continuously when a classroom is occupied. Demand-controlled HVAC package systems often used in relocatable classrooms typically operate only when the temperature of a space is different from the thermostat's set point (i.e., higher in the winter, and lower in the summer). In order to provide a continuous outdoor air supply, it is important to ensure that the HVAC thermostats are set in the "on" or continuous mode when occupied.

State-leased relocatable classrooms are required to have HVAC systems that are wall mounted. Units acquired from other sources can have either wall- or roof-mounted HVAC; the cost of roof-mounted HVAC may be somewhat greater. However, some side-mounted units may be noisier, and it is important to check the noise level from HVAC operations in the relocatable classroom. If a noisy HVAC system is turned off because it interferes with classroom activities, this effects a failure of the ventilation requirement.

Air Filters for HVAC Supply Systems

Particle filters are needed for protection of HVAC components and reduction of airborne dust, pollens and microorganisms from recirculated and outdoor air streams. For relocatable classrooms, the DGS requires installation of a replaceable filter in the HVAC system. ASHRAE Standard 62-1989R requires filters with minimum of 25-30% dust spot efficiency (ASHRAE Standard 52.1) or >60% efficiency (ASHRAE Standard 52.2 for 3 micron particle). Where system design can accommodate them, filters with >65% efficiency for 1 to 3 micron particles will improve IAQ with respect to particles.

Renovating Classrooms

When school facilities are renovated for classroom use, it is imperative that new designs provide for adequate outdoor air in the renovated spaces. A common problem occurs when a large room is retrofitted with interior walls to create several, smaller rooms, and the required number of air supply outlets or return inlets is not installed. This results in inadequate ventilation in parts or all of the renovated rooms. Ensure that new designs are evaluated for ventilation adequacies.

Flooring materials

In most school classroom settings, hard flooring surfaces, such as commercial sheet flooring, are preferable to carpet: they are easier to keep clean, and they are not as prone to water damage or mold growth. However, the DGS State Portable Classroom Program requires that units be carpeted, except in certain areas, such as bathrooms. When carpets are specified, require the classroom manufacturer to install carpets that have been certified under the Carpet and Rug Institute's Indoor Air Quality Labeling Program.

Other important issues


Building construction and renovation create dust, emissions of volatile organic compounds (VOCs), and other work hazards and these are not compatible with normal school functions. A large proportion of building-related illness is associated with the improper use or storage of building materials in occupied areas. Therefore, every effort should be made to restrict construction activities to non-school hours and to ensure that building materials are stored away from occupied areas.

Isolate construction areas

During construction, it is important to isolate construction activities from occupied areas with a floor-to-ceiling barrier that will contain dust and vapor, such as plastic sheeting. Exhaust-to-outside ventilation in construction areas should be used at all times when dust or chemical vapors are generated.

Commission HVAC system in relocatable classrooms

Before a relocatable classroom is used, be certain that the HVAC system is fully inspected by a certified professional. Have him/her certify that it heats and cools properly, provides the appropriate amount of outdoor air, and operates continuously when the classrooms are occupied. The space pressure of the building should be slightly positive with respect to outdoors. Check the noise level in the classroom associated with HVAC operation. Confirm that outdoor air intakes are located away from contaminant sources (e.g., bus parking, kitchen exhaust, etc.).

"Flush-out" all newly constructed, remodeled, or acquired classrooms.

Prior to use of any new relocatable units by staff or students, operate HVAC systems at their maximum outdoor air intake rate continuously for several days. Similarly, provide maximum flush-out by HVAC (or open windows) for newly renovated classrooms and offices. Start this "flush-out" as soon as the HVAC system is operational, and continue after furniture installation. During this period, do not recirculate return air.

"Flush-out" not "Bake-out"

Building "bake-outs", i.e., when temperatures are increased up to 100F in order to "artificially age" building materials, are not recommended. Their effectiveness has not been proven, and they may in fact damage parts of the HVAC system or building components.

Continue "flush-out" ventilation during periods of first use

Efforts to minimize exposures to school children and staff should continue in the weeks following project completion. Emissions of VOCs from building materials still pose problems during this time, when they are at their highest. This is done by delaying occupancy in renovated rooms and portable classroom for several weeks, and utilizing maximum outdoor air ("flush-out") ventilation during these periods and for the first weeks of use. Flush out periods of 1-2 weeks are recommend, although longer periods may be required. For the first days to weeks of occupant use, continue to operate HVAC systems at the maximum outdoor air setting. Finally, monitor occupants' comfort, and follow-up complaints to identify problems early.

Establish an Integrated Pesticide Management plan.

For a quick reference guide, see Pest Control in the School Environment: Adopting Integrated Pest Management, Report EPA 735-F-93-012 (available from the U.S. EPA Indoor Air Quality Information Clearinghouse, see below).


The cost of new classrooms is an investment in the future of a school. It is clear that adequate maintenance is key to protecting this investment: An ounce of prevention is worth a pound of cure.

Designate specific personnel to perform specific tasks:

Establish a regular and timely plan for testing, inspecting and performing specific maintenance tasks:


IAQ Tools for Schools Action Kit. For information, contact the U.S. EPA IAQ Information Clearinghouse (see below). This kit provides guidance for achieving and maintaining good IAQ in your schools.

Indoor Air Quality: A Guide for Educators. Available from the California Department of Education, School Facilities Planning Division (see below).

Building Air Quality: A Guide For Building Owners and Facility Managers. Available from the Superintendent of Documents,

Pest Control in the School Environment: Adopting Integrated Pest Management, Report EPA 735-F-93-012 (available from the U.S. EPA IAQ Information Clearinghouse (see below).

Indoor Air Quality / School Facilities Documents (a set of 15 documents, such as "Maintaining Acceptable IAQ During the Renovation of a School", "Maintenance of HVAC Systems and IAQ in Schools", and "Equipment for Measuring Air Flow, Air Temperature, Relative Humidity, and Carbon Dioxide in Schools"). Available from the Maryland State Department of Education, Schools Facilities Branch

Reducing Occupant Exposure to Volatile Organic Compounds (VOCs) From Office Building Construction Materials: Non-Binding Guidelines. Also applicable to school building construction. Available from DHS' Indoor Air Quality Section, see below.

Electric/Magnetic Field (EMF) Checklist for School Buildings and Grounds Construction. Available from DHS' EMF Program, see below.

This advisory was produced by the California Interagency Working Group on Indoor Air Quality in December. Direct correspondences or comments to:

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