Containment & HEPA Air Filtration

What is mold containment and why does it matter?

Mold containment is a sealed plastic enclosure around the work area, kept under negative air pressure by a HEPA-filtered fan so air flows in, not out. EPA says its purpose is to limit the release of mold into the air and surroundings, so spores and debris from removal don't spread to clean parts of the building.

Without containment, the act of removing mold can make a problem bigger. Cutting moldy drywall or pulling up carpet releases spores that ride air currents through hallways, stairwells and ductwork, then settle on furniture and surfaces in rooms that were never affected. Containment turns the work area into a controlled space with one way in and one direction of airflow.

Limited vs. full containment: what's the difference?

EPA's guide Mold Remediation in Schools and Commercial Buildings describes two levels. The larger the moldy area, the greater the need for containment, but EPA stresses that professional judgment decides. A small area with heavy growth next to occupied rooms may justify full containment, while a large, lightly contaminated wall that cleans easily may only need limited containment.

Source: U.S. EPA, Mold Remediation in Schools and Commercial Buildings, Chapter 3: Containment

Sealing the openings people forget

Inside the work area, EPA calls for sealing all supply and air vents, doors, chases and risers with polyethylene, since those are the paths spores use to travel between floors and rooms. Many crews use zippered doors set into the sheeting so the entry closes tight between trips, serving the same purpose as EPA's flapped slit entry.

How does negative air pressure keep spores in the work area?

Negative pressure means more air is pulled out of the enclosure than leaks in, so any air movement through gaps runs from the clean side into the work zone. EPA says this can be done with a HEPA-filtered fan unit exhausted outside the building, or, for small, easily contained areas, an exhaust fan ducted outdoors. It also advises providing adequate makeup air.

You can see whether it is working. According to EPA, the polyethylene should billow inward on all surfaces. If it flutters or bulges outward, containment has been lost, and the problem should be found and corrected before work continues. Equipment is sized to the volume of the enclosure, and pressure is watched throughout the job, not just at setup.

What do HEPA air scrubbers actually filter?

HEPA stands for high-efficiency particulate air. EPA's explainer What is a HEPA filter? says a HEPA filter can theoretically remove at least 99.97% of airborne particles 0.3 microns in size, including dust, pollen and mold. That size is the hardest to catch; larger and smaller particles are trapped even more efficiently. Ordinary furnace filters are rated on the MERV scale instead.

HEPA air scrubbers serve two roles. Ducted outside the containment, they create negative pressure. Running inside an area, they scrub airborne particles during and after removal. EPA notes that HEPA filters don't remove vapors or gases, so they help with spores and dust but aren't a cure for odors on their own. EPA also suggests considering MERV 8 filters in the building's HVAC system during remediation and changing them afterward.

Keep the HVAC out of it

EPA warns against running a heating or cooling system you know or suspect is contaminated, because it can spread mold throughout the building, and points to its guide Should You Have the Air Ducts in Your Home Cleaned? When a drop ceiling serves as a return-air plenum, EPA says containment should run from the floor to the ceiling deck, and air handler filters serving the area may need replacing after remediation.

1. Plan the zone. Use the assessment to size the enclosure and choose limited or full containment, following EPA guidance and the IICRC S520 standard.
2. Shut down and seal HVAC. Turn off systems serving the area and cover supply and return vents.
3. Build the barrier. Hang 6-mil fire-retardant polyethylene from floor to ceiling or deck, framed where needed, and seal seams.
4. Install the entry. Add a flapped slit or zippered door, plus an airlock or decon chamber on full containment.
5. Set negative air. Position HEPA air scrubbers, duct exhaust outdoors, and confirm the sheeting pulls inward.
6. Maintain and monitor. Check barriers and pressure daily and keep equipment running through final cleaning.

When does containment come down?

Containment stays up until removal, HEPA vacuuming and damp wiping are complete. EPA says protective equipment must be worn throughout those final cleaning stages and during HEPA vacuum filter changes. Teardown usually waits for a final inspection or post-remediation verification, because once the plastic comes down, any missed debris is back in the open. For how this affects schedules, see how long mold remediation takes, and for the bigger picture, our guide to mold removal vs. mold remediation.

Containment for homes and businesses near you

Our certified technicians set up containment for residential mold remediation and commercial mold remediation projects across DuPage and Will County from our Lisle base, including mold remediation in Willowbrook, Burr Ridge, West Chicago and Batavia. Containment supports safe mold removal and follows the mold inspection and assessment; see every phase on our mold remediation page.

Need a work area sealed off before mold removal? Reach out online or call (630) 241-1111 around the clock.