Mold remediation containment is a sealed work area held at lower air pressure than the rest of the building, so spores released during demolition cannot escape into clean space. It is polyethylene sheeting plus an air filtration device ducted to exhaust outdoors. The sheeting alone is not containment.
That last sentence is the point of this page. Below: the plastic versus the pressure, limited versus full containment, how a containment is built, what gets sealed, and how to tell a real one from plastic taped across a doorway.
A room wrapped in plastic with no negative air is theater. It photographs well and does almost nothing.
Polyethylene sheeting leaks. It leaks at every overlapped seam, every taped edge, around the door, at the floor line, and anywhere a wrinkle keeps the tape from full contact. That is not sloppy work. It is what happens when you tape thin film to a painted, textured, imperfect building. Any pressure inside the enclosure higher than the pressure outside pushes contaminated air out.
Airflow fixes that, not better tape. An air filtration device sits inside the enclosure and exhausts through a duct to the outdoors. Air leaves faster than it can seep back in, so the enclosure sits at lower pressure than the rooms around it, and every leak point now pulls air inward. Spores released by a saw blade have nowhere to go but into the filter. Remove either half, the barrier or the pressure, and you have nothing, which is why a good crew starts the machine before the first cut and leaves it running after the last one.
Read more: how air scrubbers and negative air machines work · Read more: the mold remediation process
EPA guidance ties the level of containment to the size of the contaminated area, and the threshold most of the industry works from is 100 square feet.
Limited containment suits roughly 10 to 100 square feet. A single layer of 6-mil polyethylene sealed to floor, walls and ceiling, with the entry cut as a slit and covered by a separate flap of poly so it reseals behind a worker. It still runs under negative pressure.
Full containment covers anything over 100 square feet, plus smaller jobs with complications: heavy contamination, sewage, an occupied building, growth in the HVAC system. It uses two layers of 6-mil poly rather than one, and replaces the slit entry with a decontamination chamber.
A decontamination chamber, usually shortened to decon, is a small enclosed vestibule at the containment entrance, so a worker can leave without carrying contamination out on their suit and boots. The classic build is three chambers in a row:
Flaps or zippers separate each chamber, so the work area is never open directly to occupied space. A two-stage decon is common on residential work. What matters is that there is an airlock, not one opening a worker pushes through in a contaminated suit.
| Level | Contamination area | Sheeting | Entry |
|---|---|---|---|
| Limited | About 10 to 100 sq ft | Single layer 6-mil poly | Slit entry with a covering flap |
| Full | Over 100 sq ft, or complications | Double layer 6-mil poly | Decon chamber, two or three stages |
The order matters, and most failures happen in the first three steps rather than in the plastic.
After the registers, the most common field error is the exhaust duct. A long, kinked run out a basement window can cost half the machine's real airflow, and nothing about the unit tells you it is happening.
A containment envelope is only as good as its worst penetration. Everything here is a hole until it is closed:
In older buildings the wall cavity is the leak nobody looks for. Balloon framing or a missing fire block gives contaminated air a clean path upstairs while the plastic looks perfect to everyone in the room.
You can check all of this in two minutes, with no equipment and without interrupting the crew.
Walk in on a lunch break, find the unit off and the plastic hanging slack, and that is a real finding worth raising.
Nothing here is exotic. The specifications still matter.
Containment goes up before anything is cut or removed, and comes down after clearance testing passes. Not before.
The sequence runs: assess and write a protocol, build containment, start negative air, remove contaminated material, HEPA vacuum and damp wipe, dry the assembly, run filtration through the settling period, then test.
Containments come down early all the time, because the room looks finished. Clearance testing can only tell you whether the work area is clean while that area still exists as a defined space. Sample a room whose containment came down yesterday and you are measuring a blend of the work area and the rest of the house. If the result fails, there is also no containment left to redo the work in.
Read more: removing mold damaged material · Read more: what belongs in a remediation protocol
Mold is a small slice of where this technique gets used.
Sometimes, and the boundary is the same one that applies to the rest of the work.
For a small, visible, isolated area with an obvious moisture source, roughly the 10 square foot reference point, a careful property owner with proper PPE can tape 6-mil poly over the opening, seal that room's registers, run a rented machine ducted out a window, and do the work. Bag debris inside the barrier and do not skip the respirator.
Beyond that, the hard part is not the plastic. Full containment means a decon chamber, verified pressure, a defined exit path, and the judgment to know where contamination actually ends, which is rarely where the staining ends. Where growth is hidden in a wall, where the HVAC system is involved, where the area runs past a hundred square feet, or where anyone in the building has a health concern, the job needs a built containment and a contractor.
Mold containment is a sealed work area, built from polyethylene sheeting and held at lower air pressure than the surrounding building, that keeps spores released during remediation out of clean space. The sheeting defines the area and an air filtration device ducted outdoors creates the pressure difference. Both halves are required.
EPA guidance calls for limited containment from about 10 to 100 square feet of contamination and full containment above 100. Under roughly 10 square feet with a visible, isolated source, a careful owner can reasonably build limited containment. Hidden growth, HVAC involvement or an occupant health concern moves the job to full containment regardless of size.
Negative air pressure means the work area sits at lower pressure than the space around it, created by an air filtration device exhausting through a duct to the outdoors. It matters because plastic sheeting leaks at every seam and taped edge. Under negative pressure those leaks pull air inward instead of pushing contaminated air out.
Look at the plastic. Under working negative pressure the poly is visibly drawn inward on walls, ceiling and door. Slack or outward-bowing sheeting means there is no pressure difference. Also confirm there is a duct running outdoors, that HVAC registers inside the area are taped over, and that the machine runs when nobody is working.
A decon chamber is a small enclosed vestibule at the containment entry, often three connected chambers: a dirty room where debris and outer garments come off, a transition room for wipe-down or showering, and a clean room opening onto the building. Workers remove PPE stage by stage on the way out, so contamination does not ride out on a suit.
Containment goes up before the first cut and stays up through demolition, cleaning, drying and the post-work filtration period, typically 48 to 72 hours. It comes down only after clearance testing passes. Testing with the containment already removed makes the results meaningless, because samples then measure a blend of the work area and the rest of the building.
For a small, isolated area with an obvious moisture source, yes. Six-mil poly, spring poles, a zipper door, sealed registers and a rented air filtration device ducted out a window are all easy to get. Beyond about 10 square feet, or where growth is hidden, the HVAC system is involved, or anyone has health concerns, the job needs a professional build.
Read more: air scrubbers and negative air machines · Read more: air movers
MI&T is an inspection and testing company. We do not perform mold remediation, we do not build containments, and we do not sell the materials, so we have no stake in how large a containment anyone builds.
What we do is define the problem before the work starts and verify the result after it finishes. An assessment establishes how far contamination extends, which determines whether limited or full containment is appropriate, and that boundary is often larger than the visible staining suggests. Clearance testing afterward tells you whether the containment did its job, which is why it needs to still be standing when we arrive.
If a contractor asks you to take the plastic down before testing, that is worth questioning.
Find your nearest MI&T location to schedule an inspection or clearance test.
