Introduction to Controlled Environment Drying Methods

A controlled drying environment begins with physical containment — establishing a physical boundary between the drying zone and the rest of the building that controls air movement, prevents cross-contamination, and allows the drying conditions within the zone to be managed independently of external conditions.

Why containment improves drying: without containment, the drying equipment is working against the entire connected volume of the building and the outside environment. Humid outside air entering through open doors and windows, air movement through HVAC systems, and the moisture reservoir of unaffected materials all increase the humidity load on the drying equipment. Containment concentrates the equipment's effect on the actual wet zone.

Containment materials: heavy-duty polyethylene sheeting (minimum 6 mil, preferably 10 mil) is the standard containment material. Secure sheeting to walls, floors, and ceilings using appropriate tape and framing as needed. All penetrations — doors, windows, vents, pipe penetrations — must be sealed to maintain the containment integrity. Use zipper access panels at entry points to allow personnel access while maintaining the air seal.

Negative pressure containment: when the drying zone contains Category 2 or Category 3 contamination, or when mould is present, the containment must be maintained under negative pressure — the air pressure inside the containment must be lower than the pressure outside. This ensures that any air movement through the containment boundary is inward (from clean areas into the contaminated zone) rather than outward (potentially spreading contamination to clean areas). Achieve negative pressure by exhausting HEPA-filtered air from inside the containment to outside the building using an AFD.

Containment in occupied buildings: in residential losses where occupants must remain in the property, clearly communicate the containment boundaries and access restrictions to the occupants before establishing containment. Ensure that the occupants' access to essential facilities — bathrooms, kitchen — is not eliminated by the containment zone. Where the loss affects a critical area, work with the property manager to arrange temporary accommodation.