Vapor intrusion (VI) awareness is an important development from not only a building planning perspective, but also a human health standpoint. VI is the result of harmful chemicals contaminating soil or water and then naturally dispersing into a building’s air supply. Following VI’s discovery in the 80s, many contractors, owners, developers, and architects have developed an understanding of the legal, medical, and financial risks associated with this exposure. As knowledge of this threat grows, risk factors and areas that may have a high chance of contamination become clearer – and increasingly preventable.
What substances are creating this pollution? A recent Construction Today article from Wesley Robb highlights that contamination by volatile organic compounds (like dry-cleaning solvents/industrial degreasers) create a heightened danger of VI. This means that sites formally or presently occupying dry cleaners, printers, auto repair, or manufacturers typically have the highest potential.
Although VI isn’t detectable by sight or smell, there are solutions easily implemented in new buildings where a risk may be present. Robb states that there are vapor mitigation systems complete with chemical barriers that can be included in construction specifications prior to any building activity commencing. A common mistake is that a vapor barrier included in specifications is the same as a moisture barrier. Both perform very separate functions and cannot be used interchangeably.
If plans do include a chemical vapor barrier, VI risk mitigation usually appears in the form of a chemical vapor channel installed within the footprint of the building, and a coated physical barrier that is laid right before the foundation. Once construction is finalized and a chemical is emitted, the barrier holds it back from entering the building and it is released through a ventilation pipe.
For new construction, there are five basic components for effective VI resistance:
• Permeable sub-slab support material (ex. Gravel)
• Ventilation of all sub-slab areas below occupied spaces
• Properly-sized sub-slab and riser piping
• A sealed vapor barrier
• A properly-sized blower to maintain sufficient negative pressure beneath the slab if an active system is specified
As Construction Today states, the first step to solving a vapor intrusion problem is recognizing it. To overcome the issue, awareness is very critical.
Construction Today, “In The Air”, page 11, Volume 16, Issue 4