Vapor Intrusion: What Contractors Need to Know

Applying vapor barrierDevelopers know to do their due diligence on the environmental implications of a site before commissioning a new building, they may overlook one very specific factor that can turn out to be a serious concern.

Before selecting a contractor and breaking ground for a new structure, it is important for an environmental professional to conduct a Phase I Environmental Site Assessment and, if warranted, vapor intrusion testing. Contractors need to do their due diligence to make sure the assessment is completed.

Vapor intrusion is the hazardous, potentially harmful migration of chemical vapors into a building from soil and groundwater that has been contaminated by petroleum products or volatile chemicals. These chemicals could include volatile or semi-volatile organic compounds, in addition to some inorganic analytes. When vapor intrusion occurs, similarly to when radon gas seeps into a building, the habitable zone’s air quality suffers. Certain sites are of higher risk than others due to their proximity to establishments (past or present) whose operations potentially contributed to the contaminated soil.

While developers and building owners want to avoid the possibility of vapor intrusion being a concern in their structure, it is also imperative for contractors to be aware of the chemical vapor migration. It cannot be observed by sight or by smell, and the risks associated with unmitigated vapor intrusion include both the health of its occupants and future offspring. This could also lead to possible litigation for both property owners and construction contractor executives as they may be held responsible for any related issues.

Awareness of the issues and the risks involved is the first half of the solution, and fortunately, awareness of vapor intrusion and its consequences have risen exponentially in the past decade. Furthermore, these health issues do not always manifest themselves immediately. Specifically, there has been more concern about vapor intrusion at the executive level, especially with building owners, facility operators and construction executives than ever before.

Owners are not only risking the well-being of their tenants, but also may face possible future litigation as well. Although building owners need to know that the occupants of their buildings are breathing safe and clean air, contractors and subcontractors also need to be aware that it is just a matter of time before they will have a legal responsibility to ensure this safety as well.

As more data is released, the Environmental Protection Agency (EPA) has taken further steps to do its part in mitigating the risk from vapor intrusion. To illustrate this point, the EPA has recently included vapor intrusion as a potential pathway in its Superfund Program, shedding more light on the issue.

However, building owners and executives would be wise to take note that adhering to regulations alone may not be the only reason to address potential vapor intrusion situations. Whether regulations on vapor intrusion remain the same or change in the future, the risk of future litigation due to actual or perceived vapor intrusion will remain. The good news is there are solutions to mitigate the problem.


Vapor mitigation systems are being installed at the lowest level of new structures when they are determined to be in a high-risk area and/or when contamination is confirmed by testing. There are a couple of different mitigation options available. One of the most common options comes in the form of a composite membrane system. These are often completed with a vapor venting system designed specifically to direct dangerous chemical vapors away from the structure and its habitable zone through a ventilation pipe.

For construction contractors, it is critical to be aware of this issue when they receive the specifications of a new building that includes a chemical vapor mitigation system. If the contractor overlooks the chemical vapor barrier as a simple moisture barrier, which is commonly misidentified, the vapor intrusion problem will not be mitigated. This opens the door to possible litigation for the contractor.

For the installation, contractors need to be sure to hire a qualified subcontractor who offers not only an installation warranty, but also a third party certified inspector to test that the installation has been appropriately installed and verified. Furthermore, a contractor should confirm the material for the chemical vapor mitigation system is accompanied by a manufacturer warranty.

Although it is most efficient to design a vapor mitigation system during construction of a new building, there are also options to retrofit a building when vapor intrusion is later discovered to be a real concern.  This retrofit process includes applying a specially engineered sealant product to the basement floor and walls of the existing structure. This is designed to repel the transmission of potentially harmful sub-slab vapor. This solution has proved to substantially reduce the influx of harmful vapors into an overlying building.

It is critically important as awareness of vapor intrusion grows, regulations continue to tighten, and public demand increases for safe habitable zones, that building owners and construction contractor executives take the necessary steps to ensure their structures are safe. As they have a vested interest in the health and well-being of a structure’s occupants, they need to ensure that every appropriate test is conducted and precautions are taken to reduce the risk of vapor intrusion as much as possible

Published in Construction Executive Risk Management Magazine