Dustin Smoot Published in Roof Consultants Institute: Interface

interface(Arvada, Colorado (November 8, 2012) – Dustin T. Smoot, RRC, RRO, LEED AP, Pie Consulting & Engineering Forensic Specialist, was recently published in the Roof Consulting Institute (RCI) October 2012 issue of Interface. A technical/trade publication of RCI, Interface provides education and information on all segments of the roofing industry. In an article titled Humidity “Gets High” on Medical Marijuana, Smoot shares his expertise on proper building design of “grow rooms” (dispensaries) and explains how high-humidity environments can create costly building damage.

Medicinal marijuana is gaining professional acceptance as a viable treatment for a host of conditions including cancer, AIDS, Parkinson’s disease, and overall pain management. Legalized in 17 states, (including Washington, D.C.) and pending legalization in 7 more states, “grow rooms” (dispensaries) are on the rise across the U.S. to keep up with high consumer demand. Since the operation of a “grow room” is federally illegal but legal by state law, grow rooms are often shrouded in secrecy for fear that the federal government will intervene and prosecute. The facilities that house grow rooms are often leased and not properly designed to be used for this occupation. Ranging in size from a residential closet to a commercial warehouse, a number of poorly-designed grow rooms are operating in poorly-conditioned spaces – creating costly building damage which property owners are often not even aware of.

“The nature of growing marijuana involves operating in conditions of high humidity. This atypical environment can wreak havoc on a structure built for other enterprises. In most cases, there is no easy repair. By the time the problem is discovered, it is usually too late, because the damage has been done.” – Dustin Smoot.

Grow room conditions are nearly identical to those of an indoor pool with temperatures between 75º and 85°F (24°C to 30°C) and relative humidity (RH) values between 60% and 65% or higher. The elevated level of humidity comes from the natural transpiration of the plants themselves. When plants are flowering, transpiration— the release of water vapor through their leaves—is at its peak. The high levels of relative humidity can lead to condensation on building components.

“Most buildings have not been designed to handle the resulting temperature gradient, moisture migration via air movement, and vapor diffusion from interior to exterior space. Elevated temperatures, together with the higher RH, are even more detrimental in cold climates where winter temperatures are cooler for longer periods of time. This causes the vapor drive to be directed from inside to outside, where it can be trapped within the wall/roof, or the wall/roof components can be exposed to this condition for a longer period of time before it can naturally dry out. This makes proper building envelope design very important!” – Dustin Smoot.



  • Elevated temperature and RH can produce an ideal environment for the propagation of biological growth and an increased likelihood of building material deterioration.
  • Deteriorated structural components can cause health issues due to poor indoor air quality, and can make the structure susceptible to further damage from the elements.

There are three conditions required for biological growth: moisture, warmth, and organics. The interior operating conditions, building design, and materials within the ceiling/ wall system dictate the amount of damage that can develop and the rate at which deterioration and biological growth begins.

Photo #1 illustrates a moisture probe reading of 40% moisture content, the highest reading this equipment model can indicate. The glue is migrating out of the plywood, which will cause delamination and loss of strength.

Photo #2 illustrates adjacent joist spaces that were adequately ventilated. These joist spaces had significantly less biological growth and recorded much lower wood moisture content.

With increased moisture also comes an accelerated rate of building material deterioration. Untreated wood should never be subjected to moisture levels over 20%, due to deterioration. Other roof decks of particular concern are Tectum™ or gypsum roof decks. These roof decks were never intended to be subjected to high humidity environments and can easily be weakened by the absorption of moisture.

As for wall systems, the use of wood in walls can deteriorate and propagate biological growth, and masonry wall systems are particularly susceptible to damage when freeze/thaw conditions exist.


  • Property owners should require tenant(s) to build out the space to minimize the possibility of long-term structural damage.
  • Hire a qualified building envelope consultant with experience in temperature gradients, hygrothermal analysis, and design of structures (i.e. indoor pools and refrigerated buildings).
  • Install a properly insulated building envelope with a vapor retarder or barrier on the “warm-in-winter” side of the insulation. Hygrothermal calculations should be performed on the proposed system to assure the dew point does not occur at the vapor retarder.
  • Incorporate a primary plane of air tightness in the design/construction to significantly limit the amount of moisture-laden air transport.
  • Properly ventilate the space between the grow room wall and the exterior wall.
  • Install a properly designed mechanical system to effectively ventilate and/or dehumidify the air within the grow area and minimize the humidity.

About Dustin Smoot:

Smoot, RRC, RRO, LEED AP, is a forensic specialist with Pie Consulting & Engineering, providing forensic engineering services involving building envelope components. Smoot’s technical expertise includes forensic investigation and assessment of damage from weather, construction defects, and product failures. His experience also includes the preparation of bidding documents, peer reviews with recommendations, and quality assurance observation. By working as a contractor, an observer, a consultant, and a designer, Smoot has gained extensive knowledge in building envelope systems design, construction, and failure analysis.

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