Ed Light, CSP, CIH & Paul Haas, CSP, CIH – Moisture & Mold; Practical Answers to Complex Questions

Air Date: 4-26-2019|Episode 544

Today on Iaqradio+ we welcome Ed Light and Paul Haas. They’re CIH’s but actually work with contractors to solve building problems! The “dynamic duo” (Ed and Paul are with the Indoor Air/Mechanical Engineering consulting firm, Building Dynamics), will address elusive questions such as, “Will mold grow here?” and “What do these moisture readings mean?” We are also going to have a special musical introduction from Ed Light.

Mr. Light holds degrees in Environmental Science from the University of Massachusetts (B.S.) and Marshall University (M.S.), is a Senior Fellow of the American Industrial Hygiene Association, has authored over 40 scientific publications on assessment and control of the indoor environment and has chaired several national scientific committees.  In the 1980’s, Ed established the West Virginia Department of Health IAQ Program, pioneering efforts to resolve exposure issues related to formaldehyde, asbestos, and termiticides.  In the 1990’s, he developed widely used protocols for addressing IEQ complaints (published by EPA, NIOSH and ISIAQ) and managing air quality in occupied buildings under construction (for SMACNA, promulgated by ANSI).  As a consultant, Ed has directed more than 1000 multi-disciplinary IEQ investigations, ranging from the White House to the South Pole Station.  He has been admitted as an expert witness in numerous litigations.

Paul Haas CSP, CIH is a consultant with Building Dynamics, LLC – industrial hygiene and mechanical engineering consultants. He has an MS in Industrial Hygiene from the University of Southern California and a BA in Environmental Science from the University of California, Santa Barbara. He has authored many peer-reviewed scientific publications, including widely-used protocols for addressing IEQ complaints. He is a member of ASHRAE, AIHA, and an elite group of surfers who enjoy bluegrass music. As a consultant, Paul has directed multi-disciplinary Building Science and IEQ investigations of 100’s of facilities and managing air quality in buildings under construction. He is a practicing industrial hygienist, and also participates in the successful design and construction of numerous buildings and public health aspects of the indoor environment for more than 25 years.

Z-Man’s Blog:

Moisture and Mold; Practical Answers to Complex Questions

Ed Light and Paul Haas from Building Dynamics, LLC (BDL) were guests on today’s episode of IAQradio.

Nuggets mined from today’s episode:

When does elevated relative humidity alone actually cause mold to grow?

BDL compared RH trends in an unoccupied school over two summers- one where extensive mold growth developed and one mold-free. In this example, growth was not related to peak or duration of elevated RH, but to “time of wetness,” Based on this, BDL’s recommended initiating action when RH exceeds 75% for more than two days in a month, musty odor is detected or condensation is observed. They disagree with other practitionerswho assume that mold will grow when RH exceeds 65% or that comfort levels must be achieved in unoccupied schools.

How can schools use their air conditioning to prevent mold growth without wasting excessive amounts of energy?

BDL discussed this in their paper published in the ASHRAE Journal. While the ability to dehumidify depends on system design, substantial improvement can often be achieved by fixing/adjusting equipment, reducing negative pressure (i.e., shutting off exhaust fans and closing outside air dampers in unoccupied space) or changing the fan schedule. Engineers may over-react to humidity concerns and over-ventilate or over-cool. There are more efficient ways to prevent humidity-related mold growth. In these cases, IAQ can be improved while saving energy and reducing costs. Running the HVAC system in unoccupied schools for a few hours in the late afternoon is probably sufficient to prevent mold. Data loggers can be placed in worst case rooms to be provided advance warning before mold growth occurs due to excess humidity. This can also be accomplished by custodians simply checking rooms daily for signs of dampness.

How dry is “dry” when restoring a wet building?

The objective is to ensure a condition which will not grow mold. There are many different “rules-of-thumb” in the field and no research clearly supporting specific standards. BDL is currently working on restoration of wood-framed apartment buildings under construction during last summer’s record-breaking rainfall (climate change?). They have consistently found that mold grows on wood after bleach treatment when moisture contentstill exceeds 20%. For these projects, they are clearing areas to hang drywall when moisture content drops below 20%. Drying to 15% provides even more assurance that moisture won’t remain trapped after wall and ceiling construction.

Should drying of wet buildings be based on water activity?

BDL tracked the drying of wood studs, comparing moisture meter readingswith a prototype Delmhorst water activity meter. Water activity theoretically supported mold growth (i.e., 0.8) when moisture content was acceptable (i.e., 15%). However, mold may not actually grow in the field at this level of water activity and more research is needed. Moisture meters and IR will continue to be the primary tools to track drying. Water activity measurements are presently of limited value (i.e., a few spot measurements are not representative). They may be useful for verification of drying based on moisture content. A relationship between water activity and moisture content is site-specfic.

Other quotes from Paul and Ed;

  • Many mechanical engineers are not well-versed in moisture control; Most CIHs don’t fully understand buildings.
  • Pretreatment of framing wood to prevent fungal growth is being oversold as a solution.
  • You MUST communicate to your client that the amount of available moisture is different than the amount of moisture on the surface.
  • Dewpoint is a better reference point than RH.
  • Too many people use moisture meters and infrared cameras to point to areas in a building that are wet. The question is whether the wetness is typical and normal operating condition. “The air don’t care.” Check thermostat settings. Install a data logger for several days and review the data. You can learn the HVAC operation cycles and determine how long the system runs, When the temperature goes up the RH goes down, however the available moisture may remain constant.
  • Equilibrium Relative Humidity (ERH) is different than the moisture at a material’s surface. ERH is based on materials in space, for instance Southern soft wood kiln is dried to 17%-19% water wood moisture equivalent. Restorers structurally drying buildings try to remove as many grains of moisture as possible risk over drying. Satisfactory ERH would be 20%-22% Moisture Content.
  • Wood drying needs to occur over time. Sustainable wood materials look like straws when examined under a scanning electron microscope.

Pete Consigli, Restoration Industry Global Watchdog

  • Thanked Ed for his volunteer work on the IICRC water damage standard, and recalled that Ed refused to grant permission for his name to appear in the document because the IICRC refused to publish his dissenting opinion.
  • Ed’s comments about mold in schools reminded him about Mike McGuinness, CIH recounting mold problems in New Jersey schools caused by summer carpet cleaning without HVAC system running.
  • Recalled Lew Harriman’s involvement with water activity sensor research.
  • Pete opined that water activity sensors are another tool not the solution.
  • Cited a dispute over ownership/control of the platform to which water activity readings would be uploaded to as a reason research stalled.

Ed Light’s final comments:

  • Carpet cleaning in schools to remove soil and allergens must be followed by drying, using either fans/dehumidifiers or leaving the HVAC running.with HVAC running in zones where cleaning is perform
  • The late Phil Morey, PhD, CIH was a mentor of Ed’s. However, their opinions diverged and Ed’s mold sampling gear is rusting in his basement.
  • We interrupted Ed’s work today, involving eliminating mold growth, water damage and moisture sources during renovation of an apartment buildings. BDL has expanded the scope of many low-income housing renovations, where the architect did not consider mold.

Paul expressed thankfulness to and for his family., and gave a shout-out to Silldry for developing a new method to prevent water infiltration around windows.

Z-Man signing off


Identify the term that is used to describe a property of a thermodynamic system, that is equal to the system’s internal energy plus the product of its pressure and volume.



No correct answer during the show.