This post by David Odom is part 1 of 3.

Suppose there was a tool that could predict, before a single penny was spent on construction, the likelihood of whether your building would fail. Not only that, but this tool could also provide you with enough information to make significant design changes that would dramatically decrease any risk factors. Would you be interested? Of course you would.

At the risk of oversimplifying a complex process that contains multiple variables, I believe we have created such a tool. The following moisture prediction charts have been adapted from a mold and moisture manual Liberty Building Forensics Group developed for Disney Corporation in the early 1990s. Over the past two decades, they have been beta-tested on literally thousands of hotels, and have proven time and time again to be as true today as they were 20 years ago.

Although the charts were created with hotel guest rooms and wall cavities in mind, the general principles demonstrated would hold true for most buildings. Hotels just happen to be the simplest commercial building structure, so they were the easiest to beta test.

continuous toilet exhaust

Figure 1 – Continuous Toilet Exhaust

non-continuous toilet exhaust

Figure 2 – Non-Continuous Toilet Exhaust

We took as many variables out of the charts as possible to simplify the choices. However, we must add several notes for clarification:

  1. This prediction chart assumes no rainwater leaks are present and that all moisture problems are the result of condensation.
  2. This prediction chart assumes that the hotel is located in a climate where the summertime conditions are hot and humid.
  3. This prediction chart should be used as a general guideline and not as a specific design tool since there are various other factors that can dramatically influence whether moisture problems will occur in the guest rooms or inside the wall cavities other than those items that have been identified.
  4. This chart assumes that local codes will allow the MUA to be supplied via the corridor and door undercuts.

Chart abbreviations and terms are explained as follows:

  1. PTAC Unit – Package Terminal Air Conditioning (standard wall units)
  2. FCU – Fan Coil Unit (typically used in upscale hotels)
  3. MUA – Make-Up Air
  4. Continuous Toilet Exhaust – typically used in high-rise or five-star hotels

To be continued…

Author J. David Odom is a Vice President and Senior Building Forensics Consultant with Liberty Building Forensics Group. He has managed some of the largest and most complex mold and moisture problems in the country, including the $60M construction defect claim at the Hilton Hawaiian Village in Honolulu and the $20M claim at the Martin County courthouse. He has also managed over 500 projects for the Walt Disney Corporation dating back to 1982 that have included technical issues related to corrosion, moisture, and design & construction defect-related problems. He has published numerous manuals and technical articles, including a monograph on moisture and mold for the National Council of Architectural Registration Boards (NCARB). For more information, contact J. David Odom at