Making It Rain: Structural Drying Solutions

A Note from the Editor: This is the final installment of a 3-part series by someone long-considered a structural drying expert. In parts one and two, R. David Sweet discusses an issue plaguing our industry: a lack of thorough drying, which is leading to additional structural damage. He also outlined what industry standards say about drying.

Mr. Sweet has been an independent adjuster, owned and run his own restoration company for more than two decades, has a number of IICRC and other designations and certifications, is a Registered Third-Party Evaluator, and more. This series breaks down his capstone project created to earn his Certified Mold Professional designation through the RIA. It has been read and vetted by a number of industry peers, and carefully walks through the difficult truth that many structures are not being totally dried by contractors. 

During the drying process, while most of the vapor transmission into building materials can be balanced with sufficient off-setting dehumidification, due to the cost, it often is not. In my opinion, this practice is not (in large part) drying the structure, but in reality, just re-apportioning the water vapor into materials that are/were dry. My focus in this article is the second unintended con- sequence: the vapor pressure that is forced into the remainder of the exterior envelope and interstitial spaces, and what eventually happens to it.

Consider the following: Outside of the structure it is 40°F and 30 Rh or 11 GPP, a not uncommon GPP in the wintertime in many environments. This translates into .1 inches of Hg. The inside ambient is at 90°F and 55GPP or 116 GPP. This translates into .8 inHg. This .7 inches of Hg or 105 GPP gradient will drive water vapor laden air from the ambient environment toward the exterior of the structure through the wall/interstitial cavities. This is the second law of thermodynamics in action. So, what is the issue?

When that 116GPP air is moved by vapor pressure into the wall cavities, it is cooled progressively as it moves deeper into the wall assembly. Its GPP does not drop, but the temperature does and as it does, the RH of the air mass increases as the air is cooled. Our psychometric chart tells us that this 116 GPP air will hit dew point at 72°F. Remember, we have a 40°F outside temperature that is constantly drawing/ syncing heat from the exterior of the building. This heat sync lowers the temperature of the connected building materials, with the lowest readings being to the exterior of the wall assembly and the temperature increasing inward toward the finished surface of the interior wall assembly. What are the chances that somewhere in the wall cavity, we will unknowingly create and maintain 70% or greater RH for the 24 to 48 hours necessary to support mold and/or microbially-related category 3 amplification?

I have walked onto projects at day four or five and had my client open walls only to discover that it was basically raining inside of them. Now, while this is a real issue as category 3 elements can easily be aerosolized, moving into any available air mass, I would be immediately more concerned if the Rh at equilibrium were above dew point on or in any of the interstitial cavities / low evaporative materials and/or assemblies. With a consistent equilibrium Rh inside the wall, we can produce mold amplification starting as low as 68% Rh or .68 WA (water activity) within 24 to 48 hours, or in the presence of other biological contaminates like bacteria, within hours.

Let’s look at what several drying environments look like when we consider the effect of the temperature drop in the air/materials as the air mass contacts wet assemblies.

I have used temperate outside conditions; colder outside conditions only worsen the effect observed above.

NOTE: All values in RED are levels capable of supporting microbial amplification at the surface temperatures indicated to their left. All values in BLUE are temperatures at which the ambient air is at or below dew point and we can literally make it rain in/on surfaces.

So, as we can see, in heat drying conditions, even with relatively warm air, the conditions necessary to support microbial amplification can easily be present. We should be monitoring our projects, especially heat-based-only drying projects consistently with an eye toward the psychometrics as they shift through the interstitial cavities as building materials progressively cool, even to the point of warranting the removal/ opening/ventilation of assemblies if the Rh/Aw cannot be predictably controlled. And yes, Category 1 losses are at risk of quickly (in the case of bacterial contaminants) / instantly (in the case of chemical contaminants) and within 24 to 72 hours (for mold) devolving into Mold/ Category 3 events under our care.

Lastly, we need to consider what types of contaminants may be present in these enclosed spaces. What did the water vapor and/or airborne particulate bring along with it as an aerosolized contaminant? For all my (C)IH/IEP’s out there, I believe wall cavity/interstitial space sampling is only appropriate, and in my experience, absolutely necessary on almost all, if not every, drying project. This is especially true where the conditions present produce large vapor pressure or temperature gradients between the interior and exterior conditions, and the project conditions are not known and controlled from the onset of the project.


While we are discussing a particular type of loss, the following apply to all of our losses to one degree or another. Following are a couple tough questions and some possible solutions to consider.

Real-Time Site Monitoring
In our present environment, our data collection requires we be both present on the site and essentially require our most competent lead technicians and/or project managers to survey and modify the drying plan on-site based upon their readings.

The reality: Technicians almost always produce delayed / incomplete inspections. Technicians often lack the patience to take WME readings consistently, document the meter readings and serial numbers, let alone allow the proper amount of time to allow for the thermal hygrometers to achieve an accurate reading (typically between five and 10 minutes with some models). Alternatively, remote monitoring in real-time provides the information we need to create the opportunity to have timely response and environmental management where we can KNOW we are meeting the current required demands of the project.

Monitoring Of Interstitial Environments, Their Materials, And Assemblies
At this stage, it is common to encounter practical objections to the thought of opening what, to all parties, seems to be a perfectly dryable Category 1 affected wall/floor/ceiling. But how do you know what you have actually done? If you followed the math above, you must agree that it is at least possible to create the environments suggested and the damages that would most certainly follow. I would suggest all heat drying projects, and even regular drying environments, should have monitored interstitial cavities. Left unknown, a major risk remains in the damages described above. The questions are:

  1. Who sets the appropriate conditions on a project

  2. Who is actually responsible for a failure should one occur?

  3. Will the carrier, contractor, or client be responsible if damages are left to harm occupants and discovered later?

Introduction Of More Highly-Trained, Highly-Compensated Professionals
We have identified the need, but are left with the more pressing issue: what is our solution? As a contractor, I struggle to find individuals / consultants / companies who understand these concepts and can properly apply them. From my consulting practice, I can confirm I am not alone. So, is it reasonable to assume that we now need to pull more experts and specialists onto all of our projects? Is this sustainable? Will the industry support or resist this?

In-House Technical Professionals
The best solution would be one where knowledge is taught industry-wide. That said, while companies would absolutely love to have this type of in-house talent, we lack both the training and often budgets to support them within (the typically) Xactimate-based pricing allowance. Another reason for custom price lists, based upon YOUR actual business cost. Currently, no category / selector exists for these types of professionals and without the revenue produced by acceptable billing of these types of individuals, I understand a contractor’s reserve to hire and/or train more skilled in-house resources that could grow into the skill sets we so desperately need.

Additionally, I find that many carriers tend to, initially at least, resist paying for more expensive human / intellectual capital (especially if a code cannot be found within Xactimate), suggesting that perhaps, you’re doing more work than is necessary and/or making “a mountain out of a mole hill”. This is not necessarily dishonest on their part; THEY were not given the training necessary to understand the environment wholly either. So, the portion of the industry that is reliant on carriers and TPAs for their day-to-day work can be a little bit less than interested in rocking this particular boat as the discovery of these circumstances and conditions lead to significantly larger scopes of work and significantly larger claim severity numbers. Given this, while I would like to see these functions reside in-house, I believe that another solution will need to be utilized until wider acceptance is developed.

Water Loss Consultant / IEP / RTPE
If a contractor is unable to provide well-trained, skilled technicians, a technical expert will instead be required, at least for the time being. The services of an IEP, if properly trained and experienced, or a Registered Third-Party Evaluator (RTPE) ( would be a good fit in these circumstances. But again, according to the Standard, we are up against a set of environments that the vast majority of all the consulting professionals, with the notable exception of the RTPE’s, are simply untrained in the recognition of and requisite technical expertise to manage, document, and correct mitigation environments.


I believe this to be a technical training issue at its heart. Professionals who understand drying environments wholly and are committed to the ethical revelation of the whole loss are key. Once the technical understanding widely exists, we as an industry must have the moral and ethical fortitude to begin to change our scope of work in a way that logically results in significantly increasing the average claim/indemnity/loss payment. This could be a real challenge for entities that rely primarily on controlling severity of loss to maintain relationships with referral sources. However, this will also create an entirely new industry within our current industrial hygiene and mitigation worlds – one that is essential and one that is likely to have a bright, long, and prosperous future.

Download David’s FREE eBook today! This resource from one of the industry’s top drying experts breaks down the difference between mitigation and stabilization, and walks through what is required to properly stabilize, get paid, and avoid future litigation.

R. David Sweet

David SweetAfter a short period in the capital finance markets, David became an all-lines adjuster for 5 years and subsequently founded a full- service restoration firm. He has 20+ years of experience as a CEO, COO, expert witness, and consultant, and has become extremely proficient in mitigation and remediation processes. Seeing a great need for increased efficiency, fairness, and innovation in an ever-demanding industry, he set about solving the daily issues facing the average restoration contractor. He now is passionately pursuing sharing this knowledge to benefit his peers and have a positive effect on this complex industry. David’s vision of transparent fact-based, claims processing environments serves all parties – insured, carrier, and contractor.

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