Design amnesia with mold and modular construction

December 4, 2017

Finding answers for indoor air quality (IAQ) and mold-related conundrums can come down to asking the right questions and remembering those answers.
Image courtesy Liberty Building Forensics Group

by George DuBose, CGC, Steven Gleason, PE, and Nate Sanders, CIH, LEED AP

Unfortunately, it appears to be déjà vu all over again when it comes to water-related building failures. As new buildings are being constructed, the same design and construction deficiencies of the past are being repeated, leading to potentially catastrophic mold and moisture problems.

With preventative solutions having been published for many years[2], it may seem strange the industry makes the same basic mistakes time after time. Part of the problem rests in the fact that during the Great Recession[3], a good number of the largest design/construction firms lost many key employees. As a result, the institutional knowledge that had formerly kept construction projects out of trouble disappeared along with these key thought-leaders.

Since many firms can no longer rely on legacy partners to deliver this information to the next generation, they must quickly find good alternatives, both for the sake of their projects and for the very viability of their own future. As an industry, we know we can prevent buildings from failing because we are able to fix them once they do fail.

One of the best and quickest fixes, regarding preventative measures, is the implementation of a third-party peer review that ensures design/construction firms get the right information to the right people at the right time, allowing them to address any potential issues from the earliest phases of a new building project.

A firm should establish and distribute specific written design and construction guidelines at the project’s inception, and then use periodic peer reviews throughout the design/construction process to compare progress against the original guidelines. When implemented, these steps become the foundation of a practical model for improving the performance of both new and renovated buildings.

The premise behind this model is crucial decisions must be made at each stage of a project’s life—design, construction, and operation—to avoid problems and control costs. When such choices are properly applied, the incidence of building problems substantially decreases and the initial construction cost or schedule is not affected. These achievements are possible by eliminating many redundant and unnecessary building system components or procedures that often add nothing valuable to the ultimate performance of a building.

Decisions at the design stage can virtually guarantee a successful project. Alternatively decisions at the early design stage can result in catastrophic mold and moisture problems not seen until well into operation of the building.
Image adapted from American Society of Civil Engineers (ASCE) 1988

A modular example
The emergence of modular assemblies as an option for new construction is becoming mainstream. However, this industry has had its share of mold and moisture problems, especially in warm and humid climates like the Southeast United States. Both wood-frame and steel-frame modular construction have experienced problems with condensation in crawlspaces, marriage walls, and ceiling-to-floor cavities, resulting in deterioration of the wood and wallboards, corrosion of metal floor pans, and proliferation of mold.

The greatest risk of modular construction failures has occurred when it is used for hotels, student housing, senior living, or soldier housing—generally, facilities that are domicidal or multifamily in nature. The reason for this risk probability is due to inherent similarities in requirements for the living units of these types of facilities, such as an individual cooling/heating unit, bathroom exhaust, and some sort of central HVAC makeup air system. Additionally, the abundance of modular boxes in these kinds of buildings increases the number of marriage wall interior cavities and ceiling-to-floor cavities that otherwise might not be required in other types of modular construction.

In a hypothetical case-study example, a modular construction unit had inherent interior hidden spaces that made it difficult to control the infiltration of outdoor air. (In wood-frame modular construction, this is typically the cavity between modular boxes, while in steel-frame systems, it is usually the spaces between modules.) These interior cavities provided a pathway for airflow to not only readily enter the building but also to travel long distances throughout the building, washing interior surfaces. This caused direct condensation and/or raised surface conditions that led to physical damage and mold growth on wood framing and interior drywall.

Each modular box, as it came from the manufacturer, had been designed and constructed in a vacuum of the requirements for the overall performance of the building. This was especially true in the HVAC system design and construction for building pressurization.

In modular box design coming straight from the factory, both the cooling/heating unit and the bathroom exhaust generally depend on the separate common area HVAC system for make-up air. This factor is often overlooked in the design and construction of modular facilities. In fact, the pressurization of the overall building is dependent on the pressure characteristic of each interior space, whether it is occupied by people or the area between two modular boxes. Similarly, the air leakage characteristics of modular construction buildings depends on not only the leakage rate of the modular box itself, but also on the leakiness between and around the compartments making up the building (both occupied spaces as well as the wall cavities between modular boxes).

In this example, the modular design and construction used pilings as its foundation. The resultant crawlspace adversely impacted the ability to control condensation and outdoor airflow in and throughout the building.

The modular design and construction process had a ‘modular box versus base building’ conflict inherently built into how it was delivered. Modular boxes are designed and manufactured by a separate entity from the one designing and constructing the base building. Veritably, the crawlspace, roof, attic, exterior cladding, and HVAC system are more often than not designed by one entity and constructed by another.

Inspections for code compliance can be different for the modular construction versus the base building construction. This often varies depending on the jurisdiction in which modular construction is either manufactured or constructed. In Florida, for example, modular construction is governed by the Department of Community Affairs (DCA). This includes inspection of each modular box before it leaves the manufacturing facility. The base building, on the other hand, is inspected by the local code official. This individual does not inspect the modular box since it has already received the DCA inspection and certification. While both governmental agencies rely on the same building codes, the silo inspection process competes with a more holistic process that has the overall building performance as the overarching goal.

Most designs assume a building acts as one big box, but the pressure characteristic of the building is made up of a series of small boxes (e.g. rooms, cavities, plenums, and interior spaces). This is especially true for modular construction.
Image courtesy Liberty Building Forensics Group

You can’t fake the funk
The case study on the previous page was specific to modular construction, but the general principles and challenges involved are common to today’s design and construction industry. So how can designers and contractors avoid these problems? To help avoid catastrophic mold and moisture building failures, here are four points of which every architect and contractor must be aware.

Buildings should not be designed in silos.
Despite advances in technical understanding and higher standards for building performance (e.g. enclosure airtightness), tasks like designing building envelopes are still being completed in a vacuum of other critical disciplines. On a recent project, the façade consultant was asked how the design interfaced with the overall building pressurization requirements established by the HVAC design. The answer: “We don’t consider that in our design—they do their thing and we do ours.”

Keeping silo design from happening on a project means more than using tools like building information modeling (BIM). While BIM is good for preventing field conflicts, there is much more to address concerning multidisciplinary building performance. Careful coordination between disciplines, such as the architect and HVAC designer, must occur to ensure problems like compromised wall systems, building air infiltration, and dehumidification do not become catastrophic.

Design and construction guidelines must be specific to the project.
If pertinent, one should include each problem that has been analyzed and the solutions that were provided. This step helps avoid corporate amnesia by allowing for lessons learned to be pushed forward to new team members, and for a transfer of knowledge from past expertise to become part of future decisions. Get the right information to the right person at the right time—it does no good for lessons learned to stay among only those who attended expert depositions. This information needs to be passed on to the design and construction teams.

Experts should be brought on early in the process.
Periodic peer reviews should be used to ensure the information provided to the design and construction teams is passed along at the right time. These critical project pressure points can virtually guarantee success or failure, depending on what decision is made.

When problems arise, minimize occupant outrage as quickly as possible.
This becomes one of the greatest influencers on the cost of fixing a building. J. David Odom, a senior consultant with Liberty Building Forensics Group (LBFG), and a colleague of this article’s authors, found this out in the early 1990s with projects like the Martin County Courthouse. In this case, the occupants of the buildings lost confidence in the fix and ultimately drove a much larger ‘repair’ than was necessary. The final costs increased from $2.5 million to more than $24 million because of this ‘occupant outrage factor.’ (For more on the impact of occupant outrage on a project, see Peter Sandman’s work[6].)

Handling occupant confidence (or lack thereof) is one of the key areas any designer or contractor must master. If they do not, they will encounter costs that are multiples of what the repair should be.

Building performance can be highly predictable. Design professionals should use this to their advantage by being wise about how all endeavors are approached and managed. ‘Hope’ is important for many aspects of life, but in the design and construction business, hoping for something to work is never a good premise.

 Further reading
Liberty Building Forensics Group (LBFG), the firm at which this article’s authors work, has published a series of e-books for free download:

  • “The Incredible Predictability of Moisture Problems[7];”
  • “Peer Review: The Single Most Important Factor in Reducing the Risk of a Mold and Moisture Lawsuit in Your Next Project[8];” and
  • “Moisture Damage Assessment Tool[9].”

[10]George DuBose, CGC, president of Liberty Building Forensics Group, brings more than 25 years of experience in building forensics, with a focus on failures related to mold and moisture issues. He is co-author of three manuals on indoor air quality (IAQ) and mold prevention, and has consulted on ductwork remediation projects, large-scale resort and hotel properties, multifamily residential buildings, and educational campuses. DuBose can be contacted at[11].

[12]Steven Gleason, PE, has over 25 years of experience in construction consulting, including evaluation, design, project management, and expert testimony services related to moisture intrusion and building envelope failures. He provides consulting services related to a wide variety of construction materials and building envelope components including masonry, concrete, glazing, stone, stucco, exterior insulation and finish systems (EIFS), sealants, coatings, and roofing and waterproofing systems. Gleason has consulted on more than 500 projects, ranging from residences to over 70-story high rises. He can be e-mailed at[13].

[14]Nathan Sanders, CIH, LEED AP, is a forensic Certified Industrial Hygienist, with more than a dozen years of professional experience in occupational & environmental health and safety. He has conducted hundreds of evaluations to evaluate physical, biological, and chemical hazards in occupational, residential, and community environments. Sanders develops and implements proactive pre-occupancy IAQ testing protocols, leads administrative duties for LEED-certified projects, and assists in commissioning activities in newly constructed buildings and renovated buildings. He has provided expert opinions for microbial and chemical IAQ litigation efforts. Sanders can be reached at[15].

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  2. preventative solutions having been published for many years:
  3. Great Recession:
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  6. Peter Sandman’s work:
  7. The Incredible Predictability of Moisture Problems:
  8. Peer Review: The Single Most Important Factor in Reducing the Risk of a Mold and Moisture Lawsuit in Your Next Project:
  9. Moisture Damage Assessment Tool:
  10. [Image]:
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