By George H. DuBose, CGC and Steven R. Gleason, P.E.
Certain faulty beliefs surrounding hotel performance in warm, humid coastal zones continue to persist in the design and construction industry – and waterproofing is no exception. Unfortunately, the fact that many architects and engineers rely on these myths as gospel truth during building envelope design has inevitably led to building failures that are often catastrophic in scope.
Below are two myths our experts at Liberty Building Forensics Group (LBFG) have encountered through their extensive work resolving mold and moisture problems in hotels and resorts. Both myths are followed by an explanation of why they are false, as well as a first-hand case study supporting this position.
Myth #1 – Water damage will be avoided in hotel design as long as a waterproofing membrane is installed over a concrete slab.
Truth – Many issues must be considered when waterproofing a concrete slab base. Using a waterproofing membrane over a concrete slab, which is often topped by a mortar bed and stone or similar overburden, is just the starting point.
In addition, the membrane must be sufficiently robust to do the job, and drainage must be adequately thought out. Installing a marginal membrane or an inadequate drainage system will often lead to membrane failure and cause the building to leak, especially in climates with heavy rainy seasons.
Case Study – LBFG observed a failure of this sort at a resort built into a mountainside in Mexico. The entrance to the resort was located at the top of the mountain, and the remaining portions of the facility were built down the side of the mountain utilizing multiple terrace-like levels. As such, most of the common areas were open-air terraces over occupied space below.
Waterproofing over occupied space is a critical but often misunderstood and overlooked aspect of building envelope design in hotels and resorts. Despite the presence of a waterproofing membrane on the elevated concrete slabs, water intrusion occurred through the terrace levels into the spaces below, infiltrating via penetrations and cracks in the slab (Figure 1). The extent and magnitude of the leaks were such that an elaborate system of gutters and drain piping had been installed below the slabs in an attempt to intercept and manage the leakage (Figure 2).
LBFG performed a field investigation to evaluate the factors contributing to the leakage, which revealed the following:
- The structural slabs onto which the waterproofing had been applied were nominally flat, lacking positive subsurface drainage.
- The waterproofing systems applied to the structural slabs incorporated fluid-applied asphalt and urethane-based products that had poor resistance to ponding water.
- The waterproofing membranes had been applied below the required minimum thicknesses.
- Penetrations and terminations of the waterproofing were not detailed properly.
- The waterproofing membrane had been damaged during construction due to inadequate protection.
LBFG determined that the leakage occurred as a result of marginal waterproofing products installed over a poorly drained structural slab, aggravated by improper installation and damage during construction.
Design and construction practices that can help prevent these types of problems include:
- Provide positive slope to drain at the subsurface slab level onto which waterproofing membranes will be installed.
- Utilize waterproofing products that can tolerate poor drainage and ponding water.
- Ensure that detailing at penetrations and terminations are adequately addressed during both design and construction. This can include peer review of the contractor’s submittals by a waterproofing consultant prior to installation, as well as quality assurance inspections and testing by a consultant during installation.
- Ensure that the integrity of the waterproofing membrane is verified before overburden materials are installed, preferably by both visual observations and water testing.
Myth #2– A building envelope can perform effectively on its own without any help from the HVAC system.
Truth – Put another way, this myth asserts that an architect can design a building envelope in such a way that it is HVAC failure-proof. In actuality, there isn’t a building envelope on earth that an HVAC system can’t damage or destroy in some way. Hotel guest rooms are unique in that they have a large amount of HVAC per square foot as compared to other building types, like office space. This means that large amounts of air are moved through the volume of a guest room in the forms of ventilation exhaust and supply, and also in the form of actual tempered air conditioning from the guest room unit (e.g. fan coil unit, PTAC, etc.). These large amounts of airflow and cooling or tempered air conditioning can have a significant influence on the pressure gradient across the building envelope and on the condensation potential inside the exterior wall cavity. For these reasons, there is greater risk that the HVAC system, when not designed and installed properly, can result in significant damage to even a well-designed and installed building envelope.
Case Study – Mold and moisture problems in a resort located in a warm, humid climate led to diagnostic tests that prompted the complete re-cladding of the exterior, only for the same mold problems to return the following summer (Figure 3). At that point the building owner, left wondering how the recommended repair could have been so far off from solving the actual problem, asked our experts to analyze the situation.
LBFG’s assessment revealed that the original consultants had not accurately evaluated the mold and water damage patterns and as a result, had misdiagnosed – or only partially diagnosed – the root problem. Our experts have observed that incomplete diagnoses have often been given when buildings experience complex moisture problems that originate with multiple sources. This also frequently happens when a lack of importance is placed on the influence the guest room HVAC system can have on building envelope performance.
In this particular case, one legitimate cause of moisture damage was correctly identified, but others were overlooked. A rainwater leak was detected and blame was fully attributed to this factor. However, air infiltration from a defective HVAC system was also a contributing culprit and was missed. As a result, the recommended repairs to the building envelope solved the rainwater leak but failed to address mechanical system air infiltration and humidity issues, allowing the moisture problems to reoccur.
Complicated moisture problems deserve a multi-disciplinary approach that includes both architectural and mechanical expertise. This is especially important with hotel guest room moisture problems because the HVAC system can have such a significant influence on the effective air tightness of the exterior wall system, and therefore also have a direct impact on the condensation potential inside that wall.
Each of these myths warrants careful review and appropriate modifications to standard practice by both architects and engineers. Continued circulation of faulty beliefs throughout the industry reflects a failure to appreciate the full picture when it comes to building design and construction.
The best doctor is one who understands that a specific symptom in the human body is not the root cause of the problem, but rather reflects a deeper issue that is causing a lack of harmony between the various systems of the body. In the same way, the best architects and engineers understand that they do not work in a vacuum or develop their component in a silo, independent of other building system professionals. Buildings are complex. For every one issue that is being addressed, a number of other factors must also be considered in order for the interconnected building systems to be able to perform in an integrated manner.
About the Authors
George DuBose-CGC and Steven R. Gleason, P.E. are both building experts at LBFG.
LBFG President George DuBose, with over 25 years’ experience in building failures and a focus on mold and moisture issues as well as HVAC and building envelope failures, is co-author of three manuals on IAQ and Mold Prevention, which have been used on over $4B in construction.
Steve Gleason, a Senior Forensic Engineer/ Vice President at LBFG with over 25 years’ experience in construction consulting, provides consulting services related to a wide variety of construction materials and building envelope components. He has consulted on over 500 projects ranging from residences to over 70-story high rises.
LBFG has provided mold and moisture diagnoses and solutions for buildings to owners, contractors, and developers worldwide. The firm has project experience in the U.S., Canada, Mexico, the Caribbean, Central America, the Middle East, Southeast Asia, and Europe. Contact us at email@example.com or by phone at 407/467-5518.