Mold in Office Buildings: It Won’t Go Away Timothy A. Mills, PE, LEED AP, CIT II, Certified ABAA Auditor TAM Consultants Inc. 4350 New Town Avenue, Suite 203, Williamsburg, VA 23188 757-564-4434 • tmills@tamconsultants.com Building Enclosure Symposium • NovembeBEr 11-12, 2019 M Mills • 13 Abstract This presentation is a classic case study of an ongoing problem plaguing many office building facility managers across the country: mold. Although much has been written about this subject, many people in the building profession have little knowledge about why buildings keep filling up with mold, and less knowledge about what to do about it. In this case study, the presenter will demonstrate the steps necessary to conduct a forensic investigation regarding cause of defective building systems, and review the approach, fact finding, conclusions, and recommendations. The presenter will demonstrate the implementation of antiquated design details in a 45,000-sq.-ft. office building with masonry cladding and standing-seam metal roofing. The building suffered from years of poor performance, poor indoor air quality, and unhappy occupants. This case study offers insight into reviewing and diagnosing existing construction, including interviewing staff personnel, reviewing plans, as well as reviewing maintenance records. The presenter will discuss the performance of brick and concrete masonry unit (CMU) cladding, through-wall flashing, kraft facing, and #15 felt as an air barrier, and how mechanical systems come into play and interact with the building air barrier and enclosure systems. Speaker Timothy Mills TIMOTHY MILLS graduated with a B.S. degree in engineering from Brooklyn Polytechnic Institute of New York in 1983. Prior to forming TAM Consultants in 2002, Mills had experience with a number of multidiscipline design and inspection firms. He has published numerous articles and completed nearly 1500 residential home and commercial building inspections and 300 energy audits. He is an instructor for Air Barrier Association of America (ABAA) training courses that educate and certify contractors in the proper installation of air barriers, as well as a certified ABAA Auditor in the quality assurance program. 14 • Mills Building Enclosure Symposium • NovembeBEr 11-12, 2019 INTRODUCTION All types of buildings can and do experience significant failure—often resulting in large quantities of mold growth in occupied spaces; on various finishes and furnishings; inside concealed spaces; inside walls; on ceilings, in plenum spaces, and in crawl spaces; and inside mechanical systems and ductwork. The mechanisms at play that cause these conditions are based on well-known simple concepts caused by just a few missteps in either building design, maintenance, operation, or all of these. Although much has been written about this topic over the past 25 years, a profound lack of understanding of why mold conditions persist in buildings continues in the design community, with building owners, property managers, and building facility management professionals. Building owners and operators often retain environmental consultants or remediation companies that can clean up the offending problem, only to have it reoccur. Without understanding the root cause of these issues, they are bound to reoccur. Environmental professionals are often poorly equipped to understand the intricacies of how buildings are constructed and how they function. Office buildings are no exception to invasive mold problems. These buildings are often constructed quickly and economically by developers for the highly competitive commercial leasing market. Office buildings are of all construction types, ranging from single-story combustible wood frame buildings to more complex noncombustible high-rise facilities that utilize steel and concrete. We will focus on the interaction of the building enclosure and HVAC systems and how these building systems work—or don’t work—in maintaining a mold-free building. BACKGROUND Mold issues can show up in buildings for a variety of reasons. A common intermittent reason might be a temporary roof leak, a spill, a broken pipe, or some other accident or maintenance issue. These are not the types of mold triggers that we are concerned about in this paper, as they are temporary/one-off occurrences that can be easily identified, rectified, and cleaned up as they occur. Our concern pertains to those pervasive problems that reoccur even after a remediation effort has been completed. The buildings addressed in this discussion include modern office buildings typically built within the past 30 years. Building operators or occupants may have recently become aware of mold problems due to some change in how the building is operated and/or maintained, or they may have been struggling with ongoing seasonal or occasional mold issues for many years, not knowing how to properly address them permanently. When mold issues become prevalent on the interior of the occupied spaces, usually there are initial signs of mold growth in various rooms. Key locations include: • At inside corners at the base of a wall and corner of the room • Behind furniture that is up against an outside wall • At or near a ceiling supply register where conditioned air is provided into the room • On stored paper materials • Behind framed artwork and posters • Inside closets or storage rooms where little air circulation occurs • Behind wall coverings where various-colored stains bleed through and are visible inside the room Often complaints include concerns about high interior relative humidity (55%+). At such high relative humidity (RH), office equipment can malfunction because copier or plotter paper wrinkles and will not feed through the machinery properly, causing frequent paper jams. Artwork on the walls begins to swell and wrinkle, and there may even be evidence of surface rust or corrosion occurring on metal components such as desks, chairs, filing cabinets, light fixtures, and HVAC supply registers. When mold is occurring inside concealed spaces—often inside the exterior walls—it is more typically not discovered until a maintenance operation is underway. Occupants or operators can become quite alarmed and often take action, such as retaining an environmental company to perform testing and/or hiring a remediation company to perform cleanup, but often don’t take the steps necessary to determine the root cause of the pervasive mold. This ultimately results in reoccurring episodes. Fundamentally, in order for mold to take hold, several contributing factors need to be present. These include the presence of mold spores, a food source, moisture, and the proper temperature. In general, mold spores are abundant in the air, and food sources can be found in many organic building materials. Materials with cellulose content, such as paper (i.e., drywall), glue, wood products, fabrics, and linens are excellent sources of food. Temperatures in most buildings are very suitable for mold growth. As localized RH levels increase past 70%, conditions are right for mold growth. Even mildew-resistant products, such as mildew-resistant wallpapers, can be overcome by mold and mildew over time. Mold can react to wallpaper pigments, causing undesirable colorful staining underneath the wall coverings. Whether or not excessive moisture in liquid or vapor form is present within the building systems is a critical factor in determining whether mold growth occurs. There are numerous ways in which moisture can find its way into the building and its systems, creating opportunities for mold growth. These include defects such as: • Roof leaks • Wall leaks, such as brick veneer, openings, or other cladding systems • Cracks in joints at windows, doors, and flashings • Water vapor infiltration via unintentional air leaks through the exterior enclosure components • Plumbing system leaks, both in the supply and waste piping systems Water, and in particular, water vapor entry via unintentional air movement into a building, can be greatly exacerbated by a Mold in Office Buildings: It Won’t Go Away Building Enclosure Symposium • NovembeBEr 11-12, 2019 M Mills • 15 difference in air pressure between the inside and outside portions of a leaky building enclosure. A negative air pressure inside the building relative to the exterior will tend to pull air, and with it, water in vapor form, into the building spaces and its components. The differences in air pressure across the enclosure and the airtightness of the building’s air barrier system greatly affect how much air (and with it, water vapor) transfers across the building enclosure components. In general, the total amount of water vapor transferred across a leaky (non-airtight) building enclosure—with or without an installed vapor barrier—is many times greater than vapor transfer solely as the result of vapor diffusion through the enclosure components. Therefore, air movement, or controlling it, is key to resolving mold issues. The building enclosure is generally composed of a number of building materials and components that serve different or multiple purposes. These materials may serve an architectural purpose, resist bulk water or sunlight (cladding systems), act as a heat barrier (thermal insulation), provide airtightness (air barrier), resist liquid moisture entry (weather barrier), resist water vapor entry (vapor retarder/barrier), provide structural support, and provide for interior finishes. Water vapor will always tend move from an area of high vapor pressure (i.e., warm, humid air) to an area of low vapor pressure (i.e., cooler, dryer, conditioned air). In addition, there is a “stack effect” that, in multistory buildings, causes warmer, more humid air to rise within the structure. This stack effect then creates negative pressures on the lower floors and higher pressures on the upper floors. We are referring to buildings that have limited or no roof leaks, no liquid water leaks at the exterior cladding systems, and no internal plumbing leaks. A CASE STUDY In this particular case study, we looked at a 75,000-sq.-ft., two-story office building constructed circa 1988. The building is located in the southern portion of Climate Zone 4 on the East Coast, and it is operated by a municipality providing administrative services to the local population (Figure 1). The owner had long received calls complaining of high RH and small amounts of surface mold at various areas throughout the building interior, and had more recently discovered significant pervasive mold in the exterior wall stud cavities and behind the wall coverings during a planned renovation. Building Enclosure The facility is a two-story steel frame structure with a slab-on-grade concrete first floor and a second floor constructed of open-web steel bar joists supporting a steel-form deck and poured-in-place concrete. Exterior walls are constructed primarily of non-loadbearing light-gauge metal steel-stud framing with glass fiber insulation with a kraft facing towards the inside space. Interior walls are gypsum wallboard finished with paint or vinyl wall coverings. Exterior sheathing is paper-faced gypsum with a single layer of asphalt-saturated building felt as a weather barrier, a 1-in. air space, and either brick or split-face concrete masonry units (CMUs) as an exterior cladding material. The building is constructed with steep-slope roofing consisting of standing-seam metal, installed over plywood sheathing on long-span wood trusses. Attic insulation consists of friction-fit batt fiberglass insulation, which is installed between the lower cords of the roof trusses, separating the conditioned space below from the attic space created by the wood truss assembly. Interior ceiling assemblies on both floors consist of suspended acoustical ceiling tiles on a metal grid system. Additional building enclosure components include fixed aluminum storefront windows throughout with storefront entry doors at various locations. The investigation of this property occurred during the winter, when condensation on the wall and interior portions of the building was not occurring, although all of the signs and evidence of a failed building were still visible, measured, and verified. This included such things as a poorly installed and detailed weather-resistant barrier in the wall assembly, attic ceiling assembly, and a poorly operating HVAC system. Building HVAC The building is conditioned by 17 above-ceiling, four-pipe, water-cooled and heated air handling units (AHUs) split between the first and second floors. Cold water is provided by an air-cooled chiller located outside, and hot water is provided by a boiler located in a mechanical room. These above-ceiling units include disposable single-use pleated air filters, which are replaced on a regular basis. Supply air is transported via insulated metal ducts throughout, and return air is via the above-ceiling plenum space, where return air light fixtures and/or ceiling grills are provided. The design allows fresh outdoor air to be introduced from either wall or soffit louvers connected to four outside air 16 • Mills Building Enclosure Symposium • NovembeBEr 11-12, 2019 Figure 1 – Typical floor plate (1 of 2) for the subject case study. fans, which provide filtered unconditioned outside air directly to the 17 AHUs located between the floors. These four outside air fans (OAFs) provide filtered unconditioned ducted air directly to the above-ceiling air handlers distributed throughout the building. The system relies on the above-ceiling air-handler-chilled water coils to do the job. The building also includes a total of six in-line exhaust fans, which serve various portions of the building, providing general exhaust fans for bathrooms, storage rooms, janitor closets, and elevator equipment rooms (Figure 2). Evaluation Techniques Before moving forward with an evaluation with this type of study, it is imperative that the consultant performing the study have a systematic game plan. For most forensic evaluations, the game plan can be summarized as follows: 1. State the problem in a written scope statement. Restate the client’s concerns in a definable statement that clearly identifies the problem, such as “Determine the cause of chronic high RH in the building’s interior occupied spaces and endeavor to determine cause and provide an opinion regarding what actions may be necessary at this time.” 2. Review Files. This step starts with reviewing available plans, specifications, and prior reports and studies, including maintenance records, if available. Look at the original detailing for all of the enclosure components and any modifications that have been made and the design of the HVAC systems. 3. Interview staff. These are the people who are most knowledgeable about the undesirable conditions. They can provide invaluable insight into the problem. 4. Collect data. Schedule one or more site visits to review the facility. Work methodically, eliminating non-contributing systems, and focus on those systems that may be causing the problems. Multiple site visits may be necessary and may require operating certain equipment under certain conditions, measuring pressure differentials using a micromanometer or smoke, air flow, long-term RH trends, and/or partial demolition of exterior building components, including cladding, flashings, roofing materials, and other components, looking for evidence of construction or design defects. Tools used for this effort may include thermal imaging equipment, water spray nozzle and spray-rack equipment, whole-building air-testing equipment, borescopes, quality photography gear, RH measuring equipment such as hand-held hygrometers, long-term data collectors, and various types of pin and non-penetrating moisture meters. 5. Make a list of hypotheses. Based on the information collected, make a list of conclusions and hypotheses and test their validity. Go back and collect more information if the conclusions are not fully supported by the data. Findings Building Enclosure During our review of the subject property, mold growth that had been observed and reported in the occupied portions of the building had already been cleaned, and an interior remodeling effort was underway. This effort had resulted in the removal of some of the interior drywall on exterior wall assemblies, revealing the presence of mold inside a number of the stud cavities. In some locations, as a result of the remediation work, fiberglass batt insulation, exterior gypsum sheathing, and the felt weather barrier exposing the back side of the masonry cladding and masonry air Figure 2 – Schematic diagram depicting where intentional air flow occurs across the building enclosure, including the introduction of outside air (outside air fan) and building exhaust (exhaust fan). Building Enclosure Symposium • NovembeBEr 11-12, 2019 M Mills • 17 space were removed. This visible access into the masonry cavity provided the opportunity for several important observations, including visible light through a number of vertical mortar joints in the exterior masonry cladding. This is not an uncommon defect where head joints in masonry components are often not fully bedded and tooled properly, resulting in open direct paths for water entry into the masonry cavity from the exterior. The introduction and observation of water inside the masonry cavity is not necessarily a bad thing. In fact, it is expected and normal, depending on the porosity of the exterior cladding (e.g., split-face block can be quite porous). The type of mortar and how well the mortar joints are tooled will govern the amount of water that penetrates through the cladding and into the airspace and drainage plane behind it (Figure 3). It is not uncommon to this building and many office buildings (even those constructed recently) that the building enclosure is not constructed with methods ensuring an effective air barrier (Figures 4). Although asphalt-saturated felt paper can be an effective weather barrier, it is a poor air barrier. In addition, the roof assembly, which includes a large attic where the attic insulation is installed in the bottom cords of the roof trusses, only has friction-fit kraft-face fiberglass batt insulation installed—a very poor and ineffective air barrier. In fact, in many locations, as is typical, the fiberglass batts can become loose, dislodged, or moved out of the way for a variety of maintenance or other reasons. Over the years, this results in wide-open spaces between the unconditioned attic space and the above-ceiling plenum space in the conditioned second floor below (Figure 5). 18 • Mills Building Enclosure Symposium • NovembeBEr 11-12, 2019 Figure 5 – Common condition in the case study property attic where missing thermal insulation was observed—not only causing a reduction in insulating value, but also allowing large volumes of uninhibited air flow between the ventilated attic space and the conditioned space below. Figure 4 – Thermal imaging can be useful in determining air flow at building envclosure corners. In this case, cold outside air is infiltrating the occupied space at the floor/wall intersection. Figure 3 – Case study property where lack of maintenance, leaking downspouts, poor grading, and plant growth on the walls are contributing to building failure and increased moisture in the masonry cavity. Again, this is not an uncommon construction technique, and it was used until recently and perhaps is still in use by some designers and contractors today. The absence of an effective air barrier in the exterior walls and roof/ceiling assembly permits uninhibited infiltration or exfiltration of air across the building enclosure, where unintended air infiltration or exfiltration is dependent on weather conditions (i.e., wind) or the manner in which the HVAC system introduces outside air and exhausts interior air. One can imagine that the environmental conditions can be extreme inside a masonry cavity on a summer day following a rainfall with damp masonry cladding in direct sunlight. In fact, temperatures exceeding 100°, and RH in excess of 70% are certainly achievable. Introducing the masonry cavity air into the building’s interior regularly can have severe detrimental effects. A review of the construction details on the plans indicated other areas that required further field inspection to determine construction methodology. In particular, the perimeter-wide flange structural beam supporting the second floor was detailed in such a manner to allow the wide-open annular space around the entire perimeter of the building at the second floor. This creates an opening where the masonry cavity is easily accessible and open to the above-ceiling plenum space at the first floor. Therefore, when the building pressurization is negative, outside air can easily be drawn through the masonry cavity directly into the interior of the building (Figures 6-8). Building Enclosure Symposium • NovembeBEr 11-12, 2019 M Mills • 19 Figure 6 – Case study property depicting the detailing of the exterior wall weather barrier and other building elements and the bearing condition for the second-floor structural steel bar joists and floor slab. Note opportunities for easy air transfer between the masonry cladding cavity and the above seal return air plenum. Figure 7 – Case study property. As-built condition where second- floor joist bears on exterior structural steel perimeter beam, providing an annular slot around the entire perimeter of the building, which is open to the masonry cladding cavity. Smoke pencil used to verify unintended air infiltration at this location. Figure 8 – Case study property. Direct view of the masonry cavity (back side of brick cladding visible from interior plenum space) between the second-floor steel form deck and structural steel framing. Another contributing factor is the common and poorly detailed and constructed base-of-wall detail where there is an open vapor path from the below-grade foundation wall to the building’s interior. An easy corrective detail for this condition is to simply provide a piece of self-adhered foundation waterproofing material to tie the below-grade wall to the exterior sheathing (Figures 9-14). Although during the study other potential contributing factors were reviewed, including possible roof leaks, parapet wall leaks, defective gutters, downspouts, and clogged masonry weeps, these defects were regarded as minor considering the systematic inability for the exterior enclosure to isolate the interior and exterior air. HVAC Systems In conducting a study such as this one, it is vitally important that the consultant have not only a fundamental understanding regarding conditions that contribute to mold growth and sources of moisture through the building enclosure, but also a basic understanding of how HVAC systems heat, cool, and ventilate buildings. During the interview, it became apparent that the facility staff were not fully aware of how the HVAC system operated and specifically how the building was ventilated and how outside air was provided to the AHUs throughout the first and second floors. Often facility staff are stretched thin or have responsibilities for many buildings, and their job role is reduced to chasing emergencies and changing air filters. The study should include a review of the original design documents and the listed air flow rates for the OAFs. The building’s four OAFs included two servicing the upstairs AHUs and two servicing those on the 20 • Mills Building Enclosure Symposium • NovembeBEr 11-12, 2019 Figure 9 – Case study property. Base-of-wall detail that does not provide for good separation between the always damp or wet ground condition and the base of the wall studs and gypsum sheathing. Figure 11 – Case study property. Dirt and dust staining (not mold) has accumulated over the years on the glass batt insulation. This occurs due to unintended air infiltration at a joint in the wall sheathing where the fiberglass batt insulation acts as a filter, collecting and trapping dirt and dust particles. Figure 10 – Example of extreme mold development inside an insulated wall assembly, with mold on the inside of the stud cavity as well as on the outside of the drywall finish where it occurred behind vinyl wall coverings. first floor. Two OAFs are located in the attic and two are located on the first floor above the ceiling space, providing outside air to the HVAC units on the first floor. A review of the equipment schedules and a summary of all of the exhaust air and outside air introduced into the building yielded a positive ratio where 10% more air was being introduced into the building’s interior environment than was being exhausted. This is a desirable condition where the building is positively pressurized relative to the exterior, with conditioned outside air to provide fresh air for the occupants. It will prevent unintended air infiltration through the building enclosure where outside air is brought through the enclosure, contributing to potential high RH and condensation when high RH air comes in contact with colder surfaces, either in wall assemblies or on the interior of the building. It was observed, however, in this particular instance that during spring and fall, when cooling loads are low, filtered outside air would be introduced to the air handlers. This air is not conditioned, potentially causing higher RH during humid weather. During this study it was quickly Figure 12 – Case study property. Mold development is occurring inside the stud cavity on the paper-faced sheathing. Figure 14 – Case study property. Installed WRB (building felt) has become brittle, is easily damaged, and fails upon contact. Figure 13 – Case study property. Typical condition of the back side of a completed masonry cladding (facing the air space). Note poorly executed head joints where daylight is often visible. In our experience, this is a common occurrence in masonry cladding construction. Building Enclosure Symposium • NovembeBEr 11-12, 2019 M Mills • 21 determined that the four OAFs were not operable and had not been operable for years, and facility staff were unaware of this condition (Figure 15). Again, in our experience, this is not uncommon. Normally there is no mechanism to warn or alert a building operator if the air flow in the building is functioning properly unless a fairly sophisticated building automated system (BAS) is provided. As soon as the building’s HVAC system is not providing building pressurization (typically 5-10% more air entering than is being exhausted), the potential for building failure is high. This scenario forces unintended air infiltration through any openings in the building’s enclosure, including windows, doors, and leaky weather or air barriers. If this condition occurs in the summer months, the accumulation of high-RH air within the building wall cavities and/or the building’s interior occurs quickly and creates opportunity for mold growth on interior finishes, furnishings, equipment, and inside wall cavities. If vinyl wall coverings are present on the exterior walls, mold growth almost certainly occurs behind the wall coverings, and water vapor is trapped where it can feed on the gypsum wallboard paper facing and the wall covering adhesive. LESSONS LEARNED The primary lesson is that a poorly air-sealed building enclosure plus a negatively pressurized building is a deadly combination, leading to building failure. The negative building pressure results in unintended outside air infiltration through the building enclosure, leading to an elevated interior RH during the cooling season. It is probable that a poorly sealed air enclosure by itself in this instance would not lead to building failure if the outside air fans were properly maintained consistent with the design. In this case, the poorly air-sealed building enclosure, in conjunction with a pressurized building, would likely result in high energy costs due to unintended air exfiltration. Keep in mind that buildings perform and fail differently in different climate zones. Another study could show very different results if it were located in a different climate zone, such as cold climates, where a poorly air-sealed building enclosure and a properly pressurized building will result in condensation and building damage in exterior walls. This would occur in the heating season. An entire niche industry is developing whose purpose is air-sealing existing buildings with building enclosures that leak air. In our case study, it would be relatively easy to seal up the annular space at the perimeter second-floor steel bearing line because the open masonry cavity is relatively easy to access from above the lay-in ceiling tiles. Likewise, the attic area could be separated from the second-floor ceiling plenum space by installing either a sheet air barrier or gypsum drywall air barrier to the bottom of the attic trusses. This modification is more intrusive, as it will require removal and reinstallation of the suspended ceiling system; however, it is a feasible approach. Furthermore, a more reliable method to pressurize the building with outside air while also ensuring that air is conditioned before introduction into the interior environment would be to install a dedicated outdoor air system (DOAS). Such a system would not have to rely on the air handler cooling coils to dehumidify the air before it is introduced into the building. 22 • Mills Building Enclosure Symposium • NovembeBEr 11-12, 2019 Figure 15 – Case study property where one of four outside air fans are installed in the attic space, providing ducted outside air directly to the air handler units throughout the building. This unit was inoperable.
