Deja Vu All Over Again: Risks for Moisture and Mold Problems in Modular Construction
by: George H. DuBose, CGC and Donald B. Snell, PE
The emergence of #modular construction as an option for new construction is becoming mainstream. The reasons have been reported on well. However, what has not been reported is that the modular construction industry has had mold and moisture problems, especially, when used in a warm and humid climate like the Southeast US. Both wood frame and steel frame modular construction have experienced problems with crawl space, marriage wall, and ceiling to floor cavity, condensation problems that have not only resulted in deterioration of the wood, corrosion of metal floor pans, deteriorate wallboard and mold.
The greatest risk of modular construction failures has been seen to be when this type of construction and delivery is used for hotels, student housing, senior living, soldier housing, type facilities. In general, facilities that are domicidal or multi family in nature. This is because these types of facilities have inherent similarities in a living unit that requires both an individual cooling/heating unit, bathroom exhaust, and some sort of central HVAC make up air system. In addition, there are many more modular “boxes” in these kinds of buildings increasing the number of marriage wall interior cavities and ceiling to floor cavities that otherwise might not be required in other types of modular construction. The nature of modular construction makes it difficult to repair once it is found to be damaged. Sometimes, the damage can be such that the modular building has to be deconstructed to remove damaged materials and then re-designed and re-constructed using conventional methods. This essentially makes the modular construction advantages dissolve away as the building gets converted to a traditional “stick” building.
Here are five of the key reasons that these problems are occurring and solutions to those problems:
One: Modular Construction has inherent interior hidden spaces that make it difficult to control the infiltration of outdoor air. Whether this is the cavity between modular boxes found in wood frame modular construction or spaces between modules found in the steel frame modular construction. These interior cavities provide, with ease, a pathway for airflow to not only enter the building but to also travel long distances through the building. As this air travels throughout the building it washes interior surfaces causing direct condensation or at least raised surface conditions that have been found to cause physical damage and mold growth on wood framing and interior drywall.
Two: Each modular box as it comes from the manufacturer is designed and constructed in a vacuum of the requirements for the overall performance of the building. One such area is the HVAC system design and construction for building pressurization. The modular box that comes from the factory generally has the cooling and heating unit, the exhaust for a bathroom, that are dependent upon the separate common area HVAC system for makeup air. It does not seem to be a common consideration in the design and construction of modular facilities that the pressurization of the overall building is dependent upon the pressure characteristic of each interior space, whether it is an occupied space or space between two modular boxes. Similarly, the air leakage characteristics of modular constructing buildings are dependent upon the leakage rate of more than the modular box itself, it is dependent upon the leakiness between and around the compartments that make of the building. These can be occupied spaces or these can also be the wall cavities between the modular boxes.
Three: Modular design and construction often times uses a crawl space and this adversely impacts the ability to control condensation and outdoor air flow in and throughout the building. The crawl space can be difficult to isolate from the building cavities, including the marriage wall cavities, and this allows air to flow more freely through the building.
Four: The modular design and construction process has a modular box versus base building conflict inherently built into how these buildings are delivered. The modular boxes are designed and manufactured by a separate entity that does this often in a vacuum of the design and construction of the base building. The crawlspace, roof, and attic, exterior cladding, HVAC system, are, more often than not, designed by separate entities and constructed by different entities.
Five: Inspection for code compliance can be different depending on the jurisdiction it is either manufactured or constructed in. For example, in Florida, the modular construction is governed by the Department of Community Affairs, this includes inspection of the modular box before it leaves the manufacturing facility. The base building, on the other hand, is inspected by the local code official, who does not inspect the modular box once it has received the DCA inspection and certification. While both governmental agencies rely upon the same building codes this silo inspection competes with a more holistic process that has the overall building performance as the overarching goal.
The Liberty Building Forensics Group staff has extensive expertise in investigating and resolving construction and design deficiencies in the Mid-Atlantic and Southeast states, as well as in Mexico, the Caribbean, Central America, and Southeast. Please visit http://www.buildingforensicsgroup.com/who-we-are/ for more information about the firm and our experts.