Climate change is not only accompanied by elevated temperatures and more severe weather, but also another growing problem: mold. Increased heat and storm activity are taking a toll on building envelopes, which are more likely to deteriorate and allow water intrusion. According to the U.S. EPA Climate Change Adaptation Resource Center (ARC-X), these conditions are conducive to mold and fungi growth, “increasing the likelihood of occupants’ exposure and resulting health effects.” This phenomenon is of greatest concern in humid climates, such as in the eastern half of the U.S., since high relative humidity (RH) can further encourage mold growth. And the sea level rise anticipated in coastal areas compounds the problem.
Making building facades more robust is a logical reaction. In addition, a less obvious but likely more effective response is to reengineer envelope assemblies—including interior finishes—to discourage mold entirely. This is the objective of Miami-based design firm Caplow Manzano, which is reconsidering the material composition of residential building to adapt to these climate-related threats and maintain optimal occupant health.
The firm has devised a technique called “hypostruction,” a reductionist building strategy that eschews mold-encouraging materials and void spaces so mold and fungi never have an opportunity to grow. Hypostruction stands for “less building” and refers to the removal of unwanted materials—such as toxic, fragile, or decay-prone products—from the living area inside the building’s envelope. Caplow Manzano recently collaborated with Robert Vick Architecture and Alligator Construction to complete CM1, a Miami-based house demonstrating the hypostruction concept, which was recognized as the first WELL-certified single-family home internationally.
The design firm foregrounds the elimination of drywall in achieving its aims. Black mold can germinate within 24 hours on the paper surface of drywall as well as wood studs when these materials become wet. However, removing mold-encouraging substances is just one aspect of a holistic approach that includes carefully reconsidering insulation, thermal bridging, plumbing, and accessible cavities.
Hypostruction has a few precedents, notably building scientist Joe Lstiburek’s “The Perfect Wall” concept, with the goal of optimizing the building envelope from a technical performance perspective. The Perfect Wall locates the four primary facade control layers for rain, air, vapor, and temperature in the ideal order and—most importantly—on the outside of the structure. “Keep the structure from going through temperature extremes and protect it from water in its various forms and ultraviolet radiation and life is good,” writes Lstiburek. An obvious benefit of keeping the structure and other interior components dry is the minimization of mold growth.
Although the Perfect Wall makes conceptual sense, hypostruction was motivated by a surprising physical encounter. In 2020, firm principals Ted Caplow and Nathalie Manzano were enjoying Thanksgiving dinner when a pipe ruptured inside their dining room wall. “The resulting mess of soggy insulation, crumbling drywall, warped baseboards, and corroded wiring begged the question: do we have to live with all these problems hidden inside our house?” asked Caplow. “What if we could see what was going on, remedy leaks before they happen, and not worry about mold inside our walls or above our ceiling?” This jarring event thus caused a eureka moment, and the designers set out to design a series of houses to answer these questions.
The CM1 house represents the outcome of their search. In the design of the house, the first two innovations are structural. Like the Perfect Wall, CM1 employs exterior insulation (sometimes called “outsulation”)—in this case, the design team created insulating CMU blocks by filling the masonry unit cavities with perlite beads. Thus, the house has no insulation inside the living space envelope. In addition, the team controlled thermal bridging between the interior and exterior, carefully designing the fenestration to minimize the need for solid concrete in the walls. Unlike conventional construction, the concrete transfers minimal heat between the outer and inner surfaces (in this case, stucco exterior and interior lime plaster), decreasing the opportunity for moisture build-up.
CM1’s roof is composed of a concrete slab topped with R-40 polyisocyanurate sheets, which in turn are covered by an Energy Star-rated white TPO membrane. The house is also elevated in anticipation of future flooding, and so has no ground contact. From below, the floor slab is insulated with 2” thick, R-15 spray foam insulation, which is concealed above a screen made from rice hulls.
On the interior, lime plaster coats the inside surface of the exterior wall, and repositionable plywood panels (finished with VOC-free, natural linseed oil) clad the interior partition walls. These removable panels provide complete access to all plumbing and wiring throughout the home, allowing easy modifications and—most importantly—expedited cleanup in the case of any unforeseen hazards, such as the designers’ ruptured pipe incident. The project has no wood studs, drywall, or inaccessible cavities in both walls and ceilings, and avoids materials that are toxic or vulnerable to decay.
Preliminary test results are positive. The design team has captured air quality monitoring data as well as energy performance data. According to Manzano, “We are clearly seeing excellent results: the air quality in the house is very good, there are no VOCs coming from the house, and very few particulates are generated—in a newly completed home these are unusual statements!” The house was also subjected to blower-door testing recently as part of its LEED certification, and Manzano reports that the third-party evaluator surmised that “the house had the tightest envelope of any home he has tested.” This is also a preferred characteristic of the Perfect Wall—to control airflow and its related vapor transmission.
According to Caplow, this novel approach does not add a regulatory or financial burden. “Hypostruction is within reach of almost any designer or home builder,” he says. “There are very few regulatory hurdles. All that is needed is a willingness to think differently, and take on a few design challenges, such as finding the best floor plans to optimize plumbing access, exploring methods for lighting rooms without dropped ceilings, and choosing an approach for partition walls.” Elevating a structure in anticipation of floods and sea level rise can present zoning challenges, but municipalities in storm-prone areas like South Florida are beginning to recognize the obvious advantages of elevated structures.
This resilient form of building is also economically feasible. Although the plasterwork and paneled systems are typically twice as expensive as a conventional partition wall, partitions rarely comprise more than five percent of the total construction cost. Furthermore, hypostruction eliminates the cost of drywall, tape, mud, and paint, and the approach generates additional interior volume that would otherwise be concealed within cavities. Most significantly, hypostruction reduces the externalized costs of adverse health impacts caused by mold, toxic materials, and structural deterioration. As the climate crisis worsens, we must consider this holistic perspective of life cycle cost—marrying the economics of the life of a building and the lives of its occupants—to make a compelling case for climate-adaptive architecture. “When we consider the lifetime of the home, hypostruction means fewer repairs, less renovation, and easier upgrades,” explains Caplow. “But the most important benefit is occupant health and peace of mind.”
Read more:The latest from columnist Blaine Brownell, FAIA, includes a review of: Azabudai Hill | The Rise of Wood as a Sustainable Material | Building the Future with Snow | Reimagining Grandeur | The rise of phygital spaces | the potential of STFE | an interview with Pritzker prize-winning architect Riken Yamamoto, a review of 3D-Printed Nanocellulose Materials, a roundup on sustainable manufacturers in Egypt, a review of the Grand Egyptian Museum, a look into Cairo's informal settlements, a profile on textile designer and weaver Suzanne Tick, and he also looks at emerging carbon capture and storage technologies, and the blue economy.
Keep the conversation going—sign up to our newsletter for exclusive content and updates. Sign up for free.
