Designing resilient buildings for our future climate 

One of the fundamental principles of building science is that buildings must be suited to their climate. Among the multitudes of things we must reconsider in the face of our shifting climate is how our design and building practices may need to change today to prepare for tomorrow’s reality. When designing a building today, we are really designing it for the next 50 or even 100 years and the conditions it will need to endure in that future. We know that climate change will affect temperatures, but it will also impact the location, timing, and amount of precipitation. How will buildings react to more extreme rainfall? Will more rain and weather changes potentially increase the opportunities for mold and corrosion within our buildings – affecting the health and safety of all those who will occupy them? 
To test the resiliency of our current design standards, Perkins&Will decided to test various wall types in a model that simulated increased rainfall in 2060. Would a wall commonly used today be resilient to anticipated temperature and rainfall rates of the future? 
Accurately forecasting the future weather presented a challenge. While the original research design called for the integration of morphed precipitation data into historical weather files, these files were not complete enough for the hygrothermal modeling software (WUFI) that would be used to run the test. Instead, purchased files from Weather Shift were used – these were more refined and also reflected the seasonal behavior of rain through the seasons. The files were also all for one location – Houston, Texas, in the United States, which has a clear hot-humid climate. 
Two wall types were chosen — Cold-Formed Metal Framing (CMFM) and Concrete Masonry Unit (CMU). Both are commonly used in the Midwest, the Pacific Northwest, and North Texas in education buildings, and these types were combined with five different vapor barriers as the other inputs for the modeling.  
To evaluate the results, failure conditions for both the CFMF and CMU assemblies were set. For cavity walls, failure would be the growth of mold in the assembly. There was very little existing research on failure due to moisture for the CMU walls, so a failure condition was developed according to P&W’s own specifications for Texas, which limits the percent moisture in masonry products to 12% when measured by a moisture meter. 
The results? There were no failures in the assembly for any of the conditions tested, making both wall types resilient to anticipated temperature and rainfall increases. Any mistakes during construction resulting in a less permeable vapor retarder layer will not create failures within the assembly, now or 40 years in the future. In addition, the general rule of thumb to use an air barrier in lieu of a vapor barrier in hot, moist climates holds true. 
More climate zones still need to be tested using this methodology to help us understand and mitigate possible repercussions that climate change may have for the design of building envelopes. As architects and designers, it is our responsibility to ensure the health, welfare, and safety of building occupants that will inhabit our future buildings.