Q: Single wythe insulated concrete masonry passes energy code, but how can we keep the walls leek free? And do we need a vapor barrier?
-Leaks Are Really Sad
Dear LARS:
Single wythe CMU walls have been around for a long time, and with proper detailing, they can be completely leak free. To accomplish this, we recommend a “belt and suspenders” approach. Flashing, weeps, integral water repellent and crack control are key. For extra protection a field applied, breathable, clear sealer can be applied. For partially grouted walls, it is very important to have flashing and weep holes so that if any water does get in, it has a way to escape. There are pan flashing/weep systems that work well with most single wythe wall configurations and are relatively easy to install. Another important component is integral water repellent. This is not a coating, but an ad-mixture. It repels water throughout the block, not just at the surface. Crack control is another important component, and includes horizontal joint reinforcement and control joints. For more information on strategies to keep your single wythe walls leak free, see NCMA TEK 19-2B. For the question about vapor barriers, concrete masonry mass walls behave differently from other building types, such as wood and steel frame. CMU walls absorb any condensate from vapor, and dry out before trouble can ensue, and CMU doesn’t warp or rust when exposed to moisture. Because of this, CMU structures don’t require vapor barriers per code.
Heidi Jandris grew up immersed in all things concrete block. As a kid she helped her dad build block walls and as an adult worked by his side as a welder. She received a Bachelor of Architecture degree from Pratt Institute and a Masters of Sustainable Building Systems degree from Northeastern University’s College of Engineering. She is part of the 3rd generation of her family’s business. She provides technical services to the design community while researching and implementing ways to improve the efficiency and lower the environmental impacts of their products.
