A Cup of Joe: Flow Through Assemblies


A Cup of Joe: Flow Through Assemblies


A vapor barrier’s most important function is to be impermeable to moisture in vapor form, thereby preventing the movement of water vapor through the wall cavity to the outside, and vice versa.

As our friend Dr. Joe Lstiburek has said before, a wall works by keeping the outside out and the inside in. Referencing the “perfect wall”, there is the water control layer, air control layer, vapor control layer and thermal control layer all in the right places. The wall dries outward from the vapor control layer and dries inward from the vapor control layer.

What would happen if you relied only on an air barrier? In this episode of A Cup of Joe, Joe Lstiburek continues this topic discussing flow through assemblies and what slowing the flow of vapor can do.


About Dr. Joe Lstiburek 

Dr. Joe Lstiburek is the founding principal of Building Science Corporation, one of the most influential, innovative, and respected building science firms in North America. Dr. Lstiburek’s work ranges widely, from providing expert witness testimony to overseeing research and development projects to writing for the ASHRAE Journal. His commitment to advancing the building industry has had a lasting impact on building codes and practices throughout the world, particularly in the areas of air barriers, vapor barriers, and vented and unvented roof assemblies. His commitment to education earned him the hailing, “the dean of North American building science” by the Wall Street Journal. Dr. Lstiburek holds a Bachelor of Applied Science in Mechanical Engineering, a Master of Engineering in Civil Engineering, and a Doctor of Philosophy (Ph.D.) in Building Science. Get the full scope of Dr. Lstiburek’s work, accolades, and contributions to the industry over at Building Science Corporation.