Designing a Perfect Wall: The Importance of Continuity

The Perfect Wall Assembly and the Importance of Continuity Between Control Layers


In high-performance building enclosures, the “perfect wall” has four control layers located exterior to a structure: 

  1. Water
  2. Air
  3. Vapor
  4. Thermal

Controlling water is always the first priority and the most important. Control across the field of a wall or roof is the easy part.

However, the majority of leaks occur at transitions and interfaces between elements. Problems happen where things come together – the connections between roofs, walls and punched openings such as windows and doors.

Building Science Corporation’s Dr. Joe Lstiburek explains why continuity between these four control layers is critical to the success and longevity of a high-performance wall assembly.


The perfect wall concept


The ‘perfect’ or ideal wall helps designers conceptualize how a building enclosure’s components should work together as a system. The sequence of layers represents a conceptual, climate-neutral approach with a scientific placement of the control layers that shows designers clearly how they interact and what functions each layer performs.


perfect wall building design

In the diagram, the cladding is on the outside, followed by the insulation, then the water, air, and vapor control layers, then the building structure and interior finishes. 

However, the perfect wall is a blueprint meant to remind designers of the total goals of a wall system; as such, they can use it to check systems that do not follow the configuration specified in the schematic.

Careful attention to the continuity of layers in the design phase, especially when interacting with control joints, windows, and mechanical penetrations, will help ensure that the system is air-tight and, therefore, capable of functioning as intended. Every designer must make sure that they provide all the critical control functions required for a contemporary building.


If you’d like to level up your knowledge on perfect wall design, check out this The Perfect Wall Webinar with Dr. John Straube. And once you’ve mastered that, you might be ready to go Beyond the Perfect Wall.



About Joe Lstiburek, Ph.D., P.Eng., ASHRAE Fellow, Principal, Building Science Corporation:

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.

Dr. Lstiburek is also an acclaimed educator who has taught thousands of professionals over the past three decades and written countless papers as well as the best-selling Builder Guides. His commitment to education earned him the hailing “the dean of North American building science” by the Wall Street Journal. You can find additional details on Dr. Lstiburek on our About the Blog page.