162 - Back to Basics: Air Control Layers Explained

Airtightness is one of the most important—and most measurable—parts of building performance. In Part 2 of the Back to Basics series, Steve, Jake, and Pete break down how air control layers work, why continuity matters, and how blower door testing exposes the difference between theory and reality.The crew starts with several principles that apply across multiple control layers: staying in one plane makes continuity easier, simpler details are more likely to succeed, and combining control functions in a single material can reduce opportunities for failure. They also revisit one of their favorite ideas: eliminate “confused spaces.” Attics, crawlspaces, and other areas should clearly belong either inside or outside the building enclosure.Then the conversation gets specific to airtightness. Blower doors do not lie. ACH50 provides the quantitative result, but finding the actual leaks—their size, location, and number—is just as important. The boys discuss why one blower door test is rarely enough, how wind, stack effect, and fans drive air leakage, and why two mediocre air control layers do not equal one good one.For renovations, the sequence is simple: blower door test first, air seal second, insulate third.Pete's Resources:EPA – Moisture Control Guidance for Building Design, Construction, and MaintenanceENERGY STAR Thermal Bypass ChecklistA House Needs to Breathe...Or Does It? An Introduction to Building Science by Allison Bailes