In this episode of If Walls Could Talk, W&C Editor John Wyatt talks with Tom Harris of Tom Harris PUR Consulting. In this podcast, the two tackle one of the most technical and misunderstood topics in insulation—air barriers. 

Air Barriers in Building Construction

John Wyatt and Tom Harris break down how air barriers are tested, how spray foam products qualify, and why proper verification and HVAC coordination are essential for achieving tight, code-compliant building envelopes.

Air barriers are a critical component of modern building envelopes, helping control air leakage and improve energy efficiency. This discussion explores the fundamentals of air barriers, their testing, and practical implications for contractors and homeowners.

Spray foam insulation, in both open and closed cell varieties, can function as an effective air barrier. However, not all formulations automatically qualify. Each specific product must be individually tested, as performance varies based on its chemical composition and application method. Contractors need to consult Technical Data Sheets (TDS) and Code Compliance Documents, such as ESRs (Evaluation Services Reports) or CCRRs (Code Compliance Research Reports), issued by accepted third-party organizations, to confirm that a product meets air barrier requirements.

Air barrier testing is divided into material and assembly evaluations. Material testing, conducted under ASTM E2178 ("Standard Test Method for Air Permeance of Building Materials"), measures the ability of a material to resist air passage under pressure. Assembly testing, conducted under ASTM E2357 ("Standard Test Method for Determining Air Leakage of Air Barrier Assemblies"), evaluates the performance of combined materials as part of a building envelope. These tests ensure that both individual components and the overall system effectively control air movement.

In residential construction, building codes now require confirmation that the entire building envelope meets specific air leakage limits. This is typically done through blower door testing, conducted by certified professionals. The results are reported as ACH50 (Air Changes per Hour at 50 Pascals), representing the air change rate at a pressure difference equivalent to a 20 mph wind.

Building envelope tightness directly impacts HVAC design. If a home’s air change rate is reduced without adjusting the HVAC system, it may lead to short cycling, increased humidity, lingering odors, and reduced indoor air quality. It is essential to conduct a blower door test and coordinate with an HVAC contractor to ensure the system is properly sized for the updated envelope.

Both open and closed cell spray foams can act as air barriers. Closed cell foam requires approximately one inch, while open cell foam requires around 3.5 inches to meet ASTM E2178 air barrier criteria. Proper application and verification are critical to ensure compliance with energy codes and optimal building performance.

Future discussions will focus on R-value testing, exploring the limitations of current methods and the need for updated approaches.