Understanding Air Tightness Building Regulations with Dr. Joe Lstiburek

Air tightness targets, or maximum air tightness levels, are a metric for assessing building performance. To set a target, it is critical to understand that air tightness building regulations measure the air leakage through the entire building enclosure (roof, walls, slabs, windows, doors, vents, etc).

But how are air tightness standards established? And how tight should your enclosures really be?

In this episode of A Cup of Joe, Dr. Joe Lstiburek from Building Science Corporation explores air tightness building regulations, including his experience establishing air tightness standards and realistic targets to aim for.

Is air tightness testing mandatory?

According to the Air Barrier Association of America (ABAA), air tightness tests are not mandatory tests prescribed in building codes. Having said that, they are a performance-based option that many designers require. Plus, with energy and building code standards continuing to rise, you will likely need to achieve a relatively high level of air tightness. 

Currently, the only requirements for whole building air tightness testing are in the State of Washington, the United States General Services Administration, and all United States Army Corps of Engineers projects.

What is the average air leakage rate for a building?

Air leakage rates can vary considerably from building to building. But as of January 2022, Building Enclosure Online says air leakage requirements are as follows (All of the rates have been normalized to average cubic feet per minute (CFM) per square foot (ft2) under a pressure differential of 0.3 inch water gauge (75 Pascals or 75 Pa)).

measured air leakage requirement figures for buildings
Image courtesy of Building Enclosure Online.


  • Poor building performance = ~1.00 CFM/ft2
  • A leaky building = ~0.60 CFM/ft2
  • A standard building = 0.40 CFM/ft2
  • Excellent air tightness = 0.25 CFM/ft2
  • The highest standard of air tightness = <0.11 CFM/ft2

How do you test a home for air tightness?

One of the most common and effective ways homebuilders can test their buildings for air tightness is through a blower door test

Blower door tests use – you guessed it – a blower door fan as a diagnostic tool to gauge how much air is entering and leaking from the home. The fan is attached and sealed to the door, and measures the flow rate of air through any cracks in the building envelope. 

This flow rate of air is produced at a specified pressure, and certain specifications need to be met, such as sealing the exterior doors, closing dampers, turning off the HVAC, and more. 

The goal is to find the air changes per hour (ACH) by multiplying the volumetric flow rate from outside (measured in cubic feet per minute) divided by the building volume. The lower the ACH, the more air tight the building is said to be.

Learn more about air tight building solutions

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.