Envelope leakage is measured in air changes per hour (ACH) at what pressure differential?

The standard industry protocol for measuring building envelope leakage, as required by LEED for Homes and ENERGY STAR, is the blower door test. This test measures the airflow required to create a uniform pressure differential of 50 Pascals (Pa) between the interior and exterior of the building. This pressure is equivalent to a wind speed of approximately 20 mph (32 km/h) acting on all surfaces of the building simultaneously. The resulting airflow measurement is then used to calculate the air changes per hour at 50 Pa (ACH50), which is the standard metric for quantifying envelope airtightness.

A. 25 pascals: This pressure is not the standard for final verification testing; it may be used for diagnostic purposes but not for rating the home's airtightness performance.
C. 75 pascals: This is not the standardized test pressure. While a building may experience such pressures in high winds, it is not used for repeatable, comparable testing.
D. 100 pascals: This pressure is significantly higher than the industry standard and is not used for residential envelope leakage testing under LEED protocols.

1. U.S. Green Building Council. (2021). LEED v4.1 Residential Single Family Reference Guide. Washington, DC: U.S. Green Building Council. In the "EA Prerequisite Minimum Energy Performance," the guide references compliance with ENERGY STAR Certified Homes, which mandates blower door testing. The specific testing protocol is detailed under "EA Credit Enhanced Energy Performance," which requires testing in accordance with ANSI/RESNET/ICC 380-2019, Section 4.1, specifying the 50 Pa test pressure.

2. U.S. Environmental Protection Agency. (2022). ENERGY STAR Single-Family New Homes National Program Requirements, Version 3.2. The "Rater Design Review and Field Checklists" explicitly require a Blower Door Test. The "HVAC System Quality Installation Rater Checklist," Item 7.1, specifies, "The measured envelope leakage is less than or equal to the specified design target... reported in CFM50." The "50" denotes the 50 Pascal test pressure.

3. Lstiburek, J. (2007). Builder's Guide to Hot-Humid Climates. Building Science Corporation. Chapter 5, "Airflow," page 106, states, "The most common way to measure the airtightness of a building enclosure is to use a blower door... The fan is used to blow air into or out of the building to create a pressure difference of 50 Pa." This is a foundational text often used in university building science curricula.