The 2025 Winds of (Code) Changes: Insulation and Air Leakage

by David Flaherty | 8 June 2025 6:34 pm

[1]

In 2025, the evolution of building codes and their respective updates on air infiltration will enhance energy efficiency and revolutionize how air infiltration is combated to create healthier, more sustainable living environments.

Fiberglass insulation systems continue to be a strong tool in minimizing air leakage in metal building systems, as it effectively plays a role in separating exterior environmental conditions from the interior space of the building. Insulation  reduces energy transfer rate, thus helping to maintain consistent indoor temperatures. The accompanying vapor retarders can help prevent air from escaping or entering the building when properly installed, reducing the need for additional heating and cooling.

Modern fiberglass insulation systems often include vapor barriers and reflective coatings, enhancing their ability to seal gaps and prevent air leakage. Air leakage requirements are set by energy codes and standards such as the International Energy Conservation Code (IECC) and ASHRAE 90.1. These mandate specific air leakage allowances and whole-building air leakage tests to ensure a tight building envelope which translates to an efficient and healthy interior building environment.

Before proceeding, it is essential to recall that the IECC defines air leakage as “the unintended movement of air through gaps and cracks in the building envelope, including areas around windows, doors, and other openings.”

The requirements for air infiltration (and the resulting tested values) on metal building systems are primarily governed by adopting the IECC 2021 and ASHRAE 90.1-2019. States adopting these codes generally require air leakage testing for metal buildings, with some exceptions based on climate zone and building size. For example, California, Washington, and other states also mandate these tests unless specific exemptions apply. As always, the best source for any project and state is energycodes.gov/state-portal and/or the local code official.

Why do states adopt newer energy codes? There are several factors, ranging from environmental to economic, with the key factors being alignment with federal requirements, eligibility for incentives, and ensuring access to funding and support. With the adoption, the state, and thereby officials, will adhere to new and/or additional criteria. For example, with IECC 2021, 10 percent of the counties were assigned to warmer climate zones. This change could have affected a county’s exception to the air leakage testing requirement.

What is air leakage testing?

[2]

Without getting into minute specifics,  air leakage testing on metal building systems involves using a blower door test to measure and identify air leaks, ensuring the building meets energy efficiency standards. A published guide for Best Practices to Comply With Whole-Building Air Leakage Testing Requirements For Metal Building Systems is available for free at the Metal Building Manufacturers Association website.¹

The 2021 IECC expanded air leakage requirements and has a maximum allowable 0.40 cfm/ft² air leakage. However, this was reduced to 0.35 cfm/ft² in the 2024 IECC edition, published in August 2024. As of 2025, two states, Nevada and Rhode Island, have adopted the newest code. Other notable updates are an improved energy efficiency of 10 percent over the previous version and an added section on thermal bridging requirements.

Over the last couple of years, many presentations have painted a picture of the rolling in of air leakage testing and the expected ratcheting to more efficient values. Beyond the reduced maximum allowed in IECC 2024, Washington state requires thermal envelope testing with a maximum air leakage of 0.25 cfm/ft².

Insulating metal building systems, particularly multi-layered systems, can significantly minimize air leakage beyond fulfilling an assembly U-factor criterion. The correct insulation of the respective cavities can also be a formidable factor in negating or nullifying potential condensation issues.

Further considerations

Expanding on the value of proper installation and testing, the recently published MBMA guide reads, “This testing demonstrated why results exceeded expectations and highlighted that performance of these buildings can reach any level likely to be specified by code or high-performance building standards through implementation of best practices.” More important now than ever for states that have adopted newer codes requiring air leakage testing, special attention should be paid to sealing vapor retarders to framing members, even using mechanical methods as an addition to liquid sealants at the connection points. Connections at wall to floor, roof to wall, and penetrations to the exterior should be inspected, and steps should be taken to ensure sealing.

To best prepare for a first blower door test or striving to meet one of the new, more efficient rates, be confident in the ability to find and execute the respective manufacturer’s installation instructions. It has become evident that a third-party blower door testing company will often conduct visual inspections before testing and advise on areas that could use additional air sealing.

The industry will continue to feel the winds of (code) change. As they do, count on the characteristics and flexibility of fiberglass insulation systems to meet these new energy efficiency standards for metal building systems.

Sources

^{1, 2} mbma.com/sites/default/files/documents/MBMA_Best_Practices_to_Comply_with_Whole-Building_Air_Leakage_Testing_Requirements_for_MBS_061223.pdf

www.silvercote.com/literature/

www.silvercote.com/wp-content/uploads/2024/03/SIL816_003-TD-Energy-Saver-Wall-Base-Angle-Connection.pdf

www.insulation.org

As the national accounts manager of Silvercote, Robert Tiffin leads foundation customer relationships in the United States and Canada. He drives interaction with the market, designers/specifiers, and end-use owners, as they are the critical connections to the industry’s future. As a fervent advocate of collaboration with industry associations, Tiffin connects his peers and network as the head of the Metal Building Contractors & Erectors Association (MBCEA) and the chair of the architects committee of the Metal Building Manufacturers Association (MBMA).

Mike Smith is the technical manager for Silvercote.

Source URL: https://www.metalconstructionnews.com/articles/code-changes-insulation-air-leakage/

---