Defining Air-Leakage Responsibilities for Metal Building Projects

Energy codes increasingly require continuous air barriers and, in many cases, whole-building air-leakage testing. These requirements can create uncertainty regarding the responsibilities of designers, contractors, metal building manufacturers, erectors, and other trades—particularly when the contract documents establish an overall building-performance requirement without clearly defining the products, details, and work necessary to achieve it.

This Best Practice Statement provides recommendations for defining, coordinating, installing, inspecting, and testing air-barrier systems on projects incorporating metal building systems.

For additional guidance on preconstruction detail review, air-barrier installation, quality control, and preparation for whole-building air-leakage testing, refer to MBMA’s Best Practices to Comply with Whole-Building Air Leakage Testing Requirements for Metal Building Systems. This Best Practice Statement complements that guide by addressing the definition and coordination of product-based responsibilities among contractors, erectors, suppliers, and other project participants.

Whole-building air leakage should be treated as a coordinated building-envelope performance requirement rather than a performance requirement assigned solely to the metal building system or its erector.

Air-barrier responsibilities should be defined by product, assembly, interface, and trade. Each project participant should be responsible for the materials and installation activities included within its defined scope.

The metal building erector’s responsibility should be based upon installing its contracted products and assemblies in accordance with:

• The contract documents;
• Approved shop drawings;
• Manufacturer installation instructions; and
• Project-specific air-barrier details.

A whole-building air-leakage requirement should not be assigned to an individual contractor or erector unless that party has been given clearly defined responsibility and sufficient control over the design, product selection, installation, coordination, inspection, and correction of the entire building-envelope air-barrier system.

Metal Building and Hybrid Construction

Many projects incorporating metal building systems are not constructed entirely from metal building components. They are hybrid buildings that may include concrete, masonry, conventional framing, stud-framed walls, membrane roofing, storefronts, windows, doors, louvers, mechanical equipment, and other systems and materials furnished or installed by multiple parties.

Even when the metal building system constitutes a substantial portion of the structure or exterior envelope, the air-leakage performance of the completed building depends upon all envelope components and the transitions between them.

Air leakage may occur within an individual assembly or at an interface between:
• Metal wall panels and foundations;
• Metal wall panels and masonry or conventional walls;
• Metal roof systems and adjacent roofing assemblies;
• Roof and wall systems;
• Windows, doors, storefronts, and wall assemblies;
• Curbs, louvers, vents, and mechanical equipment;
• Utility penetrations and surrounding construction; or
• Air-barrier materials furnished and installed by different trades.

Because these conditions involve multiple materials and installers, the metal building manufacturer or erector cannot independently control the air-leakage performance of the entire building.

Air-barrier requirements should be defined by the specific products and work required rather than stated only as a required whole-building result.

Before bidding and construction, the contract documents should identify:
• The materials and assemblies forming the continuous air-barrier system;
• The party responsible for furnishing and installing each component;
• Required sealants, closures, tapes, membranes, fasteners, and accessories;
• Installation requirements and acceptable tolerances;
• Responsibility for transitions between different materials and construction systems;
• Responsibility for penetrations made before and after installation;
• Required inspections and documentation;
• The applicable testing standard and required air-leakage rate;
• Responsibility for investigating identified leakage;
• Responsibility for corrective work based upon the source of leakage; and
• Responsibility for initial testing and any required retesting.

The design professional should provide sufficient details to show how air-barrier continuity is to be maintained throughout the building envelope, including transitions between the metal building system and construction furnished or installed by others.

Air-barrier transitions should not be left for individual trades to design or resolve in the field unless that design responsibility is expressly included in their contracted scope.

Division 01 Coordination

When whole-building air-leakage testing is required, the overall performance, coordination, inspection, and testing requirements should be addressed as project-wide requirements in Division 01.

The products and installation requirements for each portion of the air-barrier system should then be included in the applicable technical specification sections.

The Division 01 requirements should establish:
• The overall building air-leakage requirement;
• The applicable testing standard;
• The party responsible for administering and paying for testing;
• The qualifications and independence of the testing agency;
• The stage of construction at which testing will occur;
• Whether interim or preliminary testing is required;
• The required condition of the building during testing;
• Required participation by the design team, contractor, subcontractors, manufacturers, and testing agency;
• Procedures for locating and documenting leakage;
• Procedures for assigning and completing corrective work; and
• Responsibility for the cost of investigation and retesting.

This approach allows the air-leakage requirement to be administered as a whole-building obligation while maintaining clear, product-based responsibilities for each contractor, supplier, and installer.

Air-barrier coordination should begin before products are purchased or installation begins.

A preconstruction or preinstallation meeting should be held with the parties whose work affects the building envelope. The meeting should include the design professional, general contractor, metal building contractor or erector, applicable subcontractors, product manufacturers or suppliers, commissioning provider, and testing agency when appropriate.

The project team should review:
• The complete air-barrier boundary;
• Product compatibility;
• Manufacturer installation requirements;
• Transitions between construction systems;
• Sequencing between trades;
• Penetration and opening requirements;
• Access for inspection and corrective work;
• Protection of completed installations;
• Interim and final testing procedures; and
• Responsibility for addressing identified leakage.

Particular attention should be given to hybrid conditions and locations where one trade’s work terminates and another trade’s work begins.

Installation and Quality Control

Each installer should be provided with clear information regarding the air-barrier products and interfaces included within its scope.

The metal building erector should follow the contract documents, approved shop drawings, manufacturer instructions, and applicable project details. Installation concerns, missing details, incompatible materials, or unclear trade interfaces should be brought to the attention of the contractor and design professional before affected work proceeds whenever reasonably possible.

The project should incorporate inspections while air-barrier components and transitions remain visible and accessible. Photographs or other documentation may be used to record concealed conditions and confirm that required products were installed.

Where practical, mockups, adhesion testing, smoke testing, infrared observation, or other diagnostic methods should be considered before completion of the entire building envelope.

Early inspection and testing allow deficiencies to be corrected while the work remains accessible and reduce the cost and disruption associated with a failed final test.

Whole-Building Air-Leakage Testing

A whole-building air-leakage test measures the combined performance of the completed building envelope. It does not automatically identify the location, cause, responsible scope, or responsible party for leakage.

On a hybrid building, the test measures the collective performance of the metal building system, conventional construction, other envelope materials, doors, windows, equipment, penetrations, and the interfaces between those elements.

For that reason, failure to achieve the specified whole-building air-leakage rate should not, by itself, be considered evidence that the metal building system or its erection is defective.

When a building does not achieve the specified air-leakage rate, the project team should perform a systematic investigation to identify and document significant leakage paths before assigning corrective responsibility.

The investigation may include:
• Review of testing conditions and building preparation;
• Visual inspection;
• Smoke testing;
• Infrared imaging;
• Zone or guarded testing;
• Temporary sealing of suspected leakage locations; or
• Other appropriate diagnostic procedures.

Corrective responsibility should be assigned according to the documented location and cause of the leakage and the applicable contracted scope.

The metal building erector should correct documented installation deficiencies within its defined scope. Leakage associated with work outside that scope should be directed to the party responsible for the affected product, assembly, penetration, or interface.

Conditions requiring separate evaluation may include:
• Incomplete or unclear design details;
• Products selected or furnished by others;
• Conventional or hybrid construction outside the metal building package;
• Openings or penetrations created by other trades;
• Doors, windows, storefronts, louvers, curbs, or mechanical equipment;
• Transitions not assigned to the metal building erector;
• Damage or modifications occurring after installation; and
• The cumulative effect of leakage from multiple systems or scopes of work.

Retesting should occur after the identified deficiencies have been corrected and the building has again been placed in the required test condition.

Conclusion

Metal building manufacturers, contractors, and erectors play an important role in achieving an airtight building envelope. However, the overall performance of the completed building depends upon the design, products, installation, and coordination of all building-envelope systems and trades.

This is especially true for hybrid buildings containing multiple construction systems, materials, and installers.

The recommended best practice is to:
1. Treat whole-building air leakage as a coordinated project requirement;
2. Address overall performance, testing, and coordination through Division 01;
3. Define each participant’s scope by product, assembly, interface, and installation activity;
4. Provide complete air-barrier transition details before construction;
5. Inspect and test the work while it remains accessible; and
6. Assign corrective responsibility based upon the documented source of leakage and the applicable contracted scope.

Clearly defined responsibilities and early coordination provide the most reliable path to code compliance while reducing disputes, delays, and corrective costs at the end of the project.

Learn more about MBCEA membership and read additional best practice articles.