Consultant’s Guide to Writing a Performance-Based Airtightness and Duct-Leakage Specification
For MEP consultants and sustainability engineers working on Saudi commercial, institutional, and mixed-use building projects, the move toward performance-based specifications is both a regulatory requirement and a professional responsibility. The Saudi Building Code’s energy efficiency provisions mandate specific airtightness and duct leakage performance levels for qualifying buildings. Green building certification under LEED and Mostadam requires verified performance data as a submission requirement. And the growing expectation among institutional project owners and sovereign wealth fund-backed developers for documented building performance means that specification writers who cannot articulate measurable leakage targets — and the testing and reporting requirements that verify them — are not meeting the standard the market is beginning to demand.
This guide provides MEP consultants and project managers with the practical specification content they need to translate performance targets into contract-enforceable requirements, covering leakage targets, testing stages, sample size, system boundaries, contractor responsibilities, reporting, corrective action, and acceptance criteria.
Defining Measurable Leakage Targets
The foundation of a performance-based specification is a clear, quantified leakage target expressed in the standard metric for the type of leakage being controlled.
For building envelope airtightness, the standard metric is air changes per hour at 50 Pascals of test pressure (ACH50) or cubic metres per hour per square metre of envelope area at 50 Pascals (m³/h·m²). The Saudi Building Code’s energy efficiency provisions reference ASHRAE 90.1 thresholds, which specify a maximum envelope air leakage of 0.4 CFM75 per square foot of envelope area (approximately 7.0 m³/h·m² at 50 Pa) for commercial buildings. High-performance targets for LEED Platinum or net-zero aligned buildings should specify 1.5 to 3.0 ACH50. The specification must state the target explicitly and reference the standard under which it is defined.
For duct leakage, the standard metric is the total system leakage as a percentage of design supply airflow, measured at the standard test pressure (typically 25 Pa for low-pressure systems or 250 Pa for medium-pressure systems, per SMACNA). The Saudi Building Code specifies a maximum of 4% total duct leakage for commercial HVAC systems. High-performance specifications may specify 2% or less. The specification should state the maximum allowable leakage percentage, the test pressure, and whether the leakage limit applies to supply only, return only, or total system.
Applicable Testing Stages
A complete specification defines when testing is required, not just what is required. The appropriate testing stages for a Saudi commercial project are:
- Pre-handover envelope airtightness test: Required after the building is fully enclosed and before final fit-out. This is the primary compliance test for SBC, LEED, and Mostadam purposes.
- Pre-commissioning duct leakage test: Required after duct installation is complete and all terminals are sealed, before commissioning begins. This ensures commissioning proceeds on a verified foundation.
- Post-remediation tests: Required after any sealing remediation works to confirm that the target leakage level has been achieved. These tests produce the before-and-after evidence that documents the remediation outcome.
- Post-occupancy re-test: Recommended 12 to 24 months after occupancy to verify that airtightness performance has been maintained under operating conditions. Required for some LEED O+M and WELL certification pathways.
Sample Size and System Boundaries
For large or multi-tenancy buildings, testing every zone or system in full may not be practical within the project programme and budget. The specification should define the minimum required scope:
For envelope airtightness, the specification should require whole-building testing where possible. Where the building cannot be tested as a single zone — for example, in buildings with multiple independent ventilation zones — the specification should define which zones are to be tested, how many must achieve the leakage target, and how the test zones are defined and sealed for testing.
For duct leakage, the specification should require testing of all systems serving critical areas (operating theatres, data halls, clean rooms, laboratories) and a defined minimum percentage of all other systems. A sample of 25% to 50% of non-critical systems, selected randomly or at the consultant’s discretion, is a common approach for large building portfolios. The specification should state whether failed sample tests trigger 100% testing of the related system or zone.
Contractor Responsibilities
The specification must clearly assign responsibility for testing and remediation. The following allocation is recommended for Saudi projects:
- Main contractor responsibility: Envelope airtightness — the main contractor is responsible for achieving the envelope leakage target and for any remediation required to meet it. The main contractor commissions and pays for testing, engages an approved testing provider, and provides access and temporary sealing of intentional openings during testing.
- MEP/HVAC contractor responsibility: Duct leakage — the MEP contractor is responsible for achieving the duct leakage target and for any sealing remediation required. The MEP contractor commissions and pays for duct leakage testing using an approved testing provider and RetroTec-certified equipment.
- Specialist testing provider: All airtightness and duct leakage testing must be performed by a provider holding ATTMA certification (for envelope testing) and RetroTec certification (for duct leakage testing). Test reports must be issued on the testing provider’s letterhead and include equipment calibration records, test date, building or system details, measured leakage result, and pass/fail determination against the specified target.
Testing and Reporting Requirements
The specification should define the minimum content of test reports to ensure they are suitable for regulatory submission and certification body requirements. Required report elements include: building name, address, and project reference; test date, weather conditions, and ambient temperature; testing provider name, certification credentials, and equipment calibration reference; measured leakage value in the specified metric; target leakage value from the specification; pass or fail determination; and, for post-remediation tests, the pre-remediation leakage value for comparison.
For AeroBarrier sealing projects, the AeroBarrier performance certificate — which is generated automatically by the system’s monitoring software at the moment the target is achieved — constitutes the post-sealing test report and should be specified as an accepted document format alongside ATTMA standard test reports.
Corrective Action and Retesting
The specification must define the corrective action process for failed tests. The recommended approach is: the responsible contractor is notified of the test result and required to submit a remediation plan within five working days; remediation works are completed within the agreed programme timeline; a retest is required within ten working days of remediation completion; the contractor bears all costs of retesting and remediation; and if the second test also fails, the consultant may specify an independent investigation of the envelope or system to identify residual leakage sources before a further retest is permitted.
Required Before-and-After Documentation
For projects where remediation is anticipated — which, in Saudi Arabia’s construction market, means most projects — the specification should explicitly require before-and-after test documentation as a project deliverable. The pre-remediation test result, the remediation scope of works, and the post-remediation test result together constitute the performance record that demonstrates the contractor met their contractual obligation. This documentation should be included in the project’s Operation and Maintenance Manual and retained for the building’s life.
Conclusion
A performance-based airtightness and duct leakage specification transforms vague obligations into enforceable, verifiable contractual requirements. It protects the project owner from inheriting performance deficiencies at handover, protects the consultant from liability for outcomes they cannot control, and provides the contractor with clear targets that, if met, demonstrate professional delivery. Aeroseal Arabia works with MEP consultants across Saudi Arabia to develop project-specific specification language, provide pre-tender performance assessments, and deliver the testing and sealing services that meet the specifications once projects are underway. Contact our team to discuss specification support for your next project.
