Commercial Air Tightness Testing

Air pressure testing is mandatory under Building Regulations for new homes since 1 July 2008. The same principles apply to commercial buildings: tests locate heat-loss paths so you can reduce energy use and achieve compliance.

NSAI Certified

Commercial air leakage testing fan installed in doorway — Commercial Air Leakage Testing Fan — doorway pressurisation setup.

Multiple fans in double door for larger buildings — Multiple fans used in a double door for larger buildings

Trailer or lorry mounted fans — Trailer / lorry mounted fans for medium–large buildings

Fan Pressurisation Systems

Single fan in single door used for small buildings
Multiple fans used in single door for small–medium buildings
Multiple fans used in double door for larger buildings
Trailer or lorry mounted fans for medium to large buildings

Building Envelope Calculations

Unconditional areas (e.g., plant rooms, escape stairs, bin stores, external stores) should not be included in the total building envelope surface.

Lift shaft vents on external walls remain open; the internal surface of the shaft is not included in envelope calculations.

Riser openings to external walls should not be included in calculations.

Fan System Selection

Adequate fan capacity must be available to perform the test. The fan flow supplied should be no less than 100% of the required flow at 50 Pa to achieve the worst acceptable building specification.

Determine required fan flow

TSA
──────  ×  (required air permeability)  =  flow (m/s)
 3600

Fan installation location — decide prior to site meeting:

Access for fan equipment delivery and installation
Free of air-flow restrictions around the fan location
Acceptable route for air to flow around the building

Multi-Occupying Buildings

Apartments over retail units: a concrete floor slab defines the boundary between uses. Test the retail unit separately. A representative sample of the residential accommodation should be tested in line with the current Building Regulation requirement.

High Rise & Multi-Storey Buildings

To achieve equal pressure across storeys, multi-fan setups at different locations may be required. For buildings above 15 storeys, opening the lift shaft doors can help distribute air evenly. Health & Safety restrictions apply; ideally test when the building is empty.

Potential testing scenario

Ground floor: test the ground floor and pressurise the first floor simultaneously to equalise pressures. Analyse ground-floor flow using the ground-floor envelope (slab + external walls). If the first-floor plan is smaller, include any ground-floor roof area in the envelope.
Intermediate floor: test a representative intermediate floor while pressurising floors above and below to the same pressure. Analyse using the external walls of the test floor only.
Top floor: test the top floor while pressurising the floor below; take the envelope as the top-floor external walls + roof.
Provide sufficient open area between the test floor and adjacent floors and a route for the outside differential pressure tube.
Test at least 10% of intermediate floors unless construction methods vary substantially by level.
Pass/fail: if all measured leakage rates meet the required spec, the building passes. If any element fails, compute a combined result: Q50(ground) + Q50(top) + max Q50(intermediate) × (number of intermediate floors); divide by the building envelope area to get the final value.

Most triple-fan blower door systems deliver > 6 m³/s.

Example: an intermediate floor area of 4,000 m² with storey height 4 m needs ~2.8 m³/s per floor at an air permeability of 7 m³/(h·m²).

Top floors may require two triple-fan blower doors plus an additional double-fan on the floor below. Ground floors often have larger footprints; large portable fans are commonly used there.

If the cross-section changes significantly above level 2, apply extra diligence; additional floor levels may need testing.

Large & Complex Buildings

Very large buildings (e.g., hospitals, airport terminals — 80,000 m²+) with varying air permeability requirements can be tested in parts during construction (phased handover).

Recommendations for phased handover

Design a method to achieve the required permeability at design stage
Hire a professional contractor to install the air-tightness system
Liaise with the project manager on progress
Implement robust quality management: nominate a contractor to oversee air-tightness issues, inspect detailed sealing drawings, perform interval inspections, and require QA site audits from main and package contractors
Recommend full-scale mock-ups and/or component testing
Monthly inspections and toolbox talks to brief all contractors on the air-tightness layer
Test nominated sections during construction; record results; perform remedial works and retest until targets are achieved; compile a log for the Handover File
Constant monitoring of the air-tightness system
Test the entire building on completion

Zone / Sample Testing

Phased handover or occupancy may prevent whole-building tests. A representative sample can be reasonable, covering at least 20% of the envelope area and representative of the external envelope construction. Where samples are used to prove compliance of larger areas, the test result should be 10% below the target to provide tolerance for workmanship/detail variability.

When sample testing, consider leakage through internal walls or temporary screens isolating test zones. Leakage through these elements affects the sample result even if they aren’t part of the final external envelope.

Building Extension Testing

Where possible, test the extension as a separate entity. If not practicable (e.g., retail floor extensions), first test the existing building (or portion) to characterise performance before works commence. After extension works, test again.

Derived permeability of the extension:
(Air quantity to pressurise existing + extension) − (Air quantity to pressurise existing only) ÷ (Envelope area of the extension)

An additional test on the original building should also be carried out.

Plan & book your commercial air tightness test

Share drawings, envelope take-off, target permeability, and access constraints. We’ll confirm fan strategy and schedule.