Air tightness testing often brings to mind whole-building compliance and Part L sign-off. In reality, some of the most critical performance and safety risks sit in the smaller, less visible spaces within a building. From protected rooms to underfloor voids and vertical smoke shafts, these areas still demand the same level of attention, expertise, and verification.
In this blog, we explore the key topics from the latest episode of the Stroma Insights podcast, where our specialists discuss why targeted air tightness testing plays a vital role in performance assurance, safety, and long-term operational efficiency. You can listen to the full episode below, or keep reading for an overview of the insights and practical takeaways.
Episode 4: The Ultimate Guide to Air Testing in Small Places
Key Takeaways
- Specialist spaces such as protected rooms, underfloor plenums, and smoke shafts require targeted strategies beyond a standard building air tightness test
- A room integrity test verifies whether gas suppression systems can retain inert gas long enough to protect critical assets and support emergency response
- Leaking plenums can act as a “horizontal chimney”, reducing HVAC efficiency, increasing operational costs, and affecting indoor environmental performance
- Smoke shaft air tightness directly influences evacuation conditions, making performance verification essential for supporting occupant safety
- Early-stage testing and diagnostics help identify hidden leakage paths before areas are concealed, reducing programme risk and costly rework
Room Integrity Testing: Protecting Critical Spaces
Specialist rooms, such as server suites, archives, or plant enclosures, often rely on gas suppression systems to protect valuable assets. These systems work by reducing oxygen levels in the event of a fire, helping to prevent damage and escalation.
However, their effectiveness depends entirely on whether the space can retain the inert gas long enough for it to do its job. This is where a room integrity test becomes essential. By measuring how air leaks from the enclosure under controlled pressure conditions, the test determines whether the system can maintain sufficient gas concentration for the required duration.
In practice, this provides reassurance that investments in protection infrastructure are supported by verified performance. It also helps asset owners avoid uncertainty about whether critical environments are adequately protected.
Legal and Insurance Considerations
Many insurance policies and certification frameworks require periodic verification of room integrity. Annual testing is commonly expected to demonstrate that the enclosure continues to perform as designed.
This reflects the reality that building fabric changes over time. Maintenance works, minor alterations, or material degradation can introduce leakage paths that compromise system effectiveness. Regular testing supports compliance and provides documented assurance for insurers, facilities teams, and stakeholders.
How Testing is Carried Out
A room integrity test uses calibrated fan equipment similar to that deployed during a whole building air tightness test. At Stroma, our engineers begin by reviewing system documentation, confirming the installed suppression configuration, and checking that all components align with specification.
We then pressurise and depressurise the space incrementally, typically up to 50-60 pascals. By analysing pressure decay across staged readings, we calculate gas retention time under realistic operating conditions. Importantly, we do not temporarily seal ventilation dampers, as the objective is to replicate real-world performance.
A retention time exceeding ten minutes is generally considered a strong outcome, providing a window for emergency response and system intervention.
Common Causes of Failure
Air leakage can arise from a range of sources, including:
- Degraded door seals or brush strips
- Poorly fitted frames or thresholds
- Cable and service penetrations
- Structural movement in newer buildings
- Hidden cracks within ceiling or wall assemblies
Identifying these issues early helps prevent costly remedial works and ensures protection strategies remain effective.
Plenum Testing: Managing the “Horizontal Chimney”
Many commercial buildings use underfloor plenums as part of their heating, ventilation, and air conditioning (HVAC) strategy. These pressurised voids distribute conditioned air throughout the occupied space, supporting occupant comfort, indoor air quality, and regulatory compliance.
If a plenum leaks into external facades or adjacent voids, it can start to act like a “horizontal chimney”, allowing conditioned air to escape before it reaches where it’s needed. This reduces system efficiency, increases energy use, and can make building performance harder to control.
Plenum testing helps confirm whether airflow is delivered as intended or lost through hidden gaps. Diagnostics may involve physical inspection beneath the raised floor or smoke tracing – filling the plenum with smoke and observing where it escapes to pinpoint leakage paths.
Static Pressure vs Airflow
When assessing plenums, it’s important to distinguish between static pressure and delivered airflow. A system can appear to be performing correctly at the plant interface, showing the expected pressure readings, while still failing to distribute sufficient air across the floorplate due to leakage along the route.
At Stroma, we take a targeted building air tightness test approach that allows our engineers to assess how effectively pressure is retained within the plenum itself. This provides greater confidence that air distribution aligns with design intent and that the HVAC system is not compensating for avoidable losses.
Typical Failure Points
Common issues identified during plenum diagnostics include:
- Gaps where raised floors meet perimeter walls
- Unsealed penetrations for pipes, conduits, or data cabling
- Leakage into risers or facade cavities
- Fit-out changes introduced after initial construction
Because these voids are quickly concealed during project delivery, testing before final floor installation can simplify remediation and reduce programme risk.
Why Early Engagement Makes a Difference
Across all these scenarios, from specialist rooms to concealed voids, timing plays a decisive role in project success. Testing at earlier construction stages allows teams to identify and resolve issues before finishes are applied or access becomes restricted.
This proactive approach helps:
- Reduce rework and associated costs
- Protect programme certainty
- Validate performance assumptions
- Strengthen collaboration across the supply chain
At Stroma, we combine technical expertise with practical site experience to deliver testing strategies that align with project realities for high-rise, commercial, and residential buildings. Whether you require a targeted building air tightness test or advisory support during design and delivery, our teams are ready to help.
FAQs About Building Air Tightness Tests
What does a plenum do?
A plenum is a pressurised void, often located beneath a raised floor, that distributes conditioned air across an occupied space as part of the building’s ventilation strategy.
How do you test indoor air quality?
Indoor air quality is typically assessed through monitoring of parameters such as temperature, humidity, and pollutant concentrations. Air tightness testing supports this by helping ensure ventilation systems deliver air where intended.
What is a room integrity test?
A room integrity test measures how effectively a sealed space retains air or gas under controlled pressure conditions. It’s commonly used to verify the performance of gas suppression systems in critical environments.