Leak tests are now a common method for inspecting both new and old buildings. Using thermal imaging, Smoke tests and airtightness measurements provide valuable information on a building’s energy efficiency, structural performance, and factors affecting living comfort; however, these methods do not always achieve sufficient measurement accuracy. Tracer test As the most accurate method for detecting air leaks, it reveals even the smallest leaks that cannot be detected using the methods mentioned above or by sensory means. However, given the wide variety of methods available, identifying the correct testing method can sometimes be challenging. The test is often confused with the measurement of air leakage rates required for updating a building’s energy certificate, and when a new measurement request is received, the first step is usually to determine the nature of the site and the appropriate inspection method for it.
The test is based on detecting a gas that does not occur naturally in the air using a sensor designed for that purpose. The gas is released into the structure being tested (for example, into the insulation cavity of an exterior wall or into the backfill beneath a concrete slab) usually through a hole drilled for gas supply, after which the area is scanned with a gas sensor to locate the points from which the tracer gas is leaking into the space under investigation. The locations and significance of the leaks are presented in the investigation report. The gases most commonly used in the inspection are the Formier 5 nitrogen-hydrogen mixture (N2 95 % + H2 5 %) and sulfur hexafluoride (SF6), although there are various restrictions on the use of sulfur hexafluoride as it is a potent greenhouse gas. However, at the concentrations used, tracer gases are harmless to people in the space being inspected. Common leak points include, for example, the joints between exterior walls and the roof and floor, window frame-to-wall joints, window sills, radiator pipe fasteners, and other joints requiring tight sealing.
A basic requirement for conducting the test is that the space being tested be under negative pressure, so that both air and tracer gas flows move inward from the structure being tested. This can usually be achieved either using the building’s own ventilation system or with separate negative pressure equipment. For large renovation projects, it may be necessary to partition off a smaller area, for example by covering it with plastic sheeting, in order to maintain negative pressure during construction. From the perspective of the success and proper execution of the investigation, it is often advisable to conduct a planning visit to the site before the actual tests are performed, during which the site to be investigated is familiarized with and the implementation of the measurements is planned.
As mentioned above, the test is the most accurate method currently available for locating air leaks. This often leads to the idea that the test should be used ”just to be safe,” but the other methods listed earlier often yield more appropriate results. For example, if you want to renovate a 1950s apartment building to improve energy efficiency and no indoor air quality issues have been detected at the site, thermal imaging performed during actual use can provide a better overall picture of the repair needs. In any case, in a property that is ”leaky” in terms of airtightness, it can be challenging to pinpoint exact leak locations using a tracer gas test if the tracer gas spreads uncontrollably into the airspace of the area being inspected through large leaks. In such cases, it may be more cost-effective to start the inspection with a thermal camera or tracer smoke under strong negative pressure, and then continue with tracer tests after repairing the larger leaks. The test is most effective as a method when air leaks are negligible from an energy efficiency perspective, but radon, microbes, or other factors affecting indoor air quality can enter through the leak paths.
The spaces under investigation are often renovation sites where tracer tests are used to help determine the need for repairs or to verify the success of sealing repairs that have been carried out. Contract documents for renovation projects requiring sealing repairs now often specify that the effectiveness of the sealing work must be verified through tracer gas tests, at least on a sampling basis. In tracer tests conducted in accordance with guideline RT 14-11197, the project’s structural engineer must also define what levels of air leakage are acceptable. The objective at the site may be, for example, to prevent the entry of harmful substances, in which case the airtightness target may be very strict, or to improve energy efficiency through sealing, in which case the target level may be significantly less stringent. In addition to renovation projects, tracer tests can also be used to investigate, among other things, the spread of odors, the airtightness of ducts, hatches, and windows, or the airtightness of new building products.
In summary, the tracer test is an excellent tool in a building inspector’s arsenal when the goal is to improve construction quality as well as living comfort and health.
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