In an apartment building, not every flat is necessarily tested. The regulations allow testing by sampling: a few representative dwellings are tested, and their result applies to the building. It is quicker and cheaper, but since RE2020 this flexibility comes at a price that many developers discover too late: a factor of 1.2 on the measured value, and a 0.3 penalty if work remains to be done.
The value to achieve in apartment buildings
Under RE2020, the air permeability of a dwelling in an apartment building must be less than or equal to 1.0 m³/(h.m²) at 4 Pa (Q4Pa-surf), unless the thermal study uses a stricter value. In that case, the study value applies.
How many dwellings must be tested?
- Building under 500 m²: the whole building is tested, except for buildings with external walkways, where no internal common circulation makes it possible to test the whole: sampling is then allowed.
- Building over 500 m², up to 30 dwellings: 3 dwellings are tested.
- Building with more than 30 dwellings: 6 dwellings are tested.
Dwellings are not chosen at random. They must be spread over the top and bottom levels and an intermediate level, and the standard sets selection rules based on their size and position (smallest and largest dwelling on a level, top-floor dwelling…). The test operator defines the sample from the plans.
The 1.2 factor: sampling is not free
Since RE2020, when testing is done by sampling, the value used is multiplied by 1.2. In practice, to meet 1.0 m³/(h.m²), the tested dwellings must show at most about 0.83.
Conversely, a whole-building test is used without any increase. Note: the value used is then the overall air permeability of the building, calculated according to the standard over the whole envelope, not the result of each dwelling. For a small apartment building, this option is worth considering at design stage: the test requires more preparation (front doors, common areas), but the result is not increased.
The 0.3 penalty: dwellings must be finished
The test must be carried out once all work that can affect airtightness is complete: windows and doors, service penetrations, heating, hot water and ventilation installed. If such work remains to be done after handover, the measured values are increased by 0.3 m³/(h.m²).
The two penalties add up, in this order: the measured value is first multiplied by 1.2, then increased by 0.3. For an apartment building tested by sampling with unfinished work, you therefore need to measure at most about 0.58 to stay below 1.0. In other words, it is far better to test dwellings that are genuinely finished.
Our advice for apartment buildings
- Test the regulatory sample at intermediate stage, i.e. the dwellings that will be measured at the final test, before the linings. The defects found are corrected, then followed up by the project management team until the end of the works: this is what secures the final results.
- Schedule the final test when the sampled dwellings are genuinely finished, with ventilation and equipment installed, to avoid the 0.3 penalty.
- Compare sampling and whole-building testing at design stage for small apartment buildings: with the 1.2 factor, testing the whole building may be the safest option.
- Check the value in the thermal study: if it is lower than 1.0, the real target is even tighter.
Our support
Exp'Air 67 carries out airtightness tests on apartment buildings for developers, builders and social landlords in the Bas-Rhin, the Haut-Rhin and across the Grand Est. Qualified Qualibat 8711, we define the sample from your plans, carry out the intermediate and final tests, and advise you on the safest strategy for your project.
Read also: Airtightness testing for apartment buildings · The 5 air leaks that make an RE2020 airtightness test fail