Onsite evaluation of building airtightness durability: Long- term and mid-term field measurement study of 61 French low energy single family dwellings

The increasing weight of building leakages energy impact on the overall energy performance of low-energy buildings led to a better understanding of the actual airtightness performance of buildings. However, low expertise is available today on the durability of airtightness products in mid- and long-term scales. The French ongoing research project “Durabilit'air” (2016-2019) aims at improving our knowledge on the variation of buildings airtightness through onsite measurement and accelerated ageing in laboratory controlled conditions. This paper is issued from the second task of the “Durabilit'air” project. This task deals with the quantification and qualification of the durability of building airtightness of single detached houses. It is done through field measurement at mid-term (MT) and long-term (LT) scales.  
This paper first presents the field measurement protocol. For the MT campaign, a sample of 30 new single-detached dwellings has been selected nationwide. During the study, the airtightness of each building is to be measured once per year over a 3-year period. A part of this sample is to be also measured twice per year in order to investigate the impact of seasonal variations. The LT campaign is to be carried out with a second sample of 31 existing single-detached dwellings constructed during the last 10 years. The airtightness of each dwelling is to be measured once. 
A specific measurement protocol was defined after a detailed literature review. The protocol is mainly based on the standard ISO 9972 for the measurement method with additional requirements for the measurement conditions (same tester, same calibrated measurement device, same building preparation, same pressure difference sequences, same season…). It also includes a detailed qualitative leakage detection and questionnaire for occupants. 
The main challenge is to understand the variations of the airtightness and to identify whether it is related to the products/assembly ageing, the maintenance conditions or other factors such as the occupants’ behaviour. Secondly, this paper presents the 61 dwelling samples construction characteristics. All dwellings were tested upon completion. The air flow rates at 4 Pa per envelope area excluding lower floor of both samples show the same mean value around 0.3 m³.h^-1.m^-2 (n₅₀ of 1.4 h^-1), with larger variations among the LT sample. 
Finally, we discuss first measurement results. Regarding MT sample, results after 1-2 years show a slight increase of airflow rate at 50 PA (q₅₀) with a median value of +6%. However, with exposed timber framing, q₅₀ has increased by more than 100%. Regarding LT campaign, measurements results after 3-10 years show a more important increase of q₅₀ with a median value of 28%.  
The measurement campaigns and data analysis will continue over 2018 to complete the work in order to better understand the in situ variations of the buildings’ envelope airtightness.