building envelope

Unintended airflow through building envelopes leads to an increased demand in heating and cooling energy. The most common way to measure air leakage of buildings is the blower door test, which quantifies the overall leakage rate of one room or a building. To reduce air leakage and associated energy loss in new and existing buildings, it is necessary to identify leak locations and prioritize sealing of more substantial leaks.

Air leakage in building envelopes is responsible for a large portion of the building’s heating and cooling requirements. Therefore, fast and reliable detection of leaks is crucial for improving energy efficiency.

IEA-EBC Annex 68 “Indoor Air Quality Design and Control in Low Energy Residential Buildings” is an international collaborative project to provide new insight into methods and strategies for ensuring high indoor air quality in dwellings during both design and operation phase of their life cycle. Within the Annex 68 work, we defined a common exercise, which focusses on model-to-model comparison of different simulation tools to assess their modelling abilities with respect to combined heat, moisture and pollution transfer.

Purpose of the work

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 presents the final results of the second task of the 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.  

The work reported in this paper extends previous work on the feasibility to characterise air leakage and mechanical ventilation avoiding intrusiveness of traditional measurement techniques. The feasibility to obtain the air renovation rate itself, as well as the possibilities to express it as function of other variables (such as wind speed, atmospheric pressure, etc.), are studied. Tracer gas measurements based on N2O have been used as reference.

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.

Mandatory building airtightness testing has come gradually into force in European countries mostly because of the increasing weight of building leakage energy impact on the overall energy performance of low-energy buildings. Therefore, airtightness level of new buildings has significantly improved in the last decade.
However, until now, low expertise is available about the durability of building airtightness at mid- and long-term scales.

Envelope airtightness is incorporated in the French Energy Performance (EP) Regulation (named “RT”) and is a key factor in the reduction of energy consumption. From 2006 until 2012, the French 2005 Energy Performance Regulation (RT, 2005) did not require justification of envelope airtightness. However, constructors could get certification for airtightness through a quality management (QM) approach, in order to build better-than-regulatory buildings.

The new European regulations on energy saving were aimed at a reduction in consumption in the winter phase. This caused even warm countries such as Italy to use envelopes optimised for the winter phase only which are nevertheless unsuitable to the other seasons. The research was developed in order to understand the total yearly behaviour of different envelopes in Mediterranean climates. It started from a real case subject to: (i) monitoring; (ii) simulation of the as-built state for tuning up the software (ENERGYPLUS); (iii) parametric analysis.