More and more single-family houses are being retrofitted to achieve better energy efficiency levels. In this retrofitting process, the building envelope's airtightness is usually improved, and a ventilation system becomes necessary to create and sustain a healthy indoor air quality (IAQ). However, in France, as in many other western countries, ventilation requirements exist for new dwellings but not for residential retrofitting.

Radon gas is the second biggest cause of lung cancer after smoking and is directly linked to approximately 350 lung cancer cases in Ireland each year. It is a serious public health hazard, and the Government has published a National Radon Control Strategy to tackle the problem. The most cost-effective way of protecting the population from radon is to ensure that new dwellings are built to prevent the entry of this gas from below the building.   

Increasing indoor ventilation has the potential to dilute indoor radon and may be an appropriate first step when measured indoor radon concentrations are close to the mitigation threshold for an existing low-rise house that lacks balanced mechanical ventilation. A ventilation system that includes a heat exchange core is recommended in cold climates to reduce the energy loss associated with replacing stale indoor air with outdoor air that must be either cooled or heated to maintain thermal comfort.

The ingress of naturally occurring radioactive radon gas from the soil into buildings can occur both by convection through any openings in the foundations as a result of pressure differentials and by diffusion across an airtight barrier (World Health Organization 2009). Residential ventilation systems and exhaust devices can affect indoor radon concentrations if they result in depressurization of the conditioned spaced relative to the outdoors or to the soil below the foundations or if they supply outdoor air directly.

Radon, a naturally occurring radioactive gas, is a leading cause of lung cancer and has the potential to increase significantly due to current renovation strategies. Understanding the factors influencing radon infiltration into buildings is vital. Radon flux into buildings is a highly dynamic process influenced by various factors. The current study analyses a historical time-series dataset to determine radon entry rates into buildings and identify statistical factors driving the radon flux based on meteorological, environmental, and building characteristics.

The increasing severity and duration of climate change is that extremes – notably heatwaves, increases the risk of human thermal stress in indoor environments where people spend most of their times. Recent field measurements have demonstrated significant overheating in the EU building stock in the EU, characterized by well-insulated and air-tight envelopes. This exposes vulnerable communities to increases mortality risks that is bound to only get worse with an ever-worsening climate warming.

The Renson One residential concept focusses on the building envelope and the mechanical installations to ensure a climate-adaptive and resilient design throughout the year. Passive, renewable and energy-efficient elements are combined to address the total indoor environment and energy consumption, based on integrated control mechanisms. The high potential of external shading and ventilative cooling was proved to limit overheating and cooling consumption. Adding manual control of the windows to the simulations is a challenge to better approach reality.  

The commitment to improving the energy efficiency of buildings by 2030, with the goal of achieving carbon neutrality by 2050, has been triggered by environmental challenges and the increasing scarcity of energy resources. To this end, European countries are adopting stricter regulations on building energy consumption, as illustrated by the EPB system in Belgium. 
Considering the increase in extreme weather events, the intensity and frequency of heatwaves in many regions of the world, it is essential that buildings are able to adapt to extreme events. 

The EIA EBC Annex 80 Resilient Cooling program has focused on bringing together and extending the knowledge on the resilience of buildings to overheating (Holzer, 2024).  In the context of the Annex 80 Resilient Cooling program a research project, Recover++, has been setup to define a new resilience indicator, based on the properties and behaviour of real-world building projects under extreme climatological condition and shocks, as heatwaves under current and future weather conditions.

The increasing frequency and intensity of heatwaves highlight the necessity for resilient building design to reduce heat-stress-related discomfort and mortality among occupants. "Thermal resilience" refers to a building's capacity to endure thermal disruptions, maintain habitable conditions, and return to its intended state. This study aims to develop a thermal resilience indicator to make resilience an actionable concept for architects and HVAC engineers to assess and improve thermal resilience of buildings to overheating.