# Scottish Passive House: Insights into Environmental Conditions in Monitored Passive Houses
## 1 Introduction
### Indoor Air Quality  
Indoor air quality (IAQ) refers to the air quality in buildings particularly in relation to occupants and their health and wellbeing. This is impacted by occupant activities, moisture, temperature, ventilation, building materials, finishes, fittings, and cleaning products [43]. Good air quality in homes requires a fine balance of temperature, RH, Carbon Dioxide (CO\({}_{2}\)) and Volatile Organic Compounds (VOCs), in this paper it refers to temperature, RH and CO\({}_{2}\).  
The optimal parameters of RH for health are defined by [PERSON] _et al._ as 40%-60% humidity; beyond this range, RH can impact on respiratory infections and allergies, by reducing the infectivity of airborne-transmitted infectious bacteria and viruses [44]. In Passive House design, the RH optimal comfort range is 35%-55%, for the avoidance of \"mould and the fast growth of HDM\" [19] (p. 6). The AH comfort range defined by the Passive House standard is 6.0-9.5 g/m\({}^{3}\) with saturation being 17.3 g/m\({}^{3}\) of water vapour at 20 \({}^{\circ}\)C [19] (p. 7). Through the supply of dry air and extraction of humid air by MVHR, the AH is reduced below saturation, therefore the concentration of the water vapour corresponds to the RH [19] (p. 8). Domestic activities such as washing and drying of clothing, if not adequately ventilated can contribute to an increase in internal moisture [45].  
Internal concentrations of CO\({}_{2}\) >1000 ppm can be indicative of poor rates of ventilation, this corresponds with ventilation rates of 8 L/s per person required to maintain CO\({}_{2}\) concentrations below this threshold [46]. A review paper identified the minimum household ventilation rates of \"0.4 ac/h or below 900 ppm CO\({}_{2}\)\" to mitigate health risks [47]. High levels of CO\({}_{2}\) can make a room feel stuff and impact on occupants quality of sleep, levels of concentration, and respiration [48]. CO\({}_{2}\) is generally recognised to keep \"bad company\" when air changes are too low. It can be used as an outline indicator to human occupancy and increase in levels of VOCs and other contaminants that impact on IAQ [49]. While it does not provide accurate readings on specific VOCs and has been criticised by some [50] (p. 33), it can provide low-cost indication for IAQ.  
With the increase in building airtightness, reductions in infiltration (and increases in temperature) the levels of indoor pollutants may rise. Many of the construction materials, paints, finishing's and fittings found in homes contain VOCs and formaldehyde, which may be off-gassed affecting IAQ [51]. Whilst there is limited data to substantiate this, evidence indicates pollutants are occurring indoors, which have potential negative health consequences for the occupants [52]. The Passive House standard recognises the health implications of this, however, it does not mandate low emission building materials to reduce the chemical burden of the dwelling [19] (p. 5).  
Many VOCs are toxic to humans, and known carcinogens, which has led to regulation of their indoor concentrations [52]. However, different chemical interactions between indoor air, materials and the range of substances they off-gas [52; 53] affects the required ventilation rate. Without adequate ventilation negative impacts to the building fabric, include mould growth, toxin build-up: e.g., fatigue, respiratory problems; the extent of health impacts within the home are not yet fully understood [43], but there is increasing evidence of the effects of poor ventilation on health in dwellings [14]. [PERSON] _et al._[38] recommend the use of non- or low-polluting interior materials for use in Passive Houses where possible. Research into unintended consequences and the avoidance of these suggests that overheating particularly impacts IAQ [34] and that there is potential risk of increased emissions of formaldehyde and VOCs as a result of increased temperature or RH [54].