Characterising draught in Mediterranean multifamily housing

sustainability Article Characterising Draught in Mediterranean Multifamily Housing Jesica Fernández-Agüera , Samuel Domínguez-Amarillo * and Miguel Ángel Campano Instituto Universitario de Arquitectura y Ciencias de la Construcci ó n, Escuela T é cnica Superior de Arquitectura, Universidad de Sevilla, 41012 Sevilla, Spain; [email protected] (J.F.-A.); [email protected] (M.Á.C.) *Correspondence: [email protected]; Tel.: +34-954-55-65-95 Received: 13 March 2019; Accepted: 16 April 2019; Published: 24 April 2019   Abstract: Social housing dating from the postwar years through the end of the twentieth century is one of the major stores of European cities’ residential stock. As it is generally characterised by a poor thermal performance and an inefficient control of energy consumption, it constitutes one of the main targets for residential heritage renewal. This study aimed to locate and quantify air leaks across building envelopes in Mediterranean multifamily housing with a view to curbing the uncontrolled inflow of outdoor air that has a direct impact on occupant comfort and housing energy demand. Airtightness tests conducted in a series of protocols to quantify draught across envelope elements were supplemented with qualitative infrared thermographic and smoke tests to locate leakage pathways. Air was found to flow mainly across façade enclosures, primarily around openings, as well as through service penetrations in walls between flats and communal areas accommodating electrical and telecommunication wires and water supply, domestic hot water (DHW), and drainage pipes. The general absence of evidence of draught across structural floors or inter-flat partitions was consistent with the construction systems in place. Keywords: airtightness; social housing; air leakage locate; multifamily housing 1. Introduction Social housing, in its collective building form, is one of the backbones in the configuration of current cities in southern Europe. The considerable volume of housing built in Europe after World War II [ 1 , 2 ] and in Spain after its Civil War carries significant implications in the actual energy behaviour of the city-homes, which cannot be neglected when assessing the energy performance expected from our cities. In Seville, as an example of many cities in southern Europe, over 48% of collective residential buildings, the most common type, were built between 1939 and 1979 [ 3 , 4 ]. When added to the buildings erected in the early twentieth century, this figure increases to over 51% of the present housing stock. Consequently, over half of the city’s houses are to some extent obsolete. Of this 51%, 60% qualifies as “social housing”. This group of dwellings, which accounts for over 30% of Andalusia’s total housing stock, poses the greatest risks in terms of underperformance. Air leakage across envelopes, one of the factors that impacts energy consumption most heavily, can be estimated to account for 20% to 50% of a household’s energy demand, depending on the climate zone [ 5 – 7 ]. Hence, it is important in energy consumption and residential environmental control and air quality design [8,9]. Leakage or infiltration consists in outdoor air that flows into closed premises across cracks and other unintended envelope openings. Such uncontrolled air flows depend on the enclosure permeability and indoor/outdoor air pressure differentials. The presence of (in- or exfiltration) leakage is consequently contingent upon the existence of a direct connection between in- and outdoors and a Sustainability 2019,11, 2433; doi:10.3390/su11082433 www.mdpi.com/journal/sustainability Sustainability 2019,11, 2433 2 of 18 driving force (pressure differential). The five forces most frequently underlying building air flows are as follows [10,11]: •the chimney effect •wind pressure •indoor-outdoor duct leakage •combustion appliance extraction devices or mechanisms •mechanical ventilation. Although the main draught pathways across building envelopes have not been studied in Spain multifamily typologies, the ones most frequently identified in other countries in single family homes are depicted in Figure 1and are as follows [12–15]: • 1 and 2: Suspended ceilings, i.e., spaces between timber planks or between structural floor and perimetric connection elements, as well as service penetrations in such ceilings. •3: Windows or doors. •4: Joints at the abutment between structural floors and enclosures. •5: Seals around windows (and other openings) and window sills. •6: Seals in eaves. • 7: In-flat partitions (leaks across service penetrations for electrical switches, outlets, and similar). •8: Hatchways. •9: Openings for light fixtures. •10: Ventilation pipes and combustion chimneys. •11: Spaces around extractors and stove hoods. •12: Penetrations to accommodate piping. •13: Cracks and any other manner of openings in enclosures. •14: Joints at abutments between floors and enclosures. Sustainability 2019, 11, x FOR PEER REVIEW 2 of 18 outdoors and a driving force (pressure differential). The five forces most frequently underlying building air flows are as follows [10,11]: • the chimney effect • wind pressure • indoor-outdoor duct leakage • combustion appliance extraction devices or mechanisms • mechanical ventilation. Figure 1. The air leakage paths in houses. Source: BRE Good Building Guide 67: Part 1. Although the main draught pathways across building envelopes have not been studied in Spain multifamily typologies, the ones most frequently identified in other countries in single family homes are depicted in Figure 1 and are as follows [12–15]: • 1 and 2: Suspended ceilings, i.e., spaces between timber planks or between structural floor and perimetric connection elements, as well as service penetrations in such ceilings. • 3: Windows or doors. • 4: Joints at the abutment between structural floors and enclosures. • 5: Seals around windows (and other openings) and window sills. • 6: Seals in eaves. • 7: In-flat partitions (leaks across service penetrations for electrical switches, outlets, and similar). • 8: Hatchways. • 9: Openings for light fixtures. • 10: Ventilation pipes and combustion chimneys. • 11: Spaces around extractors and stove hoods. • 12: Penetrations to accommodate piping. • 13: Cracks and any other manner of openings in enclosures. • 14: Joints at abutments between floors and enclosures. All the airtightness tests conducted in Spain are run by a university research team [5,16–19]. They are not undertaken by public or private construction companies, which have yet to be sensitised to the problems (impact on energy demand, occupant comfort, and indoor air quality) posed when housing airtightness rates go uncontrolled. Such problems are the more severe in social housing, occupied by the most vulnerable segments of society that can afford neither to install Heating, Ventilating and Air Conditioning (HVAC) systems nor to pay the high electric power bills associated with individual room heating/cooling [20]. Despite its purportedly mild climate, Spain is the European country with the highest rate of cold weather-induced death [21]. The main aim of this research is to present a wide-ranging study on the location and quantification of the envelope air leakage in one of the largest autonomous communities in Spain, Andalusia, characterised by a climate that is highly representative of southern Europe with mild winters and warm summers (even extreme ones), and ultimately, to serve as a guide for locating air Figure 1. The air leakage paths in houses. Source: BRE Good Building Guide 67: Part 1. All the airtightness tests conducted in Spain are run by a university research team [ 5 , 16 – 19 ]. They are not undertaken by public or private construction companies, which have yet to be sensitised to the problems (impact on energy demand, occupant comfort, and indoor air quality) posed when housing airtightness rates go uncontrolled. Such problems are the more severe in social housing, occupied by the most vulnerable segments of society that can afford neither to install Heating, Ventilating and Air Conditioning (HVAC) systems nor to pay the high electric power bills associated with individual room heating/cooling [ 20 ]. Despite its purportedly mild climate, Spain is the European country with the highest rate of cold weather-induced death [21]. Sustainability 2019,11, 2433 3 of 18 The main aim of this research is to present a wide-ranging study on the location and quantification of the envelope air leakage in one of the largest autonomous communities in Spain, Andalusia, characterised by a climate that is highly representative of southern Europe with mild winters and warm summers (even extreme ones), and ultimately, to serve as a guide for locating air leakage in sustainable housing design, construction, and retrofitting. Indoor thermal conditions, particularly in social housing, have normally been conditioned by economic considerations, an extended absence of thermal systems, both cooling and heating, in homes, and a failure to provide suitable capabilities to these buildings [22]. 2. Materials and Methods The airflows were studied and characterised both quantitatively and qualitatively. The (quantitative) blower door test was run to determine the contribution to leaks of each room and its respective elements in the flats analysed. Those procedures were supplemented with (qualitative) infrared thermographic and smoke tests to locate draught pathways in building envelopes. 2.1. Location and Climate Although the regional climate can generally be defined as Mediterranean (Köppen: Csa), there are different variants in the studied area, also covering Bsh areas in transition to Bwh (Almeria area), and others where the Csa type transitions to the Bsk (Granada area). However, climatic zoning associated with the national energy labelling procedure has been adopted for a more detailed classification, as it provides a greater degree of subregional detail [ 23 ]. The buildings chosen were in different climate areas within the region, with winters ranging from very mild (zone A) to cold (zone C) and summers from warm (zone 3) to hot (zone 4). The selected building complexes, or sample groups, are located in the five most representative climatic zones of the region. Although Andalusia has a wide range of climatic zones, the most common ones, i.e., where most of the properties in the region are concentrated, have been selected. Separate predictive models were developed for each climatic zone. The mean, maxima, and minima temperature values of different climatic files are given in Table 1by the climatic zone. Table 1. Climatic data. Month 1 2 3 4 5 6 7 8 9 10 11 12 A3 T (◦C) 12.1 12.9 14.7 16.3 19.3 23.0 25.5 26.0 23.5 19.5 15.7 13.2 TM (◦C) 16.8 17.7 19.6 21.4 24.3 28.1 30.5 30.8 28.2 24.1 20.1 17.5 Tm (◦C) 7.4 8.2 9.8 11.1 14.2 18.0 20.5 21.1 18.8 15.0 11.3 8.9 A4 T (◦C) 12.6 13.3 15.1 17.0 19.7 23.5 26.1 26.7 24.2 20.4 16.4 13.8 TM (◦C) 16.9 17.6 19.6 21.4 24.1 27.9 30.5 31.0 28.4 24.5 20.5 17.9 Tm (◦C) 8.3 9.0 10.6 12.5 15.3 18.9 21.7 22.4 20.0 16.3 12.3 9.6 B4 T (◦C) 10.9 12.5 15.6 17.3 20.7 25.1 28.2 27.9 25.0 20.2 15.1 11.9 TM (◦C) 16.0 18.1 21.9 23.4 27.2 32.2 36.0 35.5 31.7 26.0 20.2 16.6 Tm (◦C) 5.7 7.0 9.2 11.1 14.2 18.0 20.3 20.4 18.2 14.4 10.0 7.3 C3 T (◦C) 6.5 8.5 11.4 13.3 17.2 22.3 25.3 24.8 21.1 16.0 10.6 7.6 TM (◦C) 13.0 15.4 19.0 20.6 25.0 31.0 34.8 34.2 29.4 23.2 17.0 13.4 Tm (◦C) 0.0 1.6 3.8 6.0 9.4 13.6 15.7 15.5 12.8 8.7 4.2 1.7 C4 T (◦C) 8.6 10.3 13.1 14.5 18.2 23.7 27.6 26.9 22.8 17.9 12.3 9.5 TM (◦C) 12.1 14.0 17.4 19.0 23.2 29.4 33.7 32.9 27.7 21.9 15.7 12.8 Tm (◦C) 5.1 6.6 8.9 10.0 13.3 18.1 21.4 21.0 17.8 13.8 8.9 6.3 2.2. Sample In southern Andalusia, multi-dwelling units prevail over the single family homes found more frequently in suburbs and metropolitan areas. Two periods of steep housing construction development and growth can be identified: from 1940 to 1979, particularly at the end of that cycle, and in the nineteen nineties and the twenty noughties, when the city acquired its present appearance [24]. The sample was divided in two: Sustainability 2019,11, 2433 4 of 18 Cluster 1, post-1979 developments—dwellings built between 1980 and 2005: This sample is very representative of the buildings constructed after the implementation of the first Spanish energy demand regulations NBE-CT-79 (on Thermal Conditions in Buildings) [25]. Cluster 2, pre-1979 developments—dwellings built between 1950 and 1979: This sample is very representative of the buildings constructed prior to the implementation of the NBE-CT-79 and has no specific thermal insulation [24]. As a rule, the façades in the area exhibit an average thermal performance, with thermal mass values in the medium or, in the oldest buildings with a single wythe masonry, in the low range. Façade thermal transmittance values are on the order of 0.5 W/m 2 K to 1.5 W/m 2 K. Typically, they consist in two masonry wythes, a thicker outer layer (normally 15 cm) and a thinner inner layer (7 cm to 4 cm) with an air space in between. Reinforced concrete portal frames and structural floors constitute the prevailing structural approach. Most windows are single glazed and either hinged or horizontally sliding, with timber, steel, or aluminum joinery (from oldest to newest), depending on the date of construction [24]. Balconies, a very common element, particularly in the older flats, grew in size in buildings erected beginning in the nineteen sixties. As those elements normally form part of fairly small flats, many have been enclosed to enlarge the rest of the dwelling. A substantial percentage of these flats also feature a laundry room adjacent to the kitchen, particularly those built after the enactment of ordinances on social housing design [ 24 ]. Flats’ (normally gas-fuelled) domestic hot water heaters are found in those spaces, which were initially fitted with slats as the sole separation from the outdoors. As in the case of the balconies, however, many of these laundry rooms have been enclosed with joinery and glazing and incorporated into the kitchen. The sample analysed consisted solely in flats in apartment buildings, normally surrounded by adjacent units on all sides as well as above and below, with the exception of the units on the top and bottom stories and along the building perimeter. The main paths in the envelope were identified on the grounds of those assumptions (Table 2). Table 2. The location and years of the sample. ID. Year Standard Climatic Zone City No. of Dwellings 1 1954 preCT79 A3 Cádiz 4 2 1968 preCT79 A3 Málaga 3 3 1971 preCT79 A3 Cádiz 3 4 1972 preCT79 A3 Cádiz 4 5 1974 preCT79 A3 Cádiz 4 6 1976 preCT79 A3 Málaga 1 7 1978 preCT79 A3 Málaga 1 8 1966 preCT79 A4 Huelva 3 9 1969 preCT79 A4 Huelva 2 10 1970 preCT79 A4 Huelva 2 11 1961 preCT79 A4 Huelva 1 12 1951 preCT79 B4 Seville 1 13 1963 preCT79 B4 Seville 3 14 1964 preCT79 B4 Seville 4 15 1965 preCT79 B4 Seville 3 16 1970 preCT79 B4 Córdoba 2 17 1973 preCT79 B4 Córdoba 1 18 1978 preCT79 B4 Seville 1 19 1959 preCT79 C3 Granada 2 20 1964 preCT79 C4 Jaén 4 21 1967 preCT79 C4 Jaén 4 22 2010 CT79 A3 Málaga 4 Sustainability 2019,11, 2433 5 of 18 Table 2. Cont. ID. Year Standard Climatic Zone City No. of Dwellings 23 2011 CT79 A3 Cádiz 8 24 2012 CT79 A3 Cádiz 8 25 2007 CT79 A4 Almería 8 26 1993 CT79 B4 Seville 1 27 1998 CT79 B4 Córdoba 7 28 2004 CT79 B4 Seville 10 29 2010 CT79 B4 Seville 8 30 2011 CT79 B4 Seville 7 31 2011 CT79 B4 Seville 5 32 2010 CT79 B4 Córdoba 8 33 2011 CT79 C3 Granada 8 34 2011 CT79 C4 Jaén 5 35 2010 CT06 B4 Seville 8 36 2011 CT06 B4 Córdoba 7 37 2011 CT06 C3 Granada 4 Total: 159 2.3. Blower Door Tests Blower door tests, a procedure endorsed by the scientific community [ 26 ], constituted the backbone of the study. The entire envelope was analysed, including both the elements in contact with the outdoors and those adjacent to other flats and communal areas (Figure 2). In the absence of specific protocols for measuring multifamily housing [ 27 ], new protocols based on Spanish and European standard UNE EN 13829:2002 [ 28 ] were developed to conduct blower door tests and to quantify air flowing both outdoors and toward adjacent flats, as described in Reference [19]. Sustainability 2019, 11, x FOR PEER REVIEW 5 of 18 26 1993 CT79 B4 Seville 1 27 1998 CT79 B4 Córdoba 7 28 2004 CT79 B4 Seville 10 29 2010 CT79 B4 Seville 8 30 2011 CT79 B4 Seville 7 31 2011 CT79 B4 Seville 5 32 2010 CT79 B4 Córdoba 8 33 2011 CT79 C3 Granada 8 34 2011 CT79 C4 Jaén 5 35 2010 CT06 B4 Seville 8 36 2011 CT06 B4 Córdoba 7 37 2011 CT06 C3 Granada 4 Total: 159 2.3. Blower Door Tests Blower door tests, a procedure endorsed by the scientific community [26], constituted the backbone of the study. The entire envelope was analysed, including both the elements in contact with the outdoors and those adjacent to other flats and communal areas (Figure 2). In the absence of specific protocols for measuring multifamily housing [27], new protocols based on Spanish and European standard UNE EN 13829:2002 [28] were developed to conduct blower door tests and to quantify air flowing both outdoors and toward adjacent flats, as described in Reference [19]. Figure 2. The location of one example case study flat. A comparison of the results of the airtightness tests run to different protocols (Figure 3) identified the envelope elements primarily responsible for inward air flows (Figure 1). The findings for the various tests were analysed to determine the relative weight of each component in a total air leakage. To establish the effect of the separations between adjacent flats and between indoors and outdoors, the units were tested under a number of conditions. Blower door tests were conducted not only on the flats as a whole but also by closing off parts of each to determine the contributions of the various envelope components, particularly the ones on building exteriors. The flats were Figure 2. The location of one example case study flat. A comparison of the results of the airtightness tests run to different protocols (Figure 3) identified the envelope elements primarily responsible for inward air flows (Figure 1). The findings for the various tests were analysed to determine the relative weight of each component in a total air leakage. Sustainability 2019,11, 2433 6 of 18 To establish the effect of the separations between adjacent flats and between indoors and outdoors, the units were tested under a number of conditions. Blower door tests were conducted not only on the flats as a whole but also by closing offparts of each to determine the contributions of the various envelope components, particularly the ones on building exteriors. The flats were consequently sealed offas described in Figure 3, in keeping with protocols developed in earlier research [19]. Overall, the leakage between adjacent flats was scantly significant; as reported in earlier research [ 18 ], only 3.6% on the average of the total envelope volume was observed to be associated with lateral draughts. Leaks to and from other flats were, therefore, disregarded in the analysis; with such a low volumetric incidence and the absence of dynamic wind pressure between adjacent walls, the contribution of any air entry or exit to the exchange rate in occupied flats could be deemed negligible. Sustainability 2019, 11, x FOR PEER REVIEW 6 of 18 consequently sealed off as described in Figure 3, in keeping with protocols developed in earlier research [19]. Overall, the leakage between adjacent flats was scantly significant; as reported in earlier research [18], only 3.6% on the average of the total envelope volume was observed to be associated with lateral draughts. Leaks to and from other flats were, therefore, disregarded in the analysis; with such a low volumetric incidence and the absence of dynamic wind pressure between adjacent walls, the contribution of any air entry or exit to the exchange rate in occupied flats could be deemed negligible. Figure 3. The blower door test protocols to locate airflow pathways. 2.4. Locating Air Leakage To supplement the airtightness analyses, the main flow paths across the envelope were located with infrared thermography and smoke tests. As both are only effective if air is moving across the envelope, they were conducted at the same time as the blower door test [29]. Although essentially qualitative and geared to locating airflows and the areas where airpermeable elements are concentrated, these tests deliver data of particular interest for building reform and improvement design. Infrared thermographic images were captured with a FLIR ThermaCAM B4 camera featuring a resolution of 320 × 240 pixels and other specifications required for infrared building inspections. The data were processed with the FLIR ExaminIR software. Figure 3. The blower door test protocols to locate airflow pathways. 2.4. Locating Air Leakage To supplement the airtightness analyses, the main flow paths across the envelope were located with infrared thermography and smoke tests. As both are only effective if air is moving across the envelope, they were conducted at the same time as the blower door test [29]. Sustainability 2019,11, 2433 7 of 18 Although essentially qualitative and geared to locating airflows and the areas where air-permeable elements are concentrated, these tests deliver data of particular interest for building reform and improvement design. Infrared thermographic images were captured with a FLIR ThermaCAM B4 camera featuring a resolution of 320 × 240 pixels and other specifications required for infrared building inspections. The data were processed with the FLIR ExaminIR software. Like thermography, smoke tests detect uncontrolled air entry in building envelopes. They consist in generating smoke (in this case, with a Smoke Pencil Pro draught detector) near the inside of certain elements of the envelope in a blower door-depressurised flat. The direction of the smoke as it moves readily identifies outdoor-indoor draughts. This test is very useful when a thermographic camera cannot be used due to the lack of significant indoor-outdoor temperature differences. Another advantage of this test over the thermographic procedure is that it can be conducted in any season of the year and calls for no preliminary preparation of the flat. This approach was consequently adopted for all the housing developments studied, most of which lacked the HVAC systems needed to create the temperature difference required by IR thermography. 3. Results and Discussion The flats studied were built between 1950 and the time of the study. In light of the morphological and constructional differences observed, the sample was divided into two clusters: flats built prior to 1979 (cluster 2), when the first provisions on building construction entered into effect in Spain, and those built after that date (cluster 1). 3.1. Quantifying Air Leakage 3.1.1. Cluster 1, Post-1979 Developments The cluster 1 findings listed in Table 1identify the contribution of each envelope component to the total airflow. The leakage attributable to wet (kitchens and bathrooms) and dry areas can be deduced by comparing the method MB to the M2 and M3 findings. The values recorded exhibited substantial scatter, as mirrored in the standard deviations and range of minimum-maximum flows (Table 3). Table 3. The statistical descriptors for airflow (m3/h) at 50 Pa in cluster 1. Mean Minimum Maximum Standard Deviation MA 1575 916 2779 416 M1 1351 685 2763 457 MB 1197 547 2729 465 M2 960 179 2499 458 M3 931 356 2240 402 The test findings for wet area envelope elements and functional openings (vents) in those areas are broken down in Table 4. Table 4. The statistical descriptors for the airflow at 50 Pa (m 3 /h), attributable to cluster 1 envelope components. Mean Minimum Maximum Standard Deviation Functional openings (vents) 378 0 756 151 Kitchen envelope 227 5 608 134 Bathroom envelope 100 3 613 111 Sustainability 2019,11, 2433 8 of 18 The volume of air flowing across functional openings such as vents and smoke extractors accounted for a significant 25% of the total flow in flats. That percentage was highly variable, however, ranging from 0 in flats where such elements were either lacking or out of order to 756 m 3 /h for nearly half of the total draught in the unit in question. When the functional openings (vents and similar) were excluded, as in method MB, most of the leaks could be attributed to the dry areas, where the largest share of window area and building service penetrations are normally located (Table 1and Figure 4a). Sustainability 2019, 11, x FOR PEER REVIEW 8 of 18 Figure 4. The contribution to the total air flow in cluster 1 flats at 50 Pa (V50): (a) wet vs dry areas and (b) the distribution in wet areas by component. When the functional openings (vents and similar) were excluded, as in method MB, most of the leaks could be attributed to the dry areas, where the largest share of window area and building service penetrations are normally located (Table 1 and Figure 4a). Of the wet areas, kitchens contributed most to airflow and bathrooms contributed the least, which is consistent with the general absence of windows in the latter (Table 3 and Figure 4b). 3.1.2. Cluster 2, Pre-1979 Developments The cluster 2 findings listed in Table 5 identify the contribution of each envelope component to airflows. On the whole, the means in this group were lower than those observed for cluster 1. The two were consequently compared in relative terms. Table 5. The statistical descriptors for airflow (m 3 /h) at 50 Pa in cluster 2. Mean Minimum Maximum Standard deviation MA 1330 830 2808 509 MB 1139 679 2045 360 M2 915 621 1526 279 M3 763 401 1544 299 The leakage attributable to wet (kitchens and bathrooms) and dry areas can be deduced by comparing the method MB to the M2 and M3 findings. As in cluster 1, the dataset exhibited considerable scatter, although less uniformly in this case. The widest range of values was observed for functional openings, where the standard deviation was higher than in cluster 1, whilst the narrower interval for the remaining components denoted a greater similarity in intra-cluster solutions. The findings for specific elements in wet area envelopes are broken down in Table 6. Table 6. The statistical descriptors for the airflow at 50 Pa (m 3 /h), attributable to cluster 2 envelope components. Flow Mean Minimum Maximum Standard deviation Functional openings (vents) 224 0 2023 382 Kitchen envelope 297 34 570 225 Bathroom envelope 107 4 402 129 The volume of air flowing across functional openings such as vents and smoke extractors accounted for 17% of the total leakage, a lower proportion than that observed in cluster 1 (Table 4). （a）(b) Figure 4. The contribution to the total air flow in cluster 1 flats at 50 Pa (V 50 ): ( a ) wet vs dry areas and (b) the distribution in wet areas by component. Of the wet areas, kitchens contributed most to airflow and bathrooms contributed the least, which is consistent with the general absence of windows in the latter (Table 3and Figure 4b). 3.1.2. Cluster 2, Pre-1979 Developments The cluster 2 findings listed in Table 5identify the contribution of each envelope component to airflows. On the whole, the means in this group were lower than those observed for cluster 1. The two were consequently compared in relative terms. Table 5. The statistical descriptors for airflow (m3/h) at 50 Pa in cluster 2. Mean Minimum Maximum Standard Deviation MA 1330 830 2808 509 MB 1139 679 2045 360 M2 915 621 1526 279 M3 763 401 1544 299 The leakage attributable to wet (kitchens and bathrooms) and dry areas can be deduced by comparing the method MB to the M2 and M3 findings. As in cluster 1, the dataset exhibited considerable scatter, although less uniformly in this case. The widest range of values was observed for functional openings, where the standard deviation was higher than in cluster 1, whilst the narrower interval for the remaining components denoted a greater similarity in intra-cluster solutions. The findings for specific elements in wet area envelopes are broken down in Table 6. Sustainability 2019,11, 2433 9 of 18 Table 6. The statistical descriptors for the airflow at 50 Pa (m 3 /h), attributable to cluster 2 envelope components. Flow Mean Minimum Maximum Standard Deviation Functional openings (vents) 224 0 2023 382 Kitchen envelope 297 34 570 225 Bathroom envelope 107 4 402 129 The volume of air flowing across functional openings such as vents and smoke extractors accounted for 17% of the total leakage, a lower proportion than that observed in cluster 1 (Table 4). The absolute values ranged over a very wide interval in this case, with a nil effect in some flats and an infiltration of over 2000 m 3 /h in others, where these elements essentially drove the entire airflow (Table 4). At 36%, these openings impacted wet area permeability less than in cluster 1, where 54% was attributable to vents and similar. An analysis of the envelope performance (in the absence of an intentional window opening) revealed that, here, most leakage could be attributed to the dry areas, although the contribution of wet and dry areas was more evenly distributed than in cluster 1 (Table 3and Figure 4), with the latter contributing 67% and the former 33% of the total (Figure 5a). Sustainability 2019, 11, x FOR PEER REVIEW 9 of 18 The absolute values ranged over a very wide interval in this case, with a nil effect in some flats and an infiltration of over 2000 m 3 /h in others, where these elements essentially drove the entire airflow (Table 4). At 36%, these openings impacted wet area permeability less than in cluster 1, where 54% was attributable to vents and similar. An analysis of the envelope performance (in the absence of an intentional window opening) revealed that, here, most leakage could be attributed to the dry areas, although the contribution of wet and dry areas was more evenly distributed than in cluster 1 (Table 3 and Figure 4), with the latter contributing 67% and the former 33% of the total (Figure 5a). Figure 5. The contribution to the total air flow in cluster 2 flats at 50 Pa (V 50 ): (a) wet vs dry areas and (b) the distribution in wet areas by component. In this cluster, kitchens accounted for nearly half of the wet area leakage. Whilst envelope leakage was the least concentrated in bathrooms, the contribution of these areas was somewhat greater than in cluster 1 (Table 4 and Figure 5b). In the dwellings built between 1950 and 1979, the air leakage paths in the wet rooms (bathrooms and kitchen) have a greater impact on the total air through the envelope (33%) compared to those built later (22%). This is mainly due to the improvement of the carpentry used in the most recent buildings and the incorporation of the casement windows, which are more airtight than the sliding ones. The average value of the airflow that enters through the vents of the kitchens and bathrooms is higher in the homes built after 1979 (378 m 3 /h at 50 Pa). This finding is logical since ventilation was not mandatory in homes built before 1979. In addition, ventilation requirements were increased when the CTE2006 regulation came into force. In the dwellings built between 1950 and 1979, the windows were made of lacquered wood, aluminum, or steel without thermal bridge break with a simple glass of 4 mm in the dry rooms (bedrooms and living room). From 1979, the windows were made of aluminum or PVC with simple glass with an air chamber, and after 2006, the windows were made of aluminum with thermal bridge break and with double glass with an air chamber. The most important elements that differentiate this behaviour are the shadings incorporated into the houses that, in homes built before 1979, were shutters, folding blinds, traditional exterior wooden rolling shutters, or rolling shutters integrated into the enclosure. In homes built after 1979, rolling shutters integrated into the enclosure and, from the 90s, compact rolling shutters were introduced. The values of air permeability found in the bathroom envelope are very similar in both periods, although the range is high because these values included dwellings that do not have windows in the bathrooms, where the value is almost 0 m 3 /h. （a）(b) Figure 5. The contribution to the total air flow in cluster 2 flats at 50 Pa (V 50 ): ( a ) wet vs dry areas and (b) the distribution in wet areas by component. In this cluster, kitchens accounted for nearly half of the wet area leakage. Whilst envelope leakage was the least concentrated in bathrooms, the contribution of these areas was somewhat greater than in cluster 1 (Table 4and Figure 5b). In the dwellings built between 1950 and 1979, the air leakage paths in the wet rooms (bathrooms and kitchen) have a greater impact on the total air through the envelope (33%) compared to those built later (22%). This is mainly due to the improvement of the carpentry used in the most recent buildings and the incorporation of the casement windows, which are more airtight than the sliding ones. The average value of the airflow that enters through the vents of the kitchens and bathrooms is higher in the homes built after 1979 (378 m 3 /h at 50 Pa). This finding is logical since ventilation was not mandatory in homes built before 1979. In addition, ventilation requirements were increased when the CTE2006 regulation came into force. In the dwellings built between 1950 and 1979, the windows were made of lacquered wood, aluminum, or steel without thermal bridge break with a simple glass of 4 mm in the dry rooms (bedrooms and living room). From 1979, the windows were made of aluminum or PVC with simple glass with an air chamber, and after 2006, the windows were made of aluminum with thermal bridge break and with double glass with an air chamber. The most important elements that differentiate this Sustainability 2019,11, 2433 16 of 18 The tests conducted showed that air flows essentially across the vertical envelope, especially in dry areas of the flats where most of the windows are located. Nonetheless, water pipe and electric wire penetrations, vents, and similar were also found to contribute notably to envelope permeability. In contrast, no significant leakage was observed across horizontal sectorisation elements (inter-storey structural floors) or inter-flat partition walls. In the elements between flats and communal areas, the permeability was observed essentially in large (not mere crack-like) service penetrations. No differences were found between the uppermost and other stories. For the type of façades expected in this type of housing, the main flow paths are associated with window-opaque enclosure joints. Whilst these were the most frequent entry pathways, the flow rates quantified by the tests run varied widely. Even within the same building or development, a significant scatter was observed in the flat performance. Those differences may be attributed to the manual construction procedures that characterise this type of buildings. Although windows were found to be the key elements in air leakage, no clear distinction could be drawn between window type and airtightness, with a wide variability within each of the two standard formats (sliding and hinged). In addition to the stochastic dimension of construction and time-mediated change, envelope air permeability was observed to be governed by a combination of factors, including • façade enclosures, primarily the joints between opaque infills and openings, although they neither were a deterministic factor nor followed a linear pattern; • service penetrations through vertical partitions separating flats from communal areas for electrical wiring, water pipes, DHW, telecommunication lines, and similar. Unsurprisingly, given the standard construction systems in place, flows were not generally observed across structural floors or inter-flat partitions. The conclusion that can be drawn from the foregoing is that efforts to enhance airtightness should focus on designing joints between openings and masonry that are less sensitive to assembly procedures and on tightening workmanship control. Author Contributions: Conceptualization, J.F.-A.; data curation, J.F.-A., S.D.-A., and M. Á .C.; formal analysis, J.F.-A. and M. Á .C.; investigation, S.D.-A.; methodology, J.F.-A.; writing—original draft, S.D.-A.; writing—review and editing, J.F.-A. and M.Á.C. Funding: This study was funded by the Spanish Ministry of Economy and Competitiveness under project BIA2012-39020-C02-01 and BES-2013-063097 support. Conflicts of Interest: The authors declare no conflict of interest. References 1. Meijer, F.; Itard, L.; Sunikka-Blank, M. Comparing European residential building stocks: Performance, renovation and policy opportunities. Build. Res. Inf. 2010,37, 533–551. [CrossRef] 2. Nicol, S.; Roys, M.; Ormandy, D.; Ezratty, V. The Cost of Poor Housing in the European Union; Instituto Nacional de Estadistica: Madrid, Spain, 2018. Available online: https://www.bre.co.uk/filelibrary/Briefing%20papers/ 92993_BRE_Poor-Housing_in_-Europe.pdf (accessed on 17 April 2019). 3. Instituto Nacional de Estadistica. Censos de Poblaci ó n y Vivienda 1991; Instituto Nacional de Estadistica: Madrid, Spain, 1992. 4. Instituto Nacional de Estadistica. Censos de Poblaci ó n y Vivienda 2011; Instituto Nacional de Estadistica: Madrid, Spain, 2011. 5. Feij ó -Muñoz, M.J.; Pardal, C.; Echarri, V.; Fern á ndez-Agüera, J.; de Larriva, R.A.; Calder í n, M.M.; Poza-Casado, I.; Padilla-Marcos, M. Á .; Meiss, A. Energy impact of the air infiltration in residential buildings in the Mediterranean area of Spain and the Canary islands. Energy Build. 2019,188, 226–238. [CrossRef] 6. Jokisalo, J.; Kurnitski, J.; Korpi, M.; Kalamees, T.; Vinha, J. Building leakage, infiltration, and energy performance analyses for Finnish detached houses. Build. Environ. 2009,44, 377–387. [CrossRef] 7. Ferdyn-Grygierek, J.; Bartosz, D.; Specjał, A.; Grygierek, K. Analysis of Accuracy Determination of the Seasonal Heat Demand in Buildings Based on Short Measurement Periods. Energies 2018 ,11, 2734. [CrossRef] Sustainability 2019,11, 2433 17 of 18 8. Alfano, F.R.d.; Dell’Isola, M.; Ficco, G.; Palella, B.I.; Riccio, G. Experimental air-tightness analysis in mediterranean buildings after windows retrofit. Sustainability 2016,8, 991. [CrossRef] 9. Meiss, A.; Padilla-Marcos, M.; Feij ó -Muñoz, J.; Meiss, A.; Padilla-Marcos, M.A.; Feij ó -Muñoz, J. Methodology Applied to the Evaluation of Natural Ventilation in Residential Building Retrofits: A Case Study. Energies 2017,10, 456. [CrossRef] 10. Sherman, M.H. Estimation of infiltration from leakage and climate indicators. Energy Build. 1987 ,10, 81–86. [CrossRef] 11. Allard, F.; Santamouris, M. Natural Ventilation in Buildings: A Design Handbook; James & James: London, UK, 1998; p. 378. 12. Van den Bossche, N.; Huyghe, W.; Moens, J.; Janssens, A.; Depaepe, M. Airtightness of the window-wall interface in cavity brick walls. Energy Build. 2012,45, 32–42. [CrossRef] 13. Cuce, E. Role of airtightness in energy loss from windows: Experimental results from in-situ tests. Energy Build. 2017,139, 449–455. [CrossRef] 14. Relander, T.O.; Heiskel, B.; Tyssedal, J.S. The influence of the joint between the basement wall and the wood-frame wall on the airtightness of wood-frame houses. Energy Build. 2011,43, 1304–1314. [CrossRef] 15. Pereira, P.F.; Almeida, R.M.S.F.; Ramos, N.M.M.; Sousa, R. Testing for building components contribution to airtightness assessment. In Proceedings of the 35th AIVC Conference Ventilation and Airtightness in Transforming the Building Stock to High Performance, Poznan, Poland, 24–25 September 2014; pp. 322–330. 16. Feij ó -Muñoz, M.J.; Pardal, C.; Echarri, V.; Fern á ndez-Agüera, J.; de Larriva, R.A.; Calder í n, M.M.; Poza-Casado, I.; Padilla-Marcos, M. Á .; Meiss, A. Methodology for the Study of the Envelope Airtightness of Residential Buildings in Spain: A Case Study. Energies 2018,11, 704. 17. Fern á ndez-Agüera, J.; Dom í nguez-Amarillo, S.; Sendra, J.J.; Su á rez, R.; Oteiza, I. Social housing airtightness in Southern Europe. Energy Build. 2019,183, 377–391. [CrossRef] 18. Fern á ndez-Agüera, J.; Dom í nguez-Amarillo, S.; Sendra, J.J.; Su á rez, R. An approach to modelling envelope airtightness in multi-family social housing in Mediterranean Europe based on the situation in Spain. Energy Build. 2016,128, 236–253. [CrossRef] 19. Fern á ndez-Agüera, J.; Sendra, J.J.; Dom í nguez, S. Protocols for measuring the airtightness of multi-dwelling units in Southern Europe. Procedia Eng. 2011,21, 98–105. [CrossRef] 20. Dom í nguez-Amarillo, S.; Fern á ndez-Agüera, J.; Sendra, J.J.; Roaf, S. Rethinking User Behaviour Comfort Patterns in the South of Spain—What Users Really Do. Sustainability 2018,10, 4448. [CrossRef] 21. D í az, J.; Carmona, R.; Mir ó n, I.J.; Ortiz, C.; Linares, C. Comparison of the effects of extreme temperatures on daily mortality in Madrid (Spain), by age group: The need for a cold wave prevention plan. Environ. Res. 2015,143, 186–191. [CrossRef] [PubMed] 22. Sendra, J.J.; Domínguez-Amarillo, S.; Rojas, P.B.; Leon, A.L. Energy Intervention in the residential sector in the south of Spain: Current challenges. Inf. Constr. 2013,65, 457–464. [CrossRef] 23. De la Flor, F.J.S.; Dom í nguez, S. Á .; F é lix, J.L.M.; Falc ó n, R.G. Climatic zoning and its application to Spanish building energy performance regulations. Energy Build. 2008,40, 1984–1990. [CrossRef] 24. Dom í nguez-Amarillo, S.; Sendra, J.J.; Jos é , I.O.S. La Envolvente T é rmica de la Vivienda Social: El Caso de Sevilla, 1939 a 1979 Title, 1st ed.; Editorial Consejo Superior de Investigaciones Científicas: Madrid, Spain, 2016. 25. Del Gobierno, P. Real Decreto 2429/1979, de 6 de Julio, Por el Que se Aprueba la Norma B á sica de Edificaci ó n NBE-CT-79, Sobre Condiciones Térmicas en los Edificios; Boletín Oficial del Estado: Madrid, Spain, 1979. 26. Sherman, M.H.; Dickerhoff, D.J. Airtightness of U.S. dwellings. Trans. Am. Soc. Heat. Refrig. Air Cond. Eng. 1998,104, 1359–1367. 27. Carrie, F.R. Comparison of Building Preparation Rules for Airtightness Testing in 11 European Countries. In Proceedings of the 35th AIVC Conference Ventilation and Airtightness in Transforming the Building Stock to High Performance, Poznan, Poland, 24–25 September 2014. 28. ATTMA. Measuring Air Permeability of Dwellings. 2010. Available online: https://www.bsria.co.uk/ download/asset/attma-tsl2.pdf (accessed on 17 April 2019). 29. ISO. ISO 18434-1:2008 Condition Monitoring and Diagnostics of Machines—Thermography—Part 1: General Procedures; International Standarisation Office: Geneva, Switzerland, 2008. 30. Alfano, D.F.R.; Dell’Isola, M.; Ficco, G.; Tassini, F. Experimental analysis of air tightness in Mediterranean buildings using the fan pressurization method. Build. Environ. 2012,53, 16–25. [CrossRef] Sustainability 2019,11, 2433 18 of 18 31. Pan, W. Relationships between air-tightness and its influencing factors of post-2006 new-build dwellings in the UK. Build. Environ. 2010,45, 2387–2399. [CrossRef] 32. Sherman, M.H.; Chan, R. Building Airtightness: Research and Practice. In Building Ventilation; Routledge: Berkeley, CA, USA, 2004; pp. 1–46. 33. Sfakianaki, A.; Pavlou, K.; Santamouris, M.; Livada, I.; Assimakopoulos, M.N.; Mantas, P.; Christakopoulos, A. Air tightness measurements of residential houses in Athens, Greece. Build. Environ. 2008 ,43, 398–405. [CrossRef] © 2019 by the authors. Licensee MDPI, Basel, Switzerland. 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