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The purpose of this paper is to investigate the distribution of dwelling airtightness test results for a developer, between 2007 and 2011. The changes in airtightness test results over time are discussed, and links between the airtightness test results and the construction technique are investigated.

A data set of airtightness test results was statistically analysed by applying probabilistic model of the distribution and using Bayesian parameter estimation techniques.

The inferred background distributions, those estimated to describe dwelling performance before secondary sealing, suggest an improvement in airtightness between 2008 and 2011, the mode decreases from 5.46±0.09 m³/m²h to 4.12±0.07 m³/m²h with a corresponding shift in practice towards a more target-driven approach. The most airtight dwellings are constructed from reinforced concrete frame, followed by “traditional” (dry lined masonry), timber frame and lightweight steel frame.

This study is limited by the size of the available data set (901 dwellings), and by the fact that the data set contains a larger proportion of flats to houses; however, the metadata has enabled the exploration of the link between construction practices and airtightness.

Developers need better guidance surrounding how to meet more stringent airtightness requirements through improvements to the primary air barrier, with incentives and support to deliver changes in practice. Furthermore, if a large number of dwellings undergo secondary sealing, this may have implications for the long-term efficiency of the dwelling stock.

This analysis investigates two issues that have not previously been studied on a significant number of dwellings: the changes to the distribution of airtightness results over time and the link between construction methods and airtightness.

Compulsory airtightness testing was introduced for new dwellings in England and Wales in 2006 and in Scotland in 2010 to ensure that they are constructed according to design air permeability targets. These targets are set to limit heat loss through air infiltration. Previous work examining the large Air Tightness Testing and Measurement Association (ATTMA) data set of UK airtightness test data suggested that, in a proportion of dwellings, the targets were being met by post-completion sealing as opposed to airtight construction, but did not quantify the prevalence of this practice. The paper aims to discuss this issue.

In this paper, the distribution of as-built airtightness and the proportion of dwellings undergoing post-completion sealing are estimated from the ATTMA data set covering 2015–2016. This is carried out by Bayesian statistical modelling, using the data set of recorded test results and a modelled representation of the testing process.

This analysis finds the mode of the as-built distribution of air permeability as 4.38 ± 0.01 m³/m²h. It predicts that 39 per cent of dwellings aiming for one of the five most common design targets have sealing interventions at the point of pressure testing to meet their target. The as-built distribution of the ATTMA data is compared to airtightness test data obtained from just before compulsory testing was introduced, showing an improvement in the modal air permeability of 3.6 m³/m²h since testing became mandatory.

This paper has investigated the available data beyond simply what is reported, to estimate what the real levels of airtightness in the UK new build stock may be.

Mechanical ventilation with heat recovery (MVHR) is increasingly being promoted in the UK as a means of reducing the CO₂ emissions from dwellings, and installers report growing activity in the retrofit market. However, the airtightness of a dwelling is a crucially important factor governing the achievement of CO₂ reductions, and the purpose of this paper is to understand the technical implications of airtightness levels in an experimental dwelling, purpose built to typical 1930s standards, at the same time as gaining the users’ perspectives on airtightness and ventilation in their homes.

In‐depth interviews were carried out with 20 households to collect information on their retrofit and improvement strategies, attitudes to energy saving and their living practices as they impinge on ventilation. The experimental house was sealed in a series of interventions, leading to successive reductions in the air permeability as measured by a 50 Pa pressurisation test. The behaviour of a whole‐house MVHR system installed in the experimental house, was simulated using IES Virtual Environment, using a range of air permeability values corresponding to those achieved in the retrofit upgrading process.

In the house considered, air permeability must be reduced below 5 m³/m²h for MVHR to make an overall energy and CO₂ saving. However, to achieve this required a level of disruption that, on the basis of the views expressed, would be unlikely to be tolerated by owners of solid wall dwellings.

The paper is the first to combine results from a user‐centred approach to exploring the existing practices of householders with a simulation of the energy and CO₂ performance at different levels of airtightness of an experimental house in which MVHR has been installed.

If the building control system is to deliver housing which achieves major reductions in carbon dioxide emissions, it is important to ensure not only that energy efficiency standards are set at an appropriate level but also that the specification of standards takes into account realised performance. It is argued in this paper that, in many cases, there is a large gap between notional performance, as defined by the calculation methods embodied in the Building Regulations, and performance achieved in practice. Although it is accepted that some variation in performance is to be expected, there are a number of areas where closer attention to the methods used to estimate thermal performance, and the inclusion of hitherto unregulated aspects, could help to achieve a much closer match between what is expected and what is achieved. In particular, the paper discusses ways in which the Regulations could be improved so that the impact of thermal bridging, construction quality, window performance and airtightness are more closely controlled.

New Zealand’s historical housing stock comprises largely single-storey detached houses, characterised by poor winter comfort with high air infiltration. Challenges with affordability and land use are shifting New Zealand’s housing stock towards double-storey, conjoined medium-density housing (MDH). Reduced external surfaces in this typology should reduce winter heat loss and infiltration, improving winter comfort and health. New concerns arise, however, regarding summertime overheating and poor indoor air quality.

A field study was undertaken where temperature, humidity, airtightness, particulate matter (PM) and total volatile organic compounds (TVOC) were measured in two unoccupied, newly built double-storey, conjoined houses, for several weeks over summer.

The reduced surface area of this typology did not reduce infiltration and demonstrated significant periods of overheating. Internal PM concentrations generally exceeded outdoor concentrations but did not exceed annual average outdoor PM10 guidelines of 20 µg m-3. Infiltration factors (Finf) were closer to more traditional houses. TVOC readings varied widely, but frequently exceeded international guidelines.

The small sample limits the applications of conclusions more widely. Recommendations to investigate a wider sample in different locations with more detailed VOC analysis over all seasons are made.

Improvements to internal environments cannot be guaranteed by housing typology changes alone and must still involve thoughtful environmental design.

Housing typology changes may not improve internal living environments.

A move to the new MDH typology may not achieve expectations of airtightness and thermal improvement. New challenges arise from significant overheating and high TVOC levels, which may lead to new negative health effects.

Exposure to poor indoor air in refurbished buildings is a matter of health concern due to the growing concentrations of various contaminants as a result of building airtightness without amendment of ventilation, or the use of building materials such as glue, paint, thinner and varnishes. Recent studies have been conducted to measure indoor air pollutants and assess the health risks affecting the quality of life, productivity and well-being of human beings. However, limited review studies have been recently conducted to provide an overview of the state of knowledge. This study aims to conduct a scoping review of indoor air quality (IAQ) in the context of refurbished or energy-retrofitted buildings.

A systematic screening process based on the PRISMA protocol was followed to extract relevant articles. Web of Science, Scopus, Google Scholar and PubMed were searched using customised search formulas. Among 276 potentially relevant records, 38 studies were included in the final review covering a period from 2015 to 2022.

Researchers mapped out the measured compounds in the selected studies and found that carbon dioxide (CO₂) (11%) and total volatile organic compounds (11%) were among the most commonly measured contaminants. Two trends of research were found including (1) the impact of ventilative properties on IAQ and (2) the impact of introducing building materials on IAQ.

The contribution of this study lies in summarising evidence on IAQ measurements in refurbished buildings, discussing recent advancements, revealing significant gaps and limitations, identifying the trends of research and drawing conclusions regarding future research directions on the topic.

The energy retrofit of the existing building stock, and specifically the thermal upgrading of the buildings’ envelopes, has been identified as a key action for both the decarbonisation of the built environment and the reduction in fuel poverty. When considering the energy retrofit of heritage buildings it is, however, important to recognise both the technical issues that this entails and the potential impact on their cultural value and the emotional responses to it. The purpose of this paper is to focus on the thermal upgrading of historic timber-framed buildings in the UK.

The paper begins by exploring the cultural significance of this form of building construction, before examining three case studies using both quantitative and qualitative methodologies.

The results show that whilst the application of energy retrofit actions to this emblematic typology may have limited success, the emotional connection of the buildings’ occupants often results in the work resulting in higher user satisfaction than would otherwise be expected.

Although limited in number, the three case studies provide an insight into the complex issues surrounding the low energy retrofit of historic timber-framed buildings. Further research into this area is encouraged.

The paper contains the monitoring of specific retrofit details, the results of which should inform future projects.

The review of the cultural significance of historic timber-frame buildings in the UK underlines the importance of the conservation and continuing survival of these buildings.

Previous heritage retrofit research in the UK has focussed on solid wall construction with little investigation into the issues surrounding the retrofit of historic timber-frame buildings. This paper explores this previously under-researched area. Additionally, this paper begins to explore the possible links between occupants’ emotional connection to historic buildings and their perceived levels of comfort.

From the 2000s onward, construction practices of urban residential buildings in China have shown a material transformation from clay brick to aerated concrete block. Moreover, the consumption of insulating materials for buildings has been increasing due to the new requirements in building energy-saving standards. This transformation and the increased consumption of insulating materials might have a vital impact on a building’s thermal comfort and its associated energy flows. Therefore, the purpose of this paper is to investigate the indoor thermal performance of urban residential buildings built with different materials and further discuss the correlations between indoor thermal comfort and the associated energy input.

This study investigated four residential buildings selected from four residential communities located in the cold climate zone of China. The Integrated Environment Solutions program was used to evaluate the thermal comfort levels and to quantify the operational energy consumption of the case study buildings. Additionally, the University of Bath’s Inventory of Carbon and Energy database was used to estimate the embodied energy consumption and CO₂ emissions.

The study found that materials transition and increasing consumption did not necessarily improve indoor thermal comfort. However, the materials transition has significantly decreased the embodied energy consumption of urban residential buildings. Furthermore, the increased utilization of insulating materials has also decreased the heating and cooling energy consumption. Therefore, overall, the environmental impacts of urban residential buildings have been reduced significantly.

In the future, residential buildings completed in the 1990s will need regular maintenance, such as adding insulation. Residential buildings completed based on the latest energy-saving requirements should optimize their ventilation design, for example, by increasing the ventilation rate and by reducing solar heat gains in the summer.

This paper investigates the effects of the materials change on thermal comfort levels and the environmental impacts of urban residential buildings in the cold climate zone of China, as these have not been the focus of many previous studies.

Concern of the deterioration of indoor environmental quality as a result of energy efficient building design strategies is growing. Apprehensions of the effect of airtight, super insulated envelopes, the reduction of infiltration, and the reliance on mechanical systems to provide adequate ventilation (air supply) is promoting emerging new research in this field. The purpose of this paper is to present the results of an indoor air quality (IAQ) and thermal comfort investigation in UK energy efficient homes, through a case study investigation.

The case study dwellings consisted of a row of six new-build homes which utilize mechanical ventilation with heat recovery (MVHR) systems, are built to an average airtightness of 2m3/m2/hr at 50 Pascal’s, and constructed without a central heating system. Physical IAQ measurements and occupant interviews were conducted during the summer and winter months over a 24-hour period, to gain information on occupant activities, perception of the interior environment, building-related health and building use.

The results suggest inadequate IAQ and perceived thermal comfort, insufficient use of purge ventilation, presence of fungal growth, significant variances in heating patterns, occurrence of sick building syndrome symptoms and issues with the MVHR system.

The findings will provide relevant data on the applicability of airtight, mechanically ventilated homes in a UK climate, with particular reference to IAQ.

IAQ data of this nature is essentially lacking, particularly in the UK context. The findings will aid the development of effective sustainable design strategies that are appropriate to localized climatic conditions and sensitive to the health of building occupants.

In this final paper in the series we set out the energy efficiency standards which should be pursued over the next five to ten years. Compared with a business as usual scenario based on past improvements, our proposed standards could go a long way to nullify the increase in carbon dioxide emissions which would be expected from the projected increase in the size of the housing stock in the next 20 years (an increase of some 4 million by 2021). Such an approach would provide an important breathing space so as to allow the development of even higher new build standards and to allow improvements in the efficiency of the existing stock. In addition to establishing an improvement programme for 2000/1 and 2005/6 the paper also assesses a number of important implementation issues. It deals with the barriers of practicability, technical risk and cost and concludes that such barriers are largely perceptual. We argue that with the establishment of very clear goals and implementation programmes, the Government together with the house building industry could achieve significantly higher standards than current regulations without major upheaval and, in the process, take a very large step towards the overall goal of creating a truly sustainable housing stock.