Professor David Johnston

In the UK it has become increasingly recognised that the heat loss from new buildings does not accord with current theoretical practices. One of the reasons for this may be attributed to unaccounted thermal bypass (ZCH, 2010 and Stafford et al., 2012). The lead author (Siddall 2009 and 2011) contended that constructing Passivhaus buildings without dedicating due care and attention to thermal bypass mechanisms could result in building performance failures. This paper reviews the test methodology for coheating, current guidance on thermal bypass, and discusses the results obtained from a small number of coheating tests that have been undertaken on Passivhaus dwellings in the UK. The results of the coheating tests suggest that the Passivhaus standard is capable of closing this performance gap, as long as the designers and builders demonstrate an appreciation of how thermal bypass may impact upon a building. Sections 2-3 of this paper examine some causes of energy performance gaps. Sections 4-5 of this paper are based on experience at Ford Close (Trinick, 2012) and highlights some of the challenges and possible solutions for those wishing to conduct their own tests, particularly with Passivhaus buildings. Section 6 offers the results from a number of Passivhaus coheating tests within the UK.

The Passive House (PH) standard is a voluntary quality assurance standard focused upon maximising the health and wellbeing of occupants, whilst reducing space heating demand to a very low level. To meet the PH standard, well-defined criteria have to be met. However, given literature that suggests a ‘performance gap’ for energy savings, the question remains, how well do PH dwellings perform in situ? This paper presents results from in situ building fabric thermal performance measurements, along with a comparison between the design intent and the measured space heating energy used by over 2000 newly built and retrofitted PH dwellings. The results reveal the in situ thermal performance of the building fabric is close to the design predictions. Within space heating measurements, a standard deviation of up to 50% has to be attributed to the broad spectrum of user behaviour; this is not specific for PH, but a general observation. Despite this, the average values for the PH developments ranged within the uncertainty of the demand calculations. With over 2000 PH dwellings averaging a space heating energy consumption of 14.6 kWh/(m

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The Passivhaus (or Passive House) Standard is one of the world’s most widely known voluntary energy performance standards. For a dwelling to achieve the Standard and be granted Certification, the building fabric requires careful design and detailing, high levels of thermal insulation, building airtightness, close site supervision and careful workmanship. However, achieving Passivhaus Certification is not a guarantee that the thermal performance of the building fabric as designed will actually be achieved in situ. This paper presents the results obtained from measuring the in situ whole building heat loss coefficient (HLC) of a small number of Certified Passivhaus case study dwellings. They are located on different sites and constructed using different technologies in the UK. Despite the small and non-random nature of the dwelling sample, the results obtained from the in situ measurements revealed that the thermal performance of the building fabric, for all of the dwellings, performed very close to the design predictions. This suggests that in terms of the thermal performance of the building fabric, Passivhaus does exactly what it says on the tin.

This paper describes an approach that has been undertaken to improve the airtightness of a number of plasterboard-lined load-bearing masonry dwellings that were constructed in the early 1970s. Such dwellings are likely to be broadly representative of many of the dwellings that will be refurbished in the UK over the next decade or so. The airtightness of the dwellings was improved by undertaking a two-stage programme of general and targeted airtightness work, in parallel with a basic domestic refurbishment programme. The results illustrate that prior to the refurbishment, the dwellings were in a poor state of repair and had an air permeability of between 24 and 26 m3/h per m2 at 50 Pa, which is substantially in excess of the UK mean of 11.5 m3/h per m2 at 50 Pa.1 The condition of the dwellings also suggests that the air permeability of these dwellings is likely to be considerably higher than that which would have been experienced when they were first built. Following the refurbishment programme, it was possible to reduce the air permeability of these dwellings by almost 55%, to a mean of just over 11 m3/h per m2 at 50 Pa. The paper also identifies a number of factors that limited the effectiveness of the airtightness work. These factors included: wear and tear of the plasterboard-lining; detailing and workmanship during the refurbishment programme; and, the partial nature of the refurbishment programme. Had it been possible to address a number of these factors during the refurbishment programme, the authors are reasonably confident that an air permeability of less than 10 m3/h per m2 at 50 Pa could have been achieved in all of the dwellings. Despite the small size of the sample (only 12 dwellings were tested), the results suggest that the airtightness of existing plasterboard-lined load-bearing masonry dwellings can be improved to a level that is comparable to the current UK Building Regulations (Approved Document Part L1) requirement for new dwellings.2

Practical application: Airtightness is crucial to improving the energy performance of buildings. In the UK, existing dwellings tend to be very leaky compared to some of their international counterparts. The use of plasterboard-lining as an internal finish to external and party walls makes a significant contribution to this poor performance, particularly where it is not edge sealed. Air leakage measurements reported here for dwellings built in the 1970s suggest that if this construction is allowed to deteriorate, very high leakage rates may result. Considerations of the impact of choice of construction on future robustness and durability of airtightness of new housing is likely to be an important practicalconsideration, particularly for social housing providers. Separating the air barrier function from the plasterboard lining appears to provide a more reliable and probably more durable solution.3 The paper goes on to describe how injecting expanding polyurethane foam into the cavity between the inner leaf of blockwork and the plasterboard-lining to form continuous ribbons of foam can seal the plasterboard lining and prevent air movement within this cavity. If this approach is undertaken in parallel with a domestic refurbishment programme, the air leakage rate of existing plasterboard-lined masonry cavity dwellings was shown to be reduced to a level comparable with the requirements of the current Part L1 for new dwellings.

An airtight and well insulated thermal envelope is crucial for the development of low energy and low carbon housing. Although this is widely recognized, there is mounting evidence, in housing at least, that the U-values achieved in practice can be much higher than those calculated, and that the gap between the predicted and the actual measured thermal performance of the building envelope can be substantial. This paper describes an approach that can be used in the field to measure the fabric performance of dwellings, a co-heating test. The paper also presents the results from 15 co-heating tests that were undertaken on dwellings that were built to conform to or exceed the insulation requirements contained within Approved Document Part L1A 2006.Whilst the total number of dwellings reported here is small, the results suggest that a significant gap can exist between the predicted steady state heat loss and the measured heat loss, and that this gap can be as much as 125%. This is likely to have significant implications in terms of the energy use and CO2 emissions attributable to these dwellings in-use.

Long term experience with Passive House buildings is illustrated with two early large scale projects, a school and an office building located in Germany. Those were monitored in lump energy performance (school, commissioned 2004) and great detail (office, commissioned 2002) respectively. Moreover, they give an indication of the characteristics of such buildings subject to changes in usage intensity. Both buildings generally performed as expected with the school facing occasional overheating in the summer due to inflexible shading controls. Following an extension in schooling hours the addition of a canteen was required and the ventilation system was adapted to the changed usage. Nevertheless the building’s user comfort and energy performance remain high,despite exceeding the Passive House primary energy target slightly due to increased electricity consumption. The office likewise meets the calculated efficiency in operation. The ground coupled cooling worked well despite greatly increased internal heat gains due to unexpected usage. This extra heat input did not, however, exhaust the geothermal (passive) cooling capacity for the future. Thermal comfort proved near optimal at all times, despite a very simple control regime of the one-circuit concrete core activation system for heating and cooling. In the last section air tightness design and measurement experience in the UK and particularly the question of long-term stability of the airtight building envelope is assessed. It was found that measurement results are not only repeatable in relatively short intervals such as a few months. The data available suggests stability of the airtight envelope over many years. Attention is required as regards the leakage of party walls of terraced buildings which need to be integrated in the overall airtightness concept. A high permeability of party walls in terraced buildings with a common airtight envelope presents a challenge for measuring air tightness. Long-term series of airtightness measurements exist for the Kranichstein House in Darmstadt/Germany and prove the stability of the chosen airtightness concept. Moreover, results for 17 early Passive House buildings in Germany in eight locations and various construction types revisited in 2001 (1.4 to 10 years after the initial airtightness test) suggest stability of air tightness values over time. Great advances have since been made in materials and methods available and the general understanding in the industry. This is supported by a large sample of 2934 Passive House projects of varied construction materials, locations, sizes and usages that yielded an average air tightness test result as low as n50 = 0.41 h-1.

In recent years, measurement protocols for the estimation of the total aggregate building heat transfer coefficient (HTC) have provided sufficient empirical evidence to indicate that buildings often do not perform as intended. However, little research has been carried out into the associated uncertainties. Within this context, this paper reviews sources of uncertainty associated with co-heating tests; characterises these uncertainties and their impact on HTC estimates; and devises a method for the calculation of HTC uncertainty. The method proposed was applied to 14 co-heating tests, showing estimated total uncertainty ranging between 2.2-21.1 Image 1 (or 4.6-26.7% of the measured value) with a mean of 10.1 Image 1 (or 8.7%). The natural variation of HTC and often-observed inaccuracy of design calculations (the ‘prediction gap’) suggest that more accurate measurements may be of little benefit. Additionally, results suggest that weather conditions, challenging building design and poor experimental technique can all significantly contribute to HTC uncertainty. However, when suitable buildings are tested by experienced technicians and under suitable weather conditions, HTC estimates from the co-heating protocol are likely to provide a useful tool to assess and understand real-world building fabric performance.

Purpose of the work The purpose of this work is to present the results of a recent study involving a novel ultrasonic technology used to detect and quantify air leaks in buildings and to assess airtightness and air permeability of building envelopes and the individual components within them. Method of approach The approach was to conduct a number of case studies including lab-based empirical verification, semi-controlled environments, and real-world environments including Passivhaus homes and commercial buildings. The new technology was used alongside a variety of airtightness tests. Content of the contribution Energy and carbon dioxide emission reductions from buildings are central to the UK's net zero climate strategy. One factor that can have a significant impact on energy use and CO emissions 2 attributable to buildings is the airtightness performance of the building fabric. Consequently, high levels of building airtightness are crucial if we are to obtain a low-carbon built environment. This paper evaluates the performance of a novel low-cost ultrasonic technology, the Portascanner® Airtight, through comparative testing with existing methodologies, including Blower Door testing, Pulse testing, and thermography. The study found that the most comprehensive evaluation of airtightness is attained when multiple methods, including the Portascanner® Airtight, are used in conjunction with one another. Notably, the Portascanner® Airtight demonstrated a unique capability in identifying leaks that could be overlooked by other technologies, particularly in scenarios where thermography is limited due to unsuitable thermal conditions. Additionally, the study found that the Portascanner® Airtight's quantification of airflow and air permeability closely aligned with results from pressurisation tests, validating its effectiveness as an instrument for airtightness testing. Results and assessment of their significance It was found that the Portascanner® Airtight was capable of detecting and quantifying smaller leaks than any other existing method, to an accuracy of within plus or minus 10% of the true value. It was also found that the instrument could be used in a greater range of applications. Conclusions The most comprehensive evaluation of airtightness is attained when multiple methods, including the Portascanner® Airtight, are used in conjunction with one another. The new technology is particularly useful as an instrument used during construction or retrofitting, to identify leaks prior to completion.

The aim of this paper is to explore the technological feasibility of achieving CO2 emission reductions in excess of 60% within the UK housing stock by the middle of this century. In order to investigate this issue, the paper describes the development of a selectively disaggregated physically based bottom-up energy and CO2 emission model of the UK housing stock. This model covers both the energy demand and energy supply side and has been used to develop and evaluate three illustrative scenarios for this sector. The results of the scenarios suggest that it may be technically easier, using currently available technology, to achieve CO2 emission reductions in excess of 80% within the UK housing stock by the middle of this century. However, achieving these sorts of reductions will require strategic shifts in both energy supply and demand side technology.

The central purpose of this paper is to develop and test a case for compulsory pressurisation testing for new dwellings. The authors have argued elsewhere in favour of such a policy. The paper reviews the available information on airtightness in the UK housing stock, the impact of airtightness on ventilation and fabric heat losses, the information that is available on the costs of making houses airtight and the logistics of pressurisation testing. The authors use this information to explore the costs and benefits that might accrue at the national level from the introduction of such a policy. While a number of areas of uncertainty are apparent, the analysis shows a modest but apparently robust economic case for the introduction of pressurisation testing of new housing.

The adoption of renewable energy technologies (RETs) into buildings will be key to making the necessary transition to a low-carbon and resilient built environment particularly, in countries such as Nigeria, which suffers from abject energy poverty, despite having diverse and significant renewable energy potential. In Nigeria, commercial buildings present a unique case because a significant proportion of the energy demand for offices is provided by privately powered off-grid fossil-fuel generators instead of RETs, such that generators are designed for in buildings. Given that this undermines achieving a low carbon future, there lacks an in-depth, and context-based empirical study addressing it, therefore, the current implications of the practice of designing for generators and the extent of RET adoption in office buildings are not fully known. The study aims to develop a theoretical framework of the contextual influencing factors to sustainability transitioning practices and processes in commercial buildings, with a focus on solar PV. A qualitative research strategy, guided by Constructivist Grounded Theory method using interviews with 34 multidisciplinary BE professional’s was employed. This led to the development of four interrelated theoretical categories, hostage syndrome’, ‘being sheltered - avoiding responsibility’, ‘following the leader’, and ‘future proofing - reflecting the local perspective’ from which a substantive theory ‘Being part of us’ was constructed. Hostage Syndrome and Being Sheltered – Avoiding Responsibility represent negative influencing factors based on what BE professional’s believe they can do or must do and manifest as ‘‘surrendering and compromising’ and ‘evading’ practices respectively. Following the Leader and Future Proofing - Reflecting the Local Perspective are positive influencing factors based on what BE professional’s believe they are expected to do or should do, and manifest as ‘copying, learning and navigating’ and ‘tailoring to suit and devising anew’ practices respectively. The theory reflects duality and co-existence of elements representing the varied manifestations of sustainability and/or being sustainable within the context of psychological, cultural, social, and historical factors, etc. It offers a framework in which the varied manifestations and their associated practices can be explained, situated, and examined, thereby, providing reliable and relatable points of reference to ground actionable interventions that would aid in the development and promotion of sustainable building strategies and policies suited to its context. The study contributes theoretically, empirically, and practically by providing new and grounded insight and understanding of issues associated with adoption. By implementing the recommendations suggested in the study, it would engender the practice of ‘designing for sustainability’ as opposed to ‘designing for generators’ within the Nigerian context. Furthermore, it will benefit further research within the SSA - and wider developing - context as well as provide valuable lessons with adopting Grounded Theory Method in construction management research for methodological pluralism.

It is estimated that in the UK, 200,000 residents live in park and holiday homes all year round, the majority of which are elderly and on low incomes. As these homes are often thermally inefficient and leaky, these residents are some of the most susceptible in society to fuel poverty. Despite this, there is a dearth of empirical data available on the in situ fabric performance of these homes. This paper presents the results obtained from undertaking a series of pressurisation tests and leakage identification on new build holiday homes. While the sample size reported is small, the results indicate almost a factor of two variation in the airtightness performance of the homes. In spite of this, all of the homes achieved an air permeability significantly lower than the default value incorporated within the industry standard Energy Efficiency Rating Calculator, suggesting that a much lower figure may be more appropriate. The results also suggest that the use of the air permeability metric within the Calculator potentially biases the performance of holiday homes due to their particular form factor, and that this bias could be mitigated against by adopting the air leakage metric within any future revisions to the Calculator.

An airtight and well insulated thermal envelope is crucial for the development of low energy and low carbon housing. Although this is widely recognized, there is mounting evidence, in housing at least, that the U-values achieved in practice can be much higher than those calculated, and that the gap between the predicted and the actual measured thermal performance of the building envelope can be substantial. This paper describes an approach that can be used in the field to measure the fabric performance of dwellings, a co-heating test. The paper also presents the results from 15 co-heating tests that were undertaken on dwellings that were built to conform to or exceed the insulation requirements contained within Approved Document Part L1A 2006. Whilst the total number of dwellings reported here is small, the results suggest that a significant gap can exist between the predicted steady state heat loss and the measured heat loss, and that this gap can be as much as 125%. This is likely to have significant implications in terms of the energy use and CO 2 emissions attributable to these dwellings in-use.

This paper presents the results and key messages that have been obtained from Phase 1 of a participatory action research project that was undertaken with 5 developers to investigate the practical design and construction issues that arise in making improvements to the airtightness of speculatively built mainstream housing. Two construction types were represented in the project, masonry cavity and light steel frame. Phase 1 of the project sought to assess in detail the design, construction and air permeability of 25 dwellings that were constructed to conform to the requirements of Approved Document Part L1 2002. While the total number of dwellings reported here is small, the results suggest that there is not a consistent approach to the way in which developers present information on air leakage to those on site, a mixture of approaches are utilised on site to achieve the same specification and there appears to be a lack of foresight in the detailed design stage, resulting in specifications that are practically very difficult to achieve. Despite this, the air permeability results suggest that dwellings constructed with a wet/mechanically plastered internal finish, can default to a reasonable standard of airtightness by UK standards, without much additional attention being given to airtightness.

This guide gives an introduction to the topics of airtightness and air leakage and discusses the basic principles of airtightness. It also illustrates a number of areas within masonry construction that may contribute to air leakage and identifies ways in which air permeability of less than 5 m3/(h.m2) @ 50Pa could be consistently achieved in typical UK volume housing.

In the UK, a rule of thumb applied to air permeability is commonly employed when estimating background ventilation rates from pressurisation test data. However, this may lead to significant errors in estimating the infiltration rates in UK new-build dwellings, resulting in poor estimation of the dwellings in-use energy and CO2 emissions, and the adoption of ventilation strategies leading to either unacceptable indoor air quality or unnecessary energy consumption. In this paper, a preliminary investigation into the applicability of the rule of thumb is undertaken. Background ventilation rates in four new-build dwellings in the UK are determined using the tracer-gas decay method and also the pressurisation (blower-door) method coupled with both the conventional n50/20 and (in the UK) q50/20 rule of thumb, and Sherman’s modified rule of thumb, which takes into account other building-related factors. The conventional method over-estimated the air-change rate in two of the dwellings and under-estimated it in the other two dwellings. The modified rule of thumb produced comparable results for two of the dwellings, but significantly underestimated the air-change rate in the other two dwellings. These results suggest that more work needs to be done to devise appropriate climate and building-related correction factors for the UK.

There is a growing body of evidence available to indicate that there is often a discrepancy between the in situ measured thermal performance of a building fabric and the steady-state predicted performance of that fabric, even when the building fabric has been modelled based upon what was actually built. However, much of the work that has been published to date does not fully investigate the validity of the assumptions within the model and whether they fully characterise the building. To investigate this issue, a typical pre-1920’s UK house is modelled in Designbuilder in order to recognise and reduce the gap between modelled and measured energy performance. A model was first built to the specifications of a measured survey of the Salford Energy House, a facility which is housed in a climate controlled chamber. Electric coheating tests were performed to calculate the building’s heat transfer coefficient; a difference of 18.5% was demonstrated between the modelled and measured data, indicating a significant ‘prediction gap’. Accurate measurements of air permeability and U-value were made in-situ; these were found to differ considerably from the standard values used in the initial model. The standard values in the model were modified to reflect these in-situ measurements, resulting in a reduction of the performance gap to 2.4%. This suggests that a better alignment between the modelling and measurement research communities could lead to more accurate models and a better understanding of performance gap issues.

This paper describes a novel approach that can be used to construct airtight drylined load-bearing masonry dwellings. This involves the application of a thin layer of ‘parging’ to the internal blockwork leaf of all external walls. Whilst this approach has so far only been undertaken on a field trial using one dwelling, the results suggest that the application of the parging layer improves the airtightness of the dwelling substantially and air leakage rates of less than 5 m3/h per m2at 50 Pa can be achieved. The paper also identifies a number of additional measures which, if undertaken, could reduce the air leakage of this dwelling even further.

Practical application: Airtight construction techniques are increasingly required in order to comply with Part L of the building regulations. Wet plastering is very successful in reducing air leakage through load-bearing masonry construction but is rarely used nowadays because of its longer drying time compared with drylining. The novel approach described in this paper provides the advantages, of both systems by applying a quick-drying airtight barrier before drylining.

Overheating in dwellings is a major consideration affecting buildings in both temperate climates like the UK, as well as in warmer climates. At the same time, it is recognised that the impacts of global warming and climate change are affecting weather patterns in the UK resulting in many changes, including long periods of hot weather in the summer and warmer wetter winters (Lowe et al., UKCP 18 science overview report. Met Office, November 2018 (updated March 2019). In order to reduce global CO2 emissions, fabric improvements are being made to buildings to make them more energy efficient. To achieve these improvements the thermal insulation and airtightness of the building is often improved. The combination of these factors not only serves to retain heat energy during winter heating periods, but it can also result in excessive rises in internal temperatures during the summer, resulting in overheating. This can result in the building occupants’ experiencing discomfort and they may even be exposed to temperatures that pose serious health risks for the most vulnerable in society. In order to provide a safe and healthy environment for occupants, we must provide energy-efficient dwellings that consider not only current but also future climate scenarios. The paper presents the initial findings of a study investigating the risk of overheating in the UK’s first large-scale Passivhaus retrofit

The Passive House (PH) Standard is a voluntary building energy performance standard focused upon reducing space heating demand to a very low level and therefore considered a viable climate change mitigation technology. Besides comfort and energy requirements, the PH standard also defines criteria with respect to ventilation. However, the question remains, how well do PH dwellings perform when they are occupied? Does the PH approach provide good indoor air quality (IAQ) for its occupants and how does IAQ compare to non-PH homes, in particular, naturally ventilated homes? Additionally, can PH certification improve the quality of installed ventilation systems? This paper summarizes indoor air quality relevant aspects of the PH standard and presents results from measurements examining in-use IAQ in more than 600 PH or PH-like, newly built or retrofitted dwellings. The results reveal that pollutant and carbon dioxide concentration are generally lower compared to naturally ventilated homes, presumably due to the requirement to install a balanced Mechanical Ventilation with Heat Recovery (MVHR) system. Results also suggest that the quality assurance measures of PH certification are capable of improving ventilation and IAQ performance. However, the lack of cooking fume capture requirements in the PH standard, in combination with efforts to avoid energy losses associated with a possible extraction kitchen hood, may lead to elevated particulate matter concentration in PHs. Future research on cooking induced IAQ impairment is encouraged to assess the effectiveness of recently published PH-specific recommendations. Future efforts in empirical IAQ research should also address the lack of high quality IAQ measurement data and the standardisation of IAQ assessment methods and protocols.

Within the UK there has been skepticism about whether Passivhaus buildings can offer high standards of comfort and occupant satisfaction. A survey has been undertaken in order to develop a better understanding as to whether or not this skepticism is warranted. The project examined suggests that homes built to the Passivhaus Standard can address many of the concerns that have been raised, however, issues such as overheating risk may require even closer examination during the design process.

Airtightness testing data is increasingly used to inform retrofit design under PAS2035. The processes and experiences of gathering this data offers learning opportunities for residents. Therefore, this paper aims to examine the processes and experiences of airtightness data collection, the data gathered and the value of the data to inform strategies for housing energy retrofit. The perspectives of an engaged resident, who is also a sustainable cities researcher, a building performance expert with over 30 years experience, a qualified thermographer and experienced building pressurisation tester with 20 years experience plus researcher observations are evaluated. Measured air-tightness data are shared (~4 to 8m3.h-1.m-2@ 50Pa), in addition to historical test data, infrared thermography of leakage points and paths, observations of testing processes and experienced perspectives. The contribution is thought on the value of the testing process to inform retrofit, from resident perspectives.

This report constitutes milestone D11 — Final Report — Domestic Sector Airtightness of the Communities and Local Government/ODPM Project reference CI 61/6/16 (BD2429) Airtightness of Buildings — Towards Higher Performance (Borland and Bell, 2003). This report presents the overall conclusions and key messages obtained from the project through design assessments, construction observations, discussions with developers and pressurisation test results. It also summarises discussion on the airtight performance of current UK housing, the implementation and impact of current and future legislation, and identifies potential areas for future work.

Purpose – Challenges to energy access in Nigeria have resulted in the widespread use of fossil fuel generating sets (generators) despite their renewable energy (RE) potential. Given the climate crisis, combined with the country’s rapid population growth and expected rise in energy and building demand, transitioning to low-carbon electricity using REs like solar photovoltaic (PV) presents opportunities beyond securing its energy future. While PV use is growing in Nigeria, this is focused on the residential sector despite the identification of the commercial sector as a high energy consumer and a key platform for its integration. This paper investigates the challenges in transitioning to solar PV in commercial buildings from a building professionals perspective Design/methodology/approach – A qualitative approach in line with grounded theory was adopted using in-depth face-to-face interviews with industry experts. Findings – Two distinct but interrelated categories emerged: being held captive and being a saviour that represented a duality of systems, and/or processes formed the core category ‘Hostage Syndrome’. The core category (theory) was generated based on the explanations and expressions by participants about their concerns, interests, and the conditions under which they operate. The findings reveal the value attributed to generators beyond an operational role and the adjustments or mechanisms adopted by building professionals during their practice. It suggests a sphere of influence beyond the obvious financial and/or institutional aspects, as determining factors to what is viewed as sustainable which will be key to transitioning to REs. Originality/value – This paper provides new and in-depth insight into understanding the conditions under which building professionals operate associated with their interpretations of ‘being sustainable’. The study highlights the need to consider psychological and cultural factors in the development of interventions, strategies, and/or policies to support RE transition, particularly towards achieving a sustainable construction industry.

Sustainability is not new concept; however, it has received increased attention because of the effects of anthropogenic activity in varied sectors of life. The built environment is one of such sectors, which is often criticized for its effects and as evident in literature, sustainability in the built environment is complex in nature. As such, the interpretations associated with it, the significance attributed to it and its adoption, are diverse in every country. Sustainability in the built environment is important, as it promotes energy friendly and efficient systems in buildings, especially in light of global climate change. However, this appears to be lacking in the Nigerian built environment. The paper aims to examine impeding factors to sustainability in the Nigerian built environment through a scoping study review. Nigeria is often described as a paradox in many ways, one of which is having a power deficit and yet abundant renewable energy sources. The paper presents a comprehensive survey of relevant literature on the perceptions of built environment professionals in Nigeria for identification of impeding factors to sustainability adoption. While impeding factors to sustainability in the Nigerian built environment is not new, the identification and understanding of the factors remains restricted and shallow. As such, it lags the required uptake for sustainable buildings reflective in other countries. In addition, a comprehensive survey of impeding factors to sustainability in the Nigerian built environment is lacking in literature, to the best of the researcher’s knowledge. The paper aims to fill this gap through a scoping review, underpinned by Daudt et al.'s (2013) adapted version of Arksey and O ’Malley's (2005) five stage framework. The main findings suggest that the Nigerian context have not been holistically embraced in existing studies, highlighting generalised impeding factors such as finance and awareness as top ranking factors. Furthermore, the review addresses concerns associated with the existing research approach and its shortcomings, as well as strategies for improvement. Further research to expand knowledge is also recommended.

Sustainability in the built environment is a key topic of discussion due to the adverse impact buildings have on the environment. This has propelled many countries to put in place sustainable development measures. This has however, been met with challenges in developing countries, primarily in Sub-Saharan Africa (SSA). SSA has a history of endemic energy crisis, despite its abundance of renewable energy resources. Reflecting this is the heavy reliance on fossil fuels for power generation in SSA countries. The findings reported in this paper form part of a wider study on the perceived barriers to sustainability by built environment professionals in SSA, with specific focus on use of renewable energy source (RES) for power generation in buildings. This paper focuses on the identification of a suitable methodology, which takes into consideration the distinctive characteristics of the SSA context for enquiry through the adoption of a scoping study review. The study addresses the concerns of methodology selection and application by reviewing strategies and methods adopted by past and current enquiry in SSA, which have primarily been aligned with theories, frameworks and research in developed countries. This is of importance due to the impact contextual, subjective and other factors can have on the outcome of enquiry as evidenced by previous research in literature. The purpose of this scoping study review was to provide a comprehensive overview of the available relevant research on barriers to sustainability in SSA, which focused on study designs with empirical evidence, which would aid in informing the selection of a methodology suited for studies specific to the context of SSA. The scoping review is underpinned by the five-stage framework of Arksey and O’Malley (2005). The results indicate that there is a need to view SSA as a distinctive case based on its context and other characteristics, which will influences its research outcomes. Based on the review, it is suggested that grounded theory method is a suitable approach because it will take into consideration the wider context.

In the UK, there are approximately 330,000 holiday homes spread across a large number of mainly privately owned sites. These homes are often sited in exposed locations, are poorly insulated and are generally heated using expensive fuels, such as electricity or LPG. There is also a lack of empirical evidence available on the in situ energy performance of these homes. Consequently, it is not possible, given the existing evidence base, to determine whether these homes suffer from the same scale of building fabric thermal ‘performance gaps’ (between assumed and realised in situ performance) that have been documented for new build UK housing. This paper presents the results obtained from undertaking detailed in situ thermal fabric tests on five new holiday homes. Whilst sample size reported here is small, the results indicate that a ‘performance gap’ exists for all of these homes. Results obtained indicate that this gap appears narrower than that documented for new build UK housing. The results also suggest that the scale of the ‘gap’ may be more a consequence of the way in which the design intent of these homes has been determined, i.e. a ‘prediction gap’.

For domestic buildings to meet current definitions of zero carbon the building fabric and services must achieve 70% reduction in energy use, taking the carbon emissions down to less than 7 Kg CO2/m2. However, there is a significant obstacle to such endeavours. The limited information on the thermal performance of buildings means that the designs are theoretical. Very few models have been tested against the as-built product and where tests have taken place the cyclical process of research and development is taking time to feed back into the design and construction processes. The gaps in our knowledge of building physics are considerable, designs are not robust and buildings are falling short of their expectations. An intensive study of 18 houses was undertaken to examine the design and onsite assembly, comparisons were made between the predicted energy performance and that achieved once the design was built. The heat losses were, on average over 40% worse than predicted. The forensic analysis of the design and construction process revealed that buildings do not perform as designed due to missing or incomplete information, incorrect detailing, ad-hoc adjustments on site, incorrect assembly of materials, poor workmanship and failure to commission buildings and their services properly. From the research, a list of problems has been produced with the aim of avoiding such defects in the future.

In the UK, there is mounting evidence that the measured in situ performance of the building fabric in new build dwellings can be greater than that predicted, resulting in a significant building fabric ‘performance gap’. This paper presents the coheating test results from 25 new build dwellings built to Part L1A 2006 or better. Whilst the total number of dwellings reported here is small, the results suggest that a substantial ‘performance gap’ can exist between the predicted and measured performance of the building fabric, with the measured whole building U-value being just over 1.6 times greater than that predicted. This is likely to have significant implications in terms of the energy use and CO2 emissions attributable to these dwellings in-use.

© 2016 Elsevier B.V. All rights reserved. This paper presents the methodology, along with some of the initial findings and observations from tests performed on two dwellings, of differing construction and form, in which a coheating test was performed using the dwelling's central heating system; this method is referred to as integrated coheating. Data obtained during the integrated coheating tests using a dwelling's heating system have been compared with data obtained during electric coheating of the same dwelling. In one instance, integrated coheating test data from one dwelling was compared to a similar adjoining control dwelling that was simultaneously subject to an electric coheating test. The results show a good agreement between the heat loss coefficients (HLC) obtained using a dwelling's own heating system and those obtained through electrical coheating. Initial analysis suggests the HLC estimate obtained from integrated coheating is likely to be more representative of how a dwelling performs in-use. The findings question the appropriateness of comparing current steady-state HLC predictions to those derived from in-use monitoring data. Integrated coheating has the potential to provide a more cost-effective and informative indication of whole house heat loss than electric coheating, as it enables in situ quantification of both fabric and heating system performance.

The adoption and integration of renewable energy technologies (RETs) into buildings is key to making the necessary transition to low-carbon and resilient built environments. However, such technologies have struggled to gain a firm foothold in countries within the sub-Saharan African (SSA) region. This is particularly the case in Nigeria, which suffers from severe energy poverty, despite its significant RE and conventional energy potential. In Nigeria, a significant proportion of the energy demand for offices is provided by self-powered off-grid fossil-fuel generators. The country is also one of the primary settings for increased construction activity. This, combined with its susceptibility to the effects of climate change, presents significant concerns relating to the resilience of its built environment. However, there has not yet been a comprehensive empirical study addressing this, as previous studies have been limited in their insight and perspectives. This study adopted a grounded theory method (GTM) aligned with Charmaz’s approach, to gain in-depth participant-driven insights into factors influencing sustainable energy use in commercial buildings, focusing on solar photovoltaics (PVs). This led to the development of a theory of the sustainability transition process of construction professionals (CPs). It provides relevant, reliable, and relatable points of reference that would be beneficial to policymakers in developing plans for actionable interventions for PV and broader sustainable measures toward green energy transition. Furthermore, it highlights the value of employing GTMs in construction management research beyond the developing context. This paper contributes theoretically, empirically, and methodologically to facilitate a better understanding of the situations (context) grounded in empirical data.

Written by an experienced team of experts, this new reference work offers the most up-to-date coverage available of building, surveying, and civil engineering terms.

Energy used for space heating accounts for the majority of anthropogenic greenhouse gas emissions from the built environment in the UK. As the fabric performance of new build dwellings improves, as part of the UK’s response to reducing national CO2 emissions, the potential for excessive overheating also increases. This can be particularly pertinent in very airtight low-energy dwellings with high levels of insulation and low overall heat loss, such as Passivhaus dwellings. The work described in this paper uses calibrated dynamic thermal simulation models of an as-built Certified Passivhaus dwelling to evaluate the potential for natural ventilation to avoid excessive summertime overheating. The fabric performance of the Passivhaus model was calibrated against whole dwelling heat loss coefficient measurements derived from coheating tests. Model accuracy was further refined by comparing predicted internal summer temperatures against in-use monitoring data from the actual dwelling. The calibrated model has been used to evaluate the impact that user-controlled natural ventilation can have on regulating internal summer temperatures. Thermal performance has been examined using simulation weather files for existing climatic conditions and for predicted future climate scenarios. The extent of overheating has been quantified using absolute and adaptive comfort metrics, which exceed the relatively restricted measures used for regulatory compliance of dwellings in the UK. The results suggest that extended periods of window opening can help to avoid overheating in this type of low-energy dwelling and that this is true under both existing and future climatic conditions.

Energy used for space heating accounts for the majority of anthropogenic greenhouse gas emissions from the built environment in the UK. As the fabric performance of new build dwellings improves, as part of the UK’s response to reducing national CO2 emissions, the potential for excessive overheating also increases. This can be particularly pertinent in very airtight low-energy dwellings with high levels of insulation and low overall heat loss, such as Passivhaus dwellings. The work described in this paper uses calibrated dynamic thermal simulation models of an as-built Certified Passivhaus dwelling to evaluate the potential for natural ventilation to avoid excessive summertime overheating. The fabric performance of the Passivhaus model was calibrated against whole dwelling heat loss coefficient measurements derived from coheating tests. Model accuracy was further refined by comparing predicted internal summer temperatures against in-use monitoring data from the actual dwelling. The calibrated model has been used to evaluate the impact that user-controlled natural ventilation can have on regulating internal summer temperatures. Thermal performance has been examined using simulation weather files for existing climatic conditions and for predicted future climate scenarios. The extent of overheating has been quantified using absolute and adaptive comfort metrics, which exceed the relatively restricted measures used for regulatory compliance of dwellings in the UK. The results suggest that extended periods of window opening can help to avoid overheating in this type of low-energy dwelling and that this is true under both existing and future climatic conditions.

In the UK, approximately 16% of the energy use can be attributed to domestic wet central heating systems. Government financial support and advances in technology have led to boilers becoming more efficient and a range of technologies are now available that claim to be able to improve the efficiency of domestic wet central heating systems. One such low cost technology is a passive deaerator. This paper presents the results obtained from installing a passive deaerator on the closed loop of a gas-fired wet central heating system, under controlled conditions in the Salford Energy House. The results indicate that although marginally less heat output was required from the boiler when the passive deaerator was operating, these savings are more or less out weighted by the boiler short cycling more frequently. Consequently, the overall reduction is gas consumption achieved by utilising the passive deaerator device is only of the order of 0.5%; this scale of savings may just be a consequence of measurement noise. The implications are that although a marginal benefit may be attributed to these products, if short cycling takes place, then these savings may become insignificant.

It is estimated that around 80% of UK dwellings have uninsulated ground floors, representing a significant heat loss mechanism in these buildings. In this research, an aggregated assessment of dwelling heat loss was made using the electric coheating test before and after a ground floor retrofit took place. Heat loss was reduced by 24% (43 ± 18 W/K) indicating that suspended timber ground floor retrofits could improve thermal comfort for occupants and contribute to government domestic energy efficiency policy targets. The findings indicate that disaggregated evaluation methods, such as spot heat flux density measurements, may overestimate the benefits of fabric retrofits. Aggregate methods may therefore be more appropriate tools with which to evaluate retrofits. The U-value improvement resulting from the suspended timber ground floor insulation retrofit, derived via aggregate measurement, was 0.55 W/m²K. Disaggregated spot heat flux density measurements indicated the improvement was 0.89 W/m2K. This research also indicates that Energy Performance Certificates, are unlikely to provide a reliable estimate of energy savings, because they rely on default assumptions for fabric U-Values and ventilation rates. This has implications for policy evaluations as well as householders, who may be excluded from financial support for retrofits.

The UK Building Regulations sets a maximum airtightness value of 8 m³/m²/h @ 50 Pa for new dwellings, and this is due to be reduced to 5 m³/m²/h @ 50 Pa or less in 2025, when the Future Homes and Buildings Standard is introduced. Compliance with these airtightness requirements must be demonstrated via the fan pressurisation test or more recently the low-pressure pulse test, as set out in CIBSE TM23:2022. Although there is no such maximum airtightness requirement when refurbishing existing dwellings, both test methods are being used to inform retrofit processes. As existing dwellings tend to have more varied and complex air leakage pathways than new build homes, this can pose challenges for the testing methods. However, there is a lack of independent empirical data available which compares high- and low-pressure airtightness test methods in existing dwellings with different airtightness characteristics. This paper presents 88 side-by-side fan pressurisation and low-pressure pulse airtightness measurements undertaken in a range existing dwellings of differing age, size, form and construction type. The results illustrate that there is 2% difference in mean airtightness reported for each test method across the sample, however, the results for individual homes can vary between -84% and 67%. The implications are that there is a need for more investigations into the relationship between high- and low-pressure test methods to ensure they can both be used with confidence to support retrofit processes.

In the UK, it has become apparent in recent years that there is often a discrepancy between the steady-state predicted and the measured in situ thermal performance of the building fabric, with the measured in situ performance being greater than that predicted. This discrepancy or gap in the thermal performance of the building fabric is commonly referred to as the building fabric 'performance gap'. This paper presents the results and key messages obtained from undertaking a whole-building heat loss test (a coheating test) on seven new-build dwellings as part of the Technology Strategy Board's Building Performance Evaluation Programme. While the total number of dwellings involved in the work reported here is small, the results illustrate that a wide range of discrepancies in thermal performance was measured for the tested dwellings. Despite this, the results also indicate that it is possible to construct dwellings where the building fabric performs thermally more or less as predicted, thus effectively bridging the traditional building fabric performance gap that exists in mainstream housing in the UK.

It is recognized that there is often a discrepancy between the measured fabric thermal performance of dwellings as built and the predicted performance of the same dwellings and that the magnitude of this difference in performance can be quite large. This paper presents the results of a number of in-depth building fabric thermal performance tests undertaken on three case study dwellings located on two separate Passivhaus developments in the UK: one masonry cavity and the other two timber-frame. The results from the tests revealed that all the case study dwellings performed very close to that predicted. This is in contrast with other work that has been undertaken regarding the performance of the building fabric, which indicates that a very wide range of performance exists in new-build dwellings in the UK, and that the difference between the measured and predicted fabric performance can be greater than 100%. Despite the small non-random size of the sample, the results suggest that careful design coupled with the implementation of appropriate quality control systems, such as those required to attain Passivhaus Certification, may be conducive to delivering dwellings that begin to ‘bridge the gap’ between measured and predicted fabric performance.

Global concern around energy use and anthropogenic climate change have resulted in an increased effort to reduce the energy demand and CO2 emissions attributable to buildings. This has led to the development of a number of low energy building standards, one of which is the internationally recognised Passivhaus Standard. The Passivhaus Standard aims to reduce the space heating energy demand of a building by adopting a ‘fabric first’ approach, thus ensuring the thermal envelope is highly insulated and airtight whilst also maximising passive solar heat gains. However, adopting such an approach does present a risk of overheating; a situation that is of particular concern when the occupants have additional healthcare requirements. This study uses 21 months of in-use monitored data to consider the overheating risk in a UK Passivhaus dwelling with vulnerable occupants using both static and adaptive thermal comfort assessment methods. The analysis of the data suggests the occurrence of substantial overheating according to PHPP, CIBSE Guide A and CIBSE TM52 criteria. The analysis was then expanded to consider a novel composite method to overcome the limitations of existing approaches, allowing overheating to be assessed during non-typical periods i.e. the heating season. This revealed apparent overheating during colder months, in addition to substantial night-time overheating. This has implications for the thermal comfort assessment of low energy dwellings and the design and operation of Passivhaus buildings, particularly those with vulnerable occupants.

From the limited information that exists on the thermal performance of dwellings there is growing evidence of a significant gap between that which is predicted and the built product. Such differences between the intended and actual measured performance are not accepted nor tolerated in other industries. The differences in the performance can be considerable, with some buildings experiencing deviation from designed thermal transmittance resulting in twice the heat loss expected. This does not bode well for the industry when new dwellings are expected to achieve zero carbon standards by 2016. Although some of the problems are related to inadequate design, many are attributable to construction processes. Using the technical reports and feedback from researchers engaged in forensic investigations of building performance, this paper presents some general observations and some re-occurring problems associated with the management of the construction process. Specific areas of concern include the interface between design and construction, sequencing and planning of works, quality of workmanship and build, and lack of quality control systems. Due to current environmental and energy concerns, emphasis has been placed on improving the efficiency of the building system to ensure the gains expected are delivered. Much of this relies on the production of quality building fabrics that provide passive solutions, which maintain thermal comfort and reduce the level of service intervention.

With the built environment being one of the largest contributors to anthropogenic emissions, it is essential that building energy demand is controlled, cleaner energy sourced and emissions reduced. However, aligning demand with supply is challenging, as building performance is variable and largely unknown. Central to understanding energy demand is the ability to quantify the energy required to comfortably condition a building and the role that the building envelope plays in effectively enclosing the space. Unfortunately, relatively little is known about building fabric features and how different aspects affect performance under real conditions. Of serious concern and a factor that impacts greatly on control, is the degree that a building’s fabric performance differs from that which is expected. Many buildings do not offer the thermal resistance required to meet their design intent. Where variations in fabric thermal performance are significant this will prove a barrier to the effective use of energy and affect the control of buildings. For effective control, the building demand under different environmental conditions should be relatively stable. The building behaviour and response must be a known quantity. This paper explores air tightness studies in existing and retrofit properties, demonstrating how some buildings have the capacity to be stripped of all conditioned air, while others prove more airtight. Furthermore, results of whole building heat loss tests on new buildings are presented showing the variance in heat loss coefficient, an established indicator of difference in designed v’s as-built performance. The work also demonstrates that energy efficient, thermally resistant, building enclosures can be built within acceptable tolerance; such fabric solutions being key to the nearly zero energy buildings required. The results provide an important step in understanding what is required to achieve the control necessary to move towards energy flexible and efficient buildings.

The methodology used for measuring the thermal performance of fabric retrofit systems which were applied to a solid wall UK Victorian house situated within an environmental chamber is explored in detail. The work describes how steady-state boundary conditions were approximated, then repeated at the Salford Energy House test facility. How established methods of measuring the fabric thermal performance of buildings in situ were adapted to test the effectiveness of retrofit measures within a steady-state environment. The results presented show that steady-state boundary conditions enable the change in fabric heat loss resulting from the retrofit of a whole house or individual element to be measured to a level of accuracy and precision that is unlikely to be achieved in the field. The test environment enabled identification of heat loss phenomena difficult to detect in the field. However, undertaking tests in an environment devoid of wind underestimates the potential reduction in ventilation heat loss resulting from an improvement in airtightness, and hides the susceptibility of retrofit measures to various heat loss mechanisms, such as wind washing. The strengths and weaknesses of the methods employed, the Energy House test facility, and a steady-state environment, for characterising retrofit building fabric thermal performance are demonstrated.

There remains a significant number of occupied and uninsulated solid wall dwellings in the UK. Deep retrofit is often required for these buildings to become energy efficient but it is difficult to determine how these buildings will respond to retrofit without a detailed understanding of their fabric thermal performance Greater certainty can however be achieved by combining theoretical models and practical field tests, prior to the design of retrofit programmes. This type of approach can then be used to inform and optimize the design of retrofit interventions. This paper presents results from a series of in situ fabric performance tests undertaken on two no-fines concrete, conjoined dwellings pre- and post-retrofit and demonstrates how empirical data can be used to inform and calibrate the thermal performance of dynamic simulation models (DSMs). This is a particularly pragmatic calibration method as it eliminates the need for actual weather data, which is expensive and prohibitive to collect and collate. The DSM inputs and outputs were compared with those obtained from Standard Assessment Procedure (SAP) calculations. The results illustrate how the fabric performance of no-fines concrete can vary between similar house types within the same development. This research also validates the effectiveness of the calibration methodology that uses the whole house Heat Transfer Coefficient (HTC) as the qualifying metric. Furthermore, results also emphasize the importance of appropriately characterizing the physical properties of existing buildings before designing retrofit strategies. This paper contributes to the growing knowledge base concerned with the energy performance gap. In this instance, SAP predicts higher absolute savings then measured in situ which is problematic when assessing the financial viability of retrofits.

The energy performance of buildings and the ability to accurately predict energy demand is of global importance. As the relative cost and environmental impact of harnessing energy increases so does our need for energy efficiency. Designing, constructing and retrofitting buildings to be more energy efficient requires a thorough understanding of the way each building behaves and responds to its climatic variations. Although the measurement of a building’s energy consumption is straightforward, understanding why consumption differs from that expected requires a detailed and systematic building performance analysis. The way a building is assembled and retrofitted affects performance, thus each aspect of a building’s makeup should be measured or monitored to understand its behaviour. When attempting to understand the performance of a building it is important to consider each element, the components used and the way that they interface to perform as a whole. The measurement of building components in the laboratory is relatively well documented but the testing and measuring of buildings once constructed in the field is an emerging science. This chapter presents the methods used to survey, measure and monitor building performance in the field and how the work is being used to inform the next generation of energy efficient buildings.

Purpose: The coheating test is the standard method of measuring the heat loss coefficient of a building, but to be useful the test requires careful and thoughtful execution. Testing should take place in the context of additional investigations in order to achieve a good understanding of the building and a qualitative and (if possible) quantitative understanding of the reasons for any performance shortfall. The paper aims to discuss these issues. Design/methodology/approach: Leeds Metropolitan University has more than 20 years of experience in coheating testing. This experience is drawn upon to discuss practical factors which can affect the outcome, together with supporting tests and investigations which are often necessary in order to fully understand the results. Findings: If testing is approached using coheating as part of a suite of investigations, a much deeper understanding of the test building results. In some cases it is possible to identify and quantify the contributions of different factors which result in an overall performance shortfall. Practical implications: Although it is not practicable to use a fully investigative approach for large scale routine quality assurance, it is extremely useful for purposes such as validating other testing procedures, in-depth study of prototypes or detailed investigations where problems are known to exist. Social implications: Successful building performance testing is a vital tool to achieve energy saving targets. Originality/value: The approach discussed clarifies some of the technical pitfalls which may be encountered in the execution of coheating tests and points to ways in which the maximum value can be extracted from the test period, leading to a meaningful analysis of the building's overall thermal performance.

The whole-life sustainability of a building should be underpinned with a demonstration of functional value and an awareness of the direct environmental impact. While a great deal of energy and resources are consumed in the construction of buildings, this is marginal when compared to the operation costs and associated energy used during a building's life cycle. Many reports identify the build costs and associated resources to be less than 1 % of the whole-life operation costs. The exact energy use of a building can vary widely, depending on the use, energy efficiency of the building and occupant behaviour; thus, a greater deal of attention should be given to understanding the energy used in buildings and how energy efficient operation is achieved.

To meet targets on fuel poverty, energy efficiency and carbon emissions existing homes need to be more energy efficient. We report the results of a participatory action research project to explore the challenges associated with energy efficiency retrofit programmes and ways to better implement future schemes. Six focus groups were held with 48 participants from a range of energy efficiency roles. Data were analysed thematically using the research question “What are the challenges presented by implementing energy efficiency retrofit programmes”. We identified four themes in the data: Funding mechanisms; Predicting performance; Installation; and People. Challenges include funding mechanisms for retrofit programmes resulting in insufficient time to plan, publicise, implement and evaluate a scheme and insufficient flexibility to specify the most appropriate intervention for individual homes. Site workers sometimes need to adapt retrofit designs because of insufficient detail from the designer and can equate quality of installation with quality of finish. Landlords and occupier behaviour can impact on the programme's success and there is a need for greater information on benefits for landlords and for energy behaviour change interventions run alongside retrofit programmes for occupiers. There is a need for outcome evaluations of retrofit schemes with the results shared with stakeholders.

Leeds was designated a core city for trialling the Government’s Green Deal domestic energy efficiency policy. Leeds Beckett University undertook a monitoring and testing program on 65 dwellings to investigate the effectiveness of the insulation measures installed and to understand any underperformance. This report outlines the findings from a series of investigations including; surveys, air tightness tests, co heating tests, in situ U-value tests, hygrothermal and thermal bridging modelling, in use monitoring and occupant interviews. The surveys revealed that the ‘whole house approach’ to retrofit was, more often, missing, and quality assurance around insulation detailing was regularly absent, leading to avoidable errors and potentially embedding problems in the installations. Furthermore, moisture issues were, in the majority of instances, over-looked or made worse despite over half the sample having some form of damp. Despite this, energy savings were observed and the appearance of the dwellings were improved, thus apparent satisfaction was generally high, even though the installs were imperfect and moisture problems were introduced. Hygrothermal modelling of IWI cases suggests that thermal bridging at party walls can increase by more than 60% and that there could be potential for rot to embedded timbers. Insulation was recorded to reduce background ventilation of the dwellings by around 25% (a factor unaccounted for in government energy models), although some dwellings were still left with air tightness levels worse than modern day UK Building Regulations limits and replacing wet plaster with IWI was seen to undermine the performance of the insulation. The heat loss coefficient of three homes were tested and showed improvements of 25% and 56% for full retrofits with IWI, and 8% for a party wall retrofit; ¾ of these savings were achieved by fabric improvements and the final quarter from incidentally making dwellings more air tight. The before and after in use monitoring suggested the average savings in energy consumption from all retrofit types (EWI, IWI or other) were between 20% and 29%, although small sampling periods limits the certainty of the results. More reliably it was observed that comfort conditions improved; before the retrofit, 14 of the homes were experiencing discomfort from cold; the retrofit brought on average 2 /3 of uncomfortable homes into more reasonable comfort bands. Nearly all of the occupants had positive experiences, although no householders had to pay for the retrofit, reporting being warmer, bringing unused rooms back into operation and feeling more pride in their homes and communities. A variety of perceptions and behaviours were observed around set point temperatures, use of heating controls and motivations for using energy, all of which contribute to make a complex policy landscape. There is huge potential for domestic retrofit and although this research suggests the current

Thermal performance is often assumed to be constant over the service life of insulation. The aim of this project was to establish the existing evidence on the impact of retrofit degradation over time, and what it means for insulation performance. This report summarises current understanding, classifying key mechanisms for degradation and makes recommendations for how to address identified knowledge gaps.