Professor David Glew

One of the primary roles of buildings is to provide a comfortable environment for occupants. Building designers and operators strive to provide thermal comfort; however, methods of evaluating thermal comfort are criticised when predictions do not reflect reality. This is especially true for sport and recreation buildings, which presents a problem for society since their continued use is essential for maintaining active lifestyles and contributing to health and wellbeing. If occupants are uncomfortable in these buildings, they may cease to use them. This thesis addresses this problem, presenting research designed to improve the measurement, evaluation and understanding of thermal comfort and its application in sport facilities. Environmental, personal and subjective data were measured against different activities in two case study multi-purpose sports halls (MPSHs). The work was undertaken to challenge the accuracy of conventional thermal comfort prediction methods and to consider how comfort perspectives of individuals engaged in different activities can inform comfort predictions. The study found the principal index used to predict thermal comfort, the Predicted Mean Vote (PMV), was a poor predictor of thermal comfort in MPSHs. Following this, modifications were made to the PMV calculation including; 1) incorporating metabolic rate (MET) reference data from the Compendium of Physical Activities, 2) removing the MET upper limit, 3) incorporating multiple MET values for varying activity phases, and finally 4) weighting MET values for different activity phases, resulting in improved predictions. Despite improvements, uncertainty in PMV persisted. To address this, an alternative comfort evaluation method was developed. Remote collection of environmental and subjective data allowed the development of a simple empirical index that successfully identified a ‘comfort zone’ for MPSH occupants. Furthermore, the results suggested that MPSH occupants enjoyed feeling warm, considering this a natural consequence of exercise and challenging conventional consensus around discomfort. However, this did not translate into demanding warmer buildings, with dissatisfaction increased where internal temperatures exceeded 20°C. This research challenges existing thermal comfort perceptions, provides enhancements to established prediction methods and presents an alternative comfort evaluation approach to improve the quality of thermal comfort research in sport facilities and beyond.

Internal Wall Insulation (IWI) retrofits reduce heat loss from homes, increase comfort and reduce fuel bills, however, they can result in unintended consequences. This paper uses thermal modelling to show that if only one side of a party wall is fitted with IWI, the surface temperature of the uninsulated side will reduce, and its risk of mould growth and surface condensation increases. This has potential implications for works under the Party Wall etc. Act 1996 that is applicable in England and Wales, and the room by room approaches to IWI retrofits.

Energy Performance Certificates (EPCs) are the adopted method by which the UK government tracks the progress of its domestic energy efficiency policies. Over 15 million EPCs have been lodged, representing a valuable resource for research into the UK building stock. However, the EPC record has a reputation of containing multiple errors. In this work, we identify many such errors and quantify how common they are. We find that 27% of EPCs in the open EPC record display at least one flag to suggests it is incorrect and estimate the true error rate of the EPC record to be between 36 and 62%. Many of these errors are caused by EPC assessors disagreeing on building parameters such as floor type, wall type and built form. Additionally, flats and maisonettes appear to cause more issues than other property types. This may be due to difficulties in assessing their location in the building and the nature of the surrounding space. We also suggest potential new methods of quality assurance which rely on machine learning and which could allow such errors to be avoided in the future.

Thermal retrofits of homes are central to the UK's fuel poverty and net zero carbon policies but there are concerns about poor quality installation and so new standards are to be introduced (PAS2035). We have explored retrofit installers' perceptions of the barriers to installing internal wall insulation (IWI) and of current regulations and standards for retrofits. We conducted four focus groups with retrofit installers. Thematic analysis identified three themes. (1) IWI is viewed as impractical in situations other than new builds, extensions and conversions as it is too time-consuming and expensive. (2) Installing IWI is perceived as an unskilled job with no need for training or referring to standards during installation. (3) Because standards lack credibility, installers can be sceptical of potential problems caused by on-site installation adaptations, for example thermal bridging. Our results show that retrofit standards have not improved retrofit quality. Awareness and credibility of standards is low, and new standards (PAS2035) will introduce additional costs which may reduce the pool of installers willing to engage in the retrofit market. Policies need to address installer training, professional identity and social practices, and reduce barriers to change in order to increase success.

The Climate Change Act committed the UK to reduce GHG emissions by at least 80 percent in 2050. This ambitious target requires millions of homes to be retrofitted and, in response, the Government has implemented multiple retrofit policies and funding mechanisms, including supplier obligations. This study reviews retrofit policies and compares the objectives and the carbon/energy savings achieved. The review focuses specifically on the 4 iterations of the supplier obligations that have been implemented since 1994. It finds that the supplier obligations have had similar objectives and followed similar trends in the retrofit measures installed. The study further identified the benefits and challenges of the Suppliers' Obligations. The paper concludes by discussing lessons learned for the design of future policies and implementation strategies to improve the energy efficiency of homes in the UK to achieve net zero by 2050.

Insulating below suspended timber ground floors affects heat transfer at the ground floor to external wall junction, which can affect the risk of surface condensation occurring. In this project, we investigate the impact of installing mineral wool insulation, between joists, below suspended timber floors in 3 solid walled homes. TRSICO is used to calculate surface temperature factors at this junction pre- and post- retrofit. Alternative retrofit scenarios of different combinations of suspended floor and solid wall insulation are also modelled to determine which minimises condensation risk. The results suggest the floor and wall junction will have surface condensation risk when uninsulated. Installing suspended floor insulation increases risk, while installing internal or external wall insulation, with or without floor insulation, reduces risk.

A substantial number of dwellings in the UK have poor building fabric, leading to higher carbon emissions, fuel expenses, and the risk of cold homes. To tackle these challenges, domestic energy efficiency policies are being implemented. One effective approach is the use of energy models, which enable sensitivity analysis to provide valuable insights for policymakers. This study employed dynamic thermal simulation models for 32 housing archetypes representative of solid-walled homes in the UK to calculate the heat loss and the sensitivity coefficient per building fabric feature, after which a metric Heat Loss Sensitivity (HLS) index was established to guide the selection of retrofit features for each archetype. The building fabric features’ inputs were then adjusted to establish both lower and upper bounds, simulating low and high performance levels, to predict the how space heating energy demand varies. The analysis was extended by replicating the process with various scenarios considering climates, window-to-wall ratios, and overshadowing. The findings highlight the external wall as the primary consideration in retrofitting due to its high HLS index, even at high window-to-wall ratios. It was also established that dwelling type is important in retrofit decision-making, with floor and loft retrofits having a high HLS index in bungalows. Furthermore, the analysis underlines the necessity for Standard Assessment Procedure assessors to evaluate loft U-value and air permeability rates prior to implementing retrofit measures, given the significance of these factors in the lower and upper bounds analysis. Researchers globally can replicate the HLS index approach, facilitating the implementation of housing retrofit policies worldwide.

Retrofitting projects can have multiple socio-environmental benefits, improving the energy efficiency of buildings, reduce environmental impacts, extending the life of buildings, promoting renewable energy use, and improving occupant comfort, health and wellbeing. Additionally, they can have economic benefits such as lowering energy bills and creating skilled jobs. However, measuring the benefits from retrofits can be challenging. This study employs the Build Upon 2 (BU2) toolkit to evaluate the economic benefits of five case study, area-based, domestic retrofit projects managed by a local authority in the North of England between 2022 and 2024. Stakeholders such as project managers, contractors, and quantity surveyors were interviewed to explore how data on economic benefits of retrofit projects can be captured and assessed using the BU2 tool. The analysis revealed a complexity of challenges in acquiring data on the financial details of the project and fuel bill savings. Recommendations to improve processes include a top-down approach to data collection and streamlining of the data collection and evaluation process.

Evaluating the performance of domestic retrofits is essential in appraising their success and identifying if they improved the lives of occupants. In the UK, billions of pounds are invested annually in retrofits through policy funding, however, current building regulations do not mandate evaluation, and monitoring requirements are poorly defined. Without agreed standardised protocols or tools, retrofit evaluations remain inconsistent and incomparable, providing little assurance to occupants, landlords, installers, or the government. Post-occupancy evaluation (POE) is a common and well-established form of building performance evaluation (BPE) used in retrofit evaluations; however, it faces challenges in multi-dwelling retrofit schemes. This research evaluated the effectiveness of occupancy evaluation surveys in five domestic retrofit projects overseen by a local authority in Northern England between 2022 and 2024. Phase one implemented a retrofit survey taken from the UKGBCs BuildUpon2 Framework. In phases two and three, iterative improvements were made to the survey based on feedback from occupants and surveyors from the previous phases. Five key barriers were identified: resources, technical challenges, surveyor engagement, trust, and accessibility. Addressing these challenges increased the survey response rate from 25% to 98%. The refinements significantly improved the quality and usefulness of the data collected, offering valuable insights for designing robust, easily implementable occupant surveys.

Internal wall insulation (IWI) is one of the few retrofit approaches to reduce heat loss through solid brick walls. Discontinuities in the insulation layer can result in thermal bridges, leading to reduced surface temperatures and the potential for condensation to form. Party wall junctions retrofitted with IWI act as discontinuities when neighbouring homes do not have IWI, leading to reduced surface temperatures on the neighbouring side. The condensation risk imposed on the uninsulated neighbour by a range of notional IWI systems are simulated, the resulting temperature factors indicate whether each system imposes a risk upon the uninsulated neighbour. Thicker, higher performing IWI systems were found to result in greater risk in the neighbouring property.

To construct buildings of the future that are both energy-efficient and moisture-resilient, it is critical to have an in-depth understanding of the varying characteristics of brick properties. This study sampled eight brick-cores taken from solid walled homes across the UK, to investigate the impact of thermal conductivity and hygrothermal parameters on U-values and moisture accumulation. Modelled U-values of uninsulated solid walls, in this sample, ranged between 1.6 and 2.6 W/m2K, with 6 of 8 the homes having surface condensation risks. There was even greater variability found in the moisture content in inner brickwork when simulated in WUFI, between 0.1 to 5.8 %, indicating some bricks are at significantly higher risk of moisture accumulation.

Of the 28 million residential properties within the UK, 19 million are poorly insulated and hence energy inefficient. It is a challenge to improve the energy efficiency of these buildings. Retrofitting measures reduce energy consumption in homes and improve occupant comfort, make homes healthier and reduce fuel bills. Local authorities across the UK are undertaking thousands of retrofits each year; however, the measurement of the impact of these retrofit activities is haphazard. The retrofit assessments taking place are fragmented, complex to implement, expensive, inconsistent in their approach, and therefore not a comparable, standardised assessment of the retrofit work done. The lessons learnt and best practices are not being shared, and there remains uncertainty around the benefits that are being delivered to communities. This research aims to understand how to improve retrofit assessments. To address this problem, the UK Green Building Council (UKGBC) developed a toolkit called the Build Upon 2 Framework. It was meant to evaluate retrofit projects and standardise how to quantify social, environmental and economic benefits of projects. In addition to collecting technical data from energy models such as the Energy Performance Certificate (EPC) and economic data from contractors, the toolkit uses the occupant questionnaire as a central tool to understand the impact of the retrofit from the occupant’s perspective. However, the questionnaire is untested; this research aims to explore its effectiveness and make recommendations on its development and implementation. It analyses the results from a case study retrofit project in the North of England where it was deployed by a local council. This research may lead to the revision of the UKGBC toolkit, which may be adopted by other organisations wishing to undertake standardised evaluations of their retrofit projects and may also be used as a reference toolkit by organisations funding retrofit to ensure their projects include consistent retrofit evaluations.

This book focuses on the impacts of the built environment, and how to predict and measure the benefits and consequences of changes taking place to address sustainability in the development and building industries.

© 2017 Elsevier LtdMould growth and surface condensation are problems for many dwellings, and the retrofitting of insulation can increase the risk of these occurring. This is especially the case for historical solid wall properties receiving external wall insulation (EWI), which often have architectural details at the roof eaves that cause discontinuities in the insulation and so can result in excessive thermal bridging. This paper presents the results of an investigation into retrofitted solid wall properties where modelling is used to investigate the problem and effectiveness of insulated coving products which are designed to reducing thermal bridging. Thermal modelling is undertaken to establish the optimum design to reduce risk. The insulated coving was found to be effective in reducing thermal bridging in all the scenarios investigated and to reduce moisture risks occurring in some solid walls situations.

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.

© 2018 Elsevier Ltd Keeping homes at a comfortable temperature and reducing household fuel bills are priorities for many governments. In the UK, several interventions have been implemented to achieve these objectives. This paper investigates one such policy lever - the Energy Price Cap - to understand if it has been designed and implemented efficiently and equitably. The price cap was introduced for customers on prepayment meters to combat increased levels of fuel poverty and a lack of competition in this group. However, the price cap was based on several assumptions of how energy is used. In this work, we assess how well the price cap accounts for real energy use using smart meter data. Households on economy 7 (EC7) tariffs were found to spend more than those on standard rate tariffs, as EC7 customers use more electricity during peak hours than assumed in government calculations. Additionally, many of the EC7 customers in this sample still use a considerable amount of gas, suggesting the EC7 heating product is either not sufficient, or is not being utilised in a cost-effective manner. Revisions to the input assumptions in government models for EC7 customers would therefore be beneficial in future price cap levels.

Measuring the performance of building fabric is increasingly important as stakeholders wish to compare as-built performance with design expectations. When measuring whole house performance (Heat Transfer Coefficient) heat losses through the floor in slab-on-ground type constructions are intractable and introduce uncertainty into measurements. As such efforts are often made to isolate them from measurements. The QUB method is a practical method of measuring whole house building performance. Previous work has shown floor losses can successfully be isolated from measurement through use of heat flux measurements and additional calculation steps. To further test this isolation procedure, three QUB tests were performed on a slab-on-ground Passivhaus dwelling. Whilst the whole house performance measurements agree with the design performance (all results within 11% of the design) the floor losses measured appear unrealistically high. The conditions of the tests, conducted in late summer and in a highly insulated property, are likely causing the heat flux measurements to capture heat being stored in the floor construction rather than heat being lost from the property. Follow up measurements in more preferable conditions are planned which will assist in determining the cause of these observations.

In situ measurement can enable accurate evaluation of a building’s as-built performance. However, when measuring whole house performance, party walls introduce measurement uncertainty. Subsequently, it is common to “adjust” measurements to isolate heat transfer through party walls. This study explores the behaviour and impact of party walls in QUB and coheating measurements of a semi-detached house, presenting empirical evidence on the validity of these measurements where a party wall is present. Two different party wall heat transfer behaviours were observed through heat flux density measurements. Thermal charging is apparent in QUB tests and the initial stages of coheating. After 48 h of coheating, the party wall has become heat saturated and exhibits stable heat transfer. Consequently, using heat flux density measurements to isolate party wall heat transfer in QUB tests, where thermal saturation has not been achieved, can result in misleading inferences. The coheating and QUB measurements without party wall adjustment are in close agreement, irrespective of differing heating patterns in the neighbouring property. The generalisation of these findings is problematic since they describe the impact of the case study-specific built form and the test conditions. Future work to explore the impact of built form and test conditions is needed.

Improved building fabric performance is essential for the decarbonisation of buildings. Evaluating fabric performance is often predicted; but inaccuracies are present within commonly used prediction methodologies. Accurate measurement of building fabric is therefore advantageous when identifying the improvement made through retrofit. The QUB/e method is a practical and effective method of measuring the whole building performance in low-to-medium thermal mass properties. In this paper, a property of high thermal mass was studied for the first time with the QUB/e method. The results identify challenges in undertaking QUB/e measurements in the application of high thermal mass including the impact of stored solar heat contributions resulting in a wider dispersion of measurements. In the case presented; a significant prediction gap is identified when comparing the predicted and measured results. The implications of the prediction gap observed include a change in the regulatory EPC band of the property. Additionally, using performance measurements would avoid overestimations of the reported decarbonisation and annual cost saving benefits of future retrofit works to improve the property at 2.3 Tonnes of equivalent CO2 emissions and £570 respectively.

Retrofit projects can have multiple socio-environmental benefits, improving the energy efficiency of buildings, reduce environmental impacts, extending the life of buildings, promoting renewable energy use, and improving occupant comfort, health and wellbeing. Additionally, they can have economic benefits such as lowering energy bills and creating skilled jobs. However, measuring the benefits from retrofits can be challenging. This study employs the Build Upon 2 (BU2) toolkit to evaluate the economic benefits of five case study, area-based, domestic retrofit projects managed by a local authority in the North of England between 2022 and 2024. Stakeholders such as project managers, contractors, and quantity surveyors were interviewed to explore how data on economic benefits of retrofit projects can be captured and assessed using the BU2 tool. The analysis revealed a complexity of challenges in acquiring data on the financial details of the project and fuel bill savings. Recommendations to improve processes include a top-down approach to data collection and streamlining of the data collection and evaluation process.

13% of the UK’s total Carbon dioxide emissions are from domestic buildings. Reducing carbon emissions from domestic buildings is an important societal need, this includes older, solid brick walled houses. Solid wall insulation: either internal or external, is the only option to improve the thermal performance of solid brick walls. however; it is also costly and complex insulation to install, and can have several unintended consequences. This thesis focusses on internally installed solid wall insulation, or internal wall insulation (IWI) IWI retrofit can be prone to discontinuities or breaks in the insulation layer, these can be caused by obstructions such as walls or floors. Areas where the IWI layer is broken act as thermal bridges, allowing greater flow of heat through the wall resulting in heat loss and cooling of surfaces at discontinuities which can be at risk of surface condensation formation, potentially leading to mould growth and damage to the building fabric. There are gaps in the knowledge regarding the impacts of discontinuities of IWI in-situ: research in this field has focussed on the use of simulation to assess this risk. The goal of this thesis is to measure the change in moisture risk at junctions of solid brick walled buildings after IWI retrofit, and the impact that discontinuities have on that risk. A field trial was undertaken in a solid brick walled house in which a selection of junctions featuring discontinuities were measured under quasi-steady state conditions. Three IWI retrofits were undertaken in sequence using different IWI systems. In-situ Surface moisture risk was calculated for each junction estimated. Discontinuities of the IWI layer were found to increase the surface condensation risk relative to pre-retrofit. The addition of insulation to discontinuities eliminated or reduced the risk of surface moisture. Simulations were also undertaken to assess the accuracy of the standard approach of assessing surface condensation risk at junctions. Improved wall thermal conductivity and environmental inputs were used in stages to assess how these improved the accuracy of predictions. Simulations were also used to carry out a sensitivity analysis and a parametric analysis of junctions with and without discontinuities of IWI. The sensitivity analysis examined the sensitivity of surface moisture risk to external wall U-value. The parametric analysis investigated how IWI system properties and environmental conditions affect surface condensation at a junction with and without a discontinuity. The findings of this thesis give guidance for the design of IWI retrofits to reduce surface moisture risks at discontinuities of the IWI layer.

The performance of building fabric is a critical component in the complex problem of heat decarbonisation. However, a growing body of evidence has shown that there is often a difference between the measured performance of building fabric and its predicted or design performance. This phenomenon is known as the performance gap. Awareness of the performance gap has popularised the concept of measuring fabric performance. This can be characterised by the U-values of individual fabric elements or the HTC (Heat Transfer Coefficient) that describes the whole house fabric performance. HTC measurements are commonly used to evaluate any performance gap. The current standardised method for HTC measurement, coheating, is extremely disruptive as it is required that a home is empty for 15 days or more for steady state conditions to be maintained within the property. As such, coheating can be considered unsuitable for uses outside of research. The QUB method is a dynamic method of HTC and U-value measurement that is completed within a single night. Owing to its short duration the QUB method could potentially be used in mainstream applications such as new build housing and retrofit where a coheating test would not be feasible. This research aims to improve and demonstrate the accuracy (closeness to true value) and precision (dispersion of repeat measurements) of the QUB method. This will identify where the method can be deployed to give informative measurements and its limitations. A method consisting of six field-based case studies was deployed in which repeated QUB measurements were completed and compared to reference HTC and U-value values to determine the accuracy and precision of the measurements. This revealed that variations in test conditions were impacting the dispersion of results and negatively affecting accuracy and precision. These included variability of the temperature ratios in unconditioned spaces, transient thermal mass effects introduced by solar radiation and changes in external temperature, and wind conditions impacting heat transfer. Where observed, this impact is linked to select building characteristics. Consequently, houses with minimal areas of indirect heat loss, insulated building fabric and not of a characteristically high thermal mass often resulted in highest levels of accuracy and precision in QUB measurements. From the results of the case studies, indicative values of accuracy and precision for the QUB HTC measurements were derived based on the building characteristics of the test homes. For homes with characteristics associated with high accuracy and precision the following levels of accuracy and precision are expected: root mean squared error (RMSE) ≤ 15 %, mean bias error (MBE) ≤ |13| %, relative range ≤ 19 % and standard deviation ≤ 7 %. For homes with characteristics associated with low accuracy and precision the equivalent metrics are RMSE ≤ 34 %, MBE ≤ |34| %, relative range ≤ 55 % and standard deviation ≤ 16 %. These values can be used by those conducting QUB HTC measurements to determine the suitability for an application and to provide context on the measurement result. The level of accuracy seen in the QUB U-value measurements was notably lower than that seen in existing work. The reasons for this could not be determined. A novel approach for adjusting HTC measurements for indirect heat loss through unconditioned spaces was proposed. This was done through use of additional temperature and heat flux density measurements and was shown to improve the accuracy and precision of measurements in all applicable instances. However, this practice may, in turn, affect the suitable use cases for the measurement. Future work should consider how these adjustments are communicated in the most understandable way. This study has demonstrated the accuracy and precision of the QUB test in a discrete number of real-world case studies. Whilst limitations of the QUB test are highlighted, its potential to give informative evaluations of building fabric performance are evident. Future work should conduct multiple QUB tests over a duration of close to one year to better understand the impact of changing test conditions. Additionally, the measurements completed in this study could be combined with data from other projects to enable an evaluation of accuracy and precision against a wider range of building characteristics. This will further the understanding gained from this study and give findings that can be generalised across the building stock.

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.

Fan pressurisation tests (FPTs) are commonly used to measure air leakage in homes, to provide evidence for compliance with energy and ventilation standards in building regulations and inform energy models. The results are presented of 37 pressurisation and co-pressurisation tests on attached homes in the UK which measured inter-dwelling air exchanges during the FPTs. On average, 21% of the air leakage measured by the FPTs was found to be inter-dwelling rather than inside-to-outside air exchange, i.e. homes are more airtight than FPTs indicate, which is important when assessing energy efficiency and ventilation performance thresholds. Not accounting for inter-dwelling air exchanges poses a risk of under-ventilation and misclassification of homes deemed suitable for natural ventilation. Using the FPT result to replace default values for airtightness in energy models used to create Energy Performance Certificates (EPCs) for 11 of the case study homes improved their energy efficiency rating (EER), indicating default airtightness values used in EPCs used were overestimating the air leakage. Using the co-pressurisation value resulted in an additional EER point. These modest improvements represented a 5%, 8% and 3% reduction in predicted annual carbon emission, space heating demand and fuel bills, respectively. Practice relevance The airtightness of homes is fundamental to their energy efficiency and ventilation requirements. The FPT is commonly used to measure airtightness in homes; however, this research has shown that the FPT can overpredict air leakage in attached homes due to the elevated pressures during the test cause inter-dwelling air exchanges not experienced under non-test conditions. This may affect the accuracy of FPTs in attached homes and the appropriateness of using the FPT result to inform building regulation compliance, ventilation decisions and energy models. The research has implications for FPT standards, testing practitioners and professional bodies, energy modellers, ventilation designers, policymakers, and regulations. The development of further knowledge, industry guidance and protocols is required for inter-dwelling air exchange taking place during the FPT, particularly for different house type, form and construction.

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.

Improving the energy efficiency of the UK housing stock is important both to meet carbon emission reduction targets and to reduce fuel poverty. For this reason, domestic properties are frequently retrofitted with energy saving measures. This study looks at how the energy consumption, thermal properties and internal temperature of 14 dwellings change as a result of a solid wall insulation (SWI) retrofit. A decrease in heat transfer coefficient of 11+6−7% was calculated for 2 dwellings, which is slightly lower than the previously modelled value of 18%. However, many houses displayed evidence that the full benefit of SWI was not being realised as, for example, energy savings were offset with increases in internal temperature. Future retrofit schemes should therefore consider supplementing the changes in fabric with increased guidance for the occupant.

Occupants affect energy consumption in buildings by contributing internal heat gains, increasing internal carbon dioxide levels and adapting their behaviour. Estimated occupancy schedules are used in building energy models for regulatory compliance purposes and when empirical data are not available. Metadata, such as personal location data, is now collected and visualised on a global scale and can be used to create more realistic occupancy schedules for non-domestic facilities, such as large retail outlets. This paper describes a protocol for extracting and using freely available metadata to create occupancy schedules that are used as inputs for dynamic simulation models. A sample set of twenty supermarket building models are used to demonstrate the impact metadata schedules have when compared with models using the estimated schedules from regulatory compliance. Metadata can be used to create bespoke occupancy profiles for specific buildings, groups of buildings and building archetypes. This method could also help reduce the gap between predicted and actual performance. In the example models, those using the regulatory compliance schedules underestimated heating demand by approximately 10% and overestimated cooling demand by over 50% when compared to models using the metadata schedules. Although this work focuses on UK facilities, this methodology has scope for global application.

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.

Environmental conditions in buildings are linked to the physical and mental wellbeing of occupants. Thus, it follows that the internal environment affects human performance and user experience during sport and activity. There are several indices that are used to evaluate occupant thermal comfort, the Predicted Mean Vote (PMV) index being the metric most commonly used. PMV is designed to evaluate comfort for sedentary occupants with low metabolic rates; however, PMV has also been used to evaluate comfort for individuals engaged in high metabolic rate activities, such as those common in sport facilities. This paper investigates the implication of using PMV to evaluate thermal comfort in sport facilities using empirical data recorded over 24 months in a multi-purpose sports hall in the North of England. Data are used to develop and propose methodological modifications to improve the standard PMV model prediction to account for occupants having higher metabolic rates. The paper evaluates the use of metabolic rate data from different sources including the Compendium of Physical Activities and quantifies the impact that the metabolic weighting approach has on predicted comfort. Finally, a novel method is proposed to modify PMV for use where occupants have high metabolic rates. Despite the improvements made, the findings suggest that even a modified PMV may not be able to accurately evaluate the thermal comfort of people engaged in non-sedentary activity, recommending that use of the PMV index is restricted to activities with metabolic rates <2 MET.

Forecasting retrofit performance often relies on building energy models, which can be inaccurate due to differences between predicted and actual performance. This introduces uncertainty to energy and carbon savings estimates. Research suggests that heat loss measurements improve model accuracy and provide more robust evaluations of retrofit effectiveness. Several whole-house heat loss measurement methods have undergone field trials for validation. However, the assessment of these measurements is limited to the specific field trial test conditions. Simulated measurements in a virtual environment could complement field trials by exploring conditions unattainable in real-world settings, increasing confidence in the measurements. This study replicated dynamic whole-house heat loss measurements from field trials in a calibrated energy model using local weather data. Differences of 7% (pre-retrofit) and 26% (post-retrofit) were observed between simulations and field trial results. The differences could be associated with the modelled heat dynamics not reflecting the true thermal behaviour of the house recorded in the field trials with a particular focus on thermal bridging heat loss. This study has shown that for simulations to be used in validating measurements, further work is needed to determine if the dynamic thermal behaviour of buildings can be replicated in simulations.

Heat exchange between chilled food storage and conditioned spaces in large food retail stores is not currently required as part of design stage regulatory compliance energy performance models. Existing work has identified that this exchange has a significant impact on store energy demand and subsequently leads to unrealistic assessment of building performance. Research presented in this article uses whole building dynamic thermal simulation models that are calibrated against real store performance data, quantifying the impact of the refrigeration driven heat exchange. Proxy refrigerated units are used to simulate the impact of these units for the sales floor areas. A methodology is presented that allows these models to be simplified with the aim of calculating a realistic process heat exchange for refrigeration and including this in thermal simulation models; a protocol for the measurement of chilled sales areas and their inclusion in the building models is also proposed. It is intended that this modelling approach and the calculated process heat exchange inputs can be used to improve the dynamic thermal simulation of large food retail stores, reduce gaps between predicted and actual performance and provide more representative inputs for design stage and regulatory compliance energy calculations.

Whole house heat loss or heat transfer coefficient (HTC) measurements are rarely undertaken to validate the performance of retrofits installed in homes. This means policy, certification and householders must rely on predictions made by energy models. Multiple domestic energy models exist, with varying underlying rules and input requirements. This means predictions made by different models may not always agree. However, few studies have compared the predictions from these models with each other, and with measured whole house heat losses for a home before and after a retrofit. This paper compares the HTC of a three bed, semi-detached, solid-walled home measured via the coheating test, with the HTCs predicted by the Reduced Data Standard Assessment Procedure (RdSAP), Building Research Establishment Domestic Energy Model (BREDEM), Dynamic Simulation Modelling (DSM) and the Passive House Planning Package (PHPP). The results show that most predicted HTCs from the models are not similar to the measured HTC, and there is a large variation between the different modelled HTCs. The paper explores why these differences occur and reflects on how to improve the accuracy and consistency of domestic energy models.

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.

Retrofitting solid walled homes is one of the greatest challenges for the UK in achieving its net zero ambitions. Solid walled homes have unique features, that require special consideration. They are among the least efficient in the UK, and their occupants are more likely to be in fuel poverty. They are also at elevated risk of surface condensation, excessive cold in winter and overheating in summer. Retrofitting these homes is a cornerstone of UK policy to tackle fuel poverty and to facilitate the delivery of decarbonised electrified heat into homes. However, installing solid wall insulation is costly and poses more risks of unintended consequences than any other retrofit. Previous projects investigating solid wall insulation have identified major failures when retrofits are installed in a ‘piecemeal’ way i.e., they did not consider how the retrofit measure affects risks of damp, inadequate ventilation, and overheating in homes. This led to the adoption of the whole house approach in new technical standards for retrofit installers (PAS 20351) to ensure that all risks of retrofit measures were always considered, even if only one measure was being installed at a time. Industry is beginning to adapt to these standards, but more research is needed to explore the benefits of adopting the whole house approach, and more guidance is needed to support retrofits in solid walled homes. Insights from this project explain how solid walled homes can be retrofitted more safely and effectively.

The DEEP case study retrofits provide compelling evidence on how a whole house approach to retrofit can reduce heat loss, surface condensation risk and overheating risks in solid walled homes. From the data collected, specific guidance is produced outlining how to install retrofits in solid walled homes more safely and effectively. Recommendations are provided on how to make measurements and modelling predictions of the technical performance of retrofits more accurate. The findings can inform evidence-led decisions at multiple levels to ensure retrofits in solid walled homes are safe and effective.

17BG was one of fifteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies was also used to evaluate the accuracy of modelled predictions around retrofit performance and risk.

56TR is one of fifteen homes being retrofitted in the DEEP project. The case studies are being used to identify the performance of, and risks associated with, retrofitting solid walled homes as well as to evaluate the accuracy of retrofit models.

01BA is one of fourteen case study homes retrofitted in the DEEP project. The case studies identify the performance of, and risks associated with, retrofitting solid walled homes. A retrofit was undertaken in stages, reflecting a piecemeal approach to retrofit, followed by undertaking activities that would be required for a whole house approach as a final stage. The data from the case studies is also being used to evaluate modelled predictions of retrofit performance and risk.

55AD and 57AD, are a pair of identical semi-detached homes, and are two of fourteen DEEP case study homes in which the comparison between a whole house and piecemeal approach to retrofit was evaluated.

00CS is one of fifteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies was used to evaluate the accuracy of modelled predictions around retrofit performance and risk.

04KG is one of fourteen case study homes being retrofitted in the DEEP project. The case studies are being used to understand the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies is also being used to evaluate modelled predictions of retrofit performance and risk.

52NP and 54NP are two of fourteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies were also used to evaluate modelled predictions of retrofit performance and risk.

This report describes the common data collection and analysis methods used in the DEEP retrofit case studies. These are generically described to avoid repetition in the individual case study reports.

Thermal and hygrothermal simulations are undertaken to estimate energy performance, condensation risks, the potential for moisture accumulation, and timber rot. These simulations use default book values to estimate the material properties of solid brick walls. This report investigates the variability of brick properties found in solid walled homes in the UK and compares these to the default book values. It also explores how varying material property inputs in models affects thermal performance and moisture risk in solid walled homes.

Surveys and air tests were performed at 160 solid and cavity walled homes in Northern England, which had a mix of insulated and uninsulated walls. Blower door tests and Pulse tests were compared and used to quantify the airtightness of the homes. An evaluation of how building characteristics affected the results was performed, and common leakage pathways were identified. Data was also collected on the condition of the homes, potential barriers to external wall insulation (EWI) retrofit, as well as perceptions of occupants.

19BA is a mid-terraced pre 1900 solid walled home where airtightness improvements and room-in-roof retrofits have been installed. Building performance testing has been undertaken to collect data on the performance and risks of these improvements, and to evaluate the accuracy of modelled predictions on the retrofit performance and risk.

07LT and 09LT are two of fourteen case study homes retrofitted in the DEEP project. The case studies have been used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data have also been used to evaluate the accuracy of the modelled predictions of the retrofit performance and risk.

08OL is one of fourteen case study homes being retrofitted in the DEEP project. The case studies are used to identify the performance of, and risks associated with, retrofitting homes without conventional cavities. The data from the case studies are used to evaluate the accuracy of modelled predictions of retrofit performance and risk.

27BG is one of fourteen solid walled DEEP case study homes. In this home building performance tests were undertaken to investigate the success and risk of retrofitting suspended timber floors and how the results compare to predictions.

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

The benefits and risks associated with installing internal wall insulation (IWI) and thin internal wall insulation (TIWI) retrofits into solid wall homes are researched and evaluated for BEIS. In order to deliver this, a holistic approach was adopted and the project was split into four main sections, each of which has an accompanying Annex to this summary report: Annex A: Review of existing literature as well as primary investigations using house surveys, householder questionnaires and installer focus groups into the sociotechnical barriers to IWI and TIWI. Annex B: Technical evaluation of the performance of IWI and six novel TIWI retrofits installed in field trial solid wall Test Houses using before and after building performance evaluations. Annex C: Modelling of the impact on annual energy consumption, EPC rating, overheating risk, condensation risk and moisture accumulation made by IWI and TIWI retrofits in a range of UK house archetypes. Annex D: Laboratory testing of test walls using hygrothermal chambers to quantify the change in moisture and thermal performance of solid brick walls when they are insulated with IWI and TIWI to determine how weather

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.