Dr Jim Parker

European energy policies call for an increased share of renewable energy sources and a more active role of the energy consumer. This is facilitated by, amongst others, buildings becoming energy flexible hubs, supporting smart energy grids with demand response strategies. While there is abundant technical research in this field, the related business and policy development is less well documented. This research scopes existing policy programmes and identifies opportunities and barriers to business development supporting energy flexible buildings. Using examples from seven European countries, this work reviews influencing niche management factors such as existing policy instruments, business development cases and identified stakeholder concerns, using literature research, narrative analysis and stakeholder research. National policy pathways show many differences but confirm that European buildings might become active players in the energy market, by providing energy storage, demand response and/or shifts in the use of energy sources. Slow sustained business development for energy flexibility services was mainly identified in the retail industry, and for energy service companies and aggregators. The direct involvement of end users in energy flexible buildings is still difficult. Stakeholders call for policy improvement, especially concerning the development of flexible energy tariffs, supporting incentives, awareness raising and more stakeholder-targeted business development.

Urban heat islands are evident throughout the world and may become more problematic in temperate climates as global warming continues. This paper characterizes the urban heat island of Leeds, a city in the temperate maritime climate of the UK. Measured weather data from rural and urban sites have been used to quantify the heat island and to create building simulation weather files for the summer of 2013. These weather files have been used to model the impact on energy consumption and thermal comfort in notional non-domestic and domestic buildings, including a hotel, office, house and apartment. The heat island intensity is found to be greatest at night, with the peak in this data set reaching 5.9 °C at 20:00 on 2nd August 2013, with an average peak value of 2.3 °C occurring at the same hour for the case study period. Daytime temperatures were however similar at urban and rural sites. In the notional hotel building, air conditioning costs were increased by up to 40% due to night-time loads whereas consumption in the notional office was similar in all locations. Air temperature, and especially night-time temperature, increased in the domestic examples by an average of approximately 95 additional hours above 25 °C. This work expands knowledge by characterizing the Leeds urban heat island, demonstrating the importance of rural reference site selection for city regions that span a range of altitude, quantifying the gap in building performance when using regional or city centre weather files, and linking building occupancy patterns to the diurnal profile of the urban heat island.

Whole building simulation is considered best practice when estimating impacts of large scale retrofit. The main aim of this paper is to illustrate the importance of a calibrated simulation model in this process. An evidence based methodology is used to calibrate a dynamic thermal simulation (DTS) model of the terminal building at Birmingham Airport with monthly utility data. A methodology has been demonstrated for the calibration of a very large building with highly variable occupancy and operating profiles. Methods for calculating model inputs from a combination of measured data and site survey results are also described. Potential economic and environmental outcomes were calculated for the model at each stage of calibration. Results confirm the importance of internal heat gains in the accurate simulation of this type of building and show large errors in estimated CO2 and cost savings from models that are not calibrated.

In the United Kingdom (UK) Energy Performance Certificates (EPC) are intended to indicate the energy efficiency potential of a building for owner/occupiers and Display Energy Certificates (DEC) provide a performance rating for an operational facility based upon metered data. This study uses dynamic thermal simulation (DTS) to evaluate the difference between the EPC and DEC results for the new International Pier at Birmingham Airport in the UK and to test the impact of EPC recommendations. The Pier building achieved an EPC rating of ‘B’ but the operational DEC rating of ‘F’ was much lower than anticipated. Differences between EPC, actual performance and simulation data have been analysed to identify the critical pieces of information that influence the disparate ratings. Conclusions consider the role of EPCs in designing this type of building and informing energy efficient operation.

Urban Heat Islands (UHI) occur in and around cities, leading to warmer temperatures than in surrounding rural areas. The UHI effect increases energy demand, air pollution levels, and heat-related illness and mortality. Solar energy is one of the most widely adopted renewable energy generation technologies in the built environment. Solar photovoltaic (PV) systems, integrated into building envelopes, can form a cohesive design, construction and energy solution for buildings, namely, building-integrated photovoltaic system (BIPV). However, the BIPV panels might potentially exacerbate the UHI intensity by trapping more heat in urban areas. This review paper uses a detailed literature survey of over 100 sources to evaluate whether the uptake of BIPV systems in urban areas contributes to an aggravation of the UHI effect. The survey found both direct and indirect impacts of BIPV systems on UHI, which also identified the fundamental causes of UHI such as the albedo effect and heat dispersion and how this would be embodied in the BIPV installations. Furthermore, this paper discusses how to mitigate the impact of BIPV systems on the UHI, as well as the future research directions around this concern in relation to the urban design.

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.

Urban green spaces are acknowledged as a vital component in a healthy city, providing a wealth of benefits. Urban green infrastructure (UGI) can help to moderate the intensity of the Urban heat Island (UHI), there is however a lack of high temporal and spatial ground-level data that quantifies the impact of UGI on air temperature and human comfort within UHI areas, and particularly for cities in temperate marine climates, which are not comprehensively understood. This paper therefore uses data from a high-resolution monitoring campaign in the UK city of Leeds to describe the diurnal characteristics of air temperature in grey and green spaces between May and August 2021. Average UHI intensity during this period was 0.9 °K, with a summer maximum of 3.1 °K occurring in late evening. Although there is variation across the monitoring sites, green space was on average 0.7 °K cooler than the grey spaces during the summer months, and up to 2.6 °K cooler on some of the hottest days. Air temperature in urban woods was up to 4.0 °K cooler on the hottest days. These measured data demonstrate the influence of UGI on air temperature in UHI areas, and quantify the impact of different types of UGI, identifying the UGI types that are most effective at regulating higher summertime air temperature. Results presented here provide valuable quantitative data that can support the protection and expansion of urban green space as part of policy development and urban planning in practice.

Whilst it is broadly understood that urban green infrastructure (UGI) helps to mitigate against the urban heat island (UHI) effect, there remains a relatively small body of measured data that quantify the impact of UGI on urban temperatures. This paper presents interim results from a long-term monitoring campaign in the city of Leeds, UK. A network of air temperature sensors housed in Stevenson shields were deployed across Leeds in the summer of 2019. Initially, a total of 17 sensors were included in this network: 10 in grey (man-made built-up areas) urban spaces, 5 in UGI, and 2 sensors at rural reference sites. The data set reported in this paper covers the period July 2019 to November 2020 at an hourly resolution. Results characterise the urban heat island intensity (UHII) and the differences between air temperatures in the urban grey and green spaces. There are both diurnal and distinct seasonal differences in the hourly temperature data. The average UHII during this period was 1.8 °C, with a summer peak of 4.9 °C occurring in late evening. Within the UHI during summer months, the green space was on average 0.5 °C cooler than the grey spaces and up to 2.8 °C cooler on the hottest days. These measured data quantify the local cooling effects of the green space, which is useful at both a macro city-scale and micro citizen-scale. Results of this nature are useful in building a quantitative evidence base that supports the retention and introduction of urban green infrastructure.

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.

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.

Urban heat islands are having a detrimental impact on the health and wellbeing of inhabitants in major cities. The impact of global warming is affecting all, but groups, including infants, the elderly and those with poor health are vulnerable and fatalities during hot weather are increasing. High temperatures adversely affect all ages, reducing the ability to function, live and work comfortably and effectively. The planning and design of buildings and their surrounding infrastructure, especially the green assets (trees, plants and vegetation) can reduce the impact of urban heat islands. The problem and challenges of Urban Heat Island are described in this chapter as well as recent research which proposes to capture climate data and the impact of green infrastructure asset and thereby providing guidance for those designing and planning urban developments.

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.

It is not practicable to test every aspect of all the buildings that are built. As we understand the behaviour of buildings from field and laboratory tests the data can be used to produce generalised assumptions about the way a building, and its component parts will behave. These models simulations are now an integral part of our understanding of the performance of buildings. While the assumptions made in models and simulations can be relatively imprecise when first developed, as their development is advanced the models become more detailed, reliable and intelligent. Researchers are constantly updating and calibrating the sensitivity of their models, using new data from the field and in-use studies to improve the reliability and accuracy with which the models can operate. The construction industry is heavily reliant on the use of models and simulations to perform a variety of design and analysis calculations, for predicting energy consumption and performance of finished buildings, and to demonstrate compliance with regulatory or voluntary performance standards.

The York Passivhaus is a 3-bed home in York, North Yorkshire, that achieved Passivhaus certification on completion in 2015. The project aim is to evaluate the building fabric and system performance of the home seven years post-completion against design targets and initial performance tests. Areas of interest are energy consumption, ventilation and air quality, thermal comfort, airtightness and building fabric. Looking at these in turn, fuel bills were used to explore how gas and electricity consumption had changed since occupation in 2016. Gas use was higher during the first year postcompletion in 2016 but has steadily declined since. Electricity use has remained relatively constant. The annual energy consumption in 2023 was 2467kWh for gas (20kWh/m2/year) and 1652kWh (13kWh/m2/year) for electricity, which is between 60 and 74 per cent less for gas and between 9 and 39 per cent less for electricity than the average UK house. The mechanical ventilation heat recovery (MVHR) system was not balanced when flow rate test results were compared against commissioning figures, as extract air flow rates were higher than intake air flow rates. This meant that the system no longer satisfied Passivhaus requirements. Air quality was monitored inside and outside of the home over 12 months. For CO2, a high level of IAQ was recorded, with an average of less than 872 ppm. CO2 levels dropped when the MVHR filters were changed coupled with the onset of warmer weather. Higher noise levels associated with the MVHR system ceased following a service. Higher levels of particulate matter (PM) were recorded at the front of the house, close to a car parking area. Three peak periods were examined to see how particulates generated externally or internally rose and fell over time. Spikes in internal PM levels were generally due to cooking or use of the woodburning stove and dissipated quickly. Elevated PM level patterns recorded outside were often mirrored inside but at a much lower level. Twenty internal sensors monitored temperature and humidity levels. Temperatures remained constant above 15°C throughout winter with all sensors staying within a 3-4°C range, indicating a low level of thermal variation across the home. However, internal temperatures were quite low – usually under 20°C, despite the space heating system defaulting to set points of 24°C during the day and 15°C at night during the winter months. This suggests that the space heating system was undersized for the current occupancy level, as design calculations were based on higher occupancy assumptions. It was assumed at the design stage that the wood-burning stove would meet 30 per cent of the home’s heating demand when during the monitoring period it was rarely used. During warmer weather, higher temperatures were recorded across the two southwest facing first-floor bedrooms. There was no evidence of overheating when the home was occupied during warmer weather. In general, the house is still extremely airtight with a mean permeability of 0.86 m3/(h.m2) @50Pa. However, this is a significant increase in air leakage in relative (rather than absolute) terms since certification was carried out in October 2015, where a mean permeability of 0.39m3/(h.m2) @ 50Pa was recorded. The little air leakage detected appears to come from window seals at casements, the boiler flue, plus some air movement behind plasterboard in the upstairs rooflights, and at wall-to-ceiling, or wall-to wall-junctions. The air leakage area has increased only slightly – from around 73cm2 to 104cm2. Therefore, after seven years the home now satisfies EnerPHit rather than Passivhaus airtightness requirements. A QUB test was used to measure fabric performance. First, a design-stage heat transfer coefficient (HTC) for the home was calculated, which was 69.5 W/K and then tested against. Three tests were done in the summer/autumn of 2022 and two in the winter of 2023. The average measurement was 76.3 W/K. This is a low HTC but 10 % greater than the designstage performance calculation. Overall, as a seven-year-old Passivhaus, the home’s performance is still exceptional compared to current-day new-build homes. Some performance aspects have deteriorated since completion, such as the airtightness and MVHR performance, which could be associated with wear and tear. It is not possible to compare changes to air quality, thermal comfort and HTC, as they were not monitored post-completion. The only area of note is thermal comfort in winter depending on the temperature sought by occupants, as the space heating system is not designed for the current occupancy level and could be considered on the cool side of comfortable.

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.

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.

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.

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.

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.

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