Dr Kate Morland

The UK Government currently pressurises and incentivises volume housebuilders to build more new homes annually, as current demand outstrips supply. However, accelerating the housebuilding production process negatively impacts new home build quality, resulting in defects that require rectification. The implementation of stringent quality management standards is recognised as improving build quality standards, as it removes a degree of uncertainty from the housebuilding process. Changes to organisational procedures in this way rely on individuals across Housebuilder organisations collectively learning new working practices from the top down. While ample academic research has explored how ideas at the individual level become codified learning at the organisational level, there is little investigating how top-down learning unfolds across Housebuilder organisations over time, or the conditions that contribute to its success or failure. This thesis, therefore, aims to enhance the understanding of top-down multi-level learning in relation to UK housebuilder quality management standards. It pursues an interpretive qualitative case study approach, using a practice view of organisational routines to inform the means of inquiry. Methods include participant observation, semi-structured interviews and document analysis. Fieldwork undertaken within three regional offices of a major UK housebuilder, studies how individuals in three different teams learnt to use a new quality management routine. An inductive approach to data analysis, using Gioia et al.’s methodology (2013), is adopted, which also includes an abductive element to determine the study’s main findings. This thesis is the first to consider multi-level learning from a housebuilder perspective and therefore contributes to both academic and housebuilder understanding of learning in relation to quality management standards. Findings here challenge several assumptions expressed in the organisational learning literature.

The build quality of new UK homes is negatively affected by poor quality management practices during the construction process. By implementing stringent quality management (QM) standards, housebuilders can improve build quality but implementing these organization-wide changes relies on housebuilder staff, designers and sub-contractors learning new working practices. This paper explores the tensions which emerge within housebuilders, as they implement new QM procedures. A longitudinal qualitative case study was conducted, where time was spent with housebuilder staff in three regional offices, two years apart. Methods include participant observation, semi-structured interviews and a review of organizational documentation. The findings highlight several learning paradoxes which arise at different stages of the housebuilding process and show how actors manage (or cope with) these paradoxes through their daily practices. This includes processes of simplifying and applying, improvising and problem-solving and aggregating and analyzing. Whilst these either-or approaches enable staff to resolve the immediate tensions that arise from different organizational processes, they often fail to meet longer-term learning objectives, detrimentally affecting build quality over time. Without structural changes to the way volume housebuilders annually report to both the UK Government and their shareholders, organizations in the UK housebuilding sector face challenges in reconciling different learning processes.

Heat pumps are a key part of the UK Government's decarbonisation strategy to achieve net zero carbon emissions by 2050. Shared-loop ground source heat pumps (GSHPs) offer domestic space and hot water heating at scale in medium-to-high-density areas where standard single-dwelling heat pumps are unsuitable. However, it is unclear whether homeowners would be willing to pay for them. This paper explores public perceptions of three shared-loop GSHP financing models. We used focus groups to understand homeowners' responses to each finance model, refined the models, and tested them in an online survey of UK homeowners. We found that while there is potential interest in joining a shared-loop GSHP network, there was distrust because the financial offers were perceived as unfair, disadvantaging some customers, and not offering long-term financial savings compared with a gas boiler. The standing charge for the shared loop was a major barrier. There was a preference for the shared-loop GSHP to be offered by a utility company, a need for personalised financial projections, and the option to delay joining. Our results suggest that to increase uptake, greater certainty around future decarbonisation incentivisation strategies is needed, along with regulation of financial models.

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.

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.

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.