Malcolm Bell

Energy efficient modernisation of housing: a UK case study

Abstract This paper sets out the results of the York Energy Demonstration Project and discusses its implications for the modernisation of low rise housing in the UK. The project consisted of three schemes, which were carried out in the early to mid 1990s and monitored over a 2-year period. Results indicate that modernisation schemes have a very important part to play in reducing CO2 emissions and that improvements in the region of 50% can be achieved at modest cost using well proven (early 1980s) technology. The possibility of additional improvements are also identified which could see emissions fall by a further 30–40%. In addition, the project identifies difficulties posed by, often small, variations in dwelling construction, which can have a disproportionate impact on costs, and by the design and use of mixed heating systems which can reduce overall heating efficiencies. The paper also discusses the impact of the demonstration project on the dissemination of good energy efficient practice within the Local Authority and highlights the lessons learned for implementation in future modernisation schemes.

Evidence for heat losses via party wall cavities in masonry construction

This paper presents empirical evidence and analysis that supports the existence of a significant heat loss mechanism resulting from air movement through cavities in party walls in masonry construction. A range of heat loss experiments were undertaken as part of the Stamford Brook housing field trial in Altrincham in the United Kingdom. Co-heating tests showed a large discrepancy between the predicted and measured whole house heat loss coefficients. Analysis of the co-heating results, along with internal temperature data, thermal imaging and a theoretical analysis indicated that the most likely explanation for the discrepancy was bypassing of the thermal insulation via the uninsulated party wall cavities. The data show that such a bypass mechanism is potentially the largest single contributor to heat loss in terraced dwellings built to the 2006 revision of the Building Regulations. A comparable convective heat bypass associated with masonry party walls was identified in the late 1970s during the course of the Twin Rivers Project in the United States, albeit in a somewhat different construction from that used at Stamford Brook. A similar effect was also reported in the United Kingdom in the mid 1990s. However, it appears that no action was taken at that time either to confirm the results, to develop any technical solutions, or to amend standards for calculating heat losses from buildings. Current conventions for heat loss calculations in the United Kingdom do not take account of heat losses associated with party walls and it is suggested by the authors that such conventions may need to be updated to take account of the effect described in this paper. In the final part of the paper, the authors propose straightforward solutions to prevent bypassing of roof insulation via party walls by for example filling the cavity of the party wall with mineral fibre insulation, or by inserting a cavity closer across the cavity in the plane of the roof insulation. Practical application: The heat bypass mechanism described in this paper is believed by the authors to contribute to a significant proportion of heat loss from buildings in the UK constructed with clear cavities such as those found in separating walls between cavity masonry dwellings. It is proposed that relatively simple design changes could be undertaken to eliminate such heat loss pathways from new buildings. In addition, simple and cost effective measures are envisaged that could be used to minimise or eliminate the bypass from existing buildings. Such an approach could give rise to a significant reduction in carbon emissions from UK housing. a The Department for Communities and Local Government, previously the Office of the Deputy Prime Minister, ODPM. References produced before the change of name are listed under ODPM. b Difficulties in the recruitment of households have delayed the long term monitoring programme to 2007 but, fortuitously, this has provided the capacity for a more detailed investigation of the party wall heat loss issues discussed in this paper with further co-heating tests (incorporating a more detailed measurements) planned for the winter of 2006/07. c A co-heating test involves electrically heating the inside of a house to a constant temperature over a period of several weeks. Correlation of the measured electrical heat input with external temperature and solar insolation then allows an estimation of the total dwelling heat loss coefficient. d House A is an end-of-terrace house with one adjacent house. House E is a mid-terrace house with two adjacent houses, D and F. e In the UK, the regulations consist of a broadly framed, performance based, legal requirement supported by detailed technical guidance on compliance. Such guidance is provided by a system of approved documents issued by the Secretary of State. The current methodology for dwelling heat loss calculations is contained in the Standard Assessment Procedure 200512 which is invoked by regulation 17A and Approved Document L1A.2 f The Building Regulations do limit the leakage of air from within each dwelling into the cavity through an overall limit on dwelling permeability. g The higher-than-normal inside-outside temperature difference during the co-heating tests implies that background ventilation rates and ventilation heat loss coefficients during these tests are likely to have exceeded those in the table. Calculations based on a semi-analytical model of air flow14 suggest that the increase is of the order of 3 WK—1 (10%) for the two-storey house A and 15 WK—1 (27%) for the three-storey house E. h Note that the correction is only used to improve the graphical presentation of the data. The heat loss coefficient is calculated directly from multiple regression of heating power against ΔT and S.

Building regulation and sustainable housing. Part 1: A critique of Part L of the Building Regulations 1995 for England and Wales

This paper presents a critique of the energy efficiency aspects of the Building Regulations for England and Wales as they relate to dwellings. It is argued that a significant improvement in the regulations is required if large reductions in CO2 emissions are to be achieved in the first half of the next century and that considerable scope for regulation improvement exists (almost 90 per cent reductions in space heating are achievable). The paper identifies the shortcomings of the methods used to demonstrate compliance and proposes new approaches which would increase consistency and enable a clear programme of improvement to be established.

Building regulation and sustainable housing. Part 2: technical issues

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

Building regulation and sustainable housing. Part 3: setting and implementing standards

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

Review of possible implications of an airtightness standard for new dwellings in the UK

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

Developing future energy performance standards for UK housing: The St Nicholas Court project – Part 1

This paper and part 1, which appeared in the last issue, set out the results of a housing field trial designed to evaluate the impact of an enhanced energy‐performance standard for dwellings. The project was designed to inform the next review of part L of the Building Regulations for England and Wales, which, following the publication of the UK governments White Paper on energy policy, is expected in 2005. The project reported explores the implications of an enhanced standard in the context of timber frame construction. Although, for programming reasons, it was necessary to terminate the research project at the end of the design phase, the results suggest that the standard investigated is well within the capacity of the industry. It was clear, however, that the whole supply chain will need to take a positive approach to the development of new solutions. The secret to a smooth and cost‐optimised transition is that the necessary development work begins immediately, not when regulation changes.