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STAMFORD BROOK
Evaluating the Impact of an Enhanced Energy Performance Standard on Load-bearing Masonry Domestic Construction Partners in Innovation CI 39/3/663 - BD2324


Stamford Brook development

Stamford Brook is a development of around 700 cavity masonry dwellings being constructed on part of the National Trust’s Dunham Massey Estate near Altrincham in Cheshire. Construction on the site commenced in 2004 and is expected to continue until around 2009/2010. The development is being carried out under a partnership agreement between the land owner, the National Trust, and the two developers Redrow and Bryant Homes. The development partners are also participating in a “Partners in Innovation” (PII) project with the Centre for the Built Environment at Leeds Metropolitan University (Leeds Met) that has investigated various aspects of the design and construction processes.

The Stamford Brook PII project is a unique record of the achievements, successes, failures, problems and solutions that can occur during the implementation of an advanced energy standard on a large scale housing development. Using participatory action research methodologies, the research project team has followed the progress of the development from initial discussions on the energy standard and environmental standard, through the detailed design process, observation of construction of the dwellings, performance testing of completed buildings and monitoring of occupied houses. The project has been a collaborative effort between land owner, housing developers, sub-contractors, supply chain, regulatory bodies, householders and the research team. The data obtained during the project and the implications on issues such as building regulation, future energy standards, dwelling design, construction processes, training, quality control procedures and occupant behaviour will inform the UK housing industry as it rises to meet the challenges resulting from climate change and the proposed new energy targets due in 2013 and 2016. It is expected that the results from the project will directly influence the development of new energy standards, building regulation, test methods, dwelling design and construction practice.

Background

Stamford Brook is located on land which once formed part of the National Trust’s Dunham Massey estate. The estate was left to The National Trust in 1976 by Lord Stamford and is now run by the Trust as a ‘Special Trust in Credit’. This means that the estate has to find all the income for its upkeep from its own resources such as from visitor income and rents from its farm tenants. It receives no external funding. When Lord Stamford left Dunham Massey to the Trust, he was concerned that it should continue to be run as a ‘traditional country estate’. With some foresight, Lord Stamford identified certain areas of land on the estate as investment land, which if necessary, could be sold to raise funds for the future upkeep of the Dunham Massey Estate. One of these was the 25 hectare parcel of land at Brookside Farm which now forms the Stamford Brook development.

Sustainable Urban Drainage

The National Trust took the decision to maintain a degree of control over the scope of the development and to work in partnership with the two chosen developers. The Trust wanted to ensure that the development was carried out in a way that was environmentally sustainable, was designed to reflect the quality and character of traditional homes in the local area, that would create and attractive urban fringe environment for the benefit of residents, wildlife and the existing local community and that could also serve as an exemplar of a sustainable development. As part of the partnership agreement a comprehensive environmental performance standard (EPS) was developed that set performance targets and requirements for energy use, water conservation, waste minimisation, recycling and material selection for the first phase of the Stamford brook development that were in addition to those required under building regulation. The additional costs to the developers of meeting the EPS criteria were funded by the National Trust from the payments made by the developers to purchase the land at Brookside Farm. The National Trust retains ownership and responsibility for the upkeep of the green spaces in and around the Stamford Brook development and all homeowners pay an annual maintenance charge towards the cost of maintaining the common areas.

Project Objectives

The overall PII project objective was to support future reviews of Part L of the Building Regulations by evaluating the various impacts on a large scale masonry housing development of a range of improvement measures that could be used to meet the requirements of an advanced energy performance standard that would likely be introduced as part of such a review. The impacts and issues that the project was designed to assess included the following:

Technical Impact
Economic Impact
Regulatory Issues
Design Process Issues
Site Project Management and Construction Process Issues
In-use Performance

Project Partners

The Centre for the Built Environment at Leeds Metropolitan University worked in partnership with the following organisations during the Stamford Brook project:

Department of Communities & Local Government

The National Trust

Redrow Homes

Bryant Homes

Bartlett School of Graduate Studies

The Concrete Block Association

Construction Industry Training Board

National House Building Council

Ventaxia

Research Methodology

The project used an action research approach, in which the research team simultaneously participated in and observed the various aspects of the development process. A combination of qualitative and quantitative tools was used to observe, assess and evaluate the design, construction and occupation phases of the development process.

The EPS08 Energy Standard used at Stamford Brook

The Energy Standard being used at Stamford Brook is the Leeds Met EPS08 energy performance standard. The EPS08 standard was originally developed by Leeds Met as a prototype energy standard for the St Nicholas Court project with the intention that it would inform the revision of the Building Regulations that was expected at the time to occur in 2008. The EPS08 standard defines elemental target U-values for the main construction elements, a maximum limit for air permeability and a limit on the carbon intensity of the heating system. In EPS08, calculated U-values include all contributions from both point and linear thermal bridges. A summary of the main requirements of the standard is given in Table 1. Compliance with the ESP08 standard is by one of three routes. This can be either the elemental standard as shown in Table 1, an equivalent mean U-value or by a carbon index calculation. The equivalent carbon emission rate for an EPS08 compliant dwelling would be around 10% to 15% better than that required under Part L1a 2006, depending upon dwelling form and size. For example, an 80 m2 semi-detached dwelling built to EPS08 would have a calculated annual Dwelling Carbon Emission Rate (DER) of 20.6 kgCO2/m2 compared to the ADL1a 2006 Target Emission Rate (TER) for an 80 m2 semi-detached dwelling of 23.2 kgCO2/m2. EPS08 also stipulates minimum performance requirements for ventilation of the dwelling as shown in Table 2.

Table 1 – EPS08 Prototype Performance Energy Standard Requirements

Table 1 – EPS08 Prototype Performance Energy Standard Requirements

Table 2 – EPS08 Prototype Ventilation Standard Requirements



Important Project Findings

Party Wall Thermal Bypass

Party wall construction

Experiments undertaken at Stamford Brook have shown that heat loss via party wall cavities in masonry dwellings can be significant. Such party wall thermal bypasses will be present in most new masonry dwellings with cavity party walls and will also be present in a large proportion of semi-detached and terraced dwellings with cavity party walls built in the UK since the 1960’s. Until now these heat losses have been overlooked in technical guidance and thermal modelling conventions. Similar bypass mechanisms will also be present in other building types and construction forms which contain clear cavities that bridge the external insulation layer. Measurements have shown that the party walls at Stamford Brook have an effective U-value of around 0.5 W/m2K to 0.7 W/m2K. Analysis of the experimental data has shown that the mechanism for heat loss via the party wall is driven by upwards air movement in the cavity. This air movement is generated by thermal stack effects and by pressure differences caused by the action of wind moving across the dwelling. Heat transfer from the internal conditioned spaces occurs by conduction through the single leaves of the party wall into the party wall cavity. The heat is then lost via bulk air movement upwards in the cavity and then by conduction and air movement into the loft space.

Leeds Metropolitan University were chosen as finalists in the 2007 Carbon Trust/Daily Telegraph Innovation Awards for their work on the party wall thermal bypass.

Airtightness Issues

The analysis of the qualitative and quantitative results from the study demonstrated that the technology adopted (cavity masonry construction) is perfectly capable of delivering the specified target air permeability of 5 m3/(h.m2) @ 50 Pa, even in dwellings of more complex forms. Achieving such consistently low levels of airtightness lied not only in the technology but in the processes that designed and managed its application. The airtightness work at Stamford Brook has demonstrated that the technology used, parged masonry walls linked to airtight top floor ceilings and ground floors, can deliver airtightness that is below 2 m3/(h.m2) @ 50Pa.

Air leakage testing

Most of the difficulties encountered were ones of process. At Stamford Brook a technology existed that, at least in principal, worked despite processes being identified that tolerated incomplete design information, that gave insufficient attention to detailed sequencing of operations, that were not systematic in their control of quality and did not provide consistent feedback to improve design and construction practices. All these aspects will be of increasing importance as the performance of new house building is required to achieve very low or zero carbon emissions.

The Gap between Designed Performance and As-Built Performance

It became clear from the measured whole house heat loss coefficients that there was a significant gap between the expected energy performance of the dwellings as designed and the reality of the energy performance as they were constructed. Measurements of party wall cavity temperatures established that a large proportion of the difference was due to the party wall thermal bypass; however, observations during the construction process and testing procedures and also infra-red thermal imaging of the houses revealed that some of the remaining discrepancy in energy performance was due to other deficiencies in the building fabric. The actual thermal bridging through linear junctions was higher than predicted and the true U-values of the floors, walls and ceilings as constructed was higher than calculated.

Acknowledgements

The Stamford Brook project is funded/resourced by the Department for Communities and Local Government (under Partners In Innovation project - CI 39/3/663), the National Trust (land owners) and the developers (Redrow Homes and Bryant Homes) with contributions from The National House Building Council, the Concrete Block Association, Vent-Axia, and Construction Skills. The contribution from all partners is gratefully acknowledged.

The research is led by the Buildings and Sustainability Group in the Centre for the Built Environment at Leeds Metropolitan University in collaboration with the Bartlett School of Graduate Studies at University College London.

Project Reports and Refereed Publications

Lessons from Stamford Brook: Understanding the gap between designed and real performance
Evaluating the impact of an enhanced energy performance standard on load-bearing masonry domestic construction
(Link to archived report on website of Department for Communities and Local Government)

Stamford Brook Final Report Pre-publication Version
Final Report: Lessons from Stamford Brook - Understanding the Gap between Designed & Real Performance (Executive Summary)
Deliverable 1: St Nicholas Court Final Project Report (2003)
Deliverable 2: Interim Report: Design Process (2004)
Deliverable 3: Interim Report: Monitoring Plan (2004)
Deliverable 4: Interim Report: Construction Process (2004)
Deliverable 5: Interim Report: Post-Construction Testing and Envelope Performance (2006)
Deliverable 5a: Technical Note – Initial Results of Household Monitoring and Occupant Interviews (2006)
Deliverable 6: Interim Report: Airtightness Monitoring, Qualitative Design and Construction Assessments (2007)
Deliverable 6: Interim Report: Appendices (2007)
Deliverable 7: Interim Report: Coheating Tests and Investigation of Party Wall Thermal Bypass (2007)

Lowe, R., Wingfield, J., Bell, M. and Bell, J.M. (2007)
Evidence for significant heat losses through party wall cavities in load-bearing masonry construction. Building Services Engineering Research and Technology, 28 (2), pp.161-181.

Roberts, D., Johnston, D. and Isle, J.A. (2005)
A Novel Approach to Achieving Airtightness in Drylined Load-bearing Masonry Dwellings. Building Services, Engineering, Research & Technology, 26 (1), pp. 63-69.

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