Council shows (30 years ago) that zero carbon isn’t rocket science
Houses built by Salford City Council in the late 1970′s significantly outperform new dwellings built to current (2010) building standards, new research by the University of Salford has shown. They are also more energy efficient than homes meeting the next (2013) revision to Building Regulations and their requirement for space heating is on a par with the zero carbon standard due to come into effect in 2016. The Salford Low Energy houses were designed for Salford City Council in a joint project with Salford University in response to escalating energy costs in the late 1970′s and concerns about what is now termed Fuel Poverty.
The council built a prototype pair of semi-detached dwellings and a terrace of six homes. Following monitoring a further 200 or so homes were built for the council. The prototype homes were monitored through 1980-82 by Salford University Industrial Centre Ltd, and 30 years on have been reassessed to see how the design performs today in terms of energy and maintenance costs and compares with current and proposed building standards.
The Salford houses were constructed within the Government’s cost ‘yardstick’ for social housing applicable at the time. And though a local Housing Association incorporated the design principles into a sheltered housing development and a private developer used it in a small development of houses and flats, the radical changes to housing policy in the 1980′s brought the council’s own programme of house building to a stop despite the obvious benefits of the approach.
From the outside the homes are entirely conventional in their appearance, so much so that for this latest research there were problems establishing which homes were built to the Salford Design.
The real innovations are beneath the brick clad exteriors. In designing the homes Dr John Randell and colleagues of Salford University went back to first principles and basic building physics to come up with a dwelling with very high thermal mass, inside a well insulated envelope which was designed to minimise cold bridges. This they combined with simple mechanically assisted ventilation.
The Salford house is ‘heavy and tight’ in construction, and similar in design approach to other very low energy homes such as those at Hockerton Housing Project and the Autonomous House in Nottingham, designed by architects Robert and Brenda Vale.
Though well insulated the Salford homes are by no-means ‘super-insulated’, with a nominal thickness of 200mm insulation all round (and just 173mm of insulation in the walls). The windows were proprietary, sliding, dual-glazed units made of treated timber. External doors were separated from main living areas by a lobby or hall and draught-stripped.
The key to the benefits of this approach is that unlike conventional brick and block construction which places the heavy materials outside the insulated envelope, in this case the thermal mass is on the inside, wrapped by insulation in the walls, floor and loft.
This provides a thermal buffer or reservoir, absorbing heat from occupants, appliances, and the sun and re-emitting this energy slowly over time. The result is a home which maintains an even day-night and day-to-day temperature and has a very low space heating requirement.
On construction the Salford homes were fitted with only one, and in some cases two, balanced flue gas convector heaters providing between 1.5 and 2.5kW of space heating. Indeed, under normal occupancy levels the homes would be habitable (if not comfortable by today’s standards) without any additional space heating at all. The high thermal mass also makes the homes very resilient to higher average and peak summer temperatures.
Other notable features include the use of orientation to minimize glazing on the North West aspect with increased glazing on the South East aspect and the use of mechanical extraction ventilation in the kitchen, bathroom and toilet.
The recent survey of the Salford houses shows that they continue to perform to specification and use about 75% less energy than the average requirement for space heating in the UK and over 40% less than homes built to the latest 2010 Building Regulations. Given that the performance of the dwellings is on a par with the energy efficiency required for the revised zero carbon standard (due to take effect in 2016), the research team believe that this design approach offers a cost effective and proven route to meeting this standard.
The report reiterates the findings of other research about the importance of occupant behaviour on energy consumption and running costs. In the houses revisited for this study household consumption varied by a factor of five, a spread largely attributed to differences in internal temperatures. What was also clear was that advice and training are essential in helping occupants to understand how to use and get the best from the thermal mass and small heating systems.
Homes which perform on a par with the proposed zero carbon standard and which were constructed using conventional building methods and materials (albeit in a revised configuration), over 30 years ago gives the lie to arguments put forward by parts of the housing sector that it is simply not possible to reach this target within the next five years.
Certainly there are issues to do with the requirements and expectations of housing built for the private sector. The Salford houses where designed for the social rather than private sector and would be unlikely to meet the requirements of the private sector market then or now. But the design principles used in Salford could equally be applied to executive homes in Surrey.
There will also be arguments over the high embodied energy and carbon of ‘heavy and tight’ homes, which can score less well under the Code for Sustainable Homes than ‘light and tight’ homes. Despite a preference in many parts of the industry for lighter construction methods, the embodied energy of ‘heavy and tight’ dwellings tends to be a small part of the lifetime carbon costs, particularly if heated and cooled passively, and can be partially addressed in other ways.
Perhaps the biggest lesson from the Salford study is that achieving homes with very low energy and running costs needs to be approached from first principles. Thermal mass, insulation and simple ventilation systems will never be a sexy as renewable energy, phase change materials and the latest boiler energy management system. But as this research shows, thirty years after they were constructed they still work.
Click here to view ‘The Salford low-energy house: learning from our past’.
CWL’s course Towards Zero Carbon Development, is a one and two day course covering the principles and practice of very low energy and low carbon design incorporating the design principles used in Salford. Click here for further information about the course, or contact Mark Letcher on 0117 902 0697.
Posted by Climate Works Ltd 6th July 2011.