Setting the standard for 2016
Scattered around Salford are some 250 ordinary-looking houses that were built in the late 1980s and which have been lived in ever since — but their thermal performance is quite extraordinary.
The effect of Building Regulations on space heating in houses from 1976 to 2010 has been to nearly halve the energy requirement — steadily at first, but more rapidly with the 2006 and 2010 regulations. A further 25% reduction is expected with the 2013 regulations, compared with 2010, followed by another 25% in 2016. By then, the space-heating requirement of new homes will be 63% less than the 1976 Building Regulations.
That information is summarised in Fig. 1. Also in that bar chart are two bars (the same one repeated for ease of comparison) labelled ‘Salford 1980’, which are conspicuous for being the shortest bars on the graph — the same as the one for the anticipated 2016 Building Regulations.
|Fig. 1: Building Regulations are having an increasingly significant effect on space-heating requirements — but have some way to go to catch up with houses built in Salford in the early 1980s.|
The significance of those two bars is that in the early 1980s about 260 houses and flats were built in Salford to a design that is still 40% more energy efficient than those compliant with the 2010 Building Regulations and which is not expected to be matched until the Building Regulations due in 2016. And they were designed over 10 years before the Passivhaus Standard was first conceived in Germany.
Significantly, too, those houses cost only about 7% more to build than traditional designs with well over three times greater energy requirement for space heating. And if you assume that a prudent builder would add a safety margin for an unfamiliar design, then experience could be expected to reduce the cost to only marginally more — or even lower.
The performance of six dwellings was extensively monitored from 1980 to 1982 by the University of Salford as part of the Government’s Energy Efficiency Demonstration Scheme and the results published.
Then nothing happened until a new study in 2009/10, again by the University of Salford, to explore the long-term energy performance of what have become known as the Salford dwellings.
The Salford dwellings do not stand out from other buildings around them, and they were difficult to track down for the latest study. Current officers of Salford City Council were not really aware of their existence and, even if they were, where they might be. It also transpired that some had been demolished, along with surrounding depilated properties, to make way for a large-scale urban-renewal project.
Helped by the publication of a press release, three sites were located and studied — comprising houses and flats. One of the houses still had the same occupants, now retired.
The new study found that the energy consumption was virtually the same as was measured from 1980 to 1982 — just over 25% of traditional. There were large variations, from below 5% to nearly 85%.
History has many lessons to teach us, so let us delve deeper.
Faced with the problem that its housing stock of some 40 000 rented dwellings was too expensive to heat, it was in 1975 that Salford City Council approached the University of Salford to help design a new low-energy dwelling.
There were five guiding principles.
• Cost to be within ‘yardstick’ limits for social housing.
• Use of established construction methods, materials and techniques.
• No limitations on normal living patterns.
• Substantially lower heating costs and energy consumption than existing housing.
• General maintenance costs not exceeding existing housing.
• Adaptable to different types of fuel and heating appliances.
The basic design was based on an internal structure with high thermal capacity surrounded by a highly insulated and well sealed envelope. The result is a ‘passive’ structure that can maintain constant equable temperatures with controllable ventilation. Ventilation rates are low in Winter to conserve heat and high in Summer for cooling.
An experimental pair of 2-bedroom semi-detached houses was built by the council, followed by a terrace of four houses and two flats. Following successful detailed monitoring, a further 200 or so dwellings were built — until radical changes in housing policy in the 1980s effectively stopped local authorities building homes. However, a private builder adopted the design for a small estate of about 50 flats and houses, and a local housing association incorporated the principles into the design of a sheltered-housing development.
|Fig. 2: The energy-saving concept of the Salford design is simple — lots of internal thermal mass and lots of insulation.|
As Fig. 2 shows, high internal thermal mass is provided by constructing the internal walls of dense concrete blocks and the floors of suspended concrete beams with block infill topped with a screed of sand and cement. The thermal capacity is about four times traditional values.
Inner walls were wet plastered to ensure good air tightness and thermal admittance.
There is 200 mm of insulation below the ground floor and in the loft. Cavity walls have 173 mm of insulation.
The windows were proprietary sliding dual-glazed units with trickle vents. Mechanical extract ventilation was provided by the kitchen, bathroom and toilet.
Cold bridging was avoided by design details.
External doors were draught stripped and separated from the main living areas by a lobby or hall
Notably, the houses do not have sophisticated features such as solar thermal or solar PV, nor, as far as we can tell from the report, mechanical ventilation with heat recovery.
Advantage was taken of solar gain for terraced development. The terraced and semi-detached houses have a NE-SW orientation, so the SE elevation was given about 25% glazing and the NE about 10%.
The external appearance is brick walls and tiled roof, though this is not critical to the design.
A range of heating systems was tested. They included heat pumps using heat from extracted air, a gas boiler, underfloor heating and warm-air heating. The relatively high capital cost and significant maintenance requirement were difficult to justify for a maximum heating demand of around 2 kW.
With such a low heat demand, the production houses were heated with just one or two balanced-flue gas convector heaters with a total output of 1.5 to 2.5 kW. One was in the living room and the other in the hall to provide equable whole-house temperatures.
Conventional central heating using water-filled radiators under windows in each room was not installed because it could not be economically justified and was not needed to maintain comfort conditions with such low heat losses and the ability of these houses to retain heat for long periods. However, subsequent tenants and estate agents thought otherwise, as discussed below.
Just how dramatic was the effect on space-heating requirements is shown in Fig. 3, based on monitoring results from 1980 to 1982. Total energy costs, including hot water and other uses of energy, for the Salford houses was only about half that of houses built to 1976 and 1985 Building Regulations. The length of the heating season was also halved — from a UK average of about seven months to three to four months.
Because of the large internal thermal mass, internal surfaces are maintained at equable temperatures day and night, increasing comfort and minimising condensation problems. Problems of freezing during the Winter are virtually eliminated, even without heating.
|Fig. 3: The design of the Salford house was aimed at reducing the energy required for space heating.|
So there is the theory and practice of 25 to 30 years ago. What of today? The latest report is based on interviews with 18 people. 15 lived in the houses. One had recently moved, and two had been forced to move as the result of the urban-renewable initiative that required their homes to be demolished.
Four of the people interviewed were tenants of the houses when they were originally built. Others had lived in them for a few months to many years. The people interviewed were aged from 18 to 85. Some lived on their own, and one household of four included young children. Seven interviewees were owner occupiers, three were privately rented, and eight were existing or former council tenants.
One major change was the replacement of all the original heating systems by conventional central heating, either by the council or by the private owners.
Views on heating were markedly different between those who had experienced heating using both convector heaters and central heating.
Two people thought that those who complained about the lack of central heating did not understand how to use the house.
A number of people thought that the original heating system was more than adequate, as they found the properties warm in Winter and cool in Summer.
There was some suggestion that those who were satisfied with the original system tended to have been those who lived in the properties from the beginning and taught to use the system correctly.
Those who did not like the original heating system were often later occupiers.
There is anecdotal evidence from private developers at the time the houses were built that houses without central heating were difficult to sell. The report comments, ‘The idea that central heating is not essential for comfort, but is generally only necessary to compensate for inadequate thermal design, was not, and is still not, generally understood or accepted.’
Some problems with condensation and mould were reported, but they were not endemic or as severe as had been common in houses in the 1970s.
Although these Salford houses are likely to meet 2016 Building Regulations, it is easy to see from Fig. 3 where further improvements could be made.
There is obviously potential for solar thermal to heat hot water and halve energy use for this purpose.
Mechanical ventilation with heat recovery, in the style of Passivhaus, could reduce the space-heating requirement.
‘Other uses’ presumably include tungsten-filament lighting, which would be replaced by compact fluorescent or LEDs in a house of the future.
And finally, what impact might a little solar PV have?
Let us conclude with a quote from a Government report: ‘The potential energy savings that would result from an adoption of the Salford, or an equivalent efficient design, are immense. Conversely, failure to build to the Salford standard will impose a massive unnecessary burden on national energy resource that will be carried forward well into the next century.’
‘Next century’ gives a hint to the age of that quote. It is from a report from the Energy Efficiency Office in 1987!
Readers who would like to see the full report can download a 19-page pdf file from the link below: