Making energy efficient homes

Materials World magazine
5 Nov 2014

To meet carbon emission targets, the UK must undertake a mass renovation of its existing housing stock. James Perkins reports. 

Traditionalists in the United Kingdom will be delighted to learn that 80% of the nation’s residential housing stock in 2050 will be made up of the houses standing today. The distinctly British brick and stone homes and terraces are an iconic part of the union’s character, but this abundance of ageing infrastructure poses a problem for the UK if it wants to reduce carbon emissions by 80% (from the 1990 baseline) by 2050.

It is a happy coincidence that these two statistics are the same, because they are inexorably linked. Homes in the UK are a vast carbon sink, where energy is being wasted through lack of insulation, outdated design and poor habits among those living inside.

According to Innovate UK, 27% of UK carbon emissions come from domestic buildings (18% non-domestic), and 73% of these built environment emissions come from heating and the provision of hot water.

Professor Phil Jones is one of the leading UK experts on the decarbonisation of homes. The Chair of Architectural Science at the Welsh School of Architecture, Cardiff University, says, ‘It is the existing buildings that have to really take the lead to achieve the targeted savings.’

Studies that Jones has been involved in show that costs rise exponentially when chasing higher carbon savings and, at first look, don’t add up as a purely economic investment. To achieve an 80% carbon reduction from a domestic home costs about £70,000, while an investment of about £10,000 will result in a 20–30% saving. This is an issue that Jones is investigating. ‘We have a project where we are retrofitting five houses in Wales and the main aim is to adopt a system approach, rather than an elemental approach, trying to combine the set of measures, which will give us some more cost effective approaches so we get 60%–70% savings in CO2 for about £25,000.’

Jones wants modelling to become more sophisticated, so the Government can identify the real benefits achieved through subsidising renovations. For example, energy-efficient homes could help tackle heat poverty and relieve pressure on the health budget.

‘When you look at the financial model for retrofitting housing, you need to look at things other than the straightforward cost savings based on today’s energy prices.’
Jones believes investment models implemented by the Government, such as The Green Deal, have been unsuccessful. The Government has already watered down its goal to build only zero-carbon homes in the UK by 2016, as it has made small houses exempt.

The technology exists

In suburban Maryland, Washington DC, sits an unassuming house that looks much like its neighbours, except for the giant solar panel spanning its roof. This is the National Institute of Standards and Technology’s (NIST) Net Zero Energy Residential Test Facility (NZERTF), which in a year has produced 491kWh of surplus energy. The solar panels alone produced 13,577kWh, despite being covered with snow for 38 days.

NZERTF is a 252m2, four-bedroom, three-bathroom house spread over two storeys and home to a computer-simulated family of four. It is built to the US Green Building Council LEED Platinum standard, which is the highest in that country.

Once again, cost is an issue. The NZERTF cost an extra £99,125 to build compared to a normal house. The estimated average energy bill for a home in the area is £2,725, which means the difference would take 36 years to pay off, based on current prices (but this is the method of calculation Jones doesn’t like).

Hunter Fanney is the mechanical engineer leading the NZERTF project. ‘We used exterior as well as interior insulation on the house, in addition to making the interior studs a little thicker than what is used in the USA. We usually refer to them as 2x4 inch studs, but these are 2x6 inch studs, which allows us to get additional insulation into the wall cavity.’ The team also insulated outside the studs themselves, something that is often overlooked.
Every technology used in the NZERTF house is commercially available and Fanney says, ‘With the right design and craftsmanship, and ensuring quality insulation and construction, we can achieve that zero-carbon house – we can do that with technology that currently exists.’

The team will continue to tweak the house and Fanney is considering installing a storage device for the excess power, but is undecided as to whether to use a battery, flywheel or other technology. Further testing will also be done on appliances.
‘If we move more towards the smart grid and there is real-time pricing imposed by power companies on the residential sector, then it will become more and more important to look at the ways storage is used to shift the energy load of the house to when the cost is lower.’

Testing continues

The search for improved building materials is continuing at The Hive, near Swindon, UK. The new construction materials testing unit is part of University of Bath’s Building Research Park and consists of eight hygrothermal cells, which are sealed on five of their six faces so that heat does not transfer through them. It is set up to allow easy assembly and disassembly of a building material on the remaining free face.

Inside each cell are moisture, humidity, temperature and heat flux sensors to measure how the material stands up to the wild and woolly weather on the site.

Principal Investigator Michael Lawrence says, ‘Data is passed through the wall of the cell to data loggers, which are wired up to the internet so the researcher can monitor it in real time.’

One of the cells is already occupied with a composite panel system made up of hemp fibre and lime, designed to be part of a prefabricated construction system. There is a flood cell, where the material can be tested for its ability to stand up to water and then researchers can observe various drying techniques. Another is the ‘bladder cell’, where the material is loaded up against the wall with a bladder, which can be pumped with air to simulate out-of-plane or blast loads, such as those exerted by the wind on the exterior of a house. A double height section allows facades to be tested and one of the hygrothermal cells could also be transformed to perform creep testing.

Making the move

People are living in zero-carbon homes in the UK right now. The Zed Factory has built a number of residential and public structures, including a four-apartment complex on Bow Road in London, and John Christophers, of Associated Architects, renovated his own family’s Victorian terrace in Birmingham to become carbon neutral, while maintaining its traditional facade.

What is clear is that it will take a collective effort from Government, the construction industry and householders to reduce energy waste in the homes in which we live.