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If Passivhaus is to be widely implemented across the United Kingdom it is necessary to assess whether The Code for Sustainable Homes and the Passivhaus technique can work together. This chapter introduces what the Governments targets are for new homes in the UK by looking at The Code for Sustainable Homes. It will also look at the code in more detail to see how the construction industry generally feel about it and the impact it is having on the push towards a greener future. Finally it will assess whether the Code can work with Passivhaus in the UK and identify any problems that might occur when trying to implement the Passivhaus technique in the UK under British Building Regulations.
'Sustainable' is a word that is often used in the world today and it may be argued that the true meaning of the word has been skewed somewhat. The United Nations Brundtland Commission provided a commonly quoted definition: "Sustainable Development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs" (World Commission on Environment and Development, 1987, p.43).
Part of the Government's strategy to reduce carbon emissions and become more sustainable included introducing The Code for Sustainable Homes in 2007 as a voluntary standard. It was then made mandatory for all new homes in 2008. The Code was created by Government through the Department for Communities and Local Government (DCLG) in close consultation with the BRE and the Construction Industry Research and Information Association (CIRIA) with further input from the house building industry. The DCLG defined the scheme as:
Both Passivhaus and the code apply to new build housing. New builds make up a small proportion of the entire UK building stock, approximately 160,000 new homes are built each year but only 15,000 are demolished (Monbiot, 2006) and official figures record that there are about 21,500,000 homes in England alone (DCLG 2009). The Government predicts that "by 2050, as much as one third of the total housing stock will have been built between now and then" (DCLG, 2007a, p.5) if their targets are met. The amount of sustainable homes that will therefore have been built by 2050 will undoubtedly have a significant effect on reducing overall emissions. The government have set targets to reduce carbon emissions on the lead up to the 2016 target of zero carbon homes. The following table shows intended future carbon improvements.
The code uses a sustainability rating system, indicated by stars to show how well each house performs in terms of overall sustainability. They can be rated from one star - which is entry level above building regulations; to six stars - which is the highest level, reflecting exemplar development in sustainability terms (DCLG, 2006) and is said to be zero carbon. The code is split into nine separate design categories which must be tested in order to decide what level the home will achieve. Minimum standards exist for a number of the categories; these must be achieved in order to meet the minimum standard. As maximum importance is given to energy efficiency and water efficiency there are minimum standards which must be met at each level of the code. This means that if a building only scores a level two for energy, but scores maximum points everywhere else, the dwelling can still only achieve a level 2 rating. The following table shows what the Code measures when assessing a home; the highlighted areas are those that have a minimum standard.
The Code has raised the awareness throughout the industry that new buildings should be built to higher levels of sustainability than ever before. This has led to a knock on effect of increased renewable energy sources being used on projects. Although this sounds great it is not necessarily a good thing as medium to high levels of the code can be reached without actually improving the building envelope but by using these sustainable technologies on site, which are often expensive and impractical. Technologies such as Photovoltaic cells are based on good scientific principals but often have minimal benefits as the money and energy it takes to create and install these products is often far larger than what they will produce day to day. Complex and impractical solutions such as these are being chosen over simple as effective solutions as they are highly visible and are becoming known as 'eco-bling' and 'green wash' amongst other terms. The antidote for this has been coined as 'eco minimalism' by prominent Architect Howard Liddle (Grant, 2008).
Recent research undertaken into the Code has found more areas of concern. The effectiveness of the methodology and calculation methods used to produce results for both energy and water categories are criticised for producing unrealistic results. The Good Homes Alliance (GHA) found that the calculation method was overly complex but also open to manipulation. It also found that many of the fittings required to meet the higher levels of the Code would be unsuitable to many users and can be easily replaced once the home is occupied. The GHA further stated that calculation of water usage takes no account of user behaviour and that credits are rewarded for rainwater and greywater reused internally. In many cases this is more costly and energy intensive than mains treatment and delivery as illustrated by the next graph.
Within the energy section of the code problems are found because it is so reliant on the SAP which has been around since the 1970's. In SAP methodology the calculated Dwelling Emission Rate (DER) is always referred back to a base Target Emission Rate (TER) the reduced emission factor for electricity means a greater percentage improvement is achieved than in reality. Therefore more CO2 emissions may be released from electricity use than is being recorded. The GHA claims to have witnessed electrically heated Code level four dwellings that emit more CO2 than a similar gas heated home built to Building Regulations (Good Homes Alliance, 2008).
Another piece of research found that an electrically heated small terraced dwelling produced twenty one percent more CO2 than its gas heated equivalent (Stothart, 2008). The GHA also found that SAP penalised more efficient building form as it has a sliding scale meaning that it's easier for larger and less efficiently formed dwellings to gain a higher SAP rating (Good Homes Alliance, 2008). This does leave many Passivhaus projects vulnerable to these problems as they are often designed to employ a compact form and are primarily concerned with space heating demand.
There are currently about four or five certified Passivhaus dwellings in the UK with many more projects in the design and construction process. The PassivHaus Institut is now affiliated with a number of UK organisations including BRE, AECB and Inbuilt and these are now accredited to issue Passivhaus certification to projects in the UK. Inbuilt state that "A well designed Passivhaus will achieve the energy credits needed to achieve Code level 4 of the Code for Sustainable Homes and with minimal uplift can be improved to reach Code level 5". This is because it is not possible to go beyond code level 4 without specifying renewable energy technologies (BRE 2009). Level 4 of the Code requires carbon dioxide emissions to be reduced by 44%. The fabric performance requirements required for level 6 of the Code are based upon the PassivHaus standard (BRE 2009). The Government's recent consultation on the definition of zero-carbon homes states that energy efficiency standards included in Building Regulations should be equivalent to Passivhaus by 2016 (DCLG, 2008).
The Code estimates a buildings energy use and carbon dioxide emissions by using SAP which is currently the energy modelling tool preferred by the Government. It was developed from the BRE Domestic Energy Model (BREDEM) method which was based upon monitoring of housing stock in the 1970s and 1980s; the first version was published in 1995 with updated versions being published in 1998, 2001 and 2005 (Clarke & Reason, 2008) a further updated version is planned to be released in 2010. SAP is primarily used to show compliance with the Code and Building Regulations but can also be used as a design tool and energy model. PHPP is a somewhat more sophisticated tool which is sensitive to location, overshading and orientation and is a more reliable indicator of the actual performance of the building (Inbuilt, 2009). It is easier to integrate PHPP into the design process than it is with SAP; PHPP is used by designers from 'concept development' through to 'detailed design', ensuring that the performance targets are met without stifling architectural expression (Inbuilt, 2009).
SAP complies with Part L1A of the Building Regulations by calculating the annual energy consumption, the cost of the energy and the associated CO2 emissions. It does this by estimating energy consumption for primary and secondary space heating, hot water and electrical energy used for fans, pumps and lighting. In comparison, PHPP has two main targets: a useful space heating limit of 15 kWh/m2/yr (the figure required for Passivhaus status); and a primary energy limit of 120 kWh/m2/yr (Clarke & Reason, 2008). SAP concentrates more on what levels of CO2 the dwelling is going to produce whereas PHPP tries to aid the designer in minimising heat loss from the dwelling by ensuring the building envelope has extremely high performance values. "Treating the fabric in isolation recognises that heat sources can be changed much more easily than the building fabric" (Clarke & Reason, 2008, p.35). The study then goes on to say that SAP does not place as much value on improving the building envelope:
The Code has managed to bring the idea of sustainable building to the forefront of British construction. The issues raised concerning the way that homes impact on the environment have largely been addressed by the Code, however there are also a number of problems that have been identified about some of the methodology and calculations used. Other criticisms received are that lower levels of the Code do not really offer 'sustainable' solutions and being able to have a nil rated certificate as a code rating means that house builders still have a way of ignoring the Code. It is therefore necessary for the Code to be able to be updated and changed over time so that it is able to evolve into a stronger, more complete policy. Some of the changes may include adapting part of the Passivhaus technique such as PHPP in order to offer a more complete and fair assessment of new homes through design and construction phases to project completion.