Blog

24 Jul

JRC Carbon Scoping Report

Dr Zoe Detko, May 2019

We have been working with Lancaster University and their Centre for Global Eco-Innovation department, looking at Passivhaus and the Carbon footprint of natural roofing slate when compared to other roofing products.

Climate change – UK housing and construction

In 2008 the UK passed its Climate Change Act, the act imposed targets for reductions of Greenhouse Gas emission by 80% of the 1990 levels by 2050. These legally-binding climate change targets will struggle to be met without greenhouse gas emissions being almost completely eradicated from UK buildings (CCC, 2019). Energy use in homes in the UK is increasing, accounting for 14% of total emissions, whilst emissions reductions have halted across the UK’s 29 million homes (CCC, 2019). A recent survey showed that 57% of those working in the building industry were working towards more sustainable practices than they had in the previous year (EDIE, 2018), highlighting that reducing emissions is becoming the forefront of many industries in order to fall in line with the Climate Change Act targets, not least the housing and construction industry.

Passivhaus

A way in which the industry are moving towards emissions reductions is by building to “Passivhaus” regulations and standards. Passivhaus is defined as “a building in which thermal comfort can be achieved solely by post-heating or post-cooling the fresh air flow required for a good indoor air quality, without the need for additional recirculation of air” (Passivhaus Trust).

There are specific standards within this that are required of a Passivhaus in a European climate, these are set out in Table One.

 Table One

Each project that is undertaken with the intention of being a Passivhaus would use the Passive House Planning Package. In order to achieve the targets set out in table one there is a requirement for very high levels of insulation, high performance windows with insulated frames, airtight building fabric, ‘thermal bridge free’ construction standard and a mechanical ventilation system with highly efficient heat recovery. It is possible to retrofit the Passivhaus ideals to an existing structure, and with this come different standards, as there are different factors to consider that may hinder a retrofit fulfilling the Passivhaus standards, these standards are referred to as EnerPHit and are shown in Table Two.

Table Two

There are no specific materials that have to be used in the construction of a Passivhaus standard building, there are only recommendations for the methods of construction and targets for the performance of the building. Although Passivhauses are built for the purpose of being low energy use buildings, they often require more building materials than a standard new build house. The embodied carbon within these materials could mean that a Passivhaus uses more energy over an 80 year period than a similar size new build home (Crawford and Stephan, 2013). There are Passivhauses that have been built from a variety of materials, looking towards lower embodied carbon, which also include the use of slate tiles for the roof (Ecoarc; Econ Associates, 2018).

The UK Government has no definite policies on what can or cannot be called a Passivhaus, or any specific standards that need to be met, although as with all consumer standards, if something is being sold as a Passivhaus, or a contractor has agreed to deliver to the Passivhaus standards then there are obliged by law to adhere to the correct standards set out above (Passivhaus Trust, 2011). Innovate UK undertook a study of low carbon housing in the UK and have compiled lists of recommendations and guidance for each stage of a Passivhaus project that should enable the house to be designed, built and inhabited to the Passivhaus standards (Innovate UK, 2016).

Although across the world there are different policies and regulations about new buildings meeting Passivhaus standards (Passivhaus International), in the UK there is no such regulation. The Passivhaus Trust are looking to integrate the Passivhaus standard in building and construction policy, and they regularly consult with different governmental groups in order to be a fundamental part of the conversation (Passivhaus Trust).

Embodied carbon in roof tiles

Reducing carbon output from buildings is not solely related to their energy efficiency, the roof of a home is important because of potential heat loss through poor insulation, but the materials used are also important for the embodied carbon they hold.

Embodied carbon in the building and construction sector is the carbon dioxide equivalent (CO2e) associated with the non-operational phase of a project. Any emissions produced by the extraction, manufacture, transportation, assembly, maintenance, replacement, deconstruction, disposal and end of life aspects of the materials used in a building (UK Green Building Council, 2015). The UK Green Building Council recognise the importance of addressing embodied carbon in the built environment and in making buildings more resource efficient (UK Green Building Council, 2015).

Roof tiles are an important material in the construction of buildings, and the different types available have varying amounts of embodied carbon. There are three main types of roof tiles used in the UK (Communities and Local Government, 2010). These are concrete tiles, clay tiles and slate tiles. Slate that is quarried in the UK is becoming increasingly more expensive and as such imports from Spain are becoming more common.

A comparison between the embodied carbon in the three most common roof tiles slate (Crishna et al, 2011), concrete, and clay (Monier (UK) Limited, 2009) as well as imported slate (Crishna et al, 2011), was undertaken and the data is set out in Table Three.

Table Three

It can be seen that per tonne, slate and imported slate have the most embodied carbon. When this data is combined with how much the tiles weigh per m2 of roof covered it is clear that, the concrete and clay weigh significantly more and as such more ‘weight’ of product is needed to complete the same m2 of are. This then shows the UK Slate has over 5 times less the embodied carbon per m2 than concrete and three times less than clay. The less expensive alternative of Spanish slate, still comes in at over 4 times less embodied carbon than concrete and almost 2.5 times less embodied carbon than clay, this is even after having to be imported.

Lifespan of the roof is also important to consider when discussing embodied carbon. Slate has a 33% longer life expectancy than concrete or clay roof tiles. Over a 240 year period a slate or Spanish slate roof will need to be installed and then replaced four times, with a total embodied carbon of 1198.57 and 1514.63 tonnes of CO2e respectively. Whilst clay and concrete would need to be installed and replaced 5 times with an embodied carbon of 7944.3 and 4567.5 tonnes of CO2e respectively. This points towards slate as not only being more carbon efficient but also resource efficient.

JRC sales figures

JRC estimate that they sold over 5.2 million tonnes of slate in 2018 alone. If this total slate sold replaced concrete or clay tiles in the construction of buildings in the UK then they have reduced the embodied carbon by around 1500 tonnes as shown in Table Four.

Table Four

References

CCC. (2019). UK housing: Fit for the future?. Committee on Climate Change.

Communities and Local Government. (2010). Housing stock report 2008. English Housing Survey.

Crawford, R.H., Stephan, A. (2013). The Significance of Embodied Energy in Certified Passive Houses. World Academy of Science, Engineering and Technology. 78

Crishna, N., Banfill, P.F.G., Goodsir, S.. (2011). Embodied energy and CO2 in UK dimension stone. Resources, Conservation and Recycling. 55 (12), 1265-1273

Ecoarc. The First Certified Passive House in Kendal, Cumbria. Available: https://ecoarc.co.uk/kendal-certified-passive-house-kendal-cumbria/

Econ Associates. (2018). Passive House Project, Nottingham – Summer Update 2018. Available: https://www.enconassociates.com/news/passive-house-project-nottingham/

Edie. (2018). THE STATE OF SUSTAINABILITY IN CONSTRUCTION. Insight.

Innovate UK. (2016). Building Performance Evaluation Programme: Findings from domestic projects. Making Reality Match Design.

Monier (UK) Limited. (2009). PAS 2050 Assessment of Concrete and Clay Roof Tiles (Plain and Interlocking) . Summary report.

Passivhaus Trust. What is Passivhaus?. Available: http://www.passivhaustrust.org.uk/what_is_passivhaus.php.

Passivhaus Trust. (2011). Claiming the Passivhaus Standard: The UK context. Technical briefing document.

UK Green Building Council. (2015). Tackling embodied carbon in buildings. The Crown Estate.