News story

First whole life carbon analysis of Ireland’s residential sector highlights shortcomings of carbon emission reduction targets

A new paper by UCD Energy Institute and NexSys researchers published in the journal Energy and Climate Change finds that Ireland’s current Climate Action Plan for reduction of residential sector carbon emissions falls short of achieving its targets when carbon emissions across the life cycle of a building are taken into account.  

Current deep retrofit rates need to be scaled up about 20-fold by the end of the decade to meet a 2030 retrofitting target of 500,000 B2 homes, and, even still, national plans for retrofit are unlikely to be sufficient to meet sectoral climate targets, the authors find.

Almost half of poorest-performing-homes would need to be retrofitted to achieve a 51% reduction by 2030, they report.

The new research was conducted by lead author Dr Richard O’Hegarty and by Assoc. Professor Oliver Kinnane, both researchers in UCD’s Energy institute and leads of the Building in a Climate Emergency Research Lab based in University College Dublin’s School of Architecture, Planning and Environmental Policy. Both researchers are part of the NexSys research partnership. 

The “unique challenge” of reducing emissions from the residential sector

Previous research by Assoc. Prof Kinnane and colleagues, which was commissioned by the Irish Green Building Council for its “Building a Zero Carbon Ireland” report, found that the construction and built environment in Ireland is responsible for 37% of our greenhouse gas emissions, the same as agriculture. Dr O’Hegarty and Assoc. Prof Kinnane have since published this landmark research in a peer-reviewed, academic paper titled “Whole Life Carbon in the Irish Built Environment”. 

In many countries, the residential sector is targeted in climate action plans for reduction of carbon emissions, but reducing greenhouse gas emissions associated with buildings presents “a unique challenge”, note the authors.

When it comes to buildings, greenhouse gas emissions can be divided into operational and embodied emissions. Operational emissions include all the greenhouse gas emissions associated with the operational energy requirements of a building, such as heating, cooling and lighting. Embodied emissions include all greenhouse gas emissions embodied in the materials and energy used in construction, maintenance and demolition of the building throughout its whole lifecycle. 

Ireland’s decarbonisation strategy largely focuses on reducing the heat demand of the poor performing building stock through deep energy retrofit (a way of minimising energy use in a building) and reducing fossil fuel reliance by switching boilers out with electrically powered heat pumps, thereby exploiting the increasingly decarbonised electricity supply.

To date, climate action plans in most countries have almost entirely focused on operational carbon, with little focus on embodied carbon. “This partial focus leads to siloed policy, often focused on retrofit of the existing stock, while high impact construction continues unabated,” write the authors in the paper.  

With more housing required to keep pace with rising populations, there will be considerable additional emissions, but these have been poorly quantified until now. 

The need for a ‘whole life carbon’ perspective

In this study, the authors adopt a ‘whole life carbon’ perspective, which takes into account operational emissions from space heating, hot water provision and electricity usage in the home, including heat pump operation, as well as embodied emissions across the life cycle of buildings in Ireland. 

They use a literature review as well as modelling based on data from several databases and sources to quantify, report and analyse greenhouse gas emissions in the Irish residential sector relating to construction, maintenance and operation of the residential sector’s whole life carbon emissions.

Embodied carbon emissions are to surpass operational carbon emissions if only operational emissions are addressed (and successfully reduced by retrofit!), the researchers warn. Both operational and embodied carbon need to be eliminated in order to fully decarbonise the Irish residential sector, they argue.    

“In Ireland we have a number of conflicting policies when it comes to the residential sector. For instance, with one policy we aim to dramatically reduce the energy related to residential buildings. With other policies, we plan to increase the amount of housing , which is necessary to house those currently without homes and our population increases over the next 10 to 20 years. But if we follow through with both of these plans, any gains that will be seen through our retrofits will be cancelled out in a real whole life carbon sense by the emissions related to the buildings that we want to build,” said Assoc. Prof Kinnane.   

Findings and recommendations 

Through modelled forecasts to 2030, the authors show that national plans that aim to reduce emissions through retrofit and electricity decarbonisation will be offset by increased embodied emissions from planned development, when analysed from a whole life carbon perspective.

The current Climate Action Plan for reduction of residential sector operational carbon falls short of achieving sectoral target reductions, and additional measures will be required if the sector is to meet its proportional share and sectoral emission ceiling.

This is because gains that might accrue from home retrofit and electricity decarbonisation will be negated by the growth in embodied emissions deriving from housing development outlined in government plans, when the sector is considered from a whole life carbon perspective. 

The authors present a range of scenarios to achieve emission reduction across the whole of the residential sector in line with the national 51% reduction targets, as well as forecasts for operational emissions including business-as-usual and national sectoral targeted reduction scenarios of 40%. 

“Entirely unprecedented changes” are required to achieve a whole life emission reduction target of 51% less than 2018, write the authors in the study. These include: a reduction in the average of a newly constructed home size from 131 m2 (2021) to 80 m2, a reduction in the number of new homes from 363,000 to 203,000, with 160,000 homes instead realised from renovation, and a 62% reduction in the embodied carbon of all materials. 

A 28% reduction would result from a targeted number of energy upgrades (500,000 homes retrofitted to B or better) and an 80% renewable energy powered grid by 2030, the authors’ models show.

Based on their findings, the researchers argue that, across the whole residential sector, there needs to be: strategic targeting of the worst performing homes for retrofit first, complete decarbonisation of electricity, reduction in the size of future homes, as well as a major reduction in the embodied carbon of building materials used for residential construction.  

They also note that activation, and renovation, of existing and vacant buildings could accelerate the number of homes available while offsetting the need for extensive new construction. New projects for these researchers, funded by the EPA (Trebuchet) and SEAI (Re-Cugi), are focused on the carbon benefits of activating vacant properties and compact urban growth of future development.

“More retrofits targeted toward the worst performing stock is important, and whatever gets built needs to be built to the highest standard from an operational carbon perspective. Primarily we need to get more creative about how we plan and develop our future urban environments. Key to this is focusing on what we have in the first place; stopping demolition and reusing what we have,” said Assoc. Prof Kinnane.  

The authors hope that this life cycle perspective will open “a new window for policy makers to look through when addressing climate change mitigation ambitions,” says lead author Dr Richard O’Hegarty. “In particular, this perspective calls for greater policy focus on not just the emissions associated with operating our buildings, but also those emissions embodied in the construction of them. For example, the activation of vacant spaces could offset the need for new construction, saving carbon while accelerating the roll out of new homes,” said Dr O’Hegarty.

“The challenge is unprecedented and requires research initiatives to not only develop new more carbon efficient materials and structures, but also to better understand what we already have. Ireland has the opportunity to showcase itself as an example for other nations with even greater emissions,” he added. 

This research was commissioned and supported by the Irish Green Building Council (IGBC) and informs their roadmap to decarbonise Ireland’s construction and built environment sector: “Building a Zero Carbon Ireland”. 

Notes

About UCD Energy Institute

UCD Energy Institute is a collaboration between academia and industry delivering positive impact through research and innovation. 

About NexSys 

Next Generation Energy Systems (NexSys) is an all-island, multidisciplinary energy research programme. NexSys is hosted by the UCD Energy Institute in partnership with eight other leading research institutions. 46 leading academics work in partnership with industry to tackle the challenges of energy decarbonisation, developing evidence-based pathways for a net zero energy system. NexSys has received €16 million in funding through Science Foundation Ireland’s (SFI) Strategic Partnership Programme (2022-26), with nine industry co-funding partners and one philanthropic donor. For further information, see: https://www.nexsys-energy.ie/