How do we de-carbonise existing housing?
The built environment contributes to around 40 per cent of the UK’s carbon footprint. In the next thirty years the government has pledged to bring all greenhouse gases emissions to net zero.
Most new-builds or residential projects over the past few years have been designed to be energy efficient reducing their carbon impact. However, across the country historic housing still stands with poor efficiency, which contributes to the industry’s carbon emission.
UK GBC outline that 80 per cent of the buildings that will exist in 2050 have already been built. Therefore, while the endeavour to reduce the carbon footprint of new infrastructure is significant, it doesn’t tackle the existing structures in our landscape that emit high levels of carbon. Thus, how do you, as architects, suggest that we de-carbonise existing housing?
Asif Din, Perkins and Will
The most significant burden on the housing market in the UK is heating our homes. It’s widely recognised that we need better insulation, airtightness, and double-glazed windows in our traditional houses. But this can only be justified when thinking of the house as a whole system rather than individual aspects, plus a robust understanding of the details is needed to do it effectively.
The most practical solution is to remove first-generation double-glazing windows which currently populate most traditional housing stock and replace them with better quality double warm edge glazing that reduces internal condensation with effective ventilation.
Airtightness and high-quality insulation requires proper ventilation, which has to be incorporated to ensure that moisture on the inside of the building effectively flows out. This allows mechanical heat recovery to become viable even in the oldest properties.
Ultimately, when designing to retrofit and create carbon-efficient homes, longevity and sustainability are the most important considerations. The average lifespan of a house should be in the region of 60-100 years. Therefore it is important that the predicted rise in our future climate’s temperature is addressed. Otherwise, any retrofit we do to reduce the heating load will increase the chance of over-heating and the need for active cooling in the future.
As the summer temperature is increasing year on year, it is important to find solutions to tackle overheating. Clues on how we can mitigate the need for active cooling in well-insulated housing can be found in other countries, in France for example, homes use features such as external shutters to reduce heat in the warmer months. However, introducing new elements will require a significant cultural shift to ensure the occupants know when and how to use them.
Only once we’ve reduced the thermal loads on our housing stock as much as possible, can we tackle the unused resource of roof space for clean, renewable energy systems in a cost-effective and meaningful manner.
Yet, costing is currently a challenge. With the development of thin insulation materials allows retrofitting of buildings is possible without the risk of changing the external appearance of our heritage buildings. Pricing will be brought down through large scale supply and production making these materials common rather than a niche in the marketplace.
There should be a cost incentive as part of any new green deal that the government proposes, for retrofitting buildings to increase their fabric performance, rather than the current penalty of paying VAT.
Therefore, in partnership with Penoyre & Prasad, we have pledged to offer net-zero carbon operational designs for all new projects from January 2020, at no additional cost to our clients. The time for action is long overdue, through this pledge we hope to encourage all stakeholders in the built environment to act against climate change, by first tackling our building’s energy emissions. https://perkinswill.com
Rodrigo Masey, MorenoMasey
At MorenoMasey, our approach has evolved to maximise the sustainability improvements a project will tolerate in terms of construction cost, client appetite and spatial impact. This is an intricate balance and negotiation. However, in practice, our advice follows the well-known energy hierarchy; be lean, be clean, be green. The order is critical and in fact, although it’s not a complete solution, if we are simply more lean we can make vast improvements on our in-use carbon demand. It is even possible, without too much imagination; to apply a wider view of being lean, to impact embodied energy too, use less stuff. The principles we apply are simple, but when executed rigorously and intelligently, they are hugely effective.
Priority one has to be minimising losses through the building fabric. Less loss equals less demand, equals less carbon. We insulate as much as possible and consider junctions between elements to eliminate gaps. A well-detailed, continuous insulated envelope is key. The carbon payback is quick for a well-designed building.
Our view is also that high performance materials will make the loss of space more palatable to less concerned clients. The weak link in the thermal envelope is always windows. These should be as high performing as possible, both for loss of heat and air tightness. On its own, this is one of the largest gains, both mathematically and physiologically, as draughty windows create a user bias to crank up the heating.
Air tightness extends to other building details and becomes increasingly important as insulation increases. It quickly becomes a construction quality issue and we work hard to make details both simple and easy to get right.
Finally, heat recovery on ventilation is essential. Once you have a detailed envelope, the building must be ventilated and through heat recovery on the ventilation, we avoid throwing warm air out of the building and needlessly reheating cold fresh air coming in. I think these principles are well understood by architects, but their importance can’t be ignored, they are not difficult to implement, but they are a challenge to get right.
We need to take a long-term view at decarbonising and the role of maintenance is often overlooked and seen as an afterthought or an inconvenience. However the truth is that the carbon cost (let alone the financial cost) of waste in construction is huge. By designing good access to serviceable building parts and creating architectural details that allow the elemental replacement of damaged components, we can extend the life of our buildings.
High quality materials that can be refinished, or that age gracefully, or can be re-used, greatly reduce the amount of skips leaving a building site and the amount of carbon going to landfill. As a final thought where nothing else seems possible, go ahead and plant a tree.
We are working to open up a conversation around the re-framing of absolute beauty to question the current thinking of either beautiful or sustainable, either luxurious or recycled. We believe that with intelligent and reflective design, there should be no compromise, this is not a zero sum problem, but it is our responsibility to help our clients understand what is possible. www.morenomasey.com
Natalie Barton, Sarah Wigglesworth Architects
De-carboning existing housing will require households to stop burning fossil fuels and timber to power and heat their home. If the UK’s current energy demand could be met by renewable, carbon-free energy, then there would be no problem. However, the infrastructure is not yet in place to do so and will not be by 2050.
The robust solution is to reduce the energy demand of homes. This energy demand comprises the energy needed to heat (or cool) a home and that required for a home to run, such as powering appliances.
Architects can have a big impact on energy demand through improving the performance of the building envelope by increasing insulation and airtightness. We can also work with building services engineers to specify renewable energy generation technology and ensure that building services and appliances are running efficiently. Smart technologies can also help households control energy use.
Gas boilers and cookers will need to be replaced with electric alternatives such as heat pumps and conduction hobs. Some community renewable generation schemes will be needed. Household behavioural changes will be useful too, for example not having windows open while the heating is on.
Retrofitting houses will not be a one-size-fits-all approach. Strategies for individual homes or building types will be required and thorough analysis of a home’s performance and its occupant’s behaviours will be needed. This was the first step of our R20 project, a retrofit of 9/10 Stock Orchard Street reducing the energy demand of the building, 20 years after its completion.
SWA and sustainability consultancy Enhabit undertook a comprehensive assessment of the building. This included using thermal imaging, carrying out airtightness tests, taking u-values of the building fabric, energy demand analysis using Passive House Planning Package software, and analysis of energy bill data. This research highlighted all the key elements of the building fabric and services to be improved, these included: Improving airtightness; reducing thermal bridging, increasing insulation and upgrading windows; improving ventilation by installing a new mechanical ventilation and heat recovery (MVHR) system, increasing solar control preventing spaces from overheating by improving external solar shading.
These retrofitting works took place while the building was occupied. For all existing housing, careful consideration will be needed regarding health and safety and people’s wellbeing. Furthermore, households will need to learn how their retrofitted home works to use it successfully.
Scaling up retrofitting will be complex with many issues to be considered. The cost can be substantial, who will pay for it and how? New national and local government policies will be required to facilitate retrofitting UK-wide. For example, what role will the Building Regulations have to play in ensuring standards and who will monitor the work?
Planning departments will need to be involved and supported and a mutually satisfactory strategy will need to be agreed with conservation organisations. While carbon-free products will need to be available, certified, and understood. Unfortunately, none of this will be easy and time is not on our side. https://www.swarch.co.uk
Pawel Nawojczyk, SHH
Although it is undeniable that the built environment is a hugely dominant contributor to the UK’s carbon emission, de-carbonising housing remains an uphill struggle that needs to be upscaled on the sustainability agenda. Pushing for new builds to be more environmentally friendly is a big mission in its own right, yet this gets much harder when existing stock is considered.
The problem of sustainability in the build environment is extremely complex, and solutions need to be tailored based amongst others on the type of property, use, occupants and size of works in question. Projects requiring authority consent carry more potential for implementation tools, including legislative requirements and consequential improvements. It is the existing stock of housing, that ismost likely to constitute the vast majority of the problem in hand, properties that simply exist with no improvements being done.
I see four main tiers of actions that will lead to the improvement of the sustainability aspects in a property:
Limiting the amount of energy needed (the easiest to implement): passive measures which improve the building fabric performance (e.g. insulation, high performance fenestrations, intelligent design maximising the use of natural light yet limiting heat loss or solar gains etc.). This often does not require too much skill and some can be done as DIY. If done properly and correct materials are specified, it ensures long life of the installation with limited or no maintenance, unaffected by the users. The benefits are felt from the outset. I would say that this is the foundation of the sustainability pyramid.
Use of efficient building installations (enhancing efficiency of energy use) such as boilers and overall heating systems, kitchen appliances, energy efficient lighting, water efficient sanitaryware, appropriate natural ventilation. Again, these are quite simple measures that can be introduced gradually by the users), yet these make a significant difference (e.g. replacing elements such as light bulbs for more efficiency without the need to replace the whole installation).
Energy harvesting and production; these are active measures and the costliest and often most complex ones to implement. For existing housing these can be less applicable. Some measures are easier than others, e.g. installation of photovoltaic panels or simple versions of rainwater harvesting. Others, such as geothermal heat exchange pumps, wind turbines or CHP installation might not be the right option or could bring insufficient sustainability benefits to offset the impact of their production, delivery, installation and maintenance.
How we behave and use the properties and provisions as end users. I would argue that this is the most critical one, if people don’t see the value in making a change, none of the above will be implemented. The point is to make sure the recommendations are respected not only when policed, but above all from one’s own desire and in accordance with our conscience as being the right thing to do. This needs to be a continuous process, sustainable in its own right and at the top of the agenda on a permanent basis. www.shh.co.uk
Joanna Clarke, Active Building Centre
The first question we need to ask is what do we mean by decarbonise? Applied to buildings, it means reducing the emissions from energy used through operation as well as the embodied carbon of their structure, materials and technologies.
Retaining existing housing is itself a significant step towards decarbonisation. Demolition, material removal and disposal and replacing with new stock should be avoided where possible. However, much of the UK’s existing housing was built before thermal performance standards existed, and are incredibly difficult to heat. Recent housing stock is also riddled with problems, mainly due to the ‘performance gap’ between housing design and construction.
Fortunately, there are solutions for improving existing housing stock. Although, there is no one panacea; a mix of technologies is needed.
Where existing gas transmission networks are concerned, repurposing needs to be considered for example. Instead of supplying homes with natural gas, they could distribute a low carbon source of energy such as hydrogen. This would enable existing infrastructure to be retained and reused, rather than becoming obsolete and requiring costly replacement.
While hydrogen can be produced from fossil fuels, it can also be produced via electrolysers that convert energy generated from solar or wind. Hydrogen could also be used directly in buildings via hydrogen boilers or fuel cells for storing renewable energy.
Active Buildings offer a low/zero carbon approach, combining renewable energy generation with storage and electric vehicles to manage a building’s interaction with energy networks. Combining reduced energy demand with use of renewable energy generation technologies can significantly lower carbon emissions from buildings and decrease pressure on the National Grid.
Decarbonising the built environment is about more than just material solutions. We also need to do more around education to upskill the existing industry; educate designers on designing for climate resilience; attract the younger generation into construction; and develop strategies to improve occupants’ understanding of their houses’ operation.
Furthermore, the industry needs to adopt a different mindset. Currently, procurement tends to focus on initial capital project cost, rather than focusing on whole life costs of buildings or carbon cost. Unless decarbonisation is regulated or incentivised, it will be very difficult to change this.
There are still challenges to be overcome: the costs of implementing solutions, the skills shortage and the industry’s understanding of retrofit, to name a few. Additionally, some building types are more difficult to retrofit than others, terraced or semi-detached houses with rear extensions and heritage buildings, for example. However, with a concerted effort from the top down, clear policy and regulation and a willingness to explore and implement new technologies, I don’t believe any of this is insurmountable. www.activebuildingcentre.com
Gary Clark, HOK
The United Nations and Intergovernmental Panel on Climate Change have defined that to fundamentally address the climate emergency, the following global carbon emission action must be carried out with immediate effect.
A 7.6 per cent reduction in carbon emissions per year is required. This will achieve net zero carbon by 2030 and limit global temperature increase to less than 1.5 deg C. To achieve net zero carbon by 2050 and to limit global temperature increase to two degree, a two per cent reduction in carbon emissions per year is required.
The scale of the challenge in the UK alone is chilling. There are 28 million households (1) in the UK, and we would therefore need to retrofit 54,000 homes every week to achieve net zero carbon emissions by 2030. Or perhaps more realistically: 18,000 homes per week by 2050. Can we do this?
The RIBA 2030 challenge illustrates the various scenarios to achieve net zero carbon and has set 2030 as a target for all new and deep retrofit buildings. The winner of the RIBA Stirling Prize 2019, the Goldsmith Street Housing project in Norwich, already achieves the 2030 target.
The challenge is that almost all existing buildings have to be near net zero by 2050. Two recently completed net zero case studies demonstrate that this is possible.
The Hiley Road Passivhaus Retrofit Project completed in 2017 by Patrick Osborne has achieved the 2030 challenge target for a total cost of £230,000, or £2,000/m2.
This was a one-off prototype and is a deep retrofit example that included a significant extension and sustainable upgrades to the entire house. The estimated additional cost to achieve near zero carbon was £60,000(2).
Energiesprong is a net zero carbon refurbishment development model that originated in the Netherlands. In 2018, Energiesprong completed its pilot project at Sneinton in conjunction with Nottingham Council, with the aim to complete 155 units by the end of 2020 (3). Though the cost of the pilot study of 10 houses was £75,000 per house, Energiesprong predicts that costs will decrease to around £40,000 per home in larger future phases.
All new and retrofit projects employ the same energy conservation design strategies:
- Fabric first, high performance insulation, airtightness, and triple glazing;
- Regenerative mechanical ventilation with thermal recovery, with automatic dimming/switch off LED lighting and ventilation;
- Integration of onsite renewables including ground source/air source heat pumps and photovoltaics; and
- Perhaps most importantly ‘measurement and verification’ performance building contracts such as Passivhaus.
For historic buildings, many of the above strategies can be carried out sensitively. Yet a more realistic target would be a 50 per cent reduction in energy demand with no use of fossil fuels and offsite renewables.
We have the knowledge, the technology and, increasingly, the experience of delivering net zero carbon homes. Based on the Energiesprong £40k figure, this would result in a total cost to UK plc of £37 billion annually over 30 years.
The point of no return has arrived. Unless the above strategies and timelines are acted upon in the UK and internationally almost immediately, we are likely heading to a world of around four degrees and an uncertain future. We must act now. www.hok.com