How to make all buildings carbon negative is a policy aim currently being developed by the Welsh Assembly Government, which aspires to be a world leader on the path to sustainability.

Wales is using legislation to shift itself into a very different direction from England. Its planning policy expresses an aim within one generation to reduce the country’s “ecological footprint” to a fair level compared with the rest of the planet’s population and resources.

In this context, the Welsh Assembly Government’s Climate Change, Environment and Rural Affairs Committee, which scrutinises the government’s delivery of such policy, is currently examining how to make all buildings carbon negative.

To consider this approach, the Future Generation Commissioner last week convened a panel of experts to offer their views. This independent commissioner’s office, with 15 staff, is, in effect, the “conscience” of the government in respect of its duties under Welsh sustainability laws – laws that include the Well-Being of Future Generations Act, which is meant to ensure that all public spending is sustainable. The act is supported by the UN Sustainable Development Goals and the notion of One Planet Development.

The panel of experts included representatives of Community Housing Cymru, Constructing Excellence in Wales, the Energy Saving Trust, the Building Research Establishment, Melin Homes, WWF, plus developers and architects. I attended representing One Planet Council.

The challenge of existing housing

The main challenge agreed upon is to improve the performance of existing housing. Housing is responsible for about 27 per cent of a typical developed country’s carbon emissions and Wales is no exception.

Since houses last frequently well over 100 years, it was felt that the total lifecycle impact of homes needed to be included in any assessment: design, materials sourcing, construction, in use phase and deconstruction.

Peter Draper and Joseph Cosier of the Energy Saving Trust felt that retrofit strategies should take advantage of triggers, such as resale and when other work is being done on the house, when there is an opportunity for a whole house retrofit to the best available standard at reasonable cost.

“Retrofits should be mandatory at these points, supported by standards and enforcement,” Mr Draper said.

I said a market needed to be created for investors in energy efficiency, as there is for energy generation plant. This is being supported by the Investor Confidence Project. Andy Sutton, associate director of BRE Wales and past president of the Royal Society of Architects in Wales, countered that most efficiency measures had too long a payback period to interest investors.

The Solcer House

One of the key things the committee wanted to know is if the so-called Solcer House should be a model for all future housing. Solcer stands for “Smart Operation for a Low Carbon Energy Region“.

The Solcer House is an experimental Passivhaus design built by Cardiff University, which generates electricity – allegedly more than it consumes, and so is deemed to be “carbon negative”.

Several experts expressed doubt about this. Mr Sutton said, “Wanting to put solar panels on every roof is not possible. All roofs can’t face south, and anyway, homes above all need to be flexible to accommodate unknown future renewable energy technologies.”

Melin Homes’ David Bolter and Rounded Development’s Peter Draper agreed that renewable energy generation was more cost-effective from the point of view of balance-of-system elements of an electricity supply system for generation to be done at local scale, using a multiplicity of renewable energy sources, including solar PV, solar thermal, wind and heat pumps.

I argued that we already have the technology we need. There should not be an over-reliance on technology to achieve results. Instead results should be achieved by excellent design that is aimed at reducing overall life cycle impacts, which include embodied carbon. Construction materials, whether in retrofit or new build, play an important part in carbon emissions. Some materials have far higher embodied carbon than others. Some materials have negative embodied carbon, such as cellulose products, which should therefore be favoured by Building Regulations (such as timber, Warmcel cellulose insulation, straw bale, wool). These “lock up” atmospheric carbon in buildings for the lifetime of the product, whereas plastic products, being based on fossil fuels, have caused carbon emissions in their production cycle and are harder to dispose of at end-of-life.

Some felt that achieving Passivhaus Standard (or nearly passive house) has now about the same design and build cost as conventional build, and is a verifiable and absolute standard. “Almost Passivhaus” can sometimes be achieved at a much lower relative cost, without the use of mechanical ventilation with heat recovery.

Passivhaus is not dependent on a building facing south, unlike passive solar design. But the Solcer House is dependent on being south facing for energy generation.

Affordability is a significant need in housing. The Solcer House is not cheap. But, for example, the Pentre Solar design is affordable and made from cellulose and local materials – timber frame plus Warmcel.

A building’s form factor affects its energy performance (this is the ratio of exposed heat-losing surface area to volume). Therefore apartment blocks and terraces should be preferred over bungalows. Increasing housing density also saves energy and reduces the cost of service provision.

Land prices

Land prices are a major factor affecting house affordability, and it was felt generally that the planning system needed changing to prevent land banking and reduce land costs.

This topic is the subject of a recently completed six-month feasibility study for a One Planet-style zero-carbon affordable housing project on the edge of an existing settlement in rural Wales.

It finds that land pricing is one of the biggest barriers and makes several recommendations to address this. It also finds that it is possible to produce such homes using a local supply chain for natural, low-tech solutions, which are inherently more sustainable and affordable than the high-tech, higher-embodied energy Solcer House model.

It favours a Community Right to Build policy as a permitted category of rural development. It advocates restricting developers from land banking (whereby land is bought and withheld in the hope of fetching a high price when it can be sold for homes) by limiting applications to renew expired planning permissions.

It recommends that smaller social housing developers – such as charities, housing co-ops and community land trusts – be favoured by local authority procurement strategies with a goal of ending the dominance or even presence in the market of large commercial home builders focused mainly on profit.

This approach could be based on the German Baugruppen model. If councils run competitions for developers where the criteria for success are social and environmental, and profits limited to 15 per cent, this creates a market for that type of developer.

Barriers to delivering transformative change in house building

The panel felt that the main barrier was the dominance of big developers. They hoped that in 20 years they would be gone, or be helped to transform to “One Planet” developers by creating a new market that includes social and environmental criteria, and curbs profit.

Other obstacles identified included the planning system – which should define the route to One Planet Wales – and the need for a program of training to upskill the workforce, including in procurement and planning.

Melin Homes’ David Bolton thought it was “astonishing that anyone can set up as a builder with no training or accreditation”.

“Builders need to be accredited with the necessary skills to provide passive house level construction services, which hardly exist at present,” he said.

“Currently anyone can set themselves up as a builder and also offer retrofit services. This is not a situation that can guarantee reliable results. Accreditation and verification of performance are required.”

For rental properties, Draper said that the minimum energy efficiency standards should aim to require a property to have an Energy Performance Certificate of at least a “B” rating by 2025 in order to be rented as a residential property, or renewed to existing tenants. Properties below this rating should then be regarded as sub-standard, and non-compliance with the MEES could lead to civil penalties for landlords.


The Welsh Government also wants to know how communities can be planned and shaped to be more energy efficient and low carbon.

Above all, the panel felt that the location of the housing is important: housing located away from public transport, employment and services such as schools, shops, community centres and entertainment will result in greater emissions from transport.

“New housing developments should promote a sense of place and community and be human scale,” WWF’s Jess McQuade said. “Planning policy should support this.”

I argued that towns and cities should be encouraged to declare intentions to, and set goals for, transforming into “One Planet” towns and cities.

Planning Policy Wales already signifies an intention for all development to reduce its ecological footprint. Other policy allows for One Planet development anywhere in towns, cities or edge of settlement, but no guidance currently exists for towns. This needs to be provided.

The committee’s conclusions will be published early next year.

David Thorpe is the author of Energy Management in Building, The One Planet Life and Sustainable Home Refurbishment.

One reply on “Should we make all buildings carbon negative?”

  1. The Solcer House is an interesting experiment but has no direct application for mass housing. It is also not a Passivhaus (does not meet the standard and is not certified and I don’t think it was ever intended to be) although perhaps it has some elements of ‘passive solar’ design.

    There is a good argument for facing PV east and west on domestic installations so that generation times match the times of highest demand (morning & evening). So rigidly insisting on buildings having south facing roofs is irrelevant. On the other hand, PV’s are technology with a relatively short lifespan compared to the building fabric. Dramatically reducing energy demand should always be the first priority over small-scale energy generation which can always be added later and becomes less relevant as the grid decarbonises anyway.

    Wales already has examples of certified Passivhaus social housing underway (EG Swansea Council projects). These are the model projects to look at for mass replication.

    Mechanical ventilation with heat recovery is critical for achieving good indoor environmental qualities, especially in the climate Wales has, and for carbon emission reductions. To leave it out might on the face of it save some construction cost, but it won’t save CO2 emissions, it won’t save money over the building lifespan and it will make for unhealthy buildings.

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