Achieving Net Zero Homes | Rethinking our approach to housebuilding

Achieving Net Zero Homes | Rethinking our approach to housebuilding

As we’ve seen in the first two articles, successfully delivering homes that emit zero carbon during operation requires a proper definition of net zero, and homes that can balance the energy grid. However, we also need to think about our approach to what we build, says Andy Sutton, Co-Founder and Director of Innovation at Sero.

For nearly 20 years, minimum energy performance standards for space heating have been set in Building Regulations Approved Document Part L with an internal floor area metric — the Fabric Energy Efficiency rate (FEE). Prior to this, Part L set the requirements for the performance of homes by ‘elemental’ components — walls, floors, roofs, doors and windows.

This approach can be argued to offer flexibility to the designers of homes to finetune the overall energy performance of the fabric for each scheme. But the cost is an absence of consistency and standardisation for those actually delivering on site. Practically every scheme is striving to achieve modestly different thermal performances in floors, walls and roofs.

This means sub-contractors moving between sites can’t repeat the same practiced details (and let’s face it, often aren’t likely to check the drawings every time), site supervisors and building control won’t know what “looks right”, cost consultants struggle to estimate build rates, manufacturers can’t offer standard details that are compliant and are hampered in delivering new products that solve known issues. All of which is before we mention DfMA/MMC/Offsite manufacturers, who must dream of being able to just deliver one wall build up across all their order book.

Components and services
Perhaps the biggest issue with the FEE approach is the failure to recognise that buildings are made from components with different lifespans, as Richard Roger’s Centre Pompidou in Paris famously illustrated nearly 50 years ago. This becomes even more important when seen in the context of a decarbonising energy grid, assuming we have the right tools to recognise that ongoing success story. The approach fails to recognise the lifecycle of home elements: for example, insulation below the slab is generally there for the life of the homes, whereas doors and windows perhaps just 25 years (with little control on their replacement).

When you factor in the services as well with typically even shorter lives, it becomes increasingly clear that the intended flexibility actually drives wrong outcomes. This is admirably illustrated by the English ‘Future Homes Standard’, which sacrifices almost all fabric improvements by presuming enhancement to services efficiencies. The result is homes that do not minimise their fundamental energy demand but satisfy their higher demand in a more efficient manner. These are not the same outcome.

Remove the complexity
For me, the solution is to remove the complexity we’ve created, and relocate the flexibility we might want. Our homes should all be required to be built to basic elemental thermal performance standards — U-Values prescribed for walls, floors, roofs, doors and windows. Indeed, Sero has just published our view on what the performance of these should be in our ‘New Build Specification’ that’s freely available.

With perhaps an alternative complex route for the particularly unusual design, the vast majority of homes built to these standards will deliver very low space heating energy demands. They won’t all be exactly the same FEE metric, but frankly as an arbitrary calculation number does that really matter.

Even without an exactly equal FEE, all these homes will be low enough in their heating energy demands that, in conjunction with the right tools and ongoing grid decarbonisation, they will be able to become zero carbon homes over time. What’s more, we hand those building on
site a fighting chance of getting consistency to help drive quality, manufacturers a chance to innovate solutions and supply standard details, and maybe even open the door a bit wider to support DfMA/Offsite.

As an architect, I value design flexibility. But knowing where to flex, and when to impose constraints, is the art of true problem solving. Slight variations between very low Fabric Energy Efficiency ratings amongst our homes won’t cost the earth, indeed will probably help save it.


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