City of York Council: Zero Carbon Homes Programme

A new build housing programme with all homes built to achieve zero carbon in use. The homes in the programme will be built to Passivhaus certification, ensuring high thermal efficiency. Residual minor heating requirements and hot water will be provided via air source heat pumps, with all other electricity usage offset by roof mounted solar PV panels. The homes themselves will be timber frame, with wood fibre insulation to ensure low embodied carbon. In addition, all schemes are low parking developments with a focus on cycling and walking with car free streets. The first homes will be complete in 2022.

The challenge

One of our major challenges is delivering Passivhaus homes on a large scale when there is little experience in the sector. In addition, we also needed additional skills in the design, commissioning and maintenance of air source heat pumps.

Build costs are also a challenge with the measures to achieve zero carbon adding a significant cost uplift to the properties. This is combined with little market data showing sales value increases for eco homes, although initial indications are that people will pay a premium.

The solution

To ensure we had the expertise to deliver the project we ran an extensive procurement for a 5+ year multi-disciplinary design team. By setting ambitious goals, reducing insurance levels, and embedding design principles at the heart of the procurement we were able to attract more specialist consultants. This has provided us with the expertise to deliver the programme, led by architects Mikhail Riches.

We have also designed using an off-site manufactured timber frame system which provides comfort to the main contractor working on Passivhaus which they will not have done at scale before, with the supplier guaranteeing the first air tightness test.

We have accessed additional grant to provide training locally on the installation and maintenance of heat pumps in preparation for construction.

The impact

The energy usage of homes will be significantly lower than a standard new build property. Over the course of a year each home will generate at least the same amount of energy as it uses, and many properties will actually create a surplus. Due to this, total energy bills are calculated to be more than 50% lower than a building regs new build property. 40% of the homes on each site will be affordable, so this saving will greatly help tackle fuel poverty for those residents and increase their disposable income.

We have also considered embodied carbon in the design process and used that data to drive decisions. This approach has been used to save a forecast 120,000Kg of Co2e just by changing the foundation design on one of the schemes.

Lessons learned

There is still significant cost involved in the design and build of environmental housing. The cost of solar PV has reduced, but Air Source Heat Pumps are still a relatively expensive item.