Watch our webinar with Schüco, exploring the future of EnerPHit and whether the standard provides a realistic and affordable roadmap to retrofitting our historic building stock.

EnerPHit has had less exposure than Passivhaus but may be even more important. Where Passivhaus is a rigorous system for creating new buildings with impressive environmental credentials, EnerPHit tries to do the same for the even more important refurbishment sector. Since we stand no chance of getting to net zero carbon without retrofitting our existing stock, this is crucial. But is EnerPHit the best approach? The speakers at this webinar gave insight into their approaches which sometimes, but not always, coincide with EnerPHit.

Speakers from left to right: Rupert Daly, Sanya Polescuk, and Lee Marshall

Lee Marshall, managing director of Viridis Building Services, said that while many people were talking about the importance of net-zero carbon, his company had been doing it for years. There are, he said, ‘loads of opportunities for innovation.’ People too often misunderstand Part L of the Building Regulations, Marshall said. The only legal requirement is to achieve a certain low level, of CO2 emissions. Everything else is up for grabs. Criterion two is about limiting standards for U-values, and criterion three is about avoidance of air conditioning and preventing overheating. But they are not, he said, prescriptive. ‘It is up to us to implement the principles in a way that reflects our design intentions.’

Marshall also argued that refurbishing to EnerPHit levels is not always the most effective solution. For instance, achieving the high level of wall insulation required could mean extra structural work to increase cavities. Yet the additional CO2 savings could equally be made by installing two PV panels. Marshall said this would free up money for retrofitting more homes. ‘If I can do more with less, that is really sustainable,’ he said. He was challenged on Twitter about the idea of substituting PV for insulation, but argued that there is a tipping point on each project beyond which making certain improvements is not financially sustainable. Finding another way to get a similar result is then the intelligent approach.

He also gave a warning about misunderstanding what can be achieved with an MVHR (mechanical ventilation with heat recovery) system. The heat exchanged in a heat exchanger is through conduction only. Yet some 65 per cent of the heat contained in moist air is in the form of latent heat and the system cannot recover this. So when manufacturers claim that their systems are 90 per cent efficient, they are only recovering 90 per cent of the total 35 per cent available – around 30 per cent. This does not invalidate the system, but the understanding is crucial.

Sanya Polescuk Architects has been given a new lease of life and a sustainable future to a 1950s terraced house in London (ph: Emanuelis Stasaitis)

Sanya Polescuk, principal architect at Sanya Polescuk Architects, talked about her experience of remodelling and retrofitting buildings for nearly two decades. She was sceptical about EnerPHit, and even more sceptical about government initiatives. The principles that she has used have not really changed in a decade, she said. Before the introduction of the term ‘fabric first’, her motto was, she said, ‘wrap up and ventilate’. She added, ‘The kind of retrofit we have been developing over years achieves a great deal for clients and the environment. Clients want more efficient buildings and lower bills. They tend to not care for certification.’

ph: Emanuelis Stasaitis

Polescuk said it was vital to really understand the materials with which you are working. For instance, upgrading a solid wall built from breathable materials, such as soft brick and lime mortar, requires a different approach to a wall made from hard bricks and cement mortar.

Talking about a recent project, Polescuk said, ‘Trying to install an air-source heat pump in a conservation area is not for the faint hearted. I wonder how the PM’s stimulus package is going to work. It is hard to see it working in an Area of Outstanding Natural Beauty, in a conservation area or in the curtilage of a listed building. It won’t work unless there is a fundamental change in outlook of the planning system.’ In her project, planners were unwilling to accept an air-source heat pump anywhere but in the back garden. She had a real fight on her hands, which she won. But it is hard to imagine that happening, successfully, at the scale that the government envisages.

Polescuk also stressed the importance of working with a sustainability consultant from the beginning. ‘The risk of causing interstitial condensation in walls can only be determined by hygrothermal performance modelling,’ she said. Often the architect uses materials from more than one manufacturer, and that means that no manufacturer will be able or willing to reassure them about performance.

Collective Architecture’s regeneration of Glasgow’s Woodside multi-storey flats tackles fuel poverty while exemplifying a shift to retrofitting high-rise housing (ph: Andrew Lee)

The last speaker, Rupert Daly of Collective Architecture, was the most enthusiastic about EnerPHit. ‘By targeting EnerPHit you have a robust methodology,’ he said. ‘There are opportunities with EnerPHit to do a step-by-step renovation, so if the budget is not there at the start you can still do the assessment in the Passivhaus planning process, then phase the work.’

Daly, who described his practice’s project to retrofit three 22-storey blocks of flats in Woodside, Glasgow using EnerPHit principles, said ‘EnerPHit gave us the opportunity to interrogate the design and the energy levels.’ The rigorous process is, he believes, valuable, even if in the end a project is not certified as EnerPHit. Although, he added, the certification process requires a level of quality assurance that brings value.

It is clear that not every retrofit will be certified as EnerPHit, just as not every new build will be to full Passivhaus standards. But its existence is certainly valuable and needs to be more widely understood, even if some designers choose, or are forced to, work in different ways. It is a valuable addition to the toolbox as the industry works towards the all-important goal of net zero carbon.