Working with tradespeople on site is key to Passivhaus success

At a time when construction costs are rising and prices for raw materials are changing week-on-week, anything that carries as high an initial investment as Passivhaus certification is at risk of being value engineered out of the process.

The way that many designers are now looking to get around this challenge is to incorporate the principles of Passivhaus in their design, but not take the project through the certification process.

This comes down to what the client considers to be valuable, and political uncertainty and high prices mean that meeting a design brief can simply be too costly. But the role of both architects and engineers is to encourage consideration of value, not just today but in the long run. Having this conversation is difficult, but the climate clock is ticking.

The biggest issue with projects that merely aim for the principles rather than certification is that it is much easier for performance gaps to emerge later once the building becomes operational.

Passivhaus is an established, unambiguous standard that is not easily diluted, so as soon as you start moving away from that, you risk the building not performing as well as it could. As a team of building services engineers, we encounter this issue increasingly where we complete our work on a newbuild, only for the client to come back a year later saying their energy bills are higher than predicted – a problem which will grow as the cost of living crisis bites in winter.

By committing to achieving Passivhaus certification, clients are protecting themselves from nasty surprises when their energy bills drop through their letterbox, and the reality is that most of the cost is in the design work it takes to get there, rather than the certification process itself.

If designers are going to the effort of working to the principles, the final step of getting the certification is a small investment of time and money that has the potential to save the client in the long run.

Our advice is always to aim for certified projects in the hope of influencing a high-quality construction build which demonstrates very little difference between design simulation and in-use energy consumption. Being trained in Passivhaus principles has helped all our engineers understand building physics – and means they are becoming more sustainability-focussed MEP designers.

Early engagement

Another significant challenge for architects when it comes to Passivhaus projects is where and how M&E becomes part of the design process and how this is modelled.

For us, it has become an education piece as there is a fine line between early engagement and duplication of efforts. For M&E consultants, the usual approach is to wait and see the architect’s detailed 3D model and then work the elements that we are responsible for.

However, this can be too late for any significant changes that we may recommend being captured. This is particularly crucial if the input would have major architectural effects. For example, passive strategies such as space planning and window design need to be taken into consideration at an early stage as these affect heating demand, one of the main Passivhaus criteria.

The key to solving this is for the M&E Passivhaus designers to be involved at the earliest RIBA stages to develop an optimised 3D model – and the resultant analysis – as it helps embed passive measures in the design. Taking an early look at detailing, wall build-ups and junctions gives M&E Passivhaus designers an opportunity to go through these crucial elements with the designers and suggest any necessary changes. 

On almost all the Passivhaus projects CPW has worked on, we have been involved from the very early RIBA stages, engaging with clients and consultants alike to make sure that there is alignment from the brief stage onward. The Institute of Global Health at the University of Oxford is a great example of this – an incredibly complex Passivhaus building, but one that was made easier by a well-informed client and design team, with a strong desire to adopt Passivhaus principles and maintain certification.

Working with tradespeople

A lot of responsibility for Passivhaus to be achieved in practice is transferred to the main contractor and their site operatives. There is a need for contractor teams to have an awareness of Passivhaus principles at the very least, and this should apply to all their supply chains. Additionally, all site operatives need to understand what decisions they can and can’t make, as improvisation on site can lead to failure – for example in air tightness tests.

The way CPW has combatted this challenge is by formalising the role of the tradesperson and then encouraging strategic liaison between the project design team and the contractors. This greater involvement helps supply some piece of mind. I went on the training which is aimed at understanding interrelationships and interdependencies between components.

It is much easier for Passivhaus experts to work with the contractor to make sure the detailing on site is as close to design parameters as possible because we know the project specifics and understand better the nuance that goes into meeting these stringent principles.

As a senior mechanical engineer and CPW’s Passivhaus lead, I can work not just with the design team, but also with tradespeople to see how their workmanship affects the design.

It is very much a two-way street, and still requires commitment from the client right through to the contractor to make Passivhaus a reality, but early engagement and full collaboration means the process need not be painful.

Agata Kepinska is a chartered senior mechanical engineer, Passivhaus designer and tradesperson liaison at M&E consultancy CPW