Sharing the lessons for Passivhaus homes

Ollie Lester shares his learning on building Passivhaus standard homes for Be First in Barking and Dagenham.

How Passivhaus differs from a traditional home

The eight home Palomar Court is part of the rejuvenated Gascoigne neighbourhood we're building in Barking for Be First, the council's direct delivery regeneration company.

What’s different though is all the homes are built to the Passivhaus standard of super insulation, high energy efficiency.

So what did I learn?

Achieving Passivhaus means significant detailing. One example is the Isoquick raft foundation for the ground floor slab that added 300mm of insulation. This was poetically described by our head of design as ‘giving your building the thermal boots it needs to keep warm’.

The level of wall insulation is also greater than normal, including 395 wall panels that were meticulously checked for airtight joints and air sealed at every junction. These were constructed offsite to reduce time and wastage.

Also, windows must have a whole window U-value of 0.80W/(m²K) or less, meaning triple glazing. It’s a myth that windows in a Passivhaus cannot be opened, occupants of a Passivhaus home can open windows whenever they wish, however the advantage of a Passivhaus is that they shouldn’t have to!

The air humidity is constantly monitored by a MVHR (mechanical ventilation & heat recovery) system which adjusts the ventilation automatically until the air quality is optimal. The aim is that 90% of heat from recycled air in the kitchen, living room and bathroom is used to heat up the supply air, providing a pleasant temperature using less energy consumption. This provides both air renewal and a healthy indoor climate.

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Palomar Court

How do you achieve super high airtightness?

The key principle for achieving airtightness is to create a single, continuous and robust airtight layer or barrier. This layer surrounds the heated volume of the building and it should be located on the warm side of the insulation, therefore fulfilling the requirement of the vapour control layer (VCL). It is important to define a single continuous airtight barrier – either it’s a complete barrier or it’s not! With the flats on Palomar Court, centralised internal service risers have been designed in so that services do not have to penetrate the airtight/vapour barrier.

Building to these meticulous standards is challenging and requires a thorough understanding of the design, building components and interfaces. You need constant quality checks, evidence gathering and record keeping to achieve Passivhaus certification. Our application consisted of a 184 page presentation of the evidence!

There has been upskilling in the supply chain, with many working on a Passivhaus project for the first time. We managed this with quality inductions, scrupulous benchmarking and interface meetings.

We also airtest at three separate hold points during the envelope construction to ensure we track and rectify any vulnerabilities. The reward is that Palomar Court is the most air tight project ever completed by Willmott Dixon. With an air change rate of 0.45 m3/m2/hr @50 Pa, it exceeds building regulations by 25 times (10m3/m2/hr @50 Pa).

Our airtesting specialist was so amazed at the readings and suggested they were easily the best results witnessed in his extensive experience of air testing!

These homes provide safe, architecturally inspired living spaces that deliver the highest standards of thermal and acoustic comfort, which then drive energy costs down throughout during lifetime of the building.

Built sustainably, with the solar panels on the roof and low energy use, Palomar Court is close to being net zero carbon in operation. Importantly, it was built with a lower embodied carbon, with around 50% less carbon emissions over its lifetime. A prime example of a brilliant building to support a better planet for us all.

This is our first Passivhaus project using our Collida technology platform, with more to come.

Benefits of a Passivhaus home

Residents living at Palomar Court enjoy much lower energy use, just an eighth of that compared with the national average, giving them much lower energy bills.

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Palomar Court won Green Building Project of the Year at the UK Green Business awards

Also, the high-quality insulation and mechanical ventilation with heat recovery means the buildings are healthier, with humidity and temperature levels remaining near constant at all times of the day. So that means no risk of condensation, no mould and with filters on the ventilation, no health problems from pollution.

The washing can even be hung up inside in winter, it will dry quicker and won’t create condensation!

Four lessons learnt

  1. It seems simple but……a great learning for Passivhaus is to start with the end in mind. That means plan for quality checks and hold points required and collaborate with all partners to ensure the intricacies are fully understood. The different products critical to achieving good air sealing are vast, with specialist tapes, EPDM’s, Membranes, Paints, Gaskets and Grommets all vital to ensure the airtight layer remains uncompromised.
  1. Be prepared for bespoke detailing; we had bespoke detailing for canopies and their support brackets as well as bolt on balconies. These can become further complicated when considering permeable materials in the cavity for fire and the arrangements for thermal bridging and fire cavity barriers.
  1. Spend time with the specialists; we were privileged to work with our inhouse team Collida and their extensive knowledge of the certification requirements was vital. Stay close to your consultants. Both WARM and Architype were also fundamental and helped with training, detailing and inspections of the works as we progressed making application and certification easier at the end of the project.
  1. Give due consideration to temporary works; obviously it is important to reduce the amount of potential weak points, so simple logistical elements should be positioned to minimise the impact. A perfect example is scaffolding for access and loading bays as each tie position needed to be carefully considered and a remedial detail required for making these good upon completion.

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