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Building type: 150 m2 mid terrace café and art studio
Method: Timber frame, insulated foundations, cellulose, heat pump, PV
Location: Bristol
Standard: Passive house classic (pending)
Embodied carbon: £75 / month*
* Calculated total energy costs, including standing charges and feed-in tariff income. See ‘In detail’ panel for more information.

When Nicole Strong and Mark Finney arrived in Bristol they were seeking a change. They got one, and a challenge, too.

Coming from Cape Town, the couple, both of whom are architectural professionals, relocated to England, Finney’s home, and set to work. Arriving in the city, Strong, who had been a senior landscape architect for the city of Cape Town, decided to turn a problem into an opportunity: having young children, she found that the city, despite its reputation as one of England’s most vibrant, was missing something. But using her background as the foundation, she set about building it.

“My background is in architecture, urban design and city planning, and I am interested in the social side of buildings and the built environment,” she said.

So what was missing? Strong parlayed her experience to create a new space that offered families somewhere to be that was neither home nor an unsuitable commercial space.

“The coffee shops are very dark and dingy, and there are not many healthy options in terms of food. There are play centres but they can be a little bit overwhelming [both] for parents and children,” she said.

The walls were collapsing and covered in algae and mould, so we had to demolish and start again

The end result is Goldfinch, a welcoming community space designed to give families the freedom to imagine, create and connect, beyond the confines of the traditional café or classroom.

“We wanted to create a space where children could be, where adults could be, where they could connect in a really beautiful space. So we found a building,” she said. The building was far from suitable, however.

The 80 m2 site, located in the Bristol suburb of Westbury-On-Trym, was home to a one-storey building in extremely bad condition that had previously housed a print shop.

Nevertheless, despite this and the bad luck of beginning the process just as the Covid-19 pandemic and its attendant lockdown shut down construction, Strong and Finney proceeded.

“It was a dilapidated building that needed to be completely rebuilt. Covid slowed things down, but we got the planning [permission],” she said.

Planning was approved for a two-storey – 75 m2 per storey – building to house the new venture.

Strong’s husband Finney, a partner in Seb + Fin Architects, took up duties as architect on the project and, despite the site’s suitability, it soon became clear that an entirely new building would need to be designed and built.

While Finney says he prefers to preserve building fabric when it is possible, his description of the existing building on the site makes it clear why the couple did not go down that road.

“We did look at a retrofit. It was a single storey, but increasingly dilapidated building and half of the site was a yard. Part of it had a corrugated tin roof, which was collapsing, the walls were collapsing and were covered in algae and mould, so we had to demolish and start again,” he said.

“The previous tenant moved out because the building was so dysfunctional. It was heated with electric bar heaters [and] frankly, it was getting dangerous”.

Sustainability consultants Ecospheric, who provided energy and life cycle assessment consultancy on the project, did attempt to see if a retrofit was possible, but the results were not positive.

“We looked at viability, but it was too restrictive,” said Kit Knowles, Ecospheric’s managing director. “First, as an infill site it was tight, as they always are, but the building was not really salvageable. It was a case of too structurally compromised, too much function required and too little space”.

Skills on site

This article was originally published in issue 46 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €15, or click here to receive the next issue free of charge

If the existing building was an inauspicious start the site at least afforded the opportunity for a new beginning. As Seb + Fin Architects, a specialist in residential architecture, is enthusiastic about the passive house and Enerphit standards, building the new building to passive standard was the obvious choice.

Finney designed the building with the ground floor resting on a concrete raft foundation with a 25 mm thick concrete slab, housed in an Isoquick insulated foundation system. The walls are made with timber I-joists with cellulose fibre insulation and an external render. “Internally, on the walls, we get good airtightness,” said Finney.

Ecospheric, in its consulting role, took major steps to ensure that the building would meet passive house standards despite the difficulty doing so given its use as a café. Knowles and his colleagues did a feasibility study to establish how the passive house standard could be met for a building with this intended use, given the specific kinds of loads a café would bring.

According to Knowles, other similar UK projects were thin on the ground at best. “There are cafés inside a university and a student accommodation unit, but those are much bigger, commercial buildings. So, this is the first time that’s been done in the UK.” This points to a general truism: while residential buildings tend to have very similar energy use profiles, non-domestic buildings are far more varied, given the broad ranges of uses they encompass, and the consequent divergence in terms of impact on energy use. For a building where the main function is a café, a substantial amount of appliance use in a relatively small building pushes up the plug loads, and therefore makes it more challenging to meet the primary energy targets for passive house.

“We did our modelling and consulted with the passive house certifiers [PH Certification],” said Knowles. “The conclusion is that it would be possible if we drew up a new profile with the Passive House Institute.”

Ecospheric also performed a whole life carbon analysis, a process analysis and engaged with the design of the mechanical and electrical systems.

“Carbon analysis was done with the creation of an ‘optioneering’ engine, looking at the viability and impact on a whole life basis, of both the active and passive elements. Once we’ve got through that we know all of the different materials and methodologies we’re using and all the mechanical and electrical elements. After that, we need to know how it is going to fit together: it’s the nitty gritty that gets it right,” Knowles said.

“Next, we used our detailing methodology process, called the ‘thirteen hats’. It’s an analysis where you put on a different hat and use that to guide our detailing process. Finally, we did the mechanical and electrical, getting involved with designing that,” he said. Construction was contracted to Earthwise Construction, a Bristol-based specialist in passive house construction and heat recovery ventilation.

Both Strong and Finney complimented Earthwise’s work, noting that few contractors have the right skills and experience – and some of the few that do only work on massive projects.

We had already done all of the joinery and then the Russian invasion of Ukraine meant birch ply became much harder to get

According to Strong, working with Earthwise was particularly reassuring because previous experiences with other builders had not always been ideal.

“Because of our specialist contractor it went as smoothly as it possibly could. When we first tried out [passive house techniques] at our home, with different contactors, there were some problems, Earthwise knew what they were doing,” said Strong.

Finney says he was glad to work with Earthwise because there are few enough contractors in the area with the right expertise.

“In Bristol, you’ve got a little group of about three people who can do this. One of them, I don’t think they touch things under half a million and are looking for more than a million: high-end houses, basically,” he said.

• The existing building was in extremely bad condition and structurally compromised The existing building was in extremely bad condition and structurally compromised
• Intello Plus membrane and ductwork for MVHR systems Intello Plus membrane and ductwork for MVHR systems
• Velux roof windows help to bring in more natural light Velux roof windows help to bring in more natural light
• Installation of two 12.5 mm layers of British Gypsum FireLine board on timber battens. Installation of two 12.5 mm layers of British Gypsum FireLine board on timber battens.
• The existing building was in extremely bad condition and structurally compromised The existing building was in extremely bad condition and structurally compromised
• The existing building was in extremely bad condition and structurally compromised The existing building was in extremely bad condition and structurally compromised
• Work underway demolishing the building as it had to be completely rebuilt Work underway demolishing the building as it had to be completely rebuilt
• Ground floor build-up features a 250 mm deep concrete raft slab with Isoquick 100 mm perimeter insulation upstand Ground floor build-up features a 250 mm deep concrete raft slab with Isoquick 100 mm perimeter insulation upstand
• Ground floor build-up features a 250 mm deep concrete raft slab with Isoquick 100 mm perimeter insulation upstand Ground floor build-up features a 250 mm deep concrete raft slab with Isoquick 100 mm perimeter insulation upstand
• Arrival of windows for installation Arrival of windows for installation
• Timber frame structure progressing Timber frame structure progressing
• Smartply Propassiv OSB, seams fully taped with Pro Clima Tescon Vana Smartply Propassiv OSB, seams fully taped with Pro Clima Tescon Vana
•  

Earthwise was also able to make suggestions during the design and build, including how to meet requirements around heating and ventilation.

“We were very nervous about meeting building regulations requirements, but the contractor suggested using two residential MVHR units,” said Finney.

“We were incredibly pleased with the contractor because they were very experienced. They were good at what they do, and so there was no need for hand-holding,” he said.

This was also important because one of the core dreams was for a healthy building for the families visiting for classes and social space at Goldfinch.

“Apart from sustainability, we wanted a healthy environment with good air circulation,” Strong said.

In addition to construction and ventilation, Earthwise also did all of the internal joinery. “That was quite novel, [and was possible] because they are joiners,” said Finney.

As it is not a residential building, however, there were additional challenges. As a result, the fact that a new build was required had some significant design benefits.

“Due to the high occupancy, the ventilation rate has got to be really high and that’s quite challenging to address, but the envelope is new so it was easier to achieve. Working around things in Enerphit is tricky: you always have cold bridges to address, whereas we just designed them out of it,” said Finney.

A Stiebel Eltron air source heat pump – selected by Ecospheric to ensure a low global warming potential refrigerant as part of the performance spec – provides heating and cooling, while photovoltaic panels feed electricity to a battery for storage and later use.

Geopolitical events also had an impact, primarily on cost: both the post-pandemic supply chain crunch and the Russian invasion of Ukraine were felt.

“We were quite fortunate because the plot was purchased and was going through the legal side during lockdown. What we did suffer from was price inflation. We were relying on a lot of timber products, which all went up by 50 per cent. That has now levelled off but not come down,” said Finney.

“We had already done all of the joinery specifications and design and then the Russian invasion of Ukraine meant birch ply became much harder to get,” he said. Nevertheless, the project was completed and signs of success are visible.

“Because it’s tight and well-insulated we were able to do all of the hot water, heating and cooling from an air source heat pump on the roof and that’s distributed by the ventilation system. The heat demand should be pretty low – it’s designed to minimise the demand,” he said.

Open for around three months at the time of publication, the next step for Goldfinch is to see if the building performs as expected. “What we are keen to do is see how it works down the road,” said Finney.

“What we often tell clients is that if you did passive house modelling it should be pretty accurate – but we want to see just how accurate,” he said.

Of particular interest to Finney is understanding the impact of materials such as concrete and expanded polystyrene, choices forced on the design by the site.

“We’re very keen on embodied carbon analysis. We were keen to use as much timber and [as many] natural materials as possible, but in this case we had to use EPS and concrete and [petrochemical-based] roof insulation. We would have avoided that on a greenfield site. Also, there was zero information on the steel and that means we have to assume the worst case scenario and that could knock us out of the top bracket,” he said.

The experience, largely positive but not without the unexpected problem of inflation in the price of materials, has only confirmed Finney’s view that all construction projects should be sustainable.

“The government needs to come to the party and incentivise good building practice. It should always be the case that choosing the green option is cheaper,” he said.

Image gallery

• Typical Northern External Wall Detail Typical Northern External Wall Detail
• Typical Western Party Wall Detail Typical Western Party Wall Detail
• Typical Southern External Wall Detail Typical Southern External Wall Detail
• First floor First floor
• Ground floor Ground floor
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