Form and function

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Building: 129 m2 mid-terrace, 19th century office building
Method: Deep retrofit with internal insulation, plus extension
Location: Tralee, County Kerry
Standard: Enerphit Classic (passive retrofit standard)
Energy bills: €14 per month for spacing heating & ventilation. Estimate. See ‘in detail’ for more.
€14 per month

A 19th century two-storey, mid-terraced commercial building with decidedly wonky party walls might not strike you as the most natural choice for a passive house retrofit, not least because external insulation was not an option, and access to the site was poor.

However, as the offices for a company that specialises in high-quality building fabric design and project management, it is not surprising that owner Jeremy Walsh — along with his architect Douglas Carson — successfully deployed a fabric-first approach to transform this exceptionally hard-to-treat building into one that meets the Enerphit standard for retrofit.

Bought in 2016 by Jeremy Walsh Project Management, number 10 Gas Terrace in Tralee did have at least a few things going for it: it was structurally sound, there was space to extend out the back, and it is located right in the commercial heart of Kerry’s bustling capital town.

Mid-terraced buildings are usually not the worst offenders when it comes to retaining heat, but this building was “freezing, absolutely freezing” for its occupants for the three odd years they had used it, Walsh says.

However, his intention was always to renovate and having overseen a major renovation and extension to his own home, also to the Enerphit standard, this project finally commenced in 2019. Walsh was first exposed to the passive house concept as far back as 2011 by a client for a project that never got off the ground, but “it kind of stuck with me ever since then”, he says, particularly for its close adherence to the science of building physics.

In 2013 Walsh went on a two-week passive house course in Germany with an eye to implementing the standard on his home, a job which he completed in 2015. Living day-to-day with high levels of comfort and low energy bills, and the monitoring of two Netatmo sensors that confirm the excellent indoor air quality, swept away any lingering doubts he had about the passive house concept, and in particular mechanical ventilation.

“Conceptually, I got it as an engineer, but it was living in it that really drove it home.”

It’s kind of everything I could have hoped for.

With his feet firmly in the passive house standard and all the detailing that it entails, it was a much shorter hop and skip to doing the same again with 10 Gas Terrace. The project was also intended to be something of a shopfront for Walsh’s business. “Essentially I wanted an office that I’d be proud of and that our company and all the staff will be proud to work in, and a by-product of that is that it would be a nice place to show off to our clients,” he says.

More specifically, he wanted a light-filled space that would allow his team to collaborate as much as possible. “I wanted a space that was going to be open plan, a space that we could collaborate, work together well and produce a good team atmosphere in the place.”

For the renovation of his own home, Walsh had worked with Douglas Carson, a family friend who runs a Dublin-based practice with his wife, Rosaleen Crushell, and opted to hire him again for Gas Terrace. Walsh naturally assumed the role of project manager and main contractor, which included looking after the civil and structural engineering, and fabric design and detailing.

You design it thinking about the person who’s coming up the street.

Carson has worked on low-energy building projects before, but appears to have relished working for Walsh because there was no large team of consultants to engage with, and because their working relationship in terms of responsibility for the passive house design was fairly fluid, although Walsh took the lead. “That’s the best way to work, I think, when you’re working with somebody; that things are blurry in terms of who is what and who does what,” Carson says.

He liked the fact that the building was in the centre of Tralee town, but not on a busy street, so access to the front was easier.

Furthermore, a co-operative neighbour facilitated access to the rear, enabling the team to crane-lift in large items like the glulam beams. But with restrictions on what could be done with the front and the very back, as the footprint of the building took up the entire site, most of the focus of the project works had to be on the “in-between stuff”.

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That said, the design of the facade is intriguing and something that Carson is quite proud of. Gas Terrace is a narrow lane that used to face onto the former Denny sausage factory in the town and, while this has now been demolished - a new commercial development is on the way - the front of the building will still only ever be approached from its left or right side. This inspired what Carson terms an oblique design approach for the facade. “That means you design it thinking about the person who’s coming up the street, as opposed to somebody who’s approaching it from the front.”

The result is achieved by sills that are incredibly deep, and an expanse of Velfac aluclad windows that are set well back into the openings. “That’s not always necessarily the optimum place to put [the windows] in terms of thermal performance, but it was kind of our response to designing it obliquely,” explains Carson. “So, when you approach the building, you don’t see any glass; it appears more like a monolithic mass of render and paint. The joinery of the doors and windows also gets to be protected from the rain.”

With no room to use external insulation on the front walls or at the rear, it had to be internal. So having the windows flush with the internal insulation also facilitated the desire not to have internal wooden sills at the upper floor level, which Carson insists “would just gather dust and never be cleaned”.

The biggest challenge with the building fabric was dealing with a hodgepodge of boundary conditions. The original stone walls made up the front facade and extended about a third of the way back, but there were other party walls and neighbouring extensions of various construction types. “Each boundary condition required a slightly different treatment but faithful to the overall insulation strategy,” Walsh says.

“Most of the existing rear walls had to be demolished as either they did not follow the boundary or were not structurally sound.” These were rebuilt with thermal blocks at ground level, and timber frame at the rear of the first floor. The original stone walls were preserved, however, and insulated internally with Isover Metac mineral wool.

The measured performance is testament to the fact that the building simply works.

Insulating internally always carries a risk of condensation, particularly against older solid wall structures, because of the risk of creating a dew point — a sudden drop in temperature where water vapour condenses to liquid — between the new insulation and the old wall. In this case, there is an air gap behind the insulation to drain away any moisture that might collect. A dynamic condensation analysis by passive house certifier Earth Cycle Technologies, using the WUFI software, also confirmed that the build-up was safe.

As a two-storey office with a long footprint, getting sufficient light was always going to be a priority, and this was achieved partly using generous roof lights. But the issue of creating sufficient ventilation for the downstairs toilet was a challenge that called for an inventive solution. “In our mind, it’s not really acceptable that you’d have a toilet and you can’t open a window to get fresh air,” says Carson. There was also no lobby to separate the WC or the adjoining shower room from the corridor outside, which extends into the kitchen.

And even though the building would be mechanically ventilated, the team still wanted to be able to get fresh air into the bathroom quickly.

The clever solution was to create a tiny courtyard, with large doors making up three of the four sides of its rectangular shape: one leading into the shower room, one into the toilet and one into the meeting room. “The challenge was to keep that in as a kind of a device to get indirect sunlight into those three spaces but, more importantly, to get fresh air very quickly when it needs to be despite the [MVHR] machines doing a lot of the ventilation work,” Carson says.

This article was originally published in issue 39 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €10, or click here to receive the next issue free of charge

Being an open-plan office with space for eight staff, but also fairly small at 140 square metres, acoustic design was another element that informed the choice of materials for the finishes, while also creating its distinctly warm northern European interior.

“What I was looking to create was a great atmosphere that people can work well together and collaborate and yet not put each other off, and so acoustics are a major part of that,” says Walsh. Previous experience of working with Brian Johnston of CLV Consulting on an office building in Killorglin reinforced the value of making this a priority.

“Even before the finishes were chosen, there were acoustic treatments on the ceilings and you could really tell the difference between something that had considered acoustics and something that hadn’t.”

Johnston performed a desktop analysis of the two open-plan floors and the meeting room (complete with polished concrete floors downstairs) and recommended the correct amount and spacing of holes in the birch plywood on the walls and ceilings as a Class C absorber. The design and the spacing of the holes had been chosen especially to achieve this effect. “There’s 50 mm mineral wool behind the perforated plywood which acts as both thermal and acoustic insulation within the service cavity, and so it is an overall neat solution,” says Walsh.

Both Carson and Walsh are delighted with the finished result, with Carson especially pleased with the exposed tongue and groove timber on some of the walls and the balustrades, creating a nice textual corduroy effect, one that is likely to remain a permanent part of the décor.

The measured performance is also testament to the fact the building simply works as it is designed to. The building’s energy demand is so small, Walsh estimates that during 2021, its solar PV array and battery will have supplied 64 per cent of its total energy needs. Indoor environmental monitoring also indicates that carbon dioxide, humidity and temperature rarely exceed comfortable levels (see ‘In detail’ for a breakdown of the figures).

Walsh says: “It’s a very calming place to work actually, and I think that’s a combination of the wood and the acoustics, so it’s just a nice place to work… it’s kind of everything I could have hoped for really.”

He struggles to pick out one favourite feature “but it’s probably the curved plywood beams on the meeting room ceiling, which is an example of what is achievable by combining great architecture, structural design and onsite workmanship”.

“We may add more splashes of colour over time, with bits and pieces of art or something like that, but for the moment, I’m just happy to be here.”

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