Above the curve - Limerick passive house showcases precision timber engineering

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€25 PER MONTH FOR SPACE HEATING & COOLING (Estimated, see ‘In detail’ for more)
Building: 223 m2 uncertified passive house
Build method: Timber frame
Location: Limerick, Ireland
Standard: Uncertified passive house

Designing a completely bespoke home on a tiny site in a very mature, built-up urban area is the kind of brief that many architects relish, not least the challenge of creating a distinctive form that functions brilliantly, while ensuring that it blends in aesthetically with neighbouring homes. Throw in the desire to build to the passive house standard, and you have quite the project.

But spend a bit of time taking in the sight of this really interesting, three-bed, single-storey dwelling in Limerick city — particularly the way in which almost the whole house orients towards its curved courtyard — and you can very quickly see why architect Barbara Carr (of local practice Studiomove Architects) and her client, John , are so pleased with it.

The new building has a bigger footprint than the original house that was demolished to make way for it, but it still blends in nicely. “The front of the house has very similar proportions to the bungalows that are there, and we didn’t want to do something that really jumped out,” Barbara says. “But inside it’s completely different. That’s why I called it the Tardis. When you come up, you can see that it’s different, but it really doesn’t shout out and I really loved that aspect of it. And then you come in the front door and there’s that sense of the sweep of the courtyard around the site that surprises you.”

The idea of wrapping the house around three sides of the site was adopted.

The Tardis certainly manages to maximise every one of the 220-odd square metres available to it, and while it butts up closely against neighbouring properties, being single storey means there is no risk of it overlooking adjacent homes.

A driving force behind the project was John and his wife’s previous experience of living in an early 20th century red-brick home. Although they really loved the house, with its period features, it was registered with the local heritage council and they felt that any attempts to insulate it would be severely restricted. Even with a 30 kW condensing boiler and heating zones, the house struggled to keep them warm in winter.

As an engineer, John had the idea of doing a self-build very firmly on his bucket list. He was in the fortunate position to be able to take some time off work to serve as the project manager and main contractor. When the opportunity arose to buy a house that came up for sale in the area, the couple decided to take the plunge, knocking down the original 1950s bungalow to create a clean slate for a new build.

“Initially all I knew was I wanted to build a warm house. That was the starting point. So, I researched what could be done, what’s out there and it kind of led me on to the whole concept of the passive house standard,“ says John.

The curved courtyard-facing rear façade comes together

“What I really liked about it, and this is from an engineering point of view... is that you could design and model the house up front and see how it would perform rather than coming up with a notional design and then hope it would work out.”

He undertook the passive house designer training course run by MosArt Architects in Wicklow (which Barbara also did), and also decided to do a lot of the work himself, particularly the mechanical and electrical, which allowed him to indulge in his enthusiasm for the latest in smart home automation technology from Loxone.

While it’s clear from the performance figures that the Tardis works as a passive house, it was agreed early on that the design wouldn’t be a slave to the standard. “We didn’t want to wind up with a box, basically, with the windows on the south,” says John. So, while a warm, comfortable home was the main aim, achieving the standard – with or without certification — was a nice-to-have rather than a must-have.

What made things tricky was the orientation. The original house faced south but straight onto a high, six metre high brick wall with an apartment block behind it. “We looked at it and thought ‘Oh, crikey’, Barbara says. “I mean, it’s a brilliant site in terms of its proximity to town and privacy, but the orientation then was really compromised by these things.”

The idea of wrapping the house around three sides of the site was adopted so that the house orients towards the courtyard garden rather than the back wall. So, while it’s not far off the L-shape form that John had suggested, “it embraces the garden rather than addressing the wall,” says Barbara. “We calculated that we’d get enough south light into the courtyard of the house in summertime, but had to play around with window sizes as the curved courtyard crept around to face north. We also reduced the high-level north and east-facing windows in size.”

Barbara says that because the form factor was not ideal for passive house — being single storey and spread out, there is a large surface area from which heat can escape — insulation and the orientation of windows was critical.

A number of different build systems were investigated, including structural insulated panels, insulated concrete formwork (ICF) and blockwork, but it was decided that a twinwalled timber frame would give the best detailing and, more importantly, would lend itself to the non-rectilinear shape of the house.

Indeed, there’s no doubting that the geometry added a layer of complexity to the build, particularly with regards to the roof. Although it’s a mono-pitch, there’s a lot going on with it.

It sweeps around in a curve, getting wider to accommodate high level windows above the kitchen and bathroom. All this, along with the curved courtyard window setting, generated a fair bit of “swearing” among the build team in its bid to make it all come together.

Given the prominence and importance of the view facing out into the courtyard, the choice of external doors and windows was an important one. John and Barbara chose an Austrian company called Josko and even visited the factory, where they fell in love with their internal Venetian doors, made of bog oak. “These add a real wow factor to the interior,” Barbara says. “They are extra high, flush-fitting, in great finishes and with a magnetic latch system. There was quite a bit of work getting them to fit correctly.”

It wasn’t in the plan, but they also opted to line the underside of zinc roof overhang in the courtyard with timber battens. It was felt that the view from inside out into the courtyard would look quite flat and dark with just the zinc roof overhang, and undermine the look of the beautiful timber windows. So, a joiner and his experienced father were commissioned to add matching battens, which they set using the radius of the curve of the building.

“It took time to get them looking right,” Barbara says. “But now it’s really beautiful. It’s warm and you can see it from inside. So, you’re looking at your timber windows from inside, and then you look up and you see these battens as well. It’s one of those things that wasn’t decided before. I think we all love it.”

On the foundation side of things, John liked the idea of an insulated raft foundation but the need to build up tight against the back wall effectively ruled that out, not to mention the – admittedly quite small – risk that an oil spill from the next door neighbour’s oil tank would damage the EPS of the insulated foundation. A standard raft foundation was installed instead.

This article was originally published in issue 38 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

The use of timber frame, supplied by Galway firm Long Life Structures, adds bonus points for a low carbon material, as does the cellulose insulation in the walls and roof.

“The roof was what attracted me to the project really,” says Emmet Nee of Long Life Structures. “I always love doing curved work, curved carpentry. We’ve gained a bit of a reputation for doing challenging houses like this.

“We see ourselves more as thermal envelope specialists rather than just timber frame suppliers. The good thing with timber frame is that the design stage of the drawings will show up any areas that require deep thinking, and that’s where you work it out. For this house we had to work out each individual roof rafter instead of doing one and repeating it 60 times.”

The twin wall system used on this project, with two cellulose-filled studs separated by another layer of cellulose, is the company’s standard build method for passive house projects, as it eliminates thermal bridging through the walls. The company also boasts an enviable record of achieving better than 0.6 air changes per hour on every house it has built to date.

“Airtightness doesn’t happen by accident, it has to be designed in,” Emmet says. “When we go to site we have our airtightness strategy honed in. The real challenge is when you’re erecting the frame — those are there areas you won’t be able to get to again. This is the reason we erect our own frames rather than sub-contract it out.”

John and his partner moved in a year ago, so they’ve experienced both a summer and a winter. “On the face of it, people think of passive houses as cheap to run and that’s it, but it’s actually a very, very comfortable house in terms of the constant temperature, with no drafts, and it’s a single zone temperature-wise throughout.”

Since they had their smart meter installed by ESB networks, John has been tinkering around with the Nilan air-to-water heating and ventilation system to see how it works best in combination with the 3.5 kW solar PV panel array and a 4.8 kW battery. “Traditionally you might have your day and night meter, but now you’ll have maybe three or four different rates over the course of 24 hours and so we’re looking at how we can maximise that capability with a PV,” he says.

The geometry added a layer of complexity to the build.

As an engineer used to project-managing more complex industrial projects, John very much enjoyed managing this build on a personal level. “One of the things that I found with building this house is that there was emotion involved. If you’re doing an industrial project, you have a specification, you’re not worried about colours or worried about would the client be happy with this or that and so on.”

“When people look at these Grand Design programmes and so on, they have no idea what’s going to happen in the background in terms of the complexity involved in it. The best thing I ever did was to do the passive designer course, to bring myself up to speed, you know, from selecting windows, to detailing, to minimising thermal bridges and so on. I’ve learned so much from it, it’s absolutely unreal.”

No doubt he enjoyed installing the state-ofthe- art smart home system that controls everything from lighting to blinds to heating. “He had great fun with that,” Barbara says. Personal joys aside, John is also clear on what the project has achieved and is actively considering applying for passive house certification.

“We pushed the envelope in terms of getting as close as you can to the passive standard without sacrificing aesthetics in an urban, built-up area.

1 & 2 Installation of the curved courtyard windows, triple glazed aluclad units from Josko; 3 timber cladding was fitted to the underside of the zinc roof overhang in the courtyard for aesthetic reasons; 4 Intello vapour control membrane and airtightness taping to ceiling; 5 the Nilan Compact P combines heat recovery ventilation along with air heating and cooling; 6 solar battery and Solis Hybrid inverter.

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