From small screen to deep green

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Building type: Steel barn converted into 204 m2 office and recording studio
Method: Flat pack I-beam timber frame, wood fibre insulation, material reuse and biodiversity focus
Location: Oxfordshire
Standard: Uncertified passive house
Energy use: Beyond net zero. Net export of 1,400 kWh from Jan to mid July 2023, excluding EV charging.
Embodied carbon: Meets LETI 2030 target and RIBA 2025 target

If you’re a fan of architectural TV shows, you will know Charlie Luxton from programmes such as Building the Dream, Homes by the Sea, and Building a New Life in the Country. What you may be less aware of is the sheer depth and breadth of his knowledge of — and commitment to — sustainable building.

Charlie heads his own small practice, Charlie Luxton Design (CLD). When the firm decided to build a new studio just outside the village of Hook Norton in Oxfordshire, it was a chance to push the envelope across a swathe of sustainability metrics in a way that is often difficult when working for a client. “If I’m going to do a project for me, I have to make it a massive education piece,” he says.

His commitment to environmental protection stretches back to his childhood in Australia, when protests to save some of the country’s old growth forests made a lasting impression on him. He moved to a farm in England at the age of nine and says playing in streams and climbing trees helped to foster his love of nature.

Charlie and his wife Kate, who is CLD’s studio manager, were finishing their own house next door when this three-and-a-halfacre plot came up for sale. It had been used to keep horses and had a steel-framed barn surrounded by heavily grazed paddock. The CLD team had been working in Charlie and Kate’s old thatch cottage down the road, but this site offered the perfect opportunity to create a purpose-built studio.

Building-within-a-building

From the outset, Charlie was keen to make use of the existing barn. “We stripped it back very carefully and engineered it so we could work with the existing concrete slab,” he says. “We took down the walls, took all the wood out of the stables for reuse, and basically tried to design a [new] building that could use as much of the existing structure as possible.”

Building on the existing slab required extra thick walls to spread the load of the new studio. But with a goal to get close to the passive house standard and a preference for natural insulation, the walls were always likely to be quite thick.

Charlie served as principal contractor and recruited as many local trades as he could. The team laid a thin layer of levelling screed and then set out to build a new timber-framed studio within the structure of the old barn.

“The idea was very much to build a building within the building,” he says, “so that we didn’t put any additional load on the frame, because the frames of those buildings are really only designed to take themselves, and the wind.”

But the barn did provide a sheltered space within which to build the studio. The CLD team chose a timber I-beam system from German wood product specialist Steico. Each of the beams was digitally modelled and precut before being delivered to site. It’s a low-waste system Charlie had grown to like on previous projects.

• Charlie Luxton in the old building. The slab and steel frame were retained, and some blocks were reused Charlie Luxton in the old building. The slab and steel frame were retained, and some blocks were reused
• Battened and counterbattened wall awaiting the powder coated corrugated iron cladding and roofing. Battened and counterbattened wall awaiting the powder coated corrugated iron cladding and roofing.
• Levelling screed to existing slab Levelling screed to existing slab
• Steico I-beam frame going up Steico I-beam frame going up
• Steico I-beam frame going up Steico I-beam frame going up
• Caberfloor chipboard on 100 mm Platinum EPS, including channels cut for 75 mm semirigid Airflow ducting, with a further 150 mm EPS beneath Caberfloor chipboard on 100 mm Platinum EPS, including channels cut for 75 mm semirigid Airflow ducting, with a further 150 mm EPS beneath
• 25 mm battens on Durelix Vapourblock airtight vapour control board and Pro Clima airtight tapes, after the Steico Zell woodfibre insulation was blown in 25 mm battens on Durelix Vapourblock airtight vapour control board and Pro Clima airtight tapes, after the Steico Zell woodfibre insulation was blown in
• Fermacell boards Fermacell boards
• Luxton and the Airflow Flexi DV1600 MVHR system Luxton and the Airflow Flexi DV1600 MVHR system
• Panelvent under Solitex Fronta vapour permeable breather membrane Panelvent under Solitex Fronta vapour permeable breather membrane
•  

“The thing about going with these precut systems is you can get an entire building on one lorry,” he says, and this was one of many ways he sought to reduce the carbon footprint of the build.

Steico laminated veneer lumber (LVL) — a mass timber product that takes dozens of thin layers of wood and glues them together to create a structural timber panel — was used for posts and beams, and around the building’s Internorm timber aluclad triple glazed windows. Durelis VapourBlock, a structural chipboard that also provides airtightness and vapour control, frames the walls and roof internally, and serves as the main airtightness layer too. The walls and roof were pumped with blown cellulose insulation (Charlie brought his local labourers down to PYC Systems in Welshpool for training in how to install it), and then lined internally with Fermacell board, which is made from recycled gypsum and paper.

The team clad the structure in dark, powder- coated standing seam steel and British- grown larch and fitted a cap of EPS insulation — salvaged from another project — above the LVL ridge beam to stop thermal bridging down through the steel joist hangers. “We were really careful about that level of detailing,” Charlie says. The roof is finished with a 20 kW solar PV array.

Design for reuse

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Inside, the team fitted 250 mm of EPS insulation over the existing slab. This was laid without any glue so that it could be easily reused in future. “We planned it all out on a computer so that we could do it with as few cuts as possible,” Charlie says. The team also used a hot wire cutter to cut the insulation as cleanly as possible, to stop microplastics from breaking off. The floors are finished with boards made from English elm.

An obsession with minimising the environmental impact of materials permeated the whole project. “We really tried to reuse as much as we can,” Charlie says. Timber reclaimed from the horse stables was reused for internal finishes. An oak-framed sliding door was salvaged from another project and re-purposed as an internal screen. Old walkways from the site were reused as solar shading. Recycled furniture and second-hand appliances were specified throughout. Outside, rather than completely dig up the concrete yard, the team simply broke up some areas of concrete and planted within it.

Charlie says that thinking about how to reuse materials at scale was one of the big takeaways from the project. “How do you use the things you’ve got to make the buildings you need?” he asks. “And how do you do that at scale? How do you find the materials, log the materials, test the materials, certify the materials?” These are some of the next big environmental questions for the building sector to get to grips with.

The CLD team also thought about how the building, and its components, might be used long into the future. “We sort of tried to imagine how you might minimise disruption for other phases of the life of the building,” he says. The building has been plumbed for future conversion to a house, and it’s been framed so that more doors can easily be installed in future. Cladding and roofing were also fixed to be easy to remove.

Minimalist heating

The finished studio achieved an airtightness score of 0.3 air changes per hour and is within the parameters for passive house certification. The building is both heated and cooled, when needed, by an air source heat pump that warms or cools supply air being drawn into the building through a Passive House Institute-certified heat recovery ventilation system from Airflow, the specialist ventilation supplier who suggested this project to Passive House Plus for this article. The system, along with the lighting system, is managed by a building automation system from Wiise.

It’s a fairly minimal approach to heating, and Charlie says it keeps the building sufficiently warm on all but the three or four coldest days of the year. But while the building was wired for infrared radiators to top up the heating, he decided against putting them in. “Given how little we would use it, I suspect the embodied energy would make no sense whatsoever,” he says.

So instead, on freezing winter mornings, an old electric radiator, covered in paint, is wheeled to provide some extra heat, and Charlie says this works well.

And what about comfort on hot days? The heat pump provides cooling too, and on the hottest day of 2022, when temperatures in Oxfordshire exceeded 38 C, the temperature in the studio was a warm-but-acceptable 26 C. An external shade limits solar gain from the high summer sun to the south-facing studio space.

The 20 kW solar PV array provides electricity to the studio, to two electric cars, and to Charlie and Kate’s own house next door. So far this year, as of 12 June, the three buildings have used 11 mW of electricity in total, but only 2.4 mW of this was imported from the grid, with the rest — almost 80 per cent — coming from solar power. Charlie is planning to install a battery next year.

Studio space

And what about the spaces inside? What kind of studio did a group of architects and designers want to create for themselves to work in? Kate says that while the old thatched cottage was a pleasant space, it wasn’t really suitable for an office. “For clients coming, it was slightly weird,” she says. For the new studio, the team wanted to have an open plan working area that fostered collaboration, but also separate rooms for calls, meetings, or quiet working. And with its light filled spaces and warm timber finishes, the new studio is certainly a beautiful space to work in.

“I know the team love coming here,” Kate says, “post-Covid there has been a culture of working from home, but we didn’t suffer from that. The guys wanted to get back into the office and be all together, and I think having this building is a huge part of that.” She adds: “It’s a place that we want our clients to come to, we want to have meetings here, we want to share it with people.” CLD does not use the whole building — about one third of the footprint is a music studio for writing and rehearsal, rented by a friend of Charlie’s, and some work was needed during the build to ensure this would be acoustically separated. “You can hear a little bit of drumming, but nothing bothersome, actually it’s really quite nice,” he says.

The needs of this space were factored into the design of the building management systems by Wiise. When musicians press record in the studio, the ventilation system – which is inaudible to the occupants but may be detectable in recordings – is temporarily turned off.

Rewilding the site

Outside, the team’s attention to detail extended well beyond the boundaries of the building. The site was heavily cropped and packed with hardcore and rubber crumb, and as soon as they got the site, Charlie wanted to start restoring biodiversity. This included planting over seven hundred native trees — particularly elm, alder and black poplar — plus new areas of wildflower flower meadow, and native scrub with crab apple, dog rose, hazel and rowan.

Charlie estimates that it will take about twenty years for the surrounding site to sequester, in the soil and new vegetation, the building’s carbon footprint (excluding the PV array – see embodied carbon section below) of sixty-seven tonnes. He says this is based on back-of-the-envelope sums, but he’s having more detailed calculations performed soon, and developing a longer-term biodiversity management plan.

He says that in the seven years since they bought the site, it has gradually become richer in wildlife, and noticeably louder with the sounds of nature. “Last year waking up at certain times of day and in certain weather was extraordinary,” he says.

“That’s just been joyous to be honest with you… the sense of wellbeing it gives you to bring a land back to biodiversity health. It just feels amazing.”

The project was a winner of the sustainability prize at the 2023 Architects’ Journal Small Projects Awards. “That was a real vindication of what we’ve done and what we’ve worked towards,” Kate says. “To get that industry recognition was so exciting and we feel incredibly proud of it.”

I asked Charlie what the biggest challenge on the building was, but he says it all went pretty smoothly. “It went really well if I’m honest,” he says. “Do you know why? Because it was incredibly rational. And that’s the biggest lesson I think is, we just need to make things a lot simpler, to make all of our buildings a lot simpler.” He says that simpler buildings mean quicker and cheaper builds, less travel to site, lower embodied energy, and more flexible and longer- lasting buildings. It makes it easier to deliver airtightness and eliminate thermal bridges, too.

“And I think it’s actually really liberating to say I can make a really simple building, and if I concentrate and work really hard on that, it can be beautiful.”

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