Barn Conversion in Wiltshire Upgraded with a SIPs Extension

Getting Out of The Ground

Rhodri chose structural insulated panels (SIPs) as the build method for the extension. “It’s well-engineered, precise and I put the shell up in just three days,” he says. Yet there were challenges, including the need to underpin the neighbour’s boundary wall, which came as an unwelcome surprise on day two. The extension lies less than a metre from the same border, so it also demanded specific fire-proofing measures, including a layer of cement fibreboard and an extra coating of fire-retardant. The groundworks for the foundations were complicated by tree roots, too, which required what Rhodri calls: “A significantly engineered slab.”

The contemporary cladding brings all elements of the property together and emphasises the integration of all the rooms, whether interior or exterior

The most significant challenge, though, and the primary cause of delays during the project, was managing surface water drainage. While far less glamorous than architectural or interior design decisions, effective drainage planning is critical to the success of any project. The site of Rhodri and Meinir’s barn presented an additional complication: high bedrock levels that made traditional solutions difficult.

Rhodri initially proposed using the existing pond for water attenuation, but this was not permitted. Instead, a tank system was required, which collects rainwater for reuse in flushing toilets and irrigating the garden, while excess water is carefully pumped into the mains drainage system at controlled volumes to prevent overloading.

The new cedar-clad terrace area, which is accessed via glazed doors, is the perfect place to sit, relax and enjoy the outdoors

Determining the appropriate tank size caused a significant three-and-a-half-month delay, as Rhodri worked to find an affordable and practical solution. The final system includes a 7,500-litre tank buried in the garden, designed to mitigate downstream flooding. Its size was calculated using a formula that factors in normal runoff, a once-in-a-century storm event, and a 30% margin for the effects of climate change. “We had to strike a balance,” Rhodri says. “The tank is one-fifth the size of the extension we built.” Despite the challenges, the solution effectively combines environmental responsibility with functionality.

The outdoor deck overlooks a central pond

Despite these complications, there were still lots of great elements. As well as the original structure being stable and well-built, Rhodri discovered that the roof was sufficiently insulated. He chose not to do anything to the thick stone walls, as wrapping them would mean the structure would no longer have been able to breathe. He also opted not to dig up the building’s floors, and instead decided to install conventional radiators behind the half-height oak panelling that runs the length of the open-plan living and dining areas. The extension, by contrast, features space-saving underfloor heating (UFH).

In addition to being the designer and project manager, Rhodri was also the builder. Though his professional life provided him with some relevant skills, the couple still needed electricians and plumbers, groundworkers, a roofer and drainage experts. “The sheer labour of completing all the remaining work nearly killed me,” says Rhodri, who will hire someone to do the tiling and floor laying if he and Meinir ever tackle another project.

“I worked full weekends and every evening for two years. I developed project fatigue and there were some dark days,” he says. With the work progressing in clear stages, the couple never moved out, although there was a short period when they had to live off takeaways.

Creating a Sun-Soaked Home

The result of the couple’s efforts is a beautifully renovated barn, featuring composite-framed glazing that opens onto the garden. The garden-facing wall, previously a later addition of infill concrete block, was replaced to enhance both aesthetics and functionality.

A single-storey extension, positioned at a right angle to this area along the boundary with a neighbouring property, introduces a new main entrance, bathroom, dressing room and a vaulted master bedroom. The entire exterior, including the original barn, is clad in black-stained British cedar, creating a cohesive, modern aesthetic.

Wide spans of glazing allows light to filter through the whole property, creating a light, airy feel

Sustainability was a key priority for Rhodri, but a shortage of air source heat pumps at the time led to the installation of a gas boiler. However, the house is pre-wired for a future upgrade to heat pump technology. Rhodri plans to add solar panels to the flat roof in the future, though the barn’s listed status will make this a challenging process. The property now features two bedrooms, as Rhodri felt adding more would have been excessive. A former stone-built artist’s studio in the garden has been repurposed as a utility room and guest suite.

The duck egg blue kitchen has been paired with timber accents to create a calming, homely feel

Outdoor amenities include additional storage, a covered dining terrace, and landscaped zones with a Japanese-inspired design, incorporating planted areas, a pond, and lawned spaces. This thoughtful integration of indoor and outdoor areas has transformed the property into a unified domestic space, where the garden plays as vital a role in daily life as the barn itself.

Finishing Touches

The new, spacious kitchen now fills one end of the original barn, with gorgeous, exposed roof timbers adding real character to the space. The kitchen cabinets came from a local supplier, with some handmade elements by Rhodri himself, such as the shelves, which he crafted from the old timber worktops. The new kitchen worktop is 20mm quartz, which looks like Carrara marble, but was the more practical, affordable choice for the couple.

Exposed timber has been paired with clean, white finishes, allowing the rustic features to shine

The interior design ties the old and the new spaces together. There is a big focus on natural materials, including engineered oak floors. These were chosen for their tactile nature and stability, particularly as Rhodri was unsure of the moisture content of the original subfloor. The simple palette of European oak finished in matt Osmo Oil and Dulux’s Ash White paint complement both the old barn and the contemporary feel of the extension. Matt black showers and taps create standout features in the compact wet zones, both of which are illuminated by rooflights in the flat roof.

“It’s very calm and minimalist,” says Rhodri. “We use art for adding some colour.” Rhodri even chose the interior features and finishes, with Meinir leaving most of the decision making up to him. “It’s great as we have really similar tastes,” she says. “I was very trusting – except for the artwork. I chose that!”

With the barn’s completion only crossing the finishing line a couple of months before the arrival of baby Steffan, this is now a truly happy family abode. According to Meinir, Steffan doesn’t like going into dark rooms, as he’s so accustomed to seeing the sky from every room in his new home. “The first two weeks after he was born, Meinir was housebound,” says Rhodri. “Yet she didn’t feel it, as there are so many different areas to enjoy. This project has helped facilitate family life. Even though it’s small in plan, we have everything we need.”