Behind the facade of an 18th-century threshing barn, an explosion of striking forms brings a radical edge to a sensitive conversion.
When architect Duncan Chapman first walked into Pheasant Barn, it reminded him of the scene of a long-forgotten Wild West shoot-out. The inside of tattered building in Faversham, Kent was criss-crossed by lines of sunlight that streamed through bullet-hole-shaped fissures in the walls. Chapman was struck by the way the light broke through the dark volume, and when his firm Circus began converting the 270-year-old building into a weekend home for a London couple, the effect was a key influence.

"The chaotic patterning of shards was quite formative," he explains. "We wanted to preserve a little of the chaos we had found." The £500,000 loft-style conversion does this in two ways. First, there are two white mezzanine pods dropped inside the barn, resembling frozen explosions. Then there is the lighting, which aims to recreate the buck-shot effect of the fissures, with random openings instead of a predictable sequence of windows. Considered chaos drove the design philosophy, with unpredictable forms contrasting with the ordered grid of the original elmwood frame.

Pheasant Barn was built in the 1730s and was used for threshing grain. Since then, it has gained a courtyard, a set of Victorian stables and grade II-listed status. Circus' conversion takes on this entire complex, with guest bedrooms and a mini-cinema in the stables, but most attention has been given to the barn. The clients, were Su and Paul Vaight, a BP executive, and they ran the contract themselves. They envisaged this cavernous space as the main living area, suitable for dining and entertaining, studying and sleeping.

The challenge for Circus was to create spaces for different functions, yet maintain the sense of a continuous expanse. It meant that the cellular approach common in this kind of conversion would not work. Instead, the architects decided to hang structures within the main area that were kept as free from the original walls as possible. At either end of the barn, two bold zones have been created with enclosed spaces underneath and mezzanines above. These jagged sculptural forms simultaneously emphasise the openness of the space and provide privacy. Made of steel frames wrapped in timber and plaster, the chunkiness could have dominated, but somehow they manage to draw attention to the space that would have been lost had the partitions extended to the roofline.

The designers wanted the contemporary additions to clearly identify themselves. "Our aesthetics had to act as a counterpoint to the existing structural rhythms," says Chapman. "We wanted them to be deliberately alien so that the new elements were readable as new. The forms are explosive, with shards moving from the centre outwards; we chose strong striking lines that could hold their identity against the barn." The point being that the new and the old are read separately and so help to emphasise each other.

Despite the obvious drama of these bursting forms, splitting the functional areas in two and setting them at opposite ends of the barn means there is a sense of balance and symmetry to the layout. "There are resonances and reverberations between them that keep them in check," says Chapman.

The arrangement also leaves a clear axis of open, light-filled space in the central area. On one side, there is a window overlooking the north Kent coastline, with a cunning, sunken seating area from which to enjoy the panorama. This seating is backed by a low-lying sculptural partition that matches the forms of the two mezzanines. On the opposite side of the barn is an even more impressive opening: 3 × 7 m barn doors, which open to reveal inner glazing that can be lifted in the summer like a sash window.

In fitting the two new structures, Circus worked with engineer John Edwards, at the time an associate with Alan Conisbee and Associates. With the lower levels too narrow to fully support the overhanging mezzanines, Circus and Edwards had to find other ways to hold them up. The limitation was the spirit of sensitive conservation: the project team was reluctant to pin new additions to the old elm struts. According to Edwards, this called for real ingenuity. "We had to do a fair amount of gymnastics so that there was minimal contact. The idea was that all the additions could be reversed, so the barn had the potential for a different future use. The way we did it, you can actually unbolt everything and put the building back to how it was 100 years ago."

In the study mezzanine above the kitchen, five different load-bearing concepts were used. The simplest is an exposed tubular post that props up a short cantilever above. There is also an exposed steel column that stands on what was once the barn's threshing floor; this forms a T-section to contrast with its tubular counterpart. Then there are steel supports hidden within the stairs, cleverly tapered to fit the stair profile. Around the back of the structure, a pair of parallel steel plates straddle a timber beam to support another jutting area above. The final support holds a corner of the mezzanine from above with a hanging tie-beam bolted to two original timbers. From this hangs a steel rod pinned to the study balcony, which also eliminates bounce.

Employing so many support techniques added complications and substantially contributed to the project's 18-month delivery time. But the variety adds to the underlying aesthetics, where unpredictability contrasts with the regularity of the barn structure. "Again, we wanted a readable counterpoint," explains Chapman.

This was also the guiding principle with the windows. When the Vaights purchased the building in 1997, there was already planning permission for a conversion, which included the possibility of inserting a series of domestic windows. But this was immediately dismissed when the client and architect saw the derelict building with light dappling through holes and catching the drifting dust in its shafts. Chapman also thought that breaking the walls up with new windows was an abuse of the barn's original form. "To us, timber sash windows did not represent the existing structure; they did not make sense of a windowless barn."

Instead, the architects opted for an "opportunistic" approach, with discreet openings in places that had previously been fissured. The result is a varied collection of windows with hatches camouflaged as weatherboarding, and openings that are too subtle to pick up from the outside. These include the main window by the sunken seating, recessed and inconspicuous, and a 12 m long slash at head height that provides a continuous vista as you walk past, but is barely perceptible from outside. "Our openings punctuate the building to refer to the idea of a single homogeneous skin," Chapman elaborates.

Cox Restoration, the historical building consultant and main contractor, is a veteran of barn conversion with more than 12 years in the business. Director David Cox says that Circus Architects' solution makes the project stand out from its peers. "What is so clever is that from the outside there is no sign of a conversion – the old lines of the weather-boarding are not broken by the usual run of windows. It is a very sensitive solution."

From inside, the effect that both architect and client were trying to preserve remains intact, with splashes of light dancing on the timber decking. Now, however, it looks less like a bullet-riddled shed than an invitation for light to play on the planes of the extraordinary mezzanine pods.