Half house, half tent: the startling Spanish villa that breaks all the rules

A bright-green steel frame perches on a steeply sloping site north of Valencia, Spain, projecting out from the hill above a busy main road. It forms a large 3D grid, some of its spaces filled with white cubic volumes, others left empty as if still awaiting their final function.

“People kept asking if it was going to be a supermarket,” says architect Fredrik Hellberg, standing beneath the 10-metre-high frame. It’s a fair question: in Nueva Santa Barbara, a new suburb where houses are variously neo-Moorish, Spanish rustic or developer modern, this startling new home is unlike any other for miles around.

It is the first completed building by Space Popular, a young London-based practice founded by Hellberg and his partner, Lara Lesmes, in 2013 in Bangkok, where for five years they taught architecture. Working in the Thai metropolis gave them the rare luxury of being able to afford bespoke craftsmanship, even on limited budgets, allowing them to have every element of their first interior projects handmade to their designs, from furniture to fittings. Their work for a local spa chain features tubular steel chairs in minty green with yellow leather seats, pink marble countertops and baby-blue reclining loungers with a retro-futuristic feel. It takes pleasure in both natural and synthetic textures, combining diaphanous pleated curtains with raw concrete, leather and glossy resin floors.

In London, they have produced dazzling polychrome structures that occupy the space between architecture, immersive installation art and virtual reality, indulging their interest in pattern, ornament and kaleidoscopic colour to the max. An exhibition at the Riba opening next week promises to be a saturated romp through the last 500 years of architectural style, exploring how mass media has influenced changing fashions. In a world where many architects spend tortured months choosing between multiple shades of beige, Space Popular revel in bright, clashing tones, mixing pinks, purples, oranges and yellows in a distinct aesthetic that fuses computer game graphics with historical architectural details, sampling from a broad spectrum with promiscuous glee.

With all this in mind, their first standalone building feels positively restrained. In part, that’s down to commercial reality: this is a house for a speculative developer who plans to rent it out, not a neon-patterned nest for an eccentric collector. Yet Lesmes and Hellberg have managed to produce something far beyond the usual developer fodder, creating a home that is fiercely inventive in ways that are more than skin-deep.

Approaching from the street, it looks like a relatively unremarkable two-storey white villa with a simple pergola projecting from its front. It is only as you begin to descend a set of stairs to enter the house halfway down the slope that you realise strange things are going on. The frame is no pergola, but a superstructure that marches through and around the entire house like a computer-generated wireframe grid made real, forming a slender armature of columns and beams just 10cm thick throughout.

The feather-light frame belies what awaits within. When you enter, you find masonry barrel-vaults springing between the beams of this wiry steel skeleton, forming ceilings of shallow brick arches, reminiscent of a wine cellar. They extend seamlessly outside to cover expansive areas of patio, making the inside and out feel like one continuous space, and creating the surreal sight of rustic terracotta vaults suspended in the wafer-thin steel frame (a conjuring trick made possible by larger, hidden I-beams).

The unsuspecting architecture critic might call these Catalan vaults, but Lesmes insists they are Valencian “Guastavino” vaults, named after local master-builder Rafael Guastavino, who patented a “tile arch system” in the 1880s and went on to take the US by storm. From the interlocking herringbone ceiling of the oyster bar at Grand Central Station in New York to Carnegie Hall and Boston Public Library, Guastavino’s leaping vaults were the epitome of beaux-arts style. But the technique was killed off by the arrival of modernism, when ornament became a dirty word.

“What we can do now is much more primitive than in Guastavino’s day,” says Lesmes, lamenting the loss of the intricate combinations of tile patterns and glazes that were once available. She says there is a small, budding revival of the technique among a younger generation of Spanish architects, and their local bricklayers have done an impressive job – connecting the bricks to each other one at a time with sticky gesso mortar, miraculously suspended in air, without the need for scaffolding or formwork.

The staircase in particular is a mesmerising tour de force, formed from intersecting vaults that bounce their way up the three floors of the house. It looks like a labour-intensive process, but it was relatively cheap, quick and efficient; the architects say that a vaulted brick staircase can cost half the price of a concrete stair, because you don’t have to close the road for a cement truck or build wooden formwork, and the bricks can be carried and quickly laid on site by a couple of people. The hollow steel frame, meanwhile, developed by local architects Alberto Burgos and Javier Cortina Maruenda, could mostly be erected without a crane, so light were the elements.

The modular nature of the structure gave a certain freedom to how the house itself could be laid out. No floor is the same, with open-plan living areas and bedrooms arranged at will, the final design settled on after months of sun-path analysis and virtual reality modelling – which allowed the client to check that the view of the sea would still be visible when occupants are seated in the living room. As you move through the house, the projecting green grid creates striking visual effects, framing distant views of the port on the horizon, and plunging beneath you from the top floor patio with the vertiginous thrill of living in a climbing frame for grownups. The architects imagine that the unoccupied parts open frame could be adapted according to the future residents’ needs, with fabric canopies to shade the terraces, or hammocks slung between the beams. As Lesmes puts it: “It is half house, half tent.”

They have designed the modular system so it can be rolled out on other plots elsewhere, always adapting to the needs of the client and the specifics of the site in question, with an easily repeatable set of construction details that could be used to create different configurations. With the sense of an endless cartesian grid, capable of being laid over any terrain, there are echoes of the 1960s radical Italian architecture collective, Superstudio, who imagined endless framed structures covering the entire planet. Their “continuous monument” and “supersurface” would allow future nomads to plug in and create shelter wherever they pleased. Fifty years on, Space Popular have realised a fragment of that vision in suburban Spain – executed with a level of craftsmanship and attention to detail that those 60s radicals could never have imagined.

• Space Popular are part of Freestyle: Architectural Adventures in Mass Media at Riba, London, 26 February until 16 May.