An open plan

Over the past two decades, Masato Igarashi has accumulated a collection of roughly 5000 books. "I've always liked books and had a lot of them, but the number of them really increased after I started this design job." The meticulously organised collection is housed in a shelving system that spans the full width and almost the full height of his multi-level home. With no internal walls (unless you count the glazing around the bathroom) and only two internal doors, the books act as a kind of spine to the design of the home: connecting each of the layers, and also telling the story of what happens where.

On the ground floor, paved with earthy unglazed tiles and rich in timber, the bookshelves house the books Masato reads most often. These are his architecture and design books – and this is where you will find his office space. Follow the staircases up through Masato's home and you will find the architecture and design tomes give way to manga, novels and other things that are "not work-related but a little more personal". One Piece and Doraemon are particular manga favourites. Masato's wife, Tomoko, also an architect, likes books too but has been more of a bit-part contributor to the home's extensive collection. "In terms of quantity, it's a 9:1 ratio of my books and my wife's [laughs]".

Situated on a 45-square-metre corner plot in a fairly ordinary residential area in Tokyo, Masato and Tomoko's home is anything but ordinary. Its boxy concrete and glass exterior conceals a cleverly layered space that is essentially only "one big room". At face value, it's a challenging environment for a couple who live and occasionally work together in the same space, but it has not come without benefits. "We've become even closer since we moved in here. We can't stay locked up in our rooms when we fight," Masato laughs.

"You can eat work, eat or relax wherever you want. We change the way we use each room based on our various needs, without limiting its use," Masato says. It's an ideal dynamic for a pair of busy Architects whose personal and professional lives are often blurred existence.

The openness of the space also affords the couple a great deal of flexibility with how they live within it. While the ground floor space facing the entrance is predominantly an office, it can just as easily host a large group of friends for dinner.

Masato's practice, IGArchitects, is relatively young, but was a natural progression for an ambitious architect who had honed his skills at larger studios and always knew he wanted to design and create unexpected spaces. "I've loved playing with LEGO since I was little. I would make things according to the instructions, but I liked deconstructing things once they were completed and then building them again and mixing with other things. I decided I wanted to do that as a job." This spirit feels evident in the irregularly stepped mezzanine layout of the home, each level connected by a staircase with its own unique design and personality (the middle of which was designed to not look like a staircase at all, but rather, pieces of furniture). And then there's the roof terrace accessed by a tree-house-style ladder. While the concrete, steel, glass and timber-rich materiality is a far cry from the primary coloured jumble of a child's LEGO creation, there is still something of a child's fantasy dream-style-loft-like house about it.

In the late morning, when I visit, the living space on the second floor is bathed in a soft wash of sunlight from the full height glazing at the upper level of the building. A diagonal shadow cuts across the richly textured concrete of the northern wall. "This is probably my favourite room in the house. It's really fascinating to see how the sunlight comes in at different times of the day and changes the look of the place," Masato says. I'm reminded of Junichiro Tanizaki's 1933 essay on Japanese aesthetics, In Praise of Shadows, in which the author muses: "And so it has come to be that the beauty of a Japanese room depends on a variation of shadows". Tanizaki references the efforts to harness and moderate light in Japanese houses via shoji screens and angled roofs, and how in traditional Japanese tea rooms, the design of the space is such that sunlight will be ushered in, not to spotlight, but to gently illuminate the tea utensils, thus making the act of drinking tea more ritualistic. In this home, it's easy to imagine how the influence of light throughout a day might elevate even the most mundane task or humble pursuit. The flexibility afforded by its layout also means a book could be read or a meal could be taken here, or there, depending on whether light or shadow is desired.

The way the light falls on the concrete walls also illuminates its texture. Each of the large concrete blocks that make up the walls bear a wood grain patterned 'finger print'. Each block of concrete was cast, reinforced and cured on-site and in place. One after the other. It's not an uncommon process in Japan but still, painstaking all the same. "I value the sense of texture. Concrete tends to look inorganic, but by transferring real wood grain patterns, the colour and shape becomes uneven and organic," Masato explained. The timber tables in the home's office space also shared this 'organic' look and feel. "This kind of texture makes stains and scratches less noticeable, so you don't have to be too nervous about taking care of it," he says. "It's just like people getting wrinkles as they get older. I choose materials that will develop a certain character as time goes by."

The concept of buildings and people ageing together gracefully is not new. In traditional Japanese homes, when shoji screens are torn, they are reattached; when tatami mats get worn out, they are repaired. Regular maintenance and acts of repair prolong their life and allow the materials to acquire character and story. "A house must be lived in. I don't like houses that only look good when they are built, but deteriorate when you start living in them".

Beyond patina, this idea of longevity and the home's next chapter was a chief consideration for Masato from the very beginning. Masato was determined to design the home in such a way that when the time came to let it go, it could potentially be reused for a variety of purposes without having to be dramatically altered or demolished.

“I hope that what we use as a house now will be used as something else – perhaps a café or a museum – when it is passed on to other people, and that it will remain in a different form and be used for a long time,” Masato says.

"Unlike clothes, you can't just replace a house when you get bored of it. It costs a lot and has a big impact on the environment and the community, so we have a responsibility when we build it."