#RESIDENTIAL ARCHITECTURE PROJECTS
Detached Floor House
Among the many requirements an architect must consider when designing a home, the wishes of the client are of course central, but local building codes are equally important. In Japan, these are described in the Building Standards Act.
In Japan, these are described in the Building Standards Act. The law plays a key role in protecting the investment, health, and very life of inhabitants by ensuring structures are secure in relation to their surrounding environment. A good architect has the capacity to design an attractive structure within these legal boundaries. Jun Yashiki’s “Detached Floor House” in Tokyo goes a step further. The fire resistance standards of the Building Standard Act serve as structure’s guiding concept – to the point that the project’s Japanese name alludes to the building code. We asked Yashiki, principal at Jun Yashiki & Associates, about the project.
Building standard “ro-jun-tai 1” [below, ro-1] requires that the exterior walls and roof of a building – in other words, its outer shell – be fire resistant, although the structure within that shell does not need to be. The idea in this project was to build a wood-framed structure, with a mortar exterior and a drywall interior sandwiching the frame. Approved methods for constructing fireproof exterior wood-framed walls already exist. The problem was that a method for connecting those walls to the floor on the second and higher levels was not clearly specified, except by members-only organizations such as the Wood Housing Industry Association. The law will probably be clarified in the future, but in this project I wanted to use currently available technology and knowledge to design the connective parts. My goal was to design a wood-framed house that met the ro-1 standards for fire resistance.
What was most important for you during the design process?
The lot sits in a quasi-fire prevention district [designated to limit fire hazards] that is densely built up with aging wood homes. The client is renting the lot, and its owner required that any structure built on it be wood-framed. We decided on a three-story home in order to provide enough living space. As we were thinking about how to comply with the relevant regulations, one of the options we put on the table was fire-proof wood walls that meet ro-1 standards. Most people building new homes will have to deal with densely built-up environments like this one, so there’s a need to think about ensuring privacy and preventing fires as a set. In order to offer a design that could be replicated in similar situations, we settled on a simple layout with a courtyard. It was important for us to address architectural design and fire resistance standards together when defining the design problem and proposing a solution.
What challenges did you face in the project? How did you respond to them?
We decided to use the freely available government-certified methods for building fire resistant wood-frame exterior walls. For the interior walls, we used two layers of reinforced drywall. The standards did not specify how to join the exterior walls to the flooring on the second and third levels, however. Our solution was to extend continuous sheets of drywall between levels and support the floor by securing it to the drywall with bolts. [This created the “detached floors” alluded to in the project’s English name.] For the flooring we used 120mm2 Massiveholz cross-laminated timber. With Massiveholz, the entire floor functions as a uniform crossbeam, which is effective from a load distribution standpoint. The simple construction, in which a single slab serves as the ceiling of one story and the floor of the next, also takes up a minimum of vertical space．This reduces the impact of a three-story structure in a neighborhood where most of the other buildings are two stories.
What did you learn from this project? What will you take from it to future projects?
In neighborhoods like this one where old wooden buildings are densely clustered together, both roads and houses need to be renovated in order to reduce the risk of disasters. This is difficult, however, because of various interrelated issues including complex land rights, narrow streets, and fire safety rules. The Detached Floor House is a fresh solution to building a three-story wooden house within the context of these many challenges. First, because the wood frame is enclosed by roofing and exterior walls, there is no need to use larger timbers in order to boost fire resistance or cover them with fireproof materials. Second, the Massiveholz flooring minimizes height, so that even when roads are widened and properties set back, it is easy to secure adequate floor space by adding an extra level. In the future, I hope to design similar structures in order to develop a more robust model.
How does this project fit into current architectural trends such as sustainability, social function, or technology?
Fire resistance was the central theme of this project. From a different perspective, however, a design-related theme also emerged: that of a house composed of a shell （roof and outer walls) plus floors secured to the shell solely with bolts. If you place value on circulation within the three-dimensional volume of space enclosed in the outer shell, you want to be able to handle the two space-dividing elements - partition walls and floors between levels – in a similar way. However, in conventional wood-framed houses, flooring is too thick from a design perspective and too limiting from a structural perspective, and thus becomes a hard-to-deal-with element. Here, the flooring becomes more similar to the partition walls from both a structural and design perspective. I believe this represents a new design strategy. The project’s English name, “Detached Floor House,” reflects the importance of this concept. Plus, the Massiveholz flooring used in conjunction with the fire resistant wood walls is efficient from both a design and a fire safety perspective. It’s one example of a new use for Massiveholz cross laminated timber.
What is the societal role of the architect?
Of the many problems we face as a society, at least some can no doubt be solved through architectural design. I believe the societal role of the architect is to discover and define overlooked problems, and then to propose and carry out solutions.
