*4.1.3 Determination of elements, variables, and their desired values*

In the third stage, we first specified "elements," considering both the standard housing and the requirements for sustainable housing design. When considering the standard housing, we analyzed two factors: "material" and "space" [10, 11]. "Material" regards housing as the complexity of material elements, such as framework, exterior, thermal insulation, windows and doors, interior, and piping. "Space" considers housing as the complexity of spatial elements, such as rooms and areas


#### **Table 1.**

*Problems related to housing and requirements for sustainable housing design identified for the design guidelines produced in Japan [extracts] [12].*

[10, 11]. Moreover, in order to cover all of the requirements for sustainable housing design, we added necessary elements, such as "equipment for harnessing renewable energy."

should be dealt with. Based on these problems, additional requirements for sustainable housing design have also been identified. After that, these additional requirements have been incorporated into the framework of "element-variable-desired

Choosing one requirement, namely "storage of electricity," the following describes the essentials of the identification and incorporation processes. In order to curb global warming, the utilization of renewable energy, particularly wind and solar power generation, is quickly increasing in many countries [13]. But the quantity of electricity extracted from solar and wind sources varies chiefly with the time of day, weather, and season. Therefore, a surge in wind and solar power generation

is also raising the risks of power failures [14, 15]. In order to cope with such

changing circumstances, we have added "storage of electricity" as a requirement for sustainable housing design. Besides, storing electricity leads to securing an emergency power source, which is one of the adaptation measures against climate

When incorporating the "storage of electricity" into the guidelines, we have added "storage battery" as a new material element. Subsequently, we have identified two variables of this new element: "type" and "linkage." The desired value of "type" has been specified as "stationary battery or electric vehicle battery." Meanwhile, the desired value of "linkage" has been determined to be "interconnection

Observing recent trends in housing-related technology and systems, we have found noticeable changes, mainly in thermal insulation performance. Japanese housing thermal performance has been gradually improving, due to progress in technology and requirements for energy saving and occupants' health. As a result, recently, a new national voluntary system, the "net-zero energy house (ZEH) certification standards," has emerged and shown higher thermal performance criteria than usual criteria [16]. Recognizing these changes, we have lifted the desired value of "thermal insulation performance" of the two material elements: "thermal insulation" and "windows and doors." To be concrete, we have revised the desired value from the highest level in the JHPIS's thermal insulation performance grades to the relevant criterion stipulated in the ZEH certification standards.

After finding a constructive opinion in recent feedback from the system users, we have determined to include it in the latest revision. This opinion's gist is that lighting fixtures utilized in living spaces should be products with brightness and color adjustment functions, for energy conservation and residents' health. The necessary brightness of indoor artificial lighting changes depending on circumstances, including residents' visual comfort and natural lighting through windows. Meanwhile, exposure to bright lights and blue light before bedtime suppresses melatonin secretion and can affect sleep and potentially cause diseases [17, 18]. Accordingly, especially in living spaces, lighting fixtures fitted with brightness and color adjustment functions are beneficial for energy conservation and residents' health. Therefore, when revising the guidelines this time, we have added an explanatory note to "LED," the desired value of lighting fixtures' type, saying "lighting fixtures used in the living spaces are fitted with brightness and color

value."

change.

with the home electrical system."

*How to Design Sustainable Structures*

*DOI: http://dx.doi.org/10.5772/intechopen.95012*

*4.2.2 Changes in the practical world*

*4.2.3 Feedback from the users*

adjustment functions."

**285**

After specifying the elements, we identified the variables and their desired values. Choosing one element, namely "thermal insulation," the rest of this section explains the details of identifying the variable and its desired value. First of all, we determined "thermal insulation performance" as the variable, considering two requirements, that is, "energy saving" and "improvement of indoor thermal performance," as well as the relevant stability conditions. Higher thermal insulation performance contributes to "environmental preservation" and "sustainable use of natural resources" due to a decrease in energy usage for air-conditioning and heating, as well as residents' better "health."

When specifying the desired value, we observed trends in technology and systems related to housing thermal insulation performance. Japanese housing thermal performance has traditionally been low. Japan's building codes have not stipulated the standards of housing thermal insulation performance. Meanwhile, since 2000, a national voluntary system, namely the Japan Housing Performance Indication Standards (JHPIS), have provided four-level thermal insulation performance grades. Consequently, we determined the desired value to be the highest level in the thermal insulation performance grades of the JHPIS.

## **4.2 The latest revision of the design guidelines**

The above sustainable housing design guidelines produced in Japan have recently been revised. This latest revision has dealt with the three aspects as mentioned before: (1) changes in the theoretical world, (2) changes in the practical world, (3) feedback from the users.
