Creating Housing With Local Design Features Particular to Okinawa Prefecture

Climate change impacts

Annual average temperatures in the Okinawa region have risen at a rate of 1.19°C per 100 years (see Note 1). In addition, the number of days with a nighttime temperature ⩾ 25°C has increased at a rate of 5.7 days per decade (see Note 2). As global warming continues, the intensity and maximum wind speed of tropical cyclones, including typhoons, are expected to increase worldwide.

Adaptation activity

Building construction in Okinawa Prefecture has shifted from predominantly wooden housing to the use of reinforced concrete and concrete blocks, due to the frequency of typhoons. Reinforced concrete buildings now account for approximately 80% of residential properties in the prefecture. In the subtropical climate, there are particular conditions affecting building construction, and "Guidelines for Developing Climate-Suitable Housing" were created in 1997 to raise-awareness of the issues. These guidelines were revised in June 2015, incorporating new procedures and environmentally-friendly building methods within the overall theme of "Developing the Future of Energy-Efficient Housing Compatible with the Culture and Climate of Okinawa."

In Okinawan housing, combatting heat is especially important, and four measures are suggested in the manual (Fig. 1). The first is the use of natural wind effect ventilation. Following the design of traditional wooden housing in Okinawa, a wide, open front to a house should allow wind from the south to enter the interior of the building and provide ventilation.

Second, in order to keep temperatures down when the sun is at its highest, interiors are kept cool by blocking direct sunlight with shade through traditional design such as the amahaji-style roof with extended (Fig. 2) eaves. The amahaji design also provides a relaxed living space. On the other hand, in order to block low sunlight in the morning and evening, the ornamental concrete “flower block” (hanaburokku) (Fig. 2), is a characteristic feature of Okinawan architecture that provides a practical combination of insulation and design.

The third is insulation for roofs and exterior walls etc., which help reduce heat retention in concrete, etc. by shielding exterior walls and roofs, thus also decreasing electricity needed for air-conditioning. Methods to cut radiant heat include using heat-resistant paint, heat-insulating blocks, and rooftop greening. Red earthenware tiles, a distinctive roofing material in Okinawa, are effective at absorbing radiant heat and rapidly dissipating stored heat in the evening, thus reducing the effects of solar radiation.

Fourth, is the sealing and insulating of openings, which helps keep interior temperatures down by reducing heat ingress. Because it is difficult to dispel heat once it has entered a building, double-glazing has been proposed, with window sashes of wood or resin.

Outputs / Expected benefits

By incorporating the ingenuity and wisdom used in traditional houses and villages, and understanding the natural environment of the region, it is possible to create homes that are suitable for the climate of Okinawa. Okinawa exterior designs not only protects buildings and the people using them from strong sunlight, and rough weather, but also enhance the visual appeal of the local landscape.

Footnote
(Note 1) Statistical period: 1897 to 2019
(Note 2) Statistical period: 1931 to 2019