密集住宅地における戸建住宅の風圧係数分布に関する実験的研究

谷口 景一朗, 赤嶺 嘉彦
日本建築学会環境系論文集, 2018, 83 巻, 750 号, pp. 679-689
https://doi.org/10.3130/aije.83.679

Abstract
This study aimed to establish a handy database of wind pressure coefficients that can assist designing buildings with better cross ventilation in a dense residential block. With this in mind, we started by surveying the blocks density of the main residential areas in Tokyo and calculated their average Gross Building Coverage Ratio (Gross BCR). It was found that almost all Gross BCR is in the range of 24% to 42%, and the average is approximately 33%. Hence, the Gross BCR of 33% was used to build the context model of the wind tunnel test whereas various experiments on the wind pressure acting on the wall/roof surface of the building under different conditions were made. Ultimately, the study deduced the following points:
1) A high correlation was found between the Gross BCR and the average wind pressure coefficient acting on each surface. Therefore, it is possible to predict the average wind pressure coefficient for any Gross BCR with good accuracy.
 2) When the target building is located at the corner of the real context block, and when the facing-the-street surface is on the windward side, a positive pressure is expected to act on these surfaces, which is advantageous for ventilation, unlike other setups. On another hand, when the building of interest is at the center of the dense blocks, the change in the wind direction has an intangible effect on the average wind pressure coefficient on the surfaces when comparing between the case where the surrounding buildings are simplified dense context and the case when the building is located center of the real context block.
 3) A sloped roof has a relatively higher negative pressure relative to a flat roof. Meanwhile, for the hipped roof, a great wind pressure coefficient differences can be somewhat ensured between the gable end side and the eaves side surfaces.
 4) It was found that changing the neighbor building condition facing the gable wall has a profound effect on the average wind pressure coefficient acting on that wall. Meanwhile, much less effect on the eave wall is found when the neighbor building, that faces the eave side, is manipulated. Yet, in both setups (either gable or eave-facing adjacencies) manipulating the neighbor building significantly change the pressure difference between the windows on a corner room, considering that one window is at the gable wall and the other eave wall. Accordingly, it can be said that it is important to design the opening carefully and seriously consider the surrounding buildings in the design phase. Designers should not only look at the pressure coefficient of each wall separately, but identifying the potentials of the pressure differences between the various walls.
 5) The stable negative pressure generating strategies can be well developed if the site prevailing wind direction and the neighbor building conditions can be obtained correctly. Such strategy can act and compensate, the courtyard in a narrow housing as an effective ventilation path between the outside wall.
 6) The negative pressure on the shed roof is quite stable, regardless of the presence of the roof monitor. The wind pressure coeffect acting on the monitor sides is always greater than acting on walls, for all wind directions. In fact, the highest negative pressure is found on the top of the roof monitor and it has the greatest potential for driving natural ventilation. Therefore, the prevailing wind direction should be carefully identified when planning an opening in roof monitor as its position will dictate either the monitor is going to be an inlet or an outlet for the cross ventilation.