Diagonal line restriction

This is one of the collective regulations for buildings, and it restricts the height of buildings. Land prices in cities are higher the closer to the city center, so there has been a growing tendency to use land more efficiently. As a result, high-rise buildings have been built along the boundaries of roads and other sites, which could damage the urban environment in terms of sunlight, lighting, ventilation, and aesthetics. To prevent this, restrictions on building height are imposed for each district. The idea is to restrict the range of buildings that can be built diagonally within a certain diagonal line drawn from the boundary line on the opposite side of the front road, the boundary line to the north of the building, and the boundary line with the neighboring land, and is called the diagonal line restriction. The details of the standards are stipulated in Article 56 of the Building Standards Act.

The details of the law are that the height of each part of a building must be limited to (1) the horizontal distance to the boundary line on the opposite side of the road in front of it multiplied by a certain coefficient, (2) regardless of direction, the horizontal distance from the part in question to the boundary line of the neighboring land multiplied by a certain coefficient and then added to a certain value, and (3) within a specific area, the horizontal distance from the part in question to the boundary line on the opposite side of the road in front of it or to the boundary line of the neighboring land in a true north direction multiplied by a certain coefficient and then added to a certain value. However, there are some relaxed regulations, such as the fact that if a building is set back from the road boundary, the starting point of the slope line can be set back the same distance on the opposite side of the road. The larger the lot, the wider the area in which tall buildings can be built.

[Shinya Katagata]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

建築物の集団規定の一つで、建物の高さに関する制限を行うもの。都市の地価は都心に近くなるほど高く、したがって土地を効率よく利用しようとする傾向が強まってきた。そのため、道路などの敷地の境界に沿って高層建築が建ち並び、日照、採光、通風、美観などの点で都市の環境が損なわれるおそれが出てきた。それを防止するため、建物の高さについての制限が地域地区ごとに行われている。この考え方は、前面道路の反対側の境界線、建物の北側の境界線、隣地との境界線などから引いた一定の斜線以内に、建築可能範囲を斜めに規制しようとするもので、斜線制限といわれる。基準の詳細は、建築基準法第56条で定められている。

　内容は、建築物の各部分の高さを、(1)前面道路の反対側の境界線までの水平距離に一定係数を乗じたもの以下に抑える、(2)方向を問わず、当該部分から隣地境界線までの水平距離にある係数を乗じ、それに一定数値を加えたもの以下に抑える、(3)特定の地域内においては、当該部分から前面道路の反対側の境界線または隣地境界線までの真北方向の水平距離にある係数を乗じ、それに一定数値を加えたもの以下に抑える、というものである。ただし、道路境界から後退して建てる場合は、道路反対側でその距離と同じだけ後退させたところを斜線の立ち上がり起点にできるなどの緩和規定がある。敷地が大きくなれば、それに伴って高い建物が建てられる範囲も広がる。

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