Overview
The reference volume is the 3D box shown at the scenario's location, computed from the floor-area ratio and building-coverage ratio of the location's zoning and from the oblique-line restrictions and the absolute height limit. The panel at the bottom right of the screen shows 「3D ボリューム」 and 「参考モデル — 地点の用途地域（A29 行の容積率・建ぺい率）と斜線制限・絶対高さから計算」. The reference volume shown is only the one for the location of the last scenario run; running a new scenario or changing the calculation inputs recomputes and replaces it.
How the zoning is determined
The zoning is taken from the polygon of 国土数値情報 A29 用途地域 (2019) that contains the scenario's location. There is no default zoning; when no polygon contains the location, no reference volume is computed. When several polygons contain the location, the smallest polygon by area is used, and 「・複数ポリゴン該当（最小面積を採用）」 is added to the zoning line. The floor-area ratio and building-coverage ratio are the values in the A29 data. For zoning without a floor-area ratio or building-coverage ratio value, no reference volume is computed.
Inputs
Site area, road width and distance to boundary are inputs because no data exists for them, and their defaults are 500 m², 8 m and 3 m. Values you do not enter use the default, and the panel at the bottom right of the screen and the PDF show that the default was used.
Calculation steps
| Item | Calculation |
|---|---|
| Building area | Site area × building-coverage ratio |
| Building footprint | A square with the same area as the building area |
| Height from oblique-line restrictions and absolute height | The lowest of the road, adjacent-lot and north-side oblique lines and the absolute height |
| Height from floor-area ratio | Site area × floor-area ratio ÷ building area × floor height 3.5 m |
| Maximum height | The lower of the height from oblique-line restrictions and absolute height and the height from floor-area ratio, never below 3.5 m |
| Floors | The integer part of maximum height ÷ 3.5 m (at least 1 floor) |
| Total floor area | The smaller of building area × floors and site area × floor-area ratio |
Oblique-line restrictions and absolute height
| Restriction | Zoning it applies to | Value |
|---|---|---|
| Road oblique line | The seven residential classes from 第一種低層住居専用地域 to 準住居地域, and 田園住居地域 | Slope 1.25 × road width |
| Road oblique line | 近隣商業地域, 商業地域, 準工業地域, 工業地域, 工業専用地域 | Slope 1.5 × road width |
| Adjacent-lot oblique line | Residential classes other than 第一種・第二種低層住居専用地域 and 田園住居地域 | 20 m + 1.25 × distance to boundary |
| Adjacent-lot oblique line | 近隣商業地域, 商業地域, 準工業地域, 工業地域, 工業専用地域 | 31 m + 2.5 × distance to boundary |
| North-side oblique line | 第一種・第二種低層住居専用地域, 田園住居地域 | 5 m + 1.25 × distance to boundary |
| North-side oblique line | 第一種・第二種中高層住居専用地域 | 10 m + 1.25 × distance to boundary |
| Absolute height | 第一種・第二種低層住居専用地域, 田園住居地域 | 10 m |
When the road width is below 4 m, the road is treated as 4 m wide and the site-side boundary as set back by (4 m − road width) ÷ 2, and the road oblique-line height is computed from that. The north-side oblique line is computed with the same value as the distance to boundary. The absolute height is computed as 10 m; a 12 m designation and height control districts are not reflected. The values of the oblique-line restrictions and the absolute height are constants based on Articles 56(1), 42(2) and 55 of the Building Standards Act.
Shadow regulation
Shadow regulation is not evaluated. While there is no reference volume, the panel at the bottom right of the screen shows 「日影規制は未評価」; after a reference volume is computed, it shows 「日影規制は未評価（対象区域・測定面・規制時間は条例指定で、本データに無い）」.
Shape of the box
When the road oblique-line height is lower than the maximum height, the top of the box is cut at a slant to follow the road oblique line. The box is translucent light blue and is placed on the ground at the location.