# 81-273 Rules for Plotting Buildings on the Daylight Evaluation Chart

Evaluation of a ** development** or

**requires drawing the new**

*enlargement***, remaining**

*buildings***and open areas on the**

*buildings***on the appropriate**

*zoning lot***, as viewed from each required**

*daylight evaluation chart (DEC)***and then scoring the**

*vantage point***. The rules for plotting**

*zoning lot***on the**

*buildings***are set forth in the following paragraphs of this Section and illustrated by an example of a**

*DEC***which fronts on a 100-foot wide**

*building***and occupies a site 170 feet long by 100 feet deep.**

*street*(a) Draw the *building*

Draw the ** building** in plan showing all

**frontages of the**

*street***. Draw the**

*zoning lot***in section perpendicular to each**

*building***on which the**

*street***fronts. On both plan and section drawings label all corners of the**

*zoning lot***. In the example they are labeled corners (a) through (h). (See illustrations of Example: Building Drawings)**

*building*EXAMPLE: BUILDING DRAWINGS

(81-273a)

(b) Establish *vantage points*

Establish on the plan all the ** vantage points** from which views must be taken.

**shall be established on the**

*Vantage points***250 feet from the intersection of the**

*center line of the vantage street***and the**

*zoning lot's far lot line***. For each**

*center line of the street***there are at least two**

*vantage street***. In the example, they are V1 and V2. For each**

*vantage points***there shall be a separate**

*vantage point***. The example will use**

*daylight evaluation chart***one.**

*vantage point*(c) Record plan and section dimensions

Record on a coordinate chart for each corner of the ** building** the following dimensions:

(1) Dimensions in plan:

The distance (S) between the corner and the ** center line of the street** as measured along a line that intersects the

**at right angles. In the example, distance (S) of corner (b) + 50 feet.**

*center line of the street*The distance (D) measured along the

**from the**

*center line of the street***to the point where the**

*vantage point***center line is intersected by the perpendicular line from the corner. In the example, distance (D) of corner (b) + 250 feet.**

*street*(2) Dimension in section:

The height (H) of the corner above ** curb level**. In the example, height (H) of corner (b) + 140 feet.

(d) Calculate plan and section angles

Determine the plan and section angles for each corner of the ** building** as viewed from the

**.**

*vantage point*(1) A plan angle is an angle on the plan formed at the ** vantage point** by the line of sight to a corner of the

**and the**

*building***. The plan angle is found by calculating the tangent. The tangent is the quotient found by dividing distance (S) by distance (D). The plan angle for the resulting tangent is found in a tangent table and is then entered on the coordinate chart in the column marked "plan angles."**

*center line of the vantage street*(2) The section angle is an angle formed by a line representing the distance in section from a corner of the ** building** to the

**and a line representing the distance in plan (S) between the corner and the**

*center line of the vantage street***. The section angle is found by calculating its tangent. The tangent is the quotient obtained by dividing the height of the corner (H) by its horizontal distance (S) from the**

*center line of the street***.**

*center line of the street*The section angle for the resulting tangent is found in a tangent table and is then entered on the coordinate chart in the column market "section angles."

EXAMPLE OF COORDINATE CHARTS

Plan Angles

Point | Distance (S) from | Distance (D) from | Tangent (S÷D) of Angle | Angle |

a | 50 | 80 | 50/80 = 0.63 | 32.0 |

b | 50 | 250 | 50/250 = 0.20 | 11.3 |

c | 70 | 80 | 70/80 = 0.87 | 41.2 |

d | 70 | 250 | 70/250 = 0.28 | 15.6 |

e | 130 | 80 | 130/80 = 1.63 | 58.4 |

f | 130 | 250 | 130/250 = 0.52 | 27.5 |

g | 150 | 80 | 150/80 = 1.88 | 61.9 |

h | 150 | 250 | 150/250 = 0.60 | 31.0 |

Section Angles

Point | Height (H) Above | Distance (S) from | Tangent (H÷S) of Angle | Angle |

a & b | 140 | 50 | 140/50 = 2.80 | 70.3 |

c & d | 320 | 70 | 320/70 = 4.57 | 77.7 |

e & f | 320 | 130 | 320/130 = 2.46 | 67.9 |

g & h | 23 | 150 | 23/150 = 0.15 | 8.7 |

(e) Plot corner coordinates

Plot each corner of the ** building** onto the

**at the point where the coordinates for that corner intersect. The plan angle coordinates are found on the horizontal axis of the chart and the section angle coordinates are found on the vertical axis. The points plotted are then connected to represent the edges of the**

*daylight evaluation chart***as shown on the plan and section drawings. A connecting line parallel to the**

*building***is drawn as a curve parallel to the closest elevation line. A connecting line perpendicular to the**

*vantage street line***is drawn parallel to the closest dotted elevation line, which is perpendicular to the**

*vantage street line***. A connecting line which is neither parallel nor perpendicular to the**

*street***is approximated on the chart by:**

*vantage street*(1) establishing points along the line in plan at 10-foot intervals;

(2) finding the coordinates of the points and plotting them on the chart; and

(3) connecting the resulting points.

The connecting lines produce a curvilinear perspective drawing of the ** building** as seen from the

**projected onto the**

*vantage point***. Since in the example**

*daylight evaluation chart***one is on a 100 foot wide**

*vantage point***, corner coordinates are plotted on a**

*street***for 100 foot wide**

*daylight evaluation chart***. In the example, corner (b) is at the intersection of plan angle 11.3**

*streets*^{o}and section angle 70.3

^{o}(See illustration of Building as Drawn on the Daylight Evaluation Chart)

BUILDING AS DRAWN ON THE DAYLIGHT EVALUATION CHART

(81-273e)

(f) Determine daylight boundaries

Draw a vertical line on the chart rising from the intersection of the ** near lot line** of the

**with the center line of the**

*zoning lot***or with a line 100 feet distant from and parallel to the**

*block***on the**

*front lot line***, whichever line is closer to the**

*vantage street***. This line and the**

*vantage street***represent the boundaries of the potential sky area that the**

*far lot line***could block. (See illustration of Building as Drawn on the Daylight Evaluation Chart)**

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