Q: Does my building envelope comply prescriptively with the ECBC?

Prescriptive Requirements for Fenestration

Location                       :  Gurugram

Climate Zone               :  Composite (Lat: 28° 42’ N; Long: 77° 54’ E)

Building Type               : Daytime Use Building

Roof Area                     : 409 m2

Roof Insulation            : Rigid Board 25 mm with R = 2.1 m2·K/W

Wall Area                      : 930 m2

Wall Insulation             :  Rigid Board 25 mm with R = 1.41 m2·K/W

Total Fenestration Area: 473 m2

Window to Wall ratio   : 409/930 = 44%

East/West and South facing windows are all 1.82880m × 0.91440m with a 0.45720 m overhang and represent 75% of the glazing on the building.

Projection Factor          :  H/V = 0.45720/1.82880 = 0.25

“M” factor                    :  0.79

(From ECBC Table 4.4, Projection Factor=0.25, E/W and S orientation for north latitude 15° or greater)

East/West and South facing glazing         : 409 × 0.75 = 306.75 m2 East/West and South facing Fenestration  : SHGC 0.20; U – factor 3.30 East/West and South Facing Fenestration: Skylight Area 6.2 m2

A: To utilize the prescriptive requirements of ECBC, vertical fenestration is limited to 60% of the gross wall area, so this building is allowed under this method.

ECBC Table 4.3 limits the SHGC value to a maximum of 0.20 for composite climate zone, however an exception exists by use of an overhang. ECBC §4.3.3 allows for an “M” Factor, or multiplier. In this case the M is 0.79. Multiplying “M” times the SHGC [0.7900 × 0.20=0.1580] and thus complies with ECBC Table 4.3.

ECBC Table 4.3: Comfort Requirements and Physical Manifestations in Buildings

HOT AND DRY CLIMATE ZONE