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
| Thermal Requirements | Physical Manifestation |
| Reduce Heat Gain | |
| Decrease exposed surface area | Orientation and shape of building |
| Increase thermal resistance | Insulation of building envelope |
| Increase thermal capacity (Time lag) | Massive structure |
| Increase buffer spaces | Air locks/lobbies/balconies/verandahs |
| Decrease air exchange rate (ventilation during day-time) | Smaller windows openings, night ventilation |