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Glass Manufacturer

Role of Glass in Green Buildings

"A green building is one which uses less water, optimises energy efficiency, conserves natural resources, generates less waste and provides healthier spaces for occupants, as compared to a conventional building."

Buildings across the world have a tremendous environmental impact during their life. Globally, Buildings are responsible for at least 40% of energy use. Construction of new buildings generate large amount of solid waste and in turn, disturb natural habitat & vegetation.

Green buildings offer immense potential to reduce consumption & regenerate resources from waste and renewable sources


A green building is one which incorporates enviornment friendly features. The building might appear the same like other buildings, but it is different in its approach.

Salient features of a Green Building are:

  • Building envelope design
  • Building system design (HVAC, lighting, electrical, and water heating)
  • Integration of renewable energy sources to generate energy on-site
  • Efficient use of water, water recycling and waste management
  • Selection of ecologically sustainable materials (with high recycled content, rapidly renewable resources with low emission potential)
  • Use of energy efficient and eco-friendly equipments
  • Indoor environmental quality (maintain indoor thermal & visual comfort and air quality)
  • Effective control and building management systems


A Green Home can have tremendous benefits, both tangible and intangible. The immediate and most tangible benefit is in the reduction in water and operating energy costs right from day one, during the entire life cycle of the building.

Tangible benefits:

  • Green buildings consume 40% ~ 60% lesser electricity as compared  to conventional buildings.
  • Green buildings consume 40% ~ 80% lesser water as compared  to conventional buildings, by utilizing ultra low fixtures, rain water harvesting, waste water recycling etc.
  • Green buildings generate lesser waste by employing waste management strategies on-site.

Intangible benefits:

  • Enhanced air quality.
  • Excellent day lighting.
  • Health & well-being of the occupants.
  • Conservation of scarce national resources.
  • Enhanced marketability for the project.


A green building rating system is an evaluation tool that measures environmental performance of a building through its life cycle. It usually comprises of a set of criteria covering various parameters  related to design, construction and operation of a green building. Rating programmes would help projects to address all aspects related to environment and are an effective tool to measure the performance of the building / project.

Two rating systems are followed in India:

  • LEED India (Leadership in Energy & Environmental Design)
  • GRIHA – (Green Rating for Integrated Habitat Assessment) National Rating System

IGBC which is a part of CII-Godrej GBC, has taken on the initiative of promoting the Green Building Concept in India. The council is represented by all stakeholders of the Construction Industry-Corporate, Government & Nodal agencies, Architects, Material manufacturers, Institutions, etc.

As part of indigenization of the LEED rating system, IGBC has been working on LEED – India for the past three years.

LEED India was formally launched in October 2006 but became operational from January 2007.

LEED-India has incorporated few changes like more emphasis on water conservation and adoption of local Indian codes and standards like NBC guidelines, MoEF guidelines for large projects, CPCB norms for DG set emissions, ECBC for energy efficiency, etc.

LEED® India

The Leadership in Energy and Environmental Design (LEED-INDIA) Green Building Rating System is a nationally and internationally accepted benchmark for the design, construction and operation of high performance green buildings.

LEED-INDIA promotes a whole-building approach to sustainability by recognizing performance in the following five key areas:

  • Sustainable site development
  • Water savings
  • Energy efficiency
  • Materials selection and
  • Indoor environmental quality

Specific LEED-INDIA programs include:

LEED® India for New Construction (LEED® India NC)

Certification Level Points
LEED – Certified 26 - 32
LEED - Silver 33 - 38
LEED - Gold 39 - 51
LEED - Platinum 52 or more

LEED® India for Core and Shell (LEED® India CS)

Certification Level Points
LEED – Certified 23 - 27
LEED - Silver 28 - 33
LEED - Gold 34 - 44
LEED - Platinum 45 - 61

IGBC, in its endeavour to extend green building concepts to all building types has developed the following rating programmes to cover commercial, residential, factory buildings, SEZ etc
Specific IGBC programs include:

  • IGBC Green Homes
  • IGBC Green SEZ
  • IGBC Green Factory Building

IGBC Green Homes Rating System

Indian Green Building Council (IGBC) Green Homes is the first rating programme developed in India, exclusively for the residential sector.

Individual Homes

Certification Level Points
LEED – Certified 32 - 39
LEED - Silver 40 - 46
LEED - Gold 47 - 54
LEED - Platinum 55 - 74

Multi-dwelling Units

Certification Level Points
LEED – Certified 30 - 37
LEED - Silver 38 - 44
LEED - Gold 45 - 52
LEED - Platinum 53 - 75

IGBC along with the Ministry of Commerce and Industry (MoCI) has prepared the Green SEZ guidelines. The objective of IGBC Green SEZ is to facilitate the creation of energy efficient, water efficient, healthy, comfortable and environ- mentally friendly SEZ.

IGBC Green Factory Building rating system

IGBC Green Factories rating system is the first of its kind addressing sustainability in industrial buildings. The programme is fundamentally designed to address national priorities and quality of life for factory workmen.

Certification Level Points
LEED – Certified 51 - 60
LEED - Silver 61 - 70
LEED - Gold 71 - 80
LEED - Platinum 81 - 100


GRIHA, an acronym for Green Rating for Integrated Habitat Assessment, is the National Rating System of India. It has been conceived by TERI and developed jointly with the Ministry of New and Renewable Energy, Government of India. It is a green building 'design evaluation system', and is suitable for all kinds of buildings in different climatic zones of the country.

The rating applies to new building stock – Commercial, Institutional and Residential types of varied functions. It is endorsed by the Ministry of New and Renewable Energy, Government of India as of November 7, 2007.

GRIHA is a five star rating system for green buildings which emphasises on passive solar techniques for optimizing indoor visual and thermal comfort.

% Point Scored Rating
50 - 60 One Star
61 - 70 Two Star
71 - 80 Three Star
81 - 90 Four Star
91 - 100 Five Star

The rating system evaluates certain credit points using a prescriptive approach and other credits on a performance based approach. The rating system is evolved so as to be comprehensive and at the same time user-friendly.

While  LEED/IGBC or GRIHA does not certify specific building (glass) products, it does recognize that the selection of glass products plays a significant role in fulfilling LEED/IGBC or GRIHA point requirements.


Glass plays a unique and important role in building design and the environment. It affects design, appearance, thermal performance and occupant comfort. The selection of the right glass is a crucial component of the design process.

India being a tropical country, we need to be careful while selecting a glass. Selection of glass has become more complex since a variety of glasses are available to choose from, ranging from performance to aesthetics.

The properties of glass have also become multifaceted, able to perform a wide variety of functions, like Solar Control to Thermal Insulation. Solar and thermal performance will often be a high priority decision along with appearance  (color, transparency and reflectivity).

AIS products can help architects achieve LEED/IGBC or GRIHA certification for their projects in a number of areas such as energy performance, recycled content, regional material, daylight and views.


Key factors which play an important role in designing the building envelope with glass are as follows.

  • Solar Factor (SF) / Solar Heat Gain Co-efficient (SHGC)
  • U-Value
  • Relative Heat Gain (RHG)
  • Visual Comfort

Solar Factor (SF) /Solar Heat Gain Co-efficient (SHGC)

A combination of the directly transmitted solar and radiant energy and the proportion of the absorbed solar energy that enters into the building’s interior. The lower the number the better solar control

U-Factor (U-Value)

This is the measurement of air-to-air thermal conductance or insulation between indoors and outdoors through the glass. The lower the number the better the insulation or thermal control.

Relative Heat Gain (RHG)

RHG is calculated as follow = (Solar heat gain factor (ASHRAE) 630° W/m2 X shading coefficient of the glass) + ( Temperature Difference x U value)

  • Heat gain due to Solar Factor contributes to 80% of RHG value
  • Heat gain due to U-value contributes to 20% of RHG value

 Visual Comfort

Visual Light Transmission

It is defined as the percentage of light transmitted through the glass. It does not determine the color of the glass.

Glass should provide for optimum daylight inside as per the outside condition. Excessive daylight creates glare and makes the occupant uncomfortable.

Energy Conservation Building Code

Energy Conservation Building Code prepared by the Bureau of Energy Efficiency sets minimum standards for external wall, roof, glass structure, lighting, heating, ventilation and air conditioning of the commercial building. ECBC provides minimum requirement  for the energy efficient design and construction of the building.


ECBC covers Buildings with an:

  • Electrical  connected load of > 500 kW or
  • Contract demand of > 600 kVA and / or
  • Building or complexes with Air-Conditioned area > 1000 SQM

The ECBC provides design norms for:

  • Building envelope
  • Lighting system
  • HVAC system
  • Electrical  system
  • Water heating and pumping systems

The code provides three options for compliance:

  • Prescriptive (Component based approach): Each system and sub-system must be complied with minimal performance requirement  as laid down by the code
  • Trade-off (System based approach): This method offers more flexibility than strictly following the prescribed values for individual element. Trade- offs typically occur within building envelope system – roofs, walls, fenestration, overhangs etc.
  • Whole Building Performance: This method helps the designer to evaluate the energy performance of a building, making it more energy efficient by necessary modifications in the design.

Climatic Zones

As per the climatic conditions, India has been divided into 5 climatic zones and ECBC takes these zones into consideration while building envelope design:

Glass Manufacturing Companies In India
  • Composite
  • Hot & Dry
  • Warm & Humid
  • Temperate
  • Cold


Window wall ratio is the ratio of total window area to the total gross exterior wall

Window Wall Ratio = Total Glazing Area / Total Gross Wall Area

  • Determination of Window Wall Ratio of a building
  • Determination of the performance values of the glazing like solar factor, U-value & Light transmission. (check value specific to each climatic zone and window wall ratio)
  • Determination of M Factor for the trade-off of solar factor requirement  by the use of shading devices such as overhangs, vertical fins etc.


Skylight is a fenestration surface having a slope of 60 degrees from the horizontal plane. Other fenestration, even if mounted on the roof of a building, is considered vertical fenestration.

Skylight shall comply with the maximum U-Factor and maximum SHGC requirements of table 1.1. Skylight area is limited to a maximum of 5% of the gross roof area of the prescriptive requirement.

Table 1.1: Skylight U-factor & SHGC requirements 

Climate Maximum U-factor Maximum SHGC
With Curb Without Curb 0 ~ 2% SRR* 2.1% ~ 5% SRR*
Composite 11.24 7.71 0.40 0.25
Hot & Dry 11.24 7.71 0.40 0.25
Warm & Humid 11.24 7.71 0.40 0.25
Moderate 11.24 7.71 0.61 0.40
Cold 11.24 7.71 0.61 0.40

*SRR: Skylight roof ratio is the ratio of the total skylight area of the roof, measured to the outside of the frame, to the gross exterior roof


In Prescriptive approach, ECBC sets values of the light transmission, solar factor, & U-value for the different climatic zones & designed window wall ratio of the building

Table 1.2: Vertical Fenestration U-Factor (W/ m2K), SHGC requirements and Minimum VLT requirements

Composite / Hot & Dry / Warm & Humid Window Wall Ratio (WWR)
0 ~ 30% 31% ~ 40% 41% ~ 50% 51% ~ 60%
Maximum Light Transmission (%)  27 20 16  13
Maximum Solar Factor / SHGC  0.25  0.25  0.20  0.20
Maximum U  3.3 3.3  3.3  3.3 
Moderate  Window Wall Ratio (WWR)
 0 ~ 30%  31% ~ 40%  41% ~ 50%  51% ~ 60%
Maximum Light Transmission (%)  27 20  16  13 
Maximum Solar Factor / SHGC  0.4 0.4  0.30  0.30 
Maximum U-value (W/SqmK)  6.9 6.9   6.9 6.9 
Cold  Window Wall Ratio (WWR)
 0 ~ 30% 31% ~ 40%   41% ~ 50%  51% ~ 60%
Maximum Light Transmission (%)  27 20  16  13 
Maximum Solar Factor / SHGC  0.51  0.51  0.51 0.51 
Maximum U-value (W/SqmK) 3.3  3.3  3.3  3.3 


Trade-off is permitted only between building envelope components. With the trade-off approach, the prescriptive requirement of SHGC can be trade-off with shading devices / overhangs and/or side-fins

  • Shading for all the fenestration getting direct solar radiation by using Sun Path analysis or shading norms
  • Internal Shading Devices (Overhangs and/or Side Fins)

Adjusted/Effective SHGC is calculated by multiplying the SHGC of the unshaded fenestration product by a multiplication factor (M)

SHGC Effective = SHGC Glass X M

Multiplication Factor (M)

           (M) Is taken out from the table 1.2 based on the projection factor (P)

Projection Factor (Overhangs / Side Fins)


SHGC requirement of a window can be affected by overhangs on a building. The term called projection factor determines how well the overhangs shade the building’s glazing.

Projection Factor is calculated by

PF = Ratio of projection divided by height from window sill to bottom of overhang (must be permanent)

ECBC provides modified SHGC values where there are overhangs and /or side-fins. An adjusted SHGC , accounting for overhangs and / or fins, is calculated by multiplying the SHGC of the unshaded fenestration product by a multiplication factor (M).

Table 1.3: SHGC ‘M’ factor adjustment for Overhangs & Side Fins

    Overhang M factors for 4 PF Side fins M factors for 4 PF

Over hang + Side Fins M factors

for 4 PF

 Project Location  Orientation







 1.00 +  0.25






 1.00 +  0.25






 1.00 +
 North latitude 15* or Greater  North  0.88   0.8 0.76 0.73 0.74 0.67 0.58 0.52 0.64 0.51 0.39 0.31
   East/West  0.79  0.65 0.56  0.5   0.8 0.72 0.65  0.6  0.6 0.39 0.24 0.16 
   South  0.79  0.64 0.52  0.43  0.79  0.69   0.6  0.56   0.6  0.33  0.1  0.02 
 North latitude less than 15°  North  0.83  0.74 0.69 0.66 0.73 0.65  0.57  0.5 0.59 0.44  0.32  0.23 
  East/West    0.8  0.67 0.59 0.53  0.8  0.72 0.63 0.58 0.61 0.41  0.26  0.16 
   South  0.78  0.62  0.55  0.5 0.74 0.65 0.57   0.5 0.53   0.3  0.12  0.04 



Vertical fenestration areas located more than 2.2m (7 ft) above the level of the floor are exempt from the SHGC requirement in (Table 1.2) if the following conditions are complied with:

  • Total Effective Aperture: The total effective aperture for the elevation is less than 0.25, including all fenestration areas greater than 1.0m (3 ft) above the floor level
  • An interior light shelf is provided at the bottom of the fenestration area, with an interior projection factor not less than”
  1. 1.0 for E/W. SE, SW, NE, and NW orientations
  2. 0.5 for S orientation, and
  3. 0.35 for N orientation when latitude is <23


This method involves developing the computer model (for thermal, visual, ventilation, and other energy consuming process) of the Proposed Design and comparing its energy consumption with Standard Design.

  • Energy simulation software is necessary to show the ECBC compliance. Energy simulation is a computer-based analytical process that helps designers to evaluate the energy performance of a building and make necessary modifications before the construction.
  • Perform hourly analysis of the whole year
  • Used to simulate air-conditioned building and predict annual energy consumption under various head

This simulation process takes into account the:

  • Building geometry and orientation.
  • Building material.
  • Building façade design.
  • Climate indoor environmental condition.
  • Occupant activities and schedules.
  • HVAC and lighting system and other parameters  to analyze and predict the energy performance of a building