Benchmarks for eco-friendly residential buildings in India

Recently, one of my close friends, after our dinner at his house, showed his monthly electricity bill and asked me to rate his monthly electricity consumption. That got me into thinking what are the available metrics and benchmarks in this industry to evaluate energy consumption of residential buildings. I did some research, and this article summarizes the findings for the readers here.

The built environment is currently responsible for 37% of global energy related carbon emissions: 27% from operational emissions - energy needed to light, heat, cool and power buildings - and the remaining 10% from materials and construction (embodied emissions). Hence reducing emissions in the building sector becomes crucial to meet climate targets.

Building lifecycle view

To start it is good to get a qualitative sketch of how energy intensive are the various phases of building construction lifecycle. This is seen in the figure below.

Ideally, it is better to build nothing if possible and accommodate people in existing infrastructure resulting in highest emission and material reduction potential. This is not mostly feasible, which makes building with reuse of existing materials the second-best option. Going further down the curve, it is better to build clever and efficiently with low carbon materials, modular construction techniques, etc. This sketch gives an intuitive understanding of the footprint distribution in various phases of the building lifecycle, but it is important to get further quantitative breakdown of these phases as well.

Embodied and operational carbon

Embodied carbon dominates the design and construction phase while operational carbon dominates in the use, maintenance and operation phase of the buildings.

Embodied carbon is dictated by the choice of construction materials and its manufacturing process, the distances these materials travel to site and how they are installed on-site. Typically, embodied carbon of the construction materials (kg CO2e per kg of material) is available in their product declaration sheets provided by the manufacturers. These product declarations vary across regions. In most parts of the world, it is becoming standardized in the form of Environmental Product declaration (EPD's) sheets. The embodied carbon of the materials becomes a part of the emission lifecycle assessment (LCA)of the buildings.  Moreover, as more product declaration are becoming available there are proprietary and open source LCA embodied carbon databases on the web which lists the embodied carbon of commonly used materials. One such open-source web tool is the Embodied carbon in construction calculator (EC3) which can be used to easily access and view material carbon-emissions data for materials manufactured within a defined geography, thus enabling carbon-smart choices during design and construction phase.

As operational carbon come from the electricity used during the building construction and from day-to day use and maintenance during residence, energy mix of the local grid (coal, gas, renewables) and off-grid solutions (solar panels with storage) dictates the operational emissions. Also, quality of building insulation and passive ventilation techniques contribute to reducing operational emissions.

A recent report from Global alliance for buildings and construction showed projected contributions from embodied and operational carbon within the building sector from 2021-2050:

In the above figure, it is interesting note that the embodied carbon only contributes 25% of the total emissions at the time of construction but rises to 49% in 30 years while the operational carbon reduces by 25% in that time period. This is attributed to standard renovation cycle (once in 15 years), causing spike in embodied carbon. The continued decarbonization of the grid globally from renewables deployment is expected to green the grid causing drop in operational carbon.

The main takeaway from this projection is that although embodied carbon constitutes a small fraction at the beginning, it is important to reduce it then and during renovation cycles making homeowner initiative to reduce embodied carbon significant. While for operational emissions, top-down grid decarbonization will play a bigger role than the homeowner initiative.

Indian context

In India the guidance on the benchmarks for embodied and operational carbon for climate positive buildings is provided by two national rating systems- the Indian Green Building Council (IGBC) and Green Rating for Integrated Habitat Assessment (GRIHA). Unfortunately, they have not become the norm because of the lack of awareness among stakeholders, unavailability of sustainable building materials on large scale, misconceptions about higher costs, but, most importantly, the reliance on a voluntary and free market approach. This has resulted in just 5 percent of buildings in India being green certified, until now.

The approach of using low carbon materials like wood, hemp, bamboo for reducing the embodied carbon in construction in some Western countries cannot be applied and scaled for India. High material quantity demand from its large population cannot be met sustainably for those materials. Further, concrete and steel, two of the most widely used construction materials today, are considered to have ‘hard-to-abate’ process emissions (Forthcoming article will go into detail on reducing embodied carbon in concrete and steel) and hard to find low-carbon replacements with equivalent strength and durability.

Benchmarks for embodied and operational carbon

IGBC proposes embodied carbon during building lifecycle not to exceed 700 kg CO2e per square meter of built-up area for all types of buildings as the benchmark. Since it is the first number of its kind in India, the technical consensus to NOT issue different benchmarks for different types of buildings (which would have been a more appropriate approach) and instead ensure a simple benchmark to encourage more projects to begin measuring their embodied carbon within its free-market voluntary system.

With the knowledge of the built-up area, type and quantity of materials used and embodied emission factors from the embodied carbon databases (such as EC3 tool), a homeowner or a real estate developer can do approximate calculation to determine if their building meets the benchmark.

For operational carbon, IGBC includes electricity consumption, water management and waste management in their guidelines. For the building’s electricity consumption, Energy performance index (EPI) is typically used as a rating metric which is calculated as follows:

As a rule of thumb, If EPI falls between 2 and 3, then your house is very energy inefficient.

If EPI falls between 1 and 2, then your house is doing ok, but there is scope for improvement.

IF EPI <1, then your house is very energy efficient.

This rule of thumb can be remembered as 1-2-3 rule. This rule of thumb is validated by empirical studies on energy savings in Indian buildings. In one such empirical study, the researchers surveyed 785 residential buildings in 4 major cities in India to determine operational energy savings potentials.

For my two-storey house, the EPI came out to be 0.9 (146 kWh/160 sq.m) with assistance from solar panels (for minimum lighting and water heating) and inverter. It is interesting note that a bigger house supplemented with solar panels and inverter can have the same EPI as a smaller house without solar panels and inverter. So, EPI as an operational carbon metric can mask the embodied carbon of the bigger house if seen in isolation. With the rise of the urban upper middle class in India, the trend of bigger houses with lower occupancy density will increase the embodied carbon while operational carbon will reduce from energy efficiency improvements in home appliances and in the usage of solar panels and stationary energy storage.

To conclude, both operational and embodied carbon needs to be assessed together to get the complete picture of the residential energy usage.

PS: I would like to thank Harish Borah for his subject matter inputs to refine the article.

Harish Borah, a subject expert in climate action and mitigation with 10-plus years of experience, was a QoC-CANSA Fellow 2023. An alumnus of NIT Silchar, the University of Manchester, and the University of Cambridge, he works as a carbon study/analysis expert for ADW Developments (UK) and serves as a technical advisor to GRIHA and IGBC in India.