What is Embodied Energy of Building Materials?

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The embodied energy of building material is the total non-renewable energy or primary energy (carbon released) used throughout its entire life cycle, i.e., extraction, manufacturing, construction, maintenance, and disposal. 

In other words, it is the sum of greenhouse gas emissions attributed to the material during its life cycle.

Embodied energy is a parameter evaluated to assess the life cycle of a building and is directly related to the sustainability of the built environment.

This article discusses the embodied energy of building materials and their purpose.

Types of Embodied Energy or Embodied Carbon

Embodied energy or carbon emissions are studied and measured in relation to the buildings as:

1. Initial embodied energy
2. Recurring embodied energy
3. Operational energy

Initial Embodied Energy

This is the non-renewable energy consumed during procurement of raw materials, processing, manufacturing, transportation, and construction. 

For example, a steel window possesses initial embodied energy from mining the ore, production, transportation, manufacturing, and transportation to the building site. Initial embodied energy is influenced by the source, type, and nature of the building material. 

Recurring Embodied Energy

It is the non-renewable energy consumed for maintenance, repair, restoration, refurbishment, or replacement of materials, components, or systems during the building's lifecycle. 

It is influenced by the durability and maintenance of building materials, systems, and components installed in the building and the lifespan of the building.

Operating Energy

It is the recurring energy consumed in buildings for heating, cooling, ventilation, and lighting, which is acquired either by passive or active energy systems. 

The operating energy increases with the increase age of the building, and with time, the initial embodied energy becomes insignificant.

Initial embodied energy is the main focus in the construction industry. For instance, concrete is the most abundant human-made material in the world, where cement production creates ~7% of the world’s CO₂ emissions and is the largest contributor to embodied carbon in the built environment. 

Embodied carbon is expected to account for nearly 50% of the overall carbon footprint of new construction between now and 2050 (UN Environmental Global Status Report 2017; EIA International Energy Outlook 2017). It is the primary cause of environmental implications like resource depletion, production of greenhouse gases, and environmental degradation.

Initial embodied energy is expressed in Mega Joules (MJ) units or Giga Joules (GJ) per unit of weight or area. The calculation of embodied energy is a complex process and is influenced by the geographical location of the technology employed for manufacturing and the production method. 

Boundary Conditions of Embodied Energy

As per the Inventory of Carbon and Energy (ICE), University of Bath, 2008, embodied energy can be stated in terms of boundary conditions:

• ‘Cradle-to-Gate’: from material extraction to manufacturing gate.
• ‘Cradle-to-Site’: from material extraction to building site.
• ‘Cradle-to-Grave’: from material extraction to end-of-life. 

ICE considers Cradle-to-Gate boundary conditions to provide general data on the building material. For detailed analysis, Cradle-to-Site boundary conditions may be considered.

Objective of Studying Embodied Energy of Building Materials

The biggest concern for civil engineers and architects should be the reduction of carbon emissions from the buildings. Studying and measuring embodied energy or carbon incorporated in building materials is essential to create more eco-conscious projects.

Life Cycle Assessment (LCA) is a useful tool used to identify the problems in the life cycle of a building that has the most impact on the environment. The assessment may require comparing different materials with the same function. For example, comparing steel, timber, or concrete frame structure.

Understanding embodied energy of materials used in architecture and construction leads to sustainable decisions rather than fashion or profit-based decisions. Table-1 below gives the selected data from the Inventory of Carbon and Energy (ICE) prepared by the University of Bath (UK).

Material	Energy MJ/kg	Carbon kg CO2/kg	Material density kg/m3
Aggregate	0.083	0.0048	2240
Concrete (1:1.5:3)	1.11	0.159	2400
Bricks (common)	3	0.24	1700
Concrete block (Medium density)	0.67	0.073	1450
Aerated block	3.5	0.3	750
Limestone block	0.85		2180
Marble	2	0.116	2500
Cement mortar (1:3)	1.33	0.208
Steel (general, av. recycled content)	20.1	1.37	7800
Stainless steel	56.7	6.15	7850
Timber (general, excludes sequestration)	8.5	0.46	480–720
Glue laminated timber	12	0.87
Cellulose insulation (loose fill)	0.94–3.3		43
Cork insulation	26		160
Glass fibre insulation (glass wool)	28	1.35	12
Flax insulation	39.5	1.7	30
Rockwool (slab)	16.8	1.05	24
Expanded Polystyrene insulation	88.6	2.55	15–30
Polyurethane insulation (rigid foam)	101.5	3.48	30
Wool (recycled) insulation	20.9		25
Straw bale	0.91		100–110
Mineral fibre roofing tile	37	2.7	1850
Slate	0.1–1.0	0.006–0.058	1600
Clay tile	6.5	0.45	1900
Aluminium (general & incl 33% recycled)	155	8.24	2700
Bitumen (general)	51	0.38–0.43
Medium-density fibreboard	11	0.72	680–760
Plywood	15	1.07	540–700
Plasterboard	6.75	0.38	800
Gypsum plaster	1.8	0.12	1120
Glass	15	0.85	2500
PVC (general)	77.2	2.41	1380
Vinyl flooring	65.64	2.92	1200
Terrazzo tiles	1.4	0.12	1750
Ceramic tiles	12	0.74	2000

Among all the building materials, cement, aluminium and steel production consume large amount of non-renewable energy and therefore should be used with care while constructing a building.

Reducing embodied energy in a building includes the application of locally available materials, designing the building for low maintenance, improving flexibility in use, and designing the building for appropriate climatic conditions. 

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