Embodied Energy - Introduction

Building envelope selection is primarily a structural, aesthetic and/or performance consideration but also has an environmental impact. It is becoming increasingly important to select materials with the least negative environmental effects. The life-cycle assessment approach can be used to determine the environmental impacts of material selection, where material contents, production methods, energy requirements, and waste are analysed to identify the real cost of material, reflecting the total amount of its environmental impact. The International Standards Organization specifies methods for the life-cycle analysis (ISO, 2006).

Life-cycle analysis is the energy required to extract, process, transport, install, recycle, or dispose of the material. The embodied energy is commonly measured in megajoules (MJ) per unit of mass (kg) or volume (m³) of the material.

There are numerous factors to consider when determining a material’s embodied energy. The table below includes the energy required for mining or harvesting the raw materials, shipping and transporting them to the manufacturing facility, processing the raw materials into the building products, and shipping them to the construction site. Disposal and recycling when the building is demolished must also be considered.

The calculation is complex and involves many project-specific variables and assumptions: How close to the project site are the points of extraction and manufacture? What will be the means of shipping? How long is the building expected to last? These and other questions may be unanswerable.

Material	Embodied energy (MJ/kg)
Aluminium	226
Cast virgin	25
Cast recycled (33%)	214
Extruded virgin	34
Extruded recycled (33%)	217
Rolled virgin	28
Rolled recycled (33%)	226
Brick	3.0
Cement
Portland	0.95
Fly ash (6–20%)	0.89 to 0.76
Fly ash (21–35%)	0.75 to 0.62
Mortar	0.22
Concrete
General	1.0
Fly ash (15%)	0.97
Fly ash (30%)	0.89
Precast	1.5
Glazing
Primary	15
Toughened	24
Insulation
Mineral wool	17
Polystyrene	87
Polyurethane	102
Fibreboard	20
Glazing fibre reinforced polymer	100
Polycarbonate	113
Paint	70
Steel
Virgin	35
Recycled	95
Stainless	7
Stone
Granite	11
Limestone	1.5
Marble	2.0
Sandstone	1.0
Slate	0.1 to 1.0
Wood
General	10
Glue laminated	12
MDF	11
OSB	15
Plywood	15
PV panels
Monocrystalline	4,750
Polycrystalline	4,070
Thin film	1,305