Embodied Carbon of Roofing

Embodied carbon is the greenhouse gas emitted in producing, transporting, installing, maintaining and disposing of building materials. It is distinct from operational carbon, the emissions from heating, cooling and powering a building. For roofs, embodied carbon includes the covering, underlayments, insulation, deck, fasteners and flashings, and the emissions from replacing them over a building's life.

Why it matters

Embodied carbon in buildings has been estimated at about 11 percent of global carbon emissions. As buildings become more energy-efficient, embodied emissions make up a growing share of their total footprint. Roofs contribute through materials that are often energy-intensive to produce, such as metals, petroleum-based membranes and insulation, and concrete or clay products fired or cured at high temperatures.

Measuring it

Embodied carbon is calculated through life cycle assessment (LCA). Results for specific products are published in Environmental Product Declarations (EPDs), which are verified by independent third parties and follow product category rules (in Europe, EN 15804; in North America and Asia, commonly ISO 21930). Comparing EPDs requires care: they must cover the same functional unit, the same life cycle stages, and comparable assumptions.

Factors that change a roof's footprint

• Service life. A material with higher initial emissions can have a lower lifetime footprint if it lasts much longer and avoids replacements.
• Recycled content and recyclability. Recycling aluminium requires only about 5 percent of the energy needed to produce primary aluminium, so recycled content sharply reduces embodied energy; end-of-life recycling also avoids landfill.
• Weight and transport. Heavy materials shipped long distances carry higher transport emissions.
• Insulation type and thickness, which affect both embodied and operational carbon.
• Maintenance, such as recoating or periodic replacement of components.

Bio-based and low-carbon options

Timber, cork, wool and cellulose-based materials store carbon absorbed during plant growth. Concrete products can use cement alternatives such as ground granulated blast-furnace slag to reduce emissions.

Policy

Embodied carbon is increasingly regulated. Buy Clean Colorado, signed in July 2021, uses EPDs for public projects; eight US states introduced embodied-carbon procurement policies in 2021; the Netherlands has limited embodied carbon since 2018, with other European countries following; and since May 2023 Toronto has required new city-owned buildings to keep upfront embodied emissions below 350 kg CO2e per m².