from architecture2030.org
We've looked at HEMPCRETE and SHEEP'S WOOL, both the carbon-smart attributes and the acknowledged challenges, questions and unknowns. Let's take a look at another Carbon-Smart Material: WOOD
CARBON IMPACT OF WOOD
Trees sequester carbon during their life, pulling carbon dioxide (CO2) from the atmosphere and storing it in their mass. For every kilogram of wood grown, 1.5 kg of CO2 is removed from the atmosphere1 and stored until the tree burns or decomposes, at which point the CO2 is re-released into the atmosphere. Due to this natural carbon sequestration, forests play a significant role in our planet’s ability to regulate warming and carbon emissions.
Global timber harvesting causes us to lose 32 million acres (13 million hectares) of forest each year, or about 60 acres per minute. Specifying wood from sustainably managed forests helps ensure that the trees we harvest are replaced, so our forests maintain a consistent level of carbon sequestration2. About 20% of anthropogenic greenhouse gas emissions are due to deforestation and forest degradation3,4.
Using reclaimed wood and wood from sustainably managed forests are the best ways to reduce embodied carbon emissions from wood.
CARBON SMART ATTRIBUTES
Specify reclaimed wood products
Wood will re-release the carbon it has sequestered at the end of its useful life through decomposition or burning. Use reclaimed, salvaged, or recycled wood products whenever possible to prolong this carbon storage.
Only specify timber from sustainably managed forests
Forest management practices can greatly influence the carbon footprint of a wood product, so specify wood and wood products from sustainably managed forests. Among other attributes, sustainably managed forests establish protected areas and conserve biodiversity, have a management plan and harvest accordingly, replant trees to replace the harvested trees, and use reduced-impact logging techniques, all of which reduce the embodied carbon impact of the timber2.
Specify fast growing wood
Fast-growing trees store carbon faster than slow-growing trees. Specify wood from sustainably managed forests that support fast growing trees and plant new trees to replace harvested timber.
Specify wood products manufactured without fossil fuels or GHG-emitting biofuels
Many wood processing plants are powered by fossil fuels or wood chips, but wood chips (a form of biomass) are not necessarily carbon neutral. Burning wood immediately releases its sequestered carbon, and it takes decades for replacement trees to absorb and sequester that same amount of carbon. Whenever possible, specify wood products that are manufactured using renewable, non-CO2 emitting energy sources.
Don’t specify wood harvested from old growth forests
The ecosystem- and carbon-impacts of harvesting old growth forests and rainforests are significant. To minimize these impacts, only specify wood from new growth, sustainably managed forests. A significant portion of carbon sequestered by trees is pushed into the soil around the tree. Harvesting old growth forests and rainforests greatly disturbs the ground, releasing much of that sequestered carbon. Additionally, old growth forests and rainforests provide diverse habitats for a wide range of species that have developed over multiple decades or centuries. Harvesting these forests can cause significant ecosystem disruptions.
Specify wood products with minimal processing
Typically, the more processing a wood product undergoes the higher the embodied carbon impact. For example, glulam timber and other engineered wood products emit more CO2 than sawn lumber due to the added manufacturing processes, which often include the application of heat and pressure and the use of adhesives1. Additionally, most engineered wood products use virgin wood and are difficult to recycle, with the exception of glulams. However, while engineered wood typically has a higher embodied carbon impact per unit weight, some engineered wood products are stronger than sawn lumber thus requiring a smaller material quantity, which may reduce emissions overall – see Design Guidance.
DESIGN & CONSTRUCTION GUIDANCE
Design for durability
Ensure that the wood products used in the building are protected from heat and water, and will last the lifespan of that building.
Understand the right structural wood product for your building’s needs
Even though engineered wood products typically have a higher carbon impact per unit weight than dimensional lumber, they are stronger and therefore require fewer members, which may reduce emissions overall. EPDs are available for many engineered wood products so it is possible to compare the carbon footprint of systems using engineered wood vs. dimensional lumber in order to select the system with the lowest overall embodied carbon footprint.
Look for low-carbon alternatives for the same application
Choose the lowest carbon wood product appropriate for each application. For example, oriented strand board (OSB) sheathing and plywood have comparable characteristics, but OSB has about double the carbon footprint of plywood sheathing1. Engineered wood products such as Laminated Veneer Lumber (LVL) and Parallel Strand Lumber (PSL) have a larger embodied carbon impact than sawn lumber, even accounting for their greater strength1.
Use Optimal Value Engineering techniques (advanced framing)
Optimal Value Engineering techniques can reduce the amount of wood needed in a building or application. For example, space studs at 24” on center instead of 16”, align studs with joists and rafters using a single top plate, align openings with stud spacing to eliminate or reduce header sizes at non-bearing walls, and eliminate unnecessary framing at wall intersections1.
Plan for reuse
Wood will release the carbon it has sequestered at the end of its useful life through decomposition. Make a plan for reusing the project’s wood products at the end of the building’s life. Consider ancient wood joinery techniques or mechanical fastening to avoid adhesives that would prevent the materials from being reused.
Use wood trusses and pre-manufactured wall panels, where appropriate
Wood trusses and pre-manufactured wall panels have been shown to use 26% less wood than traditional framing techniques, while also reducing weight and allowing for longer floor and roof spans5. However, if using engineered wood products, ensure that the additional embodied carbon from manufacturing still results in an overall embodied carbon reduction.
Why the 2030 Palette?
Over the next 15 years, an area equal to the entire building stock of the Western Hemisphere will be redesigned, reshaped, and rebuilt. How we plan and design this new construction will determine whether climate change is manageable or catastrophic. With the 2030 Palette, designers will have the tools they need to design adaptive, resilient, and Zero Net Carbon built environments.
Carbon Smart Materials Palette, a project of Architecture 2030, is an immediately applicable, high-impact pathway to embodied carbon reductions in the built environment .
WHY EMBODIED CARBON?
Annually, embodied carbon is responsible for 11% of global GHG emissions and 28% of global building sector emissions. However, as we trend toward zero operational emissions, the impact of embodied emissions becomes increasingly significant. It is therefore crucial to address embodied emissions now to disrupt our current emissions trend, and because the embodied emissions of a building are locked in once the building is constructed and cannot be taken back or reduced.
Architecture 2030’s mission is to rapidly transform the global built environment from the major contributor of greenhouse gas (GHG) emissions to a central part of the solution to the climate crisis.
Architecture 2030 pursues two primary objectives:
to achieve a dramatic reduction in the energy consumption and greenhouse gas (GHG) emissions of the built environment; and,
to advance the development of sustainable, resilient, equitable, and carbon-neutral buildings and communities.
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