Many building products advertise environmental benefits. Few back the claims with scientific evidence, and buyers have learned to ask which ones actually do. Wood products hold an advantage here because producers in several species groups have funded formal studies that measure what a product consumes and emits from forest to installation. Redwood decking became one of the first cases where production absorbs carbon dioxide from the atmosphere and stores it in the wood fiber, while competing wood plastic composite and vinyl decking increase carbon output instead. Life cycle thinking now reaches across the whole field, from life cycle cost analysis in infrastructure asset management to environmental accounting for the materials themselves.
What a Life Cycle Assessment Measures
A life cycle assessment, or LCA, quantifies the inputs and outputs of a product across its full life: timber harvesting practices, lumber manufacturing processes, energy consumption, by-product output, and air and water emissions. The boundaries of a material LCA run parallel to the construction project life cycle that frames a building, but the accounting follows the product rather than the schedule.
A 2013 comparative study of redwood decking, carried out by an independent research consortium, compared redwood against wood plastic composite and vinyl. Redwood production stored carbon in the fiber, reducing global warming potential, and produced far lower levels of air and water pollution during manufacture than the synthetic alternatives. Those two findings, carbon and pollution, drive most of the specification decisions that follow. The study ran under the standardized LCA methodology set out in the ISO 14040 family, which defines how inventory data is collected, how impacts are calculated, and how results are reported so that studies from different producers can be compared.
The Stages of a Product Life Cycle
- Raw material acquisition: harvesting and transport of the logs.
- Manufacturing: sawing, drying, planing, and packaging at the mill.
- Use phase: installation, performance, and maintenance over the service life.
- End of life: disposal, recycling, or energy recovery.
The Functional Unit
Every stage is measured against a functional unit, such as one square foot of decking in place over a 50-year service life. The unit makes different materials comparable: if one product lasts half as long, it needs twice the material to deliver the same function, and the assessment accounts for that difference instead of comparing one board to one board.
From Raw Mill Data to an Environmental Product Declaration
An LCA only earns trust when the underlying data is real. A good starting point for understanding the mechanics is an explainer on how life cycle assessment traces a product’s impacts from raw material to disposal, including which data points matter and how they flow into the final numbers.
Product category rules, or PCRs, tell every producer what to measure and how to report it, so one decking EPD can be compared with another. Without that common template, each manufacturer could choose its own boundaries, and the comparisons would mean nothing.
For the redwood update, mills supplied log volume input, lumber and by-product output, electricity and fuel usage, and the use of ancillary products ranging from hydraulic fluids to plastic strapping. Energy consumption covered every process, including dry kilns, plus energy production from biomass cogeneration plants. Assembling the record took staff through hundreds of pages of purchase orders and utility reports, and the level of detail required went far beyond the production totals a mill tracks routinely.
Data a Sawmill Must Supply
- Log volume entering the yard, by species and grade.
- Lumber and by-product output, including chips, sawdust, and bark.
- Electricity and fuel consumption by process.
- Kiln energy use and drying schedules.
- Consumables such as lubricants, hydraulic fluids, and plastic strapping.
- Air and water emissions records from permitted equipment.
Wood vs Synthetic Decking: What the Numbers Show
The comparison that matters to a specifier covers the same function with different materials. Redwood decking production sequesters carbon, while wood plastic composite and vinyl production add carbon to the atmosphere. Manufacturing pollution follows the same split, which is why results connect directly to watershed analysis and water resource assessment in regions where mills and treatment plants sit near rivers.
The durability story reinforces the environmental one. Redwood carries natural resistance to decay and insects and holds its dimensions under changing moisture, so a deck stays in service longer and needs fewer replacement cycles, which spreads the manufacturing footprint over more years of use.
| Impact category | Redwood decking | WPC decking | Vinyl decking |
|---|---|---|---|
| Carbon output of production | Absorbs and stores CO2 | Increases carbon output | Increases carbon output |
| Air pollution from manufacture | Low | Higher | Higher |
| Water pollution from manufacture | Low | Higher | Higher |
| In-service durability | Naturally resistant | UV-dependent | Temperature-sensitive |
Carbon Accounting: Sequestration vs Emissions
Life cycle results also inform policy. Green building codes and rating systems reference EPDs as evidence for material credits, and public agencies increasingly ask for them in bid documents.
Carbon accounting treats the forest differently from the factory. Growing trees pull CO2 out of the atmosphere, and lumber that stays in service keeps that carbon stored for decades. Synthetic decking starts with fossil feedstocks and energy-intensive processing, so its footprint is a net addition to the atmosphere. The gap between the two is the core finding the redwood study documented, and it is why the product is marketed on sequestration rather than on reduced emissions.
How EPDs Are Verified and Used
Study results become an Environmental Product Declaration, or EPD, a standardized document that presents transparent, verifiable, comparable information for developers of green building codes, specifiers, architects, and consumers. Specifiers pair the environmental data with engineering assumptions about design life when they compare materials, the same way design life and return period frame structural decisions.
EPDs are prepared by independent third-party organizations in accordance with internationally recognized standards, so a manufacturer does not grade its own homework. The declaration format is consistent across product categories, which is what makes line-by-line comparison possible, and green building rating systems increasingly award points for products with published EPDs.
Who Prepares and Reviews an EPD
An independent research consortium runs the assessment, a program operator manages the declaration, and an accredited third-party verifier reviews it against the standard before publication. In the redwood case, the consortium’s 2013 data became the basis for the first redwood decking EPD, reviewed under a third-party certification program. The verifier checks that the inventory matches the mill’s records, that the impact calculations follow the standard, and that the functional unit is stated clearly. Verification happens before publication, and a declaration is typically valid for a fixed term before it must be updated.
What an EPD Contains
Typical sections cover global warming potential, ozone depletion, smog formation, acidification, and water use, each expressed per functional unit. A reader can take two EPDs for competing products and compare the same impact category line by line, which is exactly what a code official or a specifier needs.
Keeping Assessments Current
An LCA is a snapshot of a specific production system at a specific time. Mills change processes, energy sources shift, and data quality improves, so the study needs revisiting the way the phases in the life cycle of a construction project each need their own review. The redwood program began a new assessment in 2018 to update the 2013 baseline, collecting and analyzing a fresh dataset across harvesting, manufacturing, energy, by-products, and emissions.
The update required a researcher from a federal forest products laboratory to spend a week on site in the redwood region gathering records from cooperating sawmills. Mills that kept routine totals at their fingertips still had to dig through hundreds of pages of reports to answer questions about lubricants, kiln energy, and cogeneration output. A full update cycle runs several months: data collection at the mills, analysis by the consortium, independent review, and publication. Mills with clean records finished their part in days, while others spent weeks locating utility bills and consumable purchases.
Who Funds and Runs Updated Assessments
The work is funded through a forestry endowment created under the 2006 Softwood Lumber Agreement between the United States and Canada. An independent consortium directs the research and a federal laboratory contributes expertise, which keeps the study out of the hands of the industry it measures.
What Mills Can Do to Prepare
- Keep log input and product output records current by species and grade.
- Track energy use by process, including kilns and cogeneration.
- Document consumables such as lubricants, hydraulic fluids, and strapping.
- Retain utility bills and emissions records in a single file.
- Assign one staff member to answer data requests so the mill speaks with one voice.
At the project level, material studies feed into the environmental impact assessment of construction projects, connecting a single product’s footprint to the whole site’s. A deck, a wall, or a roof framing package is the smallest decision where the largest environmental commitments get made, and an up-to-date life cycle assessment is the tool that keeps that decision honest.