Timber vs Steel Trusses: Embodied Carbon Face Off
Architects are finally scrutinizing the roof structure the same way they eye concrete mixes. Manufacturers that can quote a credible carbon number per square foot win specs before the drawings leave the studio. Wood players like Trussway and UFP have the advantage of biogenic storage, while Clark Dietrich’s new low-embodied-carbon (LEC) steel line tries to narrow the gap. The math below shows how wide that gap still is—and why prefabrication flips the waste conversation on its head.
Why the humble truss now matters in carbon bids
Steel, concrete and insulation usually hog the spotlight, yet roof and floor trusses can represent 8 to 12 % of a low-rise building’s cradle-to-gate footprint. New public procurement rules in New York City and California cap GWP on structural packages, so bidders must defend every pound of metal or lumber they ship.
The carbon scoreboard: three brands, one metric
- Clark Dietrich LEC cold-formed steel framing reports 1.66 kg CO₂e per kilogram at A1–A3 (Clark Dietrich EPD, 2024).
- The Canadian industry EPD for wood trusses shows 111 kg CO₂e per cubic metre, equal to roughly 0.24 kg CO₂e per kilogram after biogenic storage is counted (CWC, 2025).
- Trussway and UFP have no public EPDs today; in the absence of product-specific data, owners default to the industry average above. That gives timber suppliers a head start, but only if they publish soon.
Converting lab data to the jobsite
A typical cold-formed steel roof truss weighs about 5 lb / ft² (2.3 kg). Multiply by Clark Dietrich’s 1.66 kg CO₂e / kg and designers face ~3.8 kg CO₂e per square foot of roof area. A comparable timber truss comes in closer to 2 lb / ft² (0.9 kg). Using the industry GWP, that is just 0.22 kg CO₂e per square foot—roughly a 17-to-1 delta. Even if Clark Dietrich’s LEC claim of a 30 % improvement over its legacy steel is applied, wood still holds a tenfold margin.
Independent research backs the spread
A 2025 Chalmers University LCA found that a 12-metre steel truss emitted 842 kg CO₂e, while five nail-plate timber trusses covering the same span emitted 179 kg CO₂e, an 79 % cut (Chalmers Univ, 2025). The pattern held across all span lengths tested.
Prefabrication flips the waste script
On-site stick-built roofs can waste up to 15 % of purchased lumber off-cuts. Off-site automated saws trim that to under 3 %, according to the Structural Building Components Association’s 2024 audit. EPA data show the US generated 600 million tons of construction debris in 2018, more than double municipal trash (EPA, 2025). Every pound saved in teh factory stays out of that pile.
ROI beyond carbon counters
- Lighter timber trusses trim crane time and fastening hardware, slicing install labor by 10–15 % in multifamily walk-ups.
- Steel still rules long spans above 80 ft, so mixed-material portfolios let manufacturers chase both markets.
- Early EPD publication locks in spec loyalty; once an engineer drops a product into a BIM model, switching later is painful.
Read the small print on any EPD
Check the declared unit: Clark Dietrich reports per metric ton, the wood EPD per cubic metre. Always normalise to area or linear foot before comparing. Scrutinise the system boundary too; some steel declarations bury recycling credits in module D, which does not help an A1–A3 cap.
Bottom line for manufacturers
Publish a truss-specific EPD before your competitor does. Pair it with a clear pounds-per-square-foot table that specifiers can drop straight into their calculators. Prefabbrication cuts waste, but only transparent data wins the bid.
Frequently Asked Questions
How do I estimate the carbon per square foot of my timber truss without an EPD?
Use the Canadian Wood Council industry average of 111 kg CO₂e per m³ (CWC, 2025), measure the actual lumber volume per square foot in your design, then multiply. It will not satisfy strict buy-clean rules but gives a credible placeholder.
Steel truss suppliers claim high recycled content. Does that negate timber’s advantage?
Not yet. Even electric-arc-furnace steel with 90 % scrap still lands around 1.2–1.6 kg CO₂e per kg, an order of magnitude above wood once biogenic storage is counted (Clark Dietrich EPD, 2024).
Will biogenic carbon be accepted in US public-sector GWP caps?
Yes; both the GSA Interim IRA rules and newer state policies allow biogenic removals as long as forests are PEFC or FSC certified. Always cite chain-of-custody.
Does prefabrication help if my product is already low carbon?
Absolutely. Off-site cutting lowers material overage, trims transport miles and improves quality control, all of which compress A1–A3 impacts and save cash at the same time.
About the Author
John brings a clear, research-driven perspective on the EPD, LCA and HPD space and keeps a close pulse on environmental trends and standards in North America, helping clients understand where the industry is heading and how to get there.
