Standards & Design | Embodied Carbon

Embodied Carbon in Multiplex Construction: Materials Matter

As operational energy drops (better envelopes, heat pumps, clean BC grid), the carbon locked in construction materials becomes the dominant source of a building's lifetime emissions. For a Step 3+ multiplex, embodied carbon can be 50-80% of total lifecycle impact.

Material Carbon Comparison

Conventional Wood Frame

Low Carbon $$

BC's default for Part 9 buildings. Wood is a carbon sink when sourced from sustainably managed forests. The lowest embodied carbon option for most multiplex projects.

Mass Timber (CLT/Glulam)

Very Low Carbon $$$

Cross-laminated timber and glulam beams store carbon for the building's lifetime. Emerging for larger multiplex (6+ units) but cost premium remains 10-20% over conventional wood frame.

Concrete Foundation

High Carbon $$

Concrete is the single largest embodied carbon source in most multiplexes. Portland cement produces ~1 tonne CO2 per tonne of cement. Reduction strategies: SCMs (slag, fly ash), reduced slab thickness, optimized mix design.

Steel Structural

High Carbon $$$

Rarely used for Part 9 multiplex but appears in hybrid designs. High embodied carbon but 90%+ recyclable. Recycled steel content varies but typically 25-90% depending on source.

Embodied Carbon by Material System

Conventional wood frame

1/5

Lowest embodied carbon — BC default

Mass timber (CLT/Glulam)

1/5

Carbon-storing structure

Low-carbon concrete (SCMs)

3/5

25-50% better than standard concrete

Standard concrete

4/5

Biggest single source of embodied carbon

Steel structure

4/5

High embodied carbon but highly recyclable

Four Practical Reduction Strategies

Optimize Concrete

20-30% reduction

Use supplementary cementitious materials (SCMs) — fly ash, slag, or calcined clay — to replace 25-50% of Portland cement. Specify low-carbon concrete mixes. Reduce slab thickness where engineering allows. This single step can cut embodied carbon by 20-30%.

Specify Local Materials

5-15% reduction

BC has abundant sustainably harvested timber. Specifying BC-sourced wood reduces transportation emissions and supports local forestry. For concrete, local aggregate reduces trucking distance. Every km of transport adds embodied carbon.

Design for Material Efficiency

5-10% reduction

Optimize structural layouts to minimize material waste. Regular grid spacing reduces wood waste. Standardized window sizes reduce custom manufacturing. Modular dimensions reduce cut-offs.

Consider Mass Timber for Larger Projects

30-50% reduction in structural carbon

For 6+ unit buildings, CLT floor panels and glulam beams can replace concrete and steel while storing carbon. The cost premium is shrinking as BC's mass timber manufacturing scales. Several CLT multiplex projects have been completed in Metro Vancouver.

✓Conventional wood frame is already low-carbon. BC multiplex developers start with an advantage over jurisdictions where concrete and steel dominate.
✓The cheapest carbon reduction is low-carbon concrete. Specify SCMs in the foundation pour for minimal cost impact and significant carbon savings.
✓Embodied carbon regulation is coming. Not mandatory for Part 9 buildings today, but Vancouver is already reporting it for larger buildings. Designing low-carbon now avoids future compliance cost.

Best For

✓ Developers targeting green certification (LEED, Passive House, net-zero) where embodied carbon is evaluated
✓ Purpose-built rental where long-hold ownership values lifecycle carbon
✓ Projects in Vancouver where embodied carbon reporting may extend to multiplex-scale buildings

Usually Fails When

✕ The project is cost-constrained and cannot absorb mass timber premium (stick with conventional wood frame)
✕ The builder has no experience sourcing or specifying low-carbon concrete mixes
✕ The municipality has no embodied carbon requirements and the financing stack does not reward it

What To Verify Before Spending Money

→ Your concrete supplier's ability to provide SCM-blended mixes and EPD documentation
→ Whether mass timber is cost-competitive for your specific building size and form factor
→ Your municipality's current and planned embodied carbon reporting or regulation requirements

Frequently Asked Questions

Is embodied carbon regulated in BC? +

Not yet for Part 9 residential buildings. BC's Zero Carbon Step Code currently focuses on operational carbon (what fuel the building uses). However, the province has signalled that embodied carbon requirements are coming — likely as whole-life carbon targets by 2030. Vancouver already requires embodied carbon reporting for larger buildings.

How much of a multiplex's total carbon is embodied vs operational? +

For a Step 3+ multiplex with heat pumps, embodied carbon can represent 50-80% of total lifecycle carbon. As operational energy drops (better envelope, cleaner grid), the proportion of embodied carbon grows. This is why material choices matter increasingly.

Does mass timber make sense for a 4-plex? +

Generally no. The cost premium for CLT and the engineering complexity are hard to justify for small multiplex. Conventional wood frame (which is already low-carbon) is the pragmatic choice for 4-6 unit buildings. Mass timber starts making more sense at 6-8+ units where the structural advantages improve.

What is the cheapest way to reduce embodied carbon? +

Specify low-carbon concrete for the foundation and slab. This costs the same or marginally more ($2-5/m³ premium) and can reduce total building embodied carbon by 15-25%. It requires specifying it in the concrete order — your builder needs to ask for it.