Built Right Detail 20: Lower-Carbon Envelope Choices

A builder’s net zero envelope course by Xerox Builders · October 2026

As houses use less energy, the carbon in their materials matters more. This final Detail shows where embodied carbon sits in a Vancouver house, how insulation and concrete choices compare, the trade-offs to watch, and where BC and Vancouver rules are heading. It also closes the Built Right course.

Operational and embodied carbon

Most of this course has been about operational carbon: the emissions from heating, cooling and running a house. A tight, well-insulated, all-electric house brings it close to zero. Embodied carbon is different. It comes from making, transporting and installing the materials, and most of it is released before anyone moves in. As operating energy falls, the materials become a larger share of a house’s total climate impact.

Where the carbon is in a house

A 2022 material emissions benchmark study for the City of Vancouver looked at local Part 9 homes. They averaged about 193 kg CO₂e per m² of heated floor area, with a wide range between homes.

Within concrete, slabs were 46.5% and foundation walls 32.3% of the concrete emissions. In insulation, mineral wool board and EPS contributed most because they were used so widely. Only one home in the study used a carbon-storing insulation.

Insulation compared

Global data compiled by Project Drawdown compares the emissions to make and install the same insulating value. Conventional XPS and polyurethane/polyisocyanurate foams were highest by a wide margin, mainly because of high-global-warming blowing agents. EPS, stone wool and glass wool were far lower. Wood fibre and cellulose were lowest, and plant-based materials also store carbon in the building.

Lower-carbon swaps by location

Every swap must still work for moisture, fire, structure and the code. Confirm changes with your designer or envelope consultant.

Concrete: the biggest lever

• Better cement. Portland-limestone cement (GUL) reduces CO₂ by up to 10% compared with general use cement, with similar performance.
• Ask for the EPD. Ready-mix suppliers can provide lower-carbon mixes and product-specific EPDs.
• Use less. Size footings, walls and slabs with your engineer rather than by habit. In the Vancouver study, redesigning two homes as slab-on-grade instead of with full below-grade space cut their material emissions by about 9%.

Trade-offs

Cellulose and wood fibre must stay dry, and dense-pack cellulose needs the right density and a trained installer. Wood fibre board needs more thickness for the same R-value and supply can be limited. Mineral wool is non-combustible and vapour-open but heavier. EPS and other foams are combustible and must be protected. The lowest-carbon house is one that stays dry and lasts: never trade durability for a lower number.

Getting started on your next house

You don’t need to change everything at once. Start with the two biggest items. Talk to your ready-mix supplier and engineer about the foundation before the design is fixed, because concrete volume is set early. Then pick one insulation swap your crew can learn well, such as loose-fill cellulose in the attic, which is already common practice. Track what you use, ask suppliers for EPDs, and build up your own numbers house by house. If an owner wants a figure, an energy advisor with BEAM training can model the whole house.

Where the rules are heading

The City of Vancouver has required whole-building life cycle assessment and embodied carbon limits for Part 3 buildings since 2023; 1 to 3 storey houses are not yet under those by-law limits. Its Zero Emission Buildings bulletin for R1, RT and RA districts, which offers floor-area exclusions and other zoning relief for zero emission houses, requires applications made after 31 December 2025 to show embodied carbon 40% below a benchmark. The City’s Part 9 guide (Appendix II) sets the benchmark at 200 kg CO₂e/m² upfront (cradle-to-gate), in line with the 2022 study above, so the limit is 120 kg CO₂e/m² upfront, or 150 kg CO₂e/m² cradle-to-grave. Optional Industry Leadership Credits can ease the reduction to 30%. The calculation uses BEAM or MCE2 and is done by an NRCan-registered energy advisor or certified Passive House designer with BEAM training. Rules are changing quickly, so confirm current requirements with your city.

The whole course

Built Right has followed one house from plan to test: an air barrier you can trace without lifting your pencil, below-grade details, windows and doors, walls, roofs and penetrations, testing, and now lower-carbon materials. Each Detail is one piece of the same goal: a tight, durable, low-carbon envelope.

Site checklist

• Embodied carbon goal agreed with the owner and designer
• Lower-carbon concrete mix and EPD requested from the supplier
• Footings, walls and slab sized by the engineer
• Carbon-storing insulation used where the assembly suits it
• Foam limited to where it’s needed, with product EPDs compared
• Moisture, fire and structure checked for every swap
• Cellulose and wood fibre kept dry on site
• City requirements and incentive paths confirmed

Test yourself

Try to answer each question, then click it to check.

You have completed Built Right. Keep going with our Net Zero Homes page and the Building Science Construction Guides.