Embodied Carbon 2
We are nearing completion of our life cycle assessment (LCA). Overall it’s been an interesting process to learn what our highest carbon materials are, lower impact choices we could make, and how much deconstruction / reuse counts towards our bottom line.
A first of its kind benchmark study of residential homes in Vancouver Magwood&Trottier, 2022 models the embodied carbon emissions from 13 typical new builds with break down by material category (see buildersforclimateaction.org).
The average emissions intensity in Vancouver is estimated at 193 kg CO2/m2. Overall, our renovation comes in 45% lower than this at ~103 kg CO2/m2, with the equivalent new build emitting ~132 kg CO2/m2.
Retaining our slab, footings and foundation walls helps us save a fair chunk of embodied carbon with concrete representing, in our case, 32% of total home emissions or ~9 tons CO2.
After that, the biggest contributor to embodied carbon is our new roof. We decided to replace our roof for improved insulation, daylighting and solar PV access. With the framing, R-60 insulation and membrane material, our roof represents up to 38% (10.8 tons) of the embodied carbon of our renovation if metal, 25% (5.9 tons) if asphalt shingles.
Windows follow 17% or 4.7 tons - here we’re opting for triple pane instead of double. Higher embodied carbon but better R values. Windows are the weakest point of a building envelope for heat loss so it’s really important to maximize performance here.
Cladding is next. We’re going with Hardie board fiber cement siding, which adds 12% or 3-4 tons. The alternative (lower carbon) would be cedar siding. This is more costly and needs much more routine maintenance to keep up paint, prevent rot and pest damage. In our area of North Van, wildfire is the biggest climate threat we face. Fire retardants and charred cedar siding can provide some protection, but Hardiboard siding is flat-out rated as non combustible and feels appropriate for the location.
It’s trade-offs every step of the way! Our LCA results will be shared at Buildex 2023 and we’ll post a link to the final report on our blog @ nvnzero.com
