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Will triple-glazing make any sense under an embodied carbon regime?

July 19, 2023  By Patrick Flannery

Passive House project at 825 Pacific Street in Vancouver. Source: Cascadia Windows and Doors.

July 19, 2023 – Just as you thought it was safe to proceed with your energy-efficient façade designs that are airtight and watertight, and minimize thermal transmission, governments are about to take their entire building regulatory apparatus through another wrenching 90-degree turn.

Introducing embodied carbon: a measurement of the CO2 released into the atmosphere by the manufacture, shipping, maintenance and disposal of building materials.

In draft documents, federal code authorities are proposing voluntary embodied carbon reporting in the 2025 National Building Code, limitations to allowed embodied carbon by 2030, and net-zero carbon emissions—both operational and embodied—by 2050.

The new Treasury Board Standard on Embodied Carbon in Construction will require the reporting and reduction of the embodied carbon footprint of all new major government construction projects (starting with concrete).

What this may very well mean is that some designs and products optimized for reducing a building’s energy use may soon not meet code, or not get spec’d as part of a performance-path compliance plan.

Triple-glazing is a prime example.

Current tiered codes plan to reduce the centre-of-glass U-value of residential glazing to 0.80 by 2030.

That is pretty much impossible to achieve without triple-paned insulating glass. But triple IGUs require (obviously) an additional pane of glass in each unit, plus spacer, sealant, and a more robust framing material. These units are heavy, and glass is one of the highest embodied-carbon building products by weight there is. (Aluminum is the highest, beating even concrete. PVC is not far behind.)

Glass requires high temperatures to process, and is shipped from a just a few locations around North America. Mileage will vary by region and local energy supply, but some calculations suggest that the payoff in terms of reduced carbon emissions from the installation of triple glazing is 10 to 20 years.

So when you specify triples instead of lower-performing doubles, it takes 10 to 20 years for the energy savings in the building to catch up to the carbon released through the triples’ manufacture and shipping in the first place.

What’s more, 10 to 20 years is almost the entire life span of an IGU.

Within 10 years, the seals will start to degrade and require replacement if energy performance is to be maintained. Replacing the glazing on a big building is a massive undertaking that exceeds the carbon cost of the initial installation.

This resets the 10- to 20-year payoff clock.

Calculated over the expected life of the building, there is—at best—only about 1/3 the carbon benefit for using triples as would be suggested by an operational calculation alone. Maybe that’s better than nothing, but maybe that’s too low to justify the steep additional cost for triple glazing.

(Maybe a less-expensive, lower-performing solution would fit the bill better when combined with, say, a more-efficient HVAC system.)

The considerations above stretch to absolutely every aspect of a building plan. Design, engineering, procurement, manufacturing, equipment, transportation, installation, maintenance, and demolition/waste companies are all going to have to go back to the drawing board to re-evaluate their priorities, services, and solutions.

This, despite the world’s construction industries spending at least the last 50 years figuring out how to make buildings more energy-efficient. Maybe embodied carbon should have been prioritized right from the start—even before energy efficiency.

Patrick Flannery is the editor of Glass Canada, which serves Canada’s architectural glass industry. Its community includes glazing contractors, glass fabricators, building engineers, architects, and specifiers. Like Energy Manager Canada, Glass Canada is a member of the Annex Business Media family.

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