Chris Magwood has been building straw bale homes for over two decades

Why your super energy efficient building may be responsible for more carbon emissions than one that is merely compliant with standard building codes

Sustainable building pioneer, Chris Magwood believes the broader industry’s response to reducing building-related emissions has been to focus solely on energy efficiency. An approach, while well intentioned, he says actually results in initiatives and policies that raise emissions rather than lower them.

If carbon-intensive materials are deployed to build a highly energy-efficient structure it can paradoxically cause more greenhouse gases than one that is merely compliant with basic building codes.

Whereas if cellulose materials are used, he says, “we can feasibly and affordably capture and store vast amounts of carbon in buildings, transforming the sector from a major emitter to a major carbon sink.”

Made to measure materials

Magwood has developed an app, called BEAM, designed to assess projects carbon footprint and provide advice on how to improve it.

Inputting a building’s dimensions will reveal the carbon footprint of all material options, and by making a selection, for each assembly it will present a report at the material, assembly and whole-building levels.

Screen shots of the BEAM building materials embodied carbon calculator

?Magwood says, “our 2019 white paper showed compelling results for single family homes and small multi-unit residential buildings with wildly varying carbon footprints based on material selections.

“The same building could be responsible for emissions of over 400kg of CO2 emissions a square metre of floor area or could be responsible for over 150 kg CO2 net carbon storage a square metre and all results in between! It just depends what you choose.”

This is because of the embodied carbon, or life-cycle emissions associated with the products used. Chris prefers the term up-front embodied carbon (UEC):

Upfront embodied carbon emissions for the same building built with different materials

All stages of the product’s life have to be considered: the raw materials, the processing and manufacturing, transportation, and what happens at the end of their life.

The graphic contrast between materials with embodied negative and positive carbon over their life cycle. Source: Carbon-Storing Materials Report

Generally speaking, plastic materials such as XPS and EPS have a high embodied carbon since they are associated with the fossil fuel industry, whereas timber, straw, and other plant-based products have a negative carbon starting point because they have absorbed atmospheric carbon during their growing period. 

Using these materials safely stores atmospheric carbon in the structure of the building for decades.

The app is based on a white paper, the Carbon-Storing Materials Report, published by the Carbon Leadership Forum. 

The raw data for this is found in Opportunities for CO2 Removal and Storage in Building Materials which contains the complete data set and the full text and charts for over 300 building materials and dozens of low-rise building assemblies.

Sample from the Carbon-Storing Materials Report.

Buildings made of seaweed?

A whole new class of building materials is proposed by this report. These would be made from purpose-grown fibres such as bamboo, cork, hemp, algae, and seaweed.

Or from underutilised agricultural residues such as rice hulls, wheat straw, and bamboo leaf ash, sunflower stalks, sugar bagasse.

All have the potential to create new building products, catalyse new manufacturing hubs, create jobs, provide training and education opportunities, and reduce the need for traditional, emissions intensive disposal methods of waste fibres, since they can be composted at the end of their lives.

What’s more, the carbon avoided and carbon stored in buildings represents a new asset class of carbon products for emerging carbon marketplaces.

The report proposes that by pairing communities where biogenic materials are harvested with companies (industry partners) where manufacturing and construction services occur, “we can reduce upfront emissions in the building industry. We can also cut emissions associated with underutilised agricultural residues while catalysing new carbon and building product markets and strong economies, producing multiple co-benefits.”

Better than energy efficiency

Magwood believes that cutting upfront carbon emissions will do more to fight climate change than increasing building efficiency. “Up-front embodied emissions for buildings materials must be measured and policies enforcing caps developed for fast reductions,” he says.

He also thinks that net zero energy building codes won’t significantly reduce emissions in time to save us from drastic climate change. “It’s net zero carbon buildings not net zero energy buildings that we need”.

So what we want is for the sector to make buildings with zero upfront emissions. “Designers and builders can completely transform the carbon footprint of their buildings through carbon-smart material choices.”

David Thorpe is the author of Passive Solar Architecture Pocket Reference,  Energy Management in Buildings and  Sustainable Home Refurbishment. He lives in the UK.

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