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  • Michael McCarthy

Embodied Carbon in Buildings

Updated: Aug 20, 2020

Measuring embodied carbon in the construction of new buildings has long been a distant cousin of measuring carbon from building use.

This is rightly so. The energy used and therefore carbon emitted from a building in use is indefinite and will be at least 60 years.

However, measuring embodied carbon is becoming more recognized as something that needs to be measured and in many cases mitigated.

It was not until 2011 that a definitive inventory of carbon intensity of materials was published by the Building Services Research and Information Association (BSRIA) and the University of Bath in 2011, the Inventory of Carbon and Energy (ICE).

Embodied carbon is defined by the Inventory of Carbon and Energy (ICE) as:

“the total primary energy consumed (carbon released) from direct and indirect processes associated with a product of service with the boundaries of cradle-to-gate. This includes all activities from material extraction (quarrying / mining), manufacturing, transportation and right through to fabrication processes until the product is ready to leave the final factory gate.”

At MMC Quantity Surveyors we have long been aware of embodied Carbon. Michael McCarthy, the managing director even wrote a part of his thesis on it in 1998 when the notion of embodied carbon was in its infancy and far from main stream. In 2012 Michael undertook an ISO 14064 course in the measurement, verification and validation of greenhouse gas emissions.

As quantity surveyors, we are ideally placed to measure the embodied carbon of buildings. We already have systematically quantified the buildings, all we had to do then was to develop a rate library of carbon intensity of the components involved using the data provided by the ICE.

This is reasonably straight forward for most of the structural items such as concrete, steel, stone and glass.

It gets tricky when measuring the carbon intensity bespoke or composite items where the application of some estimation has to be employed. 95% of the embodied carbon can be measured accurately however.

As housing is the most widespread form of construction, we compared 2 different houses with approximate the same footprint but of different design and construction.

The first one is a timber and steel frame with a steel external cladding and timber upper floors.

It has a blockwork external skin up to the underside of first floor.

The second one is all concrete construction including all internal and external walls and floors.

The differences between to two forms of construction are stark.

In our calculations, the embodied carbon of the concrete house is 167 tonnes of carbon emitted and the timber frame house was 96 tonnes. An increase of 74% on the timber frame house.

In comparison to the carbon emitted from an A3 rated house, this equate to between 20 and 41 years’ worth of carbon emissions. Variable factors include how a house is used and the technology employed.

Because the timber frame house was larger, the differences in terms of kg/m2 exacerbate these figures further.

In terms of Kg/m2 of house area, the concrete house accounted for 600 kg/m2 and the timber frame house was 295kg/m2.

These figures are at extreme ends of the scale, the concrete house includes for concrete upper floors when most houses have timber upper floors. Likewise, the timber structure employs a good deal of steel, which surprisingly, because of its high strength to weight ratio, is quite energy efficient.

Actual real time comparisons may not lead to such drastic differences.

Let’s put these into context of the overall requirement for new housing as an example.

The Bigger Picture

In the next 10 years at current projections, up to 275,000 houses per annum will be required per annum in the UK to keep up with population growth.

If the average size of a house is taken at 120m2, this will require 33 million m2 of floor space each year.

At a differential of 305kg/m2 this would result in an additional 10 million tonnes of carbon emitted in the construction of these houses per annum if they are all built in concrete.

In Ireland it is estimated that 30,000 houses will be required per annum, at the same rates as applied in the UK example, this would result in an additional 1 million tonnes of emitted carbon.

As part of the overall picture of carbon emissions, embodied carbon is not an insignificant part of the overall picture and should be part of the calculations for sustainability.

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