Building designers can have a large impact on reducing upfront emissions of a building by undertaking 'whole life' carbon thinking at an early design stage. With the introduction of the new climate action bill it is time for our industry to play its part in achieving our national climate goals, writes Chartered Engineer Jeremy Walsh.

Introduction

The built environment is a major contributor to greenhouse gas emissions with the energy associated with building use accounting for 24% of energy-related CO­₂ emissions in Ireland in 2018, according to an SEAI report.

The emissions associated with the manufacturing, transportation, construction and end of life phases, commonly referred to as embodied carbon, contribute about 11% of all global carbon emissions.

As the levels of insulation and associated construction thickness have increased to comply with the necessary improvements in the building regulations (Part L) the embodied energy and associated embodied carbon, in absolute terms and as a proportion of the overall lifecycle energy of a building is rising. 

Furthermore, as the operational energy performance of new buildings is improving to the point where there is diminishing returns by improving element u-values and air tightness, it is logical that focus would progress to how the embodied energy of a building – estimated to reach 50% of building lifecycle carbon emissions by 2050 – can be reduced. 

By using a life cycle assessment tool, a recent study (full report available at Embodied-Energy-JWPM.pdf (jeremywalsh.ie) has compared the embodied energy of the two typically used house construction types, namely tradition masonry construction and timber frame. 

The results, which show that the materials in the timber frame construction produce about 40% less carbon per m² than the masonry construction materials, would intuitively be appreciated by most building designers and developers. 

Life Cycle Assessment

A Life Cycle Assessment (LCA) calculates the total impact a product, service or system has on the environment throughout its whole lifespan. This includes the raw materials, extraction of materials, energy consumption, manufacturing, transportation, use of the product, recycling, disposal and end of life.

Figure 1. Life Cycle Assessment Stages (IS EN 15978:2011) 

For this study, the buildings’ LCAs are calculated using the LCA tool ‘One Click LCA’ (by Bionnova LTD) according to EN 15978 – Sustainability Of Construction Works – Assessment Of Environmental Performance Of Buildings – Calculation Method.

This standard describes the calculation method, based on life cycle assessment and other quantified environmental information, to assess the environmental performance of a building.

The main focus of this report is on the Global Warming Potential (GWP), expressed as kg CO₂e, of the building as this is the most widely used category for comparing environmental impacts of systems. It is worth noting that the LCA tool also calculates other environmental impact categories such as Acidification Potential, Eutrophication Potential, Ozone Depletion Potential to name but a few.

Construction details

For this study two very similar recently completed near Zero Energy Building (NZEB) compliant houses in the same estate were compared up to builder’s finish (ie, no floor finishes, bathrooms, painting etc). As both buildings have the same heating and ventilation system the services (including electrics) were also not included in the comparison.

The masonry construction house is also a two-and-a-half-storey building with four bedrooms and three bathrooms. The ground, first and attic floors of the building have respective floor areas of 96.9m², 57.8m² and 45.8m², giving 200.5m² (GIFA) in total. 

Figure 2. Masonry Construction Details 

The timber frame construction house is a two-and-a-half-storey building with four bedrooms and four bathrooms. The ground, first and attic floors of the building have respective floor areas of 92.6m², 71.9m², and 51m², giving 215.5m² (GIFA, Gross Internal Floor Area) in total. 

Figure 3. Timber Frame Construction Details 

Table 1 displays some design parameters for both buildings 

Results

The results, which are not a full LCA for each building as finishes, services, etc were not included in the calculations, are useful for comparison purposes.

Figure 4. Masonry Construction Global Warming – Classifications, Resource Types 

For the masonry building, the main contributing resource type is concrete, with 44.6% of the total carbon produced by all resources excluding electricity.

Figure 5. Timber Frame Global Warming – Classification, Resource types 

For the timber frame building, the main contributing resource types are concrete and insulation, with 24.9% and 25.1% of the total carbon produced by all resources excluding electricity. 

Results comparison

Figure 6: Life-cycle stages comparison

Figure 6 displays the global warming potential per m² of both constructions with respect to their life-cycle stages, this chart clearly shows how both projects have similar carbon for all life-cycle stages apart from stages A1-A3 Materials.

The timber frame building has slightly higher B6 emissions per m² due to a lower thermal mass(according to DEAP), but the main focus when comparing the two constructions is the materials stage.

The building materials used in the timber frame construction produce 41% less carbon per m² than the masonry construction materials, a saving of 124.1 kg CO₂e per m². 

Figure 7: Resources type comparison

Figure 7 compares the CO₂ equivalent emissions per m² produced by each resource type in both constructions. Concrete is the resource with the largest difference between the two constructions, with the timber frame construction creating 36% emissions of the concrete used in the masonry construction.

The timber frame construction produced double the amount of timber emissions and 20% more insulation emissions compared to the masonry which amounts to 23.9 kg CO₂e per m² more than the masonry construction for the two resource types combined but the masonry building produced 111.4 kg CO₂e per m² more than the timber frame for concrete alone.

Conclusion

For a cradle to grave life-cycle (A1-A4, B4-B5, C1-C4 without materials associated with finishes and services), the masonry building produces 353 kg CO₂e/m² against 218 kg CO₂e/m² for the timber frame building. 

This is a saving of 135 kg CO₂e/m² or 38%. From Figure 6 it can be seen that there is very little difference in the two types of construction in most of the life-cycle stages and that stage A1-A3 materials accounts for 124.1 kg CO₂e/m² of the difference. This is without taking account of the potential biogenic storage of timber.

Figure 6 displays the global warming potential per m² of both constructions with respect to their life-cycle stages, this chart clearly shows how both projects have similar carbon for all life-cycle stages apart from stages A1-A3 Materials. The timber frame building has slightly higher B6 emissions per m² due to a lower thermal mass(according to DEAP), but the main focus when comparing the two constructions is the materials stage. The building materials used in the timber frame construction produce 41% less carbon per m² than the masonry construction materials, a saving of 124.1 kg CO₂e per m².

Figure 7 compares the CO₂ equivalent emissions per m² produced by each resource type in both constructions. Concrete is the resource with the largest difference between the two constructions, with the timber frame construction creating 36% emissions of the concrete used in the masonry construction. The timber frame construction produced double the amount of timber emissions and 20% more insulation emissions compared to the masonry which amounts to 23.9 kg CO₂e per m² more than the masonry construction for the two resource types combined but the masonry building produced 111.4 kg CO₂e per m² more than the timber frame for concrete alone.

It is clear that the use of concrete (even with 30% recycled binders), in foundations/floor slabs/intermediate floors/block walls is the reason that the traditional masonry construction has a significantly higher embodied energy than the timber frame construction. 

Portland cement, a key concrete ingredient, requires a lot of energy to manufacture with an embodied energy of 0.92 kg CO₂e and accounts for about 7% of global carbon emissions. Carbon capture technology will have to be a key element of the manufacturing of Portland cement in future in order to reduce global emissions.

Furthermore, if the end of life reuse of the timber was changed from incineration to recycling then the biogenic storage of the wood could be subtracted from the total embodied carbon of new buildings, thus progressing towards a net-zero carbon embodied building and creating a circular economy.

One of the difficulties encountered was that not all products had an Environmental Product Declaration (EPD) and substitute similar products with EPDs were used where necessary.

EPDs are currently voluntary and if it was mandatory to produce EPDs then there would be greater carbon transparency and it would allow building designers/developers to make more informed choices when deciding on what materials and construction types to use

The findings of this report, while somewhat narrow, clearly show the large impact that building designers can have reducing upfront emissions of a building by undertaking whole life carbon thinking at an early design stage.

The World Green Building Council’s publication 'Bringing embodied carbon upfront' calls for designers to “adopt a whole life approach to carbon reduction in buildings…, applying our principles in order to identify cost-effective, low and, ultimately, net-zero carbon designs while prioritising early emissions savings”.

With the introduction of the new climate action bill it is time for our industry to play its part in achieving our national climate goals.

Author: Jeremy Walsh BE CEng MIEI