The Norwegian Government has set ambitious goals for the fossil carbon intensiveness of the Norwegian economy. The built environment can make an important contribution towards achievingthose goals by:
Building energy efficient buildings;
Using low embodied energy materials;
Using construction materials as stores of atmospheric carbon dioxide.
An analysis of life cycle assessment (LCA) studies published in the scientific literature has been undertaken. The use of timber in construction has an important role to play as part of an energy reduction and carbon storage strategy for the built environment. In the majority of studies analysed there is agreement that there are environmental advantages associated with the use of timber in construction from a climate change mitigation perspective.
At the time of writing this report there is no LCA-based tool that is sophisticated enough to be used at the whole building level to assist in decision-making processes for materials to minimise environmental impacts. This can only be determined on a case-by-case basis.
However, LCA can be used to inform policy decisions regarding the use of materials to minimise the climate change impacts of the built environment in Norway, if the GWP (global warming potential) impact category is used in combination with the embodied energy data. But the methodology does have inherent uncertainties.
The original terms of reference for the report, were as follows:
General considerations on the different methods of environmental impact analysis and evaluations (LCA, EPD, HWP, BREEAM….) and what the differences are between these systems;
Conduct an analysis on wood LCAs that have been done in Norway and comparable countries, anda compilation of these data. Which factors influence the analysis and how much do single factors affect the result?
Conduct a similar analysis on competing materials like concrete and steel;
Conduct an analysis comparing the environmental impacts of wood and other materials. What is actually being compared and what does it imply for the real climate footprint?
Summarise the results, evaluation of their importance and the use such findings can have for political decisions in the future.
The report begins with a description of the Norwegian built environment and forest products’ sectors and then gives an overview of the methodologies used in LCA and the strengths and weaknesses of the technique. LCA is a complex subject and there is still debate about the methodologies and impact categories. LCA does not have the level of accuracy needed in many impact categories in order to make comparative assessments and only the impact categories global warming potential and ozone layer depletion potential are considered to be sufficiently robust to give accurate and reliable data.
A review of building assessment schemes has also been undertaken. LCA comprises only a minor part of building assessment schemes, such as the Building Research Establishment Environmental Assessment Method (BREEAM) and Leadership in Energy and Environmental Design (LEED) and these have little to say about the choice of materials for construction. These schemes have some value in promoting more environmentally-conscious designs, but they are not sufficiently robust to be used
as tools to inform policy-making, or building material choices.
The report focuses on issues surrounding carbon sequestration in forests and how atmospheric carbon can be stored in long-life products in the built environment. One of the advantages of using timber in construction is the potential for the storage of biogenic carbon (derived from atmospheric carbon dioxide) in long-life structures. Although this does have a role to play in climate change mitigation, this literature review has revealed that most studies show that the effects of substitution for high embodied energy materials and for fossil fuels for energy production are much more significant. The overwhelming majority of LCAs of timber products have shown that the amount of atmospheric carbon stored in the wood (measured as CO2 equivalents) is always larger than the GHG (greenhouse gas) emissions associated with the processing of the material. Additional benefits arise when the wood is incinerated at the end of the life cycle, with substitution of fossil fuels. The highest fossil fuel substitution benefits arise when coal is replaced with timber wastes/by-products. In a Norwegian context, the highest benefits will arise if wood is used as a fuel for cement kilns, or as a carbon-source
for aluminium anodes, followed by a replacement of oil for heating then natural gas for heating or electricity production.
This report also reviews the scientific literature of published LCA studies of commonly-used building materials (timber, cement/concrete, aluminium, steel, poly(vinyl chloride)). It is shown that the outcomes of the LCAs are very heavily dependent upon the assumptions made and the system boundaries used. It is not possible to arrive at definitive a value of (for example, global warming potential, GWP) that is characteristic for a material, but there is a range of values. The methodology used to determine the environmental impacts is complex and many studies are not readily amenable to
comparative studies. This is because of differences in functional unit, supporting databases, assumptions regarding material life, maintenance, end-of-life scenarios, etc. In addition, most studies lack sufficient transparency to allow for proper verification of the results obtained. LCAs also inevitably contain simplifications, which may affect the accuracy of the data. Most studies do not employ a sensitivity analysis to show how the assumptions and variabilities affect the results. It is necessary to consider the whole life cycle when making materials choices and the only way to do this is at the whole building level. However, this increases the degree of uncertainty in the calculations and involves assumptions and the introduction of scenarios which may not be realistic or reasonable.
A variety of factors can affect the LCA of building materials over their lifetime, which can be divided into uncertainties and variabilities. Uncertainties arise from lack of precise knowledge regarding processes or the use of assumptions. Variabilities can arise due to different choices regarding the use of materials, such as frequency and type of maintenance, different disposal methods, transport distances, etc. Combinations of uncertainty and variability can be difficult to separate. There is considerable scope for uncertainty to affect the data, especially when the in-service and end-of-life stages of the life cycle are included.
Consequently, there is considerable variability in the methodology applied for LCAs, which has a significant influence on the output and hence the task of making comparative assertions is extremely difficult. However, there has been some degree of consensus reached with the introduction of environmental product declarations (EPDs) and standardisation of procedures; known as product category rules (PCRs). Nonetheless, there is still concern that inter-product comparisons are not reliable, due to uncertainties and variations in the assumptions made, the use of different databases, etc. The main advantage with EPDs which are produced in conformity with the European standard
EN 15804, is that the impacts have to be reported separately for different life cycle stages. Of these, the cradle to factory gate life cycle stage (modules A1-A3) is likely to be the most reliable, since this part of the life cycle involves the least assumptions and the most accurate data.
This study has largely focussed on data concerned with the embodied energy associated with materials and the global warming potential (GWP) environmental impact category, because these have the lowest uncertainties. GWP data is strongly influenced by the time-frames of the study and by a range of different factors that have to be taken into account when making comparative studies:
Greenhouse gas (GHG) emissions associated with the manufacture of construction materials, maintenance, replacement and disposal;
GHG emissions associated with operational energy requirements, if these are relevant and realistic and have not been introduced to favour one material over another;
Carbon emissions and storage from forestry operations and sequestration by growing biomass;
Substitution effects associated with the use of timber in comparison to other building materials;
End-of-life scenarios, such as recycling, or incineration with energy recovery.
The embodied energy used to produce construction materials is an important consideration when analysing the environmental impacts. This initial embodied energy is to be distinguished from the recurring embodied energy which arises due to maintenance of the materials and the operating energy, which is energy consumed due to the operational requirements (e.g., heating) of the building. As the operating efficiency of buildings improves, the embodied energy will be a larger proportion of the overall energy requirements. The embodied energy also represents a greater proportion of the overall
energy consumption of the sector in a growing market. Sawn timber products are lower embodied energy materials when compared, on a functional unit basis, with non-renewable construction products. The increased use of timber in construction will result in more carbon storage in the harvested wood products carbon pool at a critical time. This can form part of a wider strategy to move to a low fossil carbon economy.
Although timber is the dominant material used in single-family dwellings, it is little used in multipleoccupancy buildings. The Norwegian forests are currently absorbing levels of carbon dioxide which are equivalent to about 40% of the annual emissions, but this will fall as the age structure of the forests matures. In order to maintain these high levels of sequestration it is necessary to increase the harvesting intensity of Norwegian forests. The carbon in the HWPs produced should be stored in long life products in the built environment for the maximum climate change mitigation effect. The use of timber in high-rise non-residential and multiple-occupancy residential construction would give
benefits from a climate change mitigation perspective. The Norwegian forest products sector should use the opportunity provided by the increased use of timber in multi-occupancy and multi-storey buildings to develop an export industry in pre-fabricated structures. Adding value to the forest products sector is essential. By encouraging a cross laminated timber industry in Norway, there will be potential for export of multi-occupancy buildings using modular construction methods to exterior markets, such as the UK.