The use of wood and timber products in the construction of buildings is repeatedly pointed towards as a mean for lowering the environmental footprint. With several countries preparing regulation for life cycle assessment of buildings, practitioners from industry will presumably look to the pool of data on wood products found in environmental product declarations (EPDs). However, the EPDs may vary broadly in terms of reporting and results. This study provides a comprehensive review of 81 third-party verified EN 15804 EPDs of cross laminated timber (CLT), glulam, laminated veneer lumber (LVL) and timber. The 81 EPDs represent 86 different products and 152 different product scenarios. The EPDs mainly represent European production, but also North America and Australia/New Zealand productions are represented. Reported global warming potential (GWP) from the EPDs vary within each of the investigated product categories, due to density of the products and the end-of-life scenarios applied. Median results per kg of product, excluding the biogenic CO2, are found at 0.26, 0.24, and 0.17 kg CO2e for CLT, glulam, and timber, respectively. Results further showed that the correlation between GWP and other impact categories is limited. Analysis of the inherent data uncertainty showed to add up to ±41% to reported impacts when assessed with an uncertainty method from the literature. However, in some of the average EPDs, even larger uncertainties of up to 90% for GWP are reported. Life cycle assessment practitioners can use the median values from this study as generic data in their assessments of buildings. To make the EPDs easier to use for practitioners, a more detailed coordination between EPD programs and their product category rules is recommended, as well as digitalization of EPD data.

Purpose.The built environment has demonstrated the limited nature of applications of consequential LCA (LCA), whereas attributional LCA (ALCA) is applied in most situations. Therefore, this study aims to clarify the contexts in which CLCA might be applied and the state of CLCA on buildings by examining the following research questions: (i) How are the goal, scope and methodological aspects and associated gaps of CLCA of buildings addressed in the literature? (ii) How can these insights guide the applications of CLCA on buildings? Methods. The study employed the Systematic Literature Review methodology, which yielded 37 relevant studies. The study examined the sample regarding intended applications, the contexts of micro or meso/macro decision-making support, and the consequential life-cycle inventory modelling (CLCI) of time horizons, market delimitations, market volume trends, affected suppliers, constrained supplies and substitution. Furthermore, the basis for choosing either an ALCA or a CLCA approach was evaluated based on the ILCD Handbook. Results and discussion. Many studies include an empirical assessment, yet with half of those combining it with an evaluation of selected methodological aspects, CLCA on buildings seems to still be in the earlier exploration phase. In general, the empirical CLCAs emphasize the decision-making aspect in the stated application of the study. Furthermore, CLCA studies show an almost equal distribution of focus between the micro and meso/macro levels of decision support. This entails that CLCA on buildings currently applies to both material-and building-level assessments and policy situations. The inclusion of CLCI modelling elements varies: e.g., nine studies only include substitution as the single CLCI element. Additionally, modelling methods are described at various levels of detail, and with critical differences in the transparency of documentation. This, therefore, suggests that the consistency of included CLCI elements is inadequate, as is how they should be modelled. Conclusions and recommendations. Building on the ILCD Handbook, this study presents a proposal for deciding when to select CLCA on buildings. This is a proposal for a simple and clear distinction threshold between the micro and meso/macro levels. Additionally, CLCA on buildings need a more harmonized approach to CLCI modelling to increase and improve, which the built environment community could achieve by settling on a standard for the inclusion of CLCI elements and associated modelling methods.

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Buildings can potentially be carbon sinks by use of wood under correct circumstances because wood sequesters CO2 i.e., biogenic carbon, from the atmosphere by photosynthesis during growth. Consequential life cycle assessment (CLCA) works as a decision support tool to assess consequences from a change in demand by including only the processes that are affected by this demand through market-based modelling. This study aims to review current research about CLCA on wood in buildings. First, by examining methodological approaches linked to CLCA modelling and biogenic carbon accounting of wood in buildings. Second, to evaluate conclusions of studies using CLCA on wood in buildings. We conducted a literature review of 13 articles that fulfilled the criteria of stating to conduct a CLCA concerning either buildings, components, or materials where wood is one of the materials. The application of the reviewed studies include: method development, reuse, testing end of life aspects, CLCA inventory modelling, and comparison of ACLA and CLCA. The CLCA inventory of small-scale studies comprise a wide spectrum of methods ranging from simplistic to advanced methods, often retrospective. All large-scale studies integrate sophisticated modelling of prospective analysis. Dynamic time-dependent biogenic carbon accounting and indirect land use change (iLUC) are rarely represented. Although, both aspects have an impact on whether wood buildings respectively work as carbon sinks or provide net GHG emissions. Wood multi-storey buildings generally perform environmentally better than concrete and steel buildings due to wood displaces these materials and residues substitute fossil energy. End of life scenarios, choice of substituted production, retro- and prospective data, and the share of recycled steel further influence carbon mitigating potential of wood in buildings. Research of CLCA on wood in buildings are many-fold. Some studies partially evade inclusion of some CLCA aspects i.e., market delimitation, market trend, affected suppliers, and substitution. A simultaneously high integration of both CLCA, time-dependent biogenic carbon accounting, and iLUC in the same study is almost absent. Consequently, more empirical and methodological CLCA studies are needed while including dynamic time-dependent biogenic carbon accounting to improve understanding of implications of policy decisions in transitions towards increased use of wood in buildings.