Environmental assessment of wooden roof compositions

. The construction industry has high energy consumption and environmental impact, such as greenhouse gases, acidification, and the like, leading to concerns about the environmental impact of buildings on climate change. Sustainable and ecological construction requires innovation in materials and their durability to support a low-carbon and efficient city. The construction industry needs measures to reduce emissions, and buildings are assessed using methods such as Life Cycle Assessment, which allows for a holistic view and supports sustainable development. Timber roofs are crucial in the fight against the environmental crisis, as buildings have a significant impact on lower greenhouse gas emissions.


Introduction
The construction industry is characterized by high energy consumption and large production of emissions such as greenhouse gases, acidification, eutrophication, and others [1].It is obvious that the increasing pressure on the environment due to human activity is beginning to cause bad effects on the environment.Climate change and loss of biodiversity are becoming increasingly unbearable [2].To create a healthy and sustainable environment, changes in society are necessary.Making these changes and adjustments is a worldwide challenge to mitigate global warming.One of the main contributors to negative environmental impacts is the construction industry.The largest emissions of greenhouse gases are produced either during the extraction of materials, transport to the construction site or because of the energy consumed during the operation of the building and because of the materials and energy required for the construction of the building and their disposal after the demolition of the building [3].Indeed, buildings account for approximately 40% of global energy-related CO2 emissions [4].Life Cycle Assessment (LCA) is a technique for assessing the impact of a product on the environment in all phases of the life cycle -i.e., from the extraction of raw materials through the processing of materials, production, distribution, use, repairs, maintenance to disposal or recycling [5].The goal of LCA is to compare the range of effects of environmental impacts assigned to goods and services to improve processes, promote economy, and provide a solid basis for qualified decisions [6].The term life cycle refers to the idea that an objective and comprehensive assessment requires an assessment of the production of raw materials, production, distribution, use and disposal, including "intermediate transport" and all other actions necessary for the existence of the product.This article is focused on the analysis of the composition of wooden roofs using environmental indicators.

Material and methods
The LCA method was used to evaluate the composition of roofs with a border from the cradle to the gate with choices according to the EN 15978 standard [7].System boundaries and modules found in this study are shown in Fig. 1 [8].The characteristics of the examined roof compositions are described in Table 1.The environmental impacts were calculated per functional unit [FU] of 1 m 2 of usable area and the estimated lifespan is 50 years.One Click LCA software [9] was used to determine environmental indicators, life cycle and circularity of materials.Environmental impact indicators such as Global warming potential (GWP) expressed as kg CO2eq, Biogenic carbon storage (BS) expressed as kg CO2eqbio, Ozone depletion potential (ODP) expressed in kg CFC11eq, Acidification potential (AP) expressed in kg SO2eq, Eutrophication potential (EP) expressed in kg PO4eq, Photochemical ozone creation potential (POCP) expressed in kg C2H4eq, Abiotic depletion potential (ADPelements) for non-fossil sources expressed in kg Sbeq and Abiotic depletion potential (ADPfossil fuels) for fossil resources expressed in MJ.The results of the LCA analysis was subjected to a multicriteria analysis using the MCA7 tool [10] to select the appropriate composition of the wooden roof.

Results and discussion
Table 2 shows the results for the investigated impact categories for the twenty designed wooden roof compositions.Fig. 2 shows the results for GWP expressed as kg of CO2eq emissions.According to the results, roof composition C17 (116.7 kg CO2eq) achieves the worst results and composition C7 (39.2 kg CO2eq) achieves the best result.Fig. 3 shows biogenic carbon BS.The best result is achieved by composition C4 (92.8 kg CO2eqbio) and composition C17 (281.4 kg CO2eqbio) has the worst impact on the environment.Fig. 4 shows the results of ODP.The best result is achieved by compositions C9 and C10 (2.45E-06 and 2.3E-06 kg CFC11eq) and the worst result by C3 and C16 (1.9E-05 and 2.08E-05 kg CFC11eq).In terms of SO2eq emissions, C17 has the worst result (0.49 kg SO2eq) and C1 has the best result (0.15 kg SO2eq) in AP (Fig. 5).The results for EP shown in Fig. 6 show that C1 achieves the best result (0.03 kg PO4eq) and C16 the worst result (0.09 kg PO4eq).The best result in terms of POCP (kg C2H4eq) is achieved by composition C15 and C18 with a value of 0.02 kg C2H4eq, and the worst result is achieved by composition C8 and C19 (0.07 kg C2H4eq) (Fig. 7).Fig. 8 presents results for abiotic depletion potential (ADP-elements) for non-fossil sources.Composition C14 achieves the best result (0.02 kg Sbeq), composition C4 and C18 the worst result (0.4 kg Sbeq).And finally, the abiotic depletion potential (ADPfossil fuels) for fossil resources is shown in Fig. 9. Composition C15 achieves the best result (711 MJ) and composition C17 the worst result (2058 MJ).
Table 2. Results of impact categories for roof compositions (C1-C20).Table 3 presents the largest material contributors to GWP within the cradle-to-gate boundary (A1-A3) and their percentage of roof composition.

Conclusion
Roof structures play a key role in the energy efficiency of buildings and in the prevention of heat loss.The modernisation and renovation of roof structures can make a significant contribution to reducing energy costs for heating and cooling and increasing the overall comfort of living.It is also important to select the right material and construction for roofing to minimize the need for maintenance and increase the overall service life of the structure.There are various programmes and institutions in the European Union that aim to promote the renovation of buildings and improve their energy efficiency.At Member State level, there are specific regulations and standards for the energy sources used in the construction and renovation of buildings.In some countries, funding is also available to support the modernisation of buildings.Nowadays, the renovation of buildings is seen as a positive investment for the future and a step towards environmental protection and thermal comfort.
It is important for us to realise that every step we take towards improving energy management and protecting nature has a positive impact on our overall quality of life.Roof structures are one of the key elements in the renovation of buildings and the right choice of materials and construction can have a significant impact on the overall efficiency and quality of the building.This study presents the results of the evaluation of timber roof compositions from an environmental aspect.Based on the assessment of the proposed compositions, it can be concluded that the best rating was achieved by the C7 composition with KVH timbers, wood fibre insulation, a ventilated gap and an aggregate capping layer.The results of the environmental indicators show that the use of wood fibre and cellulose insulation in the compositions is up to 66% lower for GWP, 88% for ODP, 69% for AP, 65% for EP, 77% for POCP, 94% for ADP-elements and 65% for ADP-fossil fuels compared to the compositions with sheep wool, cork, or linen insulation.The KVH composition with wood-fibre insulation also performs the best in the multi-criteria analysis including all LCA categories.Further research work will focus on the in-depth analysis and comparison of buildings and their structures in terms of life cycle costs, circularity, and circular economy.

Fig. 1 .
Fig. 1.System boundary (From the cradle to the gate with options).

Table 3 .
Materials with the largest share of emissions in the GWP category (C1-C20).