Background Construction is the largest industrial sector employer in the EU. The “cradle to grave” aspects linked with the creation, use and disposal of buildings, however, create major environmental problems. Construction activities consume more raw materials than any other industrial sector; and as a result also account for the largest share of greenhouse gas (GHG) emissions: accounting for some 40% of the total GHG emissions in terms of energy use. Furthermore, construction and demolition activities produce the largest waste stream – some 25% of European total waste (78% of which is concrete cement-based products, 11% wood). Improving the durability of different construction materials, such as concrete and wood, would allow substantial benefits in terms of raw materials use, related energy consumption and CO2 emissions, and waste quantities. Moisture ingress (entry) is responsible for the premature degradation of construction materials as a result of phenomena such as gel cracking, efflorescence or steel corrosion in reinforced concrete. Swelling (dimensional changes) of wood upon water absorption limits the use of some species (e.g. oak, beech) to some exterior applications. Water-induced biological attacks (by fungi, insects and micro-organisms) lead to the need to use biocides to reach their expected service life. Silicone-based water repellent treatments have the unique property of being impermeable to liquid water but permeable to water vapour. This explains why silicones are already widely used in different industries. They therefore provide a good technical platform to develop new water repellents that can increase the durability of wood and cement-based materials and the dimensional stability of wood. Moreover, it should be noted that improving the durability of concrete materials using silicon-based materials as a water repellent, will also reduce the humidity in buildings, improving the living and working environment of people within, with the added benefit of a positive impact on health. Objectives The overall objective of the 'SILEX' project is to extend the lifetime/usability of buildings made of wood and/or cement, by applying environmental friendly silicon-based water repellents. In comparison with the current treatment processes, silicones also have a beneficial environmental profile. The project will address environmental problems specific to each material: use of biocides and fungicides for wood; volatile organic compound (VOC-)release for concrete and cement based materials. Specific project goals are: To demonstrate the effectiveness and market introduction of a new series of environmentally-friendly silicon-based water repellents for cement and wood-based construction materials; To reduce VOC emissions by 80-90% in comparison with concrete, silane-based impregnation treatments; A reduction of biocides (75% of current loading) used for the conservation of some wood species (pine, beech); An extension of the usability of oak and beech thanks to an improvement of their dimensional stability (i.e. the aim is to reduce dimensional change by 50%); and A reduction of CO2 emissions thanks to the increased lifetime of wood and concrete materials. Expected results The development of sustainable materials will lead to new green solutions for the construction industry. The main expected results are: An increase of durability/usability of EU-grown wood. The use of the silicon-based product is expected to enable a decrease of the required biocide used to extend wood service life and to decrease wood dimensional instability upon moisture entry. For pine, the project expects to match the current service life of treated pine with a reduction in biocide use of at least 75%; for beech, the project expects to increase the service life from five years up to 25 years in comparison with untreated wood and to improve dimensional stability by at least 50%; for oak, the project expects to reduce dimensional changes by 50% and reduce leaching of extractible under natural ageing in order to allow oak to be used in class III applications; A decrease by 80-90% of VOCs released upon hydrophobic impregnation of concrete. VOCs released upon reaction of hydrophobers should decrease from 500g/l to 50 -100 g/l; A reduction in CO2 emissions as result of the increase in the lifetime of the treated material (fewer CO2 emissions for repairs and transport).