Effects from natural weathering on long-term structural performance of wood-polymer composite cladding in the building envelope

Abstract

The structural use of wood-polymer composites (WPC) in façades has not been fully investigated, which can be attributed to a lack of practical experience. In this study, three different extruded compounds were tested in Central Europe after one year of natural weathering. Their strength loss was quantified using the flexural strength and pull-though resistance of screws positioned differently in the test sheets. It was found that pull-through is affected by fiber orientation in the same way as is bending strength. Screws at the panel edges parallel to the main fiber orientation showed 26% higher values, whereas the difference between 10 mm and 15 mm edge distance was not significant. Also, round pre-drilled holes instead of slotted ones did not translate into higher resistance values. As far as aging is concerned, the flexural strength became far more degraded by global radiation than did fastener pull-through strength. It can therefore be argued that flexural characteristics alone are not a realistic indicator of the structural durability of a WPC façade.