An ecological solution for wooden window frame enlargements

Wooden window frame enlargements are often used to close the building skin around windows. However, windows, and their respective enlargements, are required to meet stringent demands concerning cost, element weight, and insulation against heat loss and noise, safety, and burglary protection, among other things. Currently, the most typical wood window frame enlargements are made of two particle-board panels with a polyurethane core, where the particle board often is laminated on the outside with a PVC skin for protection. Today’s building processes often call for the installation of building components such as doors or windows at lower levels of the building before the building is protected from the elements above. Also, as windows and doors are installed before all the primary construction processes such as concrete pouring or brick layering are completed, chances are that high levels of humidity from such activities create a detrimental environment for wood-based materials. This paper presents the development of an alternative material to make wooden window frame enlargements that are inert to humidity yet other properties are being maintained or exceeded. Research looking for such a material looked at different materials like wood (Balsa or Poplar), Cork, extruded rigid polystyrene (XPS), and polyethyleneterephthalate (PET). Tests revealed that only the solutions using XPS and PET were able to achieve U-values of less than 0.6 W/m2K at a thickness of 58mm. However, additional tests also revealed a better performance of PET-based panels in terms of being able to shape the panel and in terms of screw retention. Also, thanks to the use of recycled PET, an environmentally friendly, low-cost solution could be found that is inert to humidity.