In 2011, Martijn started trading in used window frames he stocked in his garage. Today, Martijn Kozijn primarily sells new window frames, but there al still a number of used windows on offer, as well as a number of surplus lots. These are often new, but incorrectly dimensioned doors or windows that have never been installed. These batches of used and overstock windows can be found in the webshop under the “op=op” (finished=finished) section.