There are different ways in which we can join the uPVC profile pieces together to fabricate our sash windows. The standard method is a 45° mitre weld, which is really the starting point for the majority of uPVC windows found in the UK today. This method is achieved by welding the uPVC together rather than it being held together with pins, screws and glue as in timber and aluminium windows. The main advantage of welding is that the window frame becomes a single product; the frame is melted and pressed together creating exceptionally strong welds. The only downside of the standard 45° mitre weld is that where the frames have been joined it creates an evident plastic groove. Investment in new cutting-edge machinery has allowed us to offer a 45° mitre weld but finished with a seamless groove instead. This method is also known as ‘zip-welding’ and it delivers two key benefits. Firstly, by pushing the sprue back inside the window it means more of the internal surfaces are joined, creating an exceptionally strong weld and secondly, it delivers a high precision and almost invisible joint. At the most authentic end of the spectrum you’ll find our 90° fully mechanical timber look joints. This method has been driven by demand for heritage windows and the joints have been designed to replicate traditional Victorian timber sash windows. It doesn’t get any more authentic than that.