Condensation left on windows can, over time, lead to damage on bothuPVCand wooden window frames. uPVC windows are designed to be hardwearing. But when the inside seals constantly flip between being wet and then getting exposed to intense sunlight, they expand and contract, making them dry out...
Feel around the window frame during the next cold or windy day. If you can feel air coming through the seals, you'll need to insulate the window. To detect small leaks, you may need to moisten your fingertips before running them along the seams. Wet skin is more sensitive to shifts ...