I fitted a 25mm polycarb roof system to an existing timber conservatory.The problem I've got is the tap on plastic cover strip that goes over the sheeting joints, no matter how I tap them on they keep coming off. The sheets are 25mm thick and the metal strip that fastens down onto the joist is less than the thickness of the sheet ie it is about 15mm and the plastic cover strip has to be flattened so it clicks into the metal strip, but it has to be pushed down about 6 or 7mm and as I work along the strip it pops out again !!!! Anyone done these before ? any tips please ?