Cast Iron Sewer Pipes In DFW Area

[JayCinta Henry]

Since which year,  generally, did builders change from cast iron sewer pipes/piping to PVC for sewer lines in the DFW general area?  I want to add a category of exclusion or extra attention if a house was built prior to PVC piping change at the time of purchase. Alternatively, to add sewer line inspection if the house was built before the switch.