R
roberta1000
Not necessarily.Well just check the plans to the externsion and the rain water does run into the foul drain! The externsion was built in 1982 so Building regs must have been on the blink back then!
My house was built around 1975 and has a combined foul/rainwater system because that's all that was available in the local infrastructure.
Not really a problem if it was designed that way from the start except that the sewage plant ends up having to handle vast quantities of diluted waste. (Less chance of a choked sewage pipe too IMHO).