We are building a side extension to our 1960's house. The extension will be built on top of the waste pipes. We have previously had an issue with a pipe blocking from our downstairs toilet. We had a firm put a camera down there and discovered an old metal rod had been left in the pipe presumably from a previous blockage. Now we are at the stage of whether we should replace all the old pipes going under the new extension or just the pipe that has the blockage, which joins the pipe about half way under the extension. We are torn- if the pipes are ok should we just leave them or because they are 60 years old should we bite the bullet and replace? Wise mumsnetters please advise.