I have a one bath row home in Baltimore. Currently, my tub drains very poorly. The toilet appears to drain okay, so I'm thinking the blockage is in the shower drain somewhere. I will be adding a clothes washer and dish washer to the equation. I am replacing the tub with a corner shower unit and the plumber plans on replacing the piping to the main drain. The drain is cast iron and runs about 30 feet under a patio into the sewer under the alley. My plumber says there is no way to tell if the entire drain should be replaced or not until he gets under the bathroom and starts taking the tub drain apart. I'm trying to find out how long cast iron will last - I'm not sure how long the current drain has been there. I've heard 75-100 years. The drain is in the dirt under my patio, but being in the city, no tree roots or anything like that should cause problems.

I will be tearing out the last 8 ft of my patio and pouring a concrete slope so that I may park on it. Is there any way to replace the entire cast iron with pvc without having to remove the 20 ft of patio between where I will be tearing out and house? Can the old cast iron be removed and new pvc installed through this 8 foot open area? Is the old cast iron most likely fine and should I just replace the drainage from the shower?

Thanks for any help you can provide.

Depends... If that drain is cast iron, I would leave it. You can trace it with a metal locater real easy. If it is terracotta then I would not park over it unless there is a concrete pad. To replace line needs trenching. A rerouting may be possible but require more undesirable bends in the lateral piping around the patio area. I wouldn't do it.. . nm:)