Hi Tammy,
washing machine less than 3 feet away starts backing up in shower.
does not overflow from standpipe. Standpipe is 18" high , 1 1/2 " inside diam.galvanized. I'm thinking to cut standpipe near bottom and install 2" abs with no hub coupler and make it obviously higher
If it doesn't over flow there's no advantage to increasing the height of the stand pipe.
Has the washer always backed up in the shower or did this just start?
I need a answer to this. If it backed up in the shower from day one then it's a design flaw and there's not much you can do. However, if this is a new problem this indicates a partial blockage downstream from the shower that can be snaked and cleared. Let me know, Tom