Thanks Zal. I got a 4' concrete walkway in front of the bays with floor heat. To extend the bay, I thought I'll have to break it down to make the foundation for the new wall. If I break it down, I think most likely I'll damage the pex.
Overachiever, thanks for your input. $50-60K was real cheap! With the inflation, I think it costs 2X or more now. Did you have to hire a GC for your project? I've been thinking whether it's a good idea to extend the bay even longer (i.e. 25' more) so the automatic can wash a car and dry the other car at the same time. But this will make the project more complicated as I'll have to build a new catch basin.