Euro 4 asks:

We have a detached rec-room in the back of our house. It is all wired for electric, has AC etc. We want to build a bathroom. Is it more cost effective to build the bathroom within the existing structure like an interior remodel, or build a completely new add-on to the rec-room?

Also, would the building codes/permits be any different for either way of doing this?

Best answer:

Answer by lewie
if you live in CA you’ve got big hassles w/building permits. it’s probably not legal to add a bath to a detached room.

as for cost effectiveness building a wall or two and putting in a door is MUCH cheaper than pouring a new slab and then building on it. also consider the space restrictions as to building inside or adding outside