A lot of people would prefer a ‘no curb’ shower where the floor flows in evenly from the bathroom. However, from the builder’s point of view this can be difficult.
Question: Why do showers have a curb in the first place?
You most likely answered, “To work as a dam; to keep the water in.”
You are correct; however, the answer is more complicated. That clumsy looking toe-catcher called the curb hides the fact that the shower floor is higher than the bathroom floor. Why? The reason for this is that to obtain the slope needed to drain the water, the perimeter of the shower floor must be raised. So, just how is a shower pan sloped? In the olden days, my father said this was often done with a cement gravel mixture called a mud set. Nowadays it is accomplished with a pre-made pan on which tile can be directly applied. Either way this sloping makes for a difference in floor levels which needs to be covered by a curb.
So how do you make a shower curb-less? First, you need to lower the floor in the shower area before you build your shower. But this is problematic in the fact that the floor joists are normally installed at the same level with each other. This means to lower the floor in the shower something must to be done with the floor joist. We have worked on many older homes in which they simply just cut off the top 2 inches of the floor to lower the floor. Was structural integrity considered? Probably not! These same homes had old growth lumber where a 2” x 10” actually was a 2”x 10”. Nowadays a 2”x10” measures 1-1/2” x 9- ¼”. So it is unlikely you can just cut off 2” from your floor. The key to this is conundrum is to consider the shower floor during the planning phase of your project and lowering the joist for the shower area when the home is being framed. See photos.