Photos and a floor plan would help us tremendously. 1/4” grid paper works the best for making a drawing, use each square to represent 1’.

I've attached a picture of what the bump out look like from the outside of the house. I used paint to create a drawing with measurements of what my existing bathroom looks like noting the proposed new location of my sink and toilet in the bump out area.

Hi Thomas Thomson. Full disclosure I am not a contractor or a renovator. But I am a homeowner who has a very similar bump out with the open area underneath. In my bump out I have my kitchen sink, with all the plumbing, and some cabinets.. My plumbing comes up from the heated basement and into the floor joists of the bumpout . The bumpout is of course heated as it houses my kitchen sink. The drain pipes are PVC with copper plumbing. It all works.

If the subfloor of my bump out opened up into my basement. I wouldn't be worried about my pipes freezing. However, the subfloor of mine does not. In fact I'm sort of questioning the construction technique used. Because most of what I've read online on how most bump outs are constructed I should see some sort of evidence of sistering of the floor joist from the basement. But I don't. Which is leaving me to believe that the subfloor is constructed similar to how one would add a deck or porch onto a house. But in my situation the roof structure may be supporting all the weight.

It looks to me like they created the bump out to move the bathtub over there, and then maybe found out it couldn't be done. I'd have an experienced contractor and plumber take a look.

Calidesign I kind of thought about that myself. The problem is, that area is literally short length wise by a 1/2 inch to fit most standard tubs, and it's not quite wide enough for a standard tub without being in the way of either door. Plus the only power outlet in the whole bathroom is in that bump out. At one point I was considering actually moving my tub there. But instead of having it slide in to fit that space turn it 90 degrees. If I did this I could get rid of that 6" space and wall it off straight. Then I could open that extra space up into our bedroom. If I did that it would allow me to move the sink and toilet to where the tub is now. This would actually solve a lot of problems for me in terms of plumbing. I really could possibly leave the toilet where it currently sits. But my whole goal with this process is so that I can eventually widen the bathroom door as well. Both entries into the bathroom won't allow a wheelchair or other walking aid to pass through easily. At some point in my life either myself or my wife is going to end up in a wheel chair. It's just a matter of who beats who.

On a side note though. While turning the tub a full 90 degree in that spot sounds like a great idea. The width of the tube itself would actually decrease the ability to get something like a wheel chair in and out of that room easily. I just have to face it. I got a small bathroom and I'm trying to make use of what is otherwise a wasted space.