Sizing
- Usable depth is roughly three inches — plan around it rather than fighting it
- Add height, or add a dividing shelf, rather than trying to gain depth
- A wide niche without a divider becomes a shelf of clutter
- Consider a separate low ledge for razors in a shared shower
Placement
Exterior walls hold insulation you do not want to compromise, and wet walls carry the supply and vent lines. That often leaves one usable bay, which is why the niche position should be settled before the tile layout is finalised rather than after.
A flat sill holds a shallow puddle after every shower. In hard water that becomes a permanent white ring within months.