A half bath contains a toilet and sink, but no bath or shower. If it contained a shower, but no bath it would be a 3/4 bath. If it has both a shower and a tub, then it is considered to be a full bath. A half bath can be added if you have slab floors. The issue with adding a half bath is whether there is suitable drainage. In most cases where there is no suitable drainage, it can be added. Whether you want to do so depends on your budget, as it can be quite pricey.