Dear James: We are in the planning stages to add a half-bathroom on our first floor for my elderly mother. What are some basic design tips to consider and errors to avoid? —Cathy D. Dear Cathy: As our population ages, adding a first-floor full or half-bathroom is becoming a typical home improvement project. Although this is not a difficult project, it must be planned properly during the design phase in order to make the new bathroom most usable, attractive, and functional. One of the first considerations when adding a bathroom, even just a lavatory, is stealing enough space from another room. Sometimes, for convenience to water and drains, the bathroom door is located off the kitchen area. This definitely is a mistake and may even violate building codes in some areas. Sanitation may be an issue, and people just don’t want bathroom sounds and odors nearby where they eat. Another …