Expect layers of history
An older bathroom may have been remodelled several times. Walls and floors can contain multiple finish layers, patched framing, abandoned pipes or wiring, and dimensions that do not match modern products.
Test before disturbing suspect materials
Older-building caution: some older construction materials can contain hazardous substances. Before sanding, cutting or demolition, follow local requirements for assessment and safe handling. Do not identify suspect materials by appearance alone.
Allow for correction work
Budget and schedule assumptions should recognize that concealed deterioration or non-current work may be discovered after demolition. Decide in advance who has authority to approve corrective work and how pricing will be documented.
Preserve character selectively
Original trim, tile patterns or fixtures can inspire the new design even when they cannot all be retained. Pairing a few character elements with modern water-management and electrical systems can keep the room from feeling generic.