Foundation and soil. Much of Houston sits on expansive clay soil, and older homes are a mix of slab and pier-and-beam foundations. Foundation condition can materially change the cost and sequencing of a renovation, and it's worth having evaluated before scope is finalized.
Flood plain and drainage. Some Houston neighborhoods include properties in or near mapped flood plains. Depending on location, this can affect elevation requirements for additions and the permitting timeline. A qualified professional should be able to speak to this for your specific address.
Deed restrictions and neighborhood character. Established neighborhoods such as River Oaks, Memorial, Tanglewood, and West University often carry deed restrictions or civic association guidelines that affect setbacks, height, and exterior materials. These should be reviewed early, not after design is underway.
Permitting timelines. The City of Houston's permitting process, and any applicable HOA or civic association review, both take time. Renovations that involve structural changes, additions, or new plumbing/electrical circuits typically require permits — budget realistic time for this in your project timeline.