The $30,000 kitchen remodel becomes $40,000. The bathroom update budgeted at $12,000 closes at $17,500. The deck addition that started at $18,000 ends somewhere around $25,000. If you've renovated before, you've probably lived one of these scenarios. If you haven't, you will. Renovation budget overruns aren't bad luck. They're a predictable feature of how renovation projects are scoped, quoted, and executed. Understanding why they happen makes it possible to plan around them rather than being surprised by them. The Quote Reflects What the Contractor Can See Every renovation quote is a response to what the contractor can observe during their site visit. They see the visible condition of surfaces, the accessible portions of walls, and whatever the current scope of work requires them to address. They don't see what's behind the drywall. When walls open, reality reveals itself. In older homes especially, what's inside walls is often different from what building codes require today. Outdated knob-and-tube wiring.…