What usually goes wrong in a whole home renovation, and how is it avoided?

Almost every overrun traces back to a gap between trades rather than to any single trade. The electrician finishes and leaves, the drywall crew is booked for the following week, and the inspection lands in between. Three days become ten. The second cause is discovering what is behind the walls after demolition, which is why an older house should carry a contingency of ten to fifteen percent from the start rather than a change order argued about later.