Common building science failures include building envelope issues like window and door leaks, stucco installation failures, and inadequate moisture barriers that allow uncontrolled water and air infiltration. Mechanical system problems involve improperly designed or maintained HVAC systems that create pressure imbalances, inadequate ventilation, or moisture control failures. Design conflicts occur when building components work against each other, such as exhaust systems creating negative pressure that leads to unwanted infiltration. Construction defects from installation errors compromise building envelope integrity or system performance. Each failure type creates specific environmental problems that require building science expertise to properly diagnose and resolve.