Final answer:
Leaving a one inch gap above the insulation in a cathedral ceiling is crucial for proper ventilation and moisture prevention, with fiberglass batts being a common insulation choice for their effectiveness.
Step-by-step explanation:
The best way to vent and insulate a cathedral ceiling is to leave a one inch gap above the insulation. This gap allows for proper ventilation, reducing the potential for moisture accumulation and providing a way for any heat that does pass through the insulation to escape. Fiberglass batts are commonly used for insulation because they trap air in small spaces, taking advantage of air's low conductivity and making it an effective insulator. However, the best practice is not to fill the cavity completely but to maintain that ventilation gap for optimal performance.