Definition: Sealing the envelope of a home—windows, doorways, outer walls, roof and floors—against air leaks reduces drafts, controls moisture, keeps out pollutants and improves overall comfort. Collectively, sealing such leaks is known as weatherization and it is one of the easiest and most cost-effective ways to increase home comfort and energy efficiency. Before weatherizing a home, a Home Performance Assessment is conducted to find the air leaks that are not obvious by "feel".