The walls, windows, doors, and a building’s roof — the building’s envelope — have a major impact on energy performance, specifically heating and cooling demands. Air leakage (gaps around windows, for example) and thermal losses (from poor insulation) account for a large amount of energy loss. Improving envelope performance can be as simple as caulking and weather stripping around windows and doors. In older buildings, there are a multitude of major upgrades that improve energy performance, reduce maintenance, and refresh the building’s appearance. For example, exterior insulation finishing systems provide insulation and can extend the building’s life. Replacing older windows with new high-efficiency windows can also reduce energy-use, while improving comfort levels inside the building.