Good whole-house air sealing is a great way to cut heating and cooling bills and increase your comfort year round. In fact, sealing leaking ductwork and other areas of your home can lead to a 20% increase in your HVAC efficiency. While it is a good idea to maximize your home’s energy efficiency, you must be careful not to over-insulate your home. An air tight home is prone to indoor air pollution, harmful indoor gases, and other volatile organic compounds. While it may seem that the air inside your home is cleaner than the air outside, microbial pollutants like pet dander, mold, and pollen can build up in your home, creating a toxic environment "up to 10 times more polluted than the air outside"
Examples of where to insulate. 1. In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. (1A) attic access door 2. In finished attic rooms with or without dormer, insulate (2A) between the studs of “knee” walls, (2B) between the studs and rafters of exterior walls and roof, (2C) and ceilings with cold spaces above. (2D) Extend insulation into joist space to reduce air flows. 3. All exterior walls, including (3A) walls between living spaces and unheated garages, shed roofs, or storage areas; (3B) foundation walls above ground level; (3C) foundation walls in heated basements, full wall either interior or exterior. 4. Floors above cold spaces, such as vented crawl spaces and unheated garages. Also insulate (4A) any portion of the floor in a room that is cantilevered beyond the exterior wall below; (4B) slab floors built directly on the ground; (4C) as an alternative to floor insulation, foundation walls of unvented crawl spaces. (4D) Extend insulation into joist space to reduce air flows. 5. Band joists. 6. Replacement or storm windows and caulk and seal around all windows and doors. Source: Oak Ridge National Laboratory