Energy Efficient Home Improvement Credit Insulation and Air Sealing Essentials

The cost of increasing the insulation and reducing air leaks in a home may be eligible for a federal tax credit when the improvements meet the 2021 International Energy Conservation Code (IECC).

The 2021 IECC provides guidance to ensure the energy-efficient construction of new residential buildings and building retrofits. This includes insulation and air sealing criteria to construct a building’s thermal envelope to reduce energy bills. The envelope (or enclosure) of a building consists of walls, roof, floor, foundation, windows, and doors. Heat can be lost or gained through any of these building components, especially through gaps where different parts of the building such as walls, ducts, pipes, vents, or other interfaces meet.

Insulation and Insulating Material

Insulating your home not only reduces your energy and carbon footprint, it also saves on heating and cooling costs and improves comfort.

In the United States, southern climate zones that have mostly warmer weather are called “cooling dominated.” Northern climate zones that experience long, cold winters are “heating dominated.” Insulation solutions may change depending on the climate zone.

Use the following map to determine your climate zone or use Find My Climate Zone.

An insulating material’s resistance conducting heat is measured by R-value. An R-value means that the material is better able resist heat flow and provide better insulation. The R-value depends on the type of insulation and its thickness. You can use the following table to estimate the required insulation R-value for common components in your climate zone, or you can go directly to the IECC for the full range of envelope code requirements.

In the table above, one method to meet the R-value criteria for walls is by adding a continuous layer of exterior insulation between the wall sheathing and the siding. In existing homes, it may be easier to meet the insulation R-value criteria for some envelope components than others. For example, meeting the ceiling R-value in an uninsulated attic may only require adding more insulation. Because of interior drywall and exterior sheathing, meeting the R-value requirements for existing wood-frame walls may require the addition of continuous insulation. The best time to add continuous insulation is when you are already planning to re-side the building. If you have uninsulated wall cavities and live in a temperate climate, drilling small holes into walls, blowing in insulation, and sealing the holes—an approach commonly known as drill and fill—is a common method to insulate walls in older homes.

The 2021 IECC also prescribes criteria for insulating supply and return ducts located outside conditioned space—space that is heated or cooled. For ducts 3 inches (76 mm) in diameter and larger, the R-value must be at least R-8. For ducts smaller than 3 inches (76 mm) in diameter must be at least R-6.

Air Sealing 

Air sealing reduces the amount of air that leaks into and out of your home. Reducing air leakage is a cost-effective way to reduce heating and cooling costs, improve durability, increase comfort, and create a healthier indoor environment.

Caulking and weatherstripping are two simple and effective air-sealing techniques that offer quick returns on investment—often paying for themselves in one year or less. Caulk is generally used for cracks and openings between stationary house components such as around door and window frames. Weatherstripping is used to seal components that move, such as doors and operable windows.

In an existing home, air sealing some components may be easier than others and may only be practical if done during a major renovation, such as when re-siding.

Walls and rim joists typically make up more than 40% of the total envelope area of a house, so a method to deal with those cracks and construction gaps goes a long way. As described above with wall insulation, if you are already planning to re-side your home, you’ll have ready access to the bare walls—insulating and air sealing the entire area will never be easier or less expensive! Adding continuous exterior insulation, at least 1 inch thick and carefully taped and detailed to block air passage, is only incrementally more expensive than the siding. While the energy savings payback of this upgrade is longer than with caulking and weatherstripping—often between 5 and 10 years—the comfort and noise improvements are immediately noticeable.

The 2021 IECC prescribes building envelope components and criteria to limit air leakage. The table below lists some of the components and criteria included in the IECC.