What is a Good R Value for Exterior Walls?


Insulation is critical for saving energy and keeping homes and buildings comfortable. While insulation is important, knowing how much insulation is enough can be a bit tricky.

When determining exterior wall insulation, R-value and thermal bridging are two components that you should always keep in mind.

What is R-Value Anyway?

Almost every form of insulation will have an R-value listed on the packaging of the material itself.

R-value is simply a measure of a material's thermal resistance to heat flow. It is used to determine how well a material insulates. The higher the R-value, the greater the material's insulating properties.

R-value or thermal resistance is typically used to evaluate the insulation in each component of the overall building envelope - walls, roofs, and floors, as well as windows and doors. Materials that are better at insulating will have a higher R-value than those that are not. Some materials are able to achieve higher R-values while using less material due to their better insulating properties. When designing an exterior wall, it is important to determine the required R-value for the exterior wall before selecting the insulation that will meet that requirement.

The R-value of exterior walls is crucial for maintaining the energy efficiency and comfort of a building. Exterior walls are responsible for separating the interior living space from the outside environment, and their R-value determines how well they can keep heat in during the winter and out during the summer.

A high R-value in exterior walls means that the walls are well insulated and can help reduce energy costs by keeping the interior temperature consistent. A low R-value in exterior walls, on the other hand, means that the walls are not well insulated and can result in energy loss, which can lead to higher energy bills and an uncomfortable living space.

Choosing the right insulation materials and ensuring proper installation can help increase the thermal resistance of exterior walls and improve the overall energy efficiency and comfort of a building.

Thermal Bridging

Thermal bridging occurs when a conductor, something that is good at moving heat, bridges or pierces through insulation. A common example is a nail or a wood or steel stud inside of a wall that breaks the plane of insulation. While the insulation used in a wall may have an R-value of R-13, the R-value of the studs will be much lower. Each fastener used in the wall will have a much lower R-value too.

When looking at a wall as an entire wood framed wall assembly, roughly 23% is wood as a thermal bridge. Taking that into account, it is important to understand the reduction in thermal efficiency. Even with R-13 insulation used in the walls, the studs, fasteners, and other wall components will decrease the R-value of the wall as a whole. Sometimes the effect of thermal bridging can be dramatic.

Building and Energy Codes are recognizing the influence of thermal bridging on wall assemblies and are recommending an exterior layer of rigid insulation R-5 be applied.

R-Value and Exterior Walls

A good R-value for exterior walls will depend on the climate and specific energy efficiency goals of a building. Generally speaking, the higher the R-value, the better the insulation. For example, in colder climates, a higher R-value is typically recommended to keep the heat inside the building and to reduce heating costs.

According to the U.S. Department of Energy, R-values for exterior walls in colder climates should be at least R-13 to R-23. In milder climates, a lower R-value may be sufficient. For example, in a moderate climate, an R-value of R-13 to R-15 is typically recommended. It's important to note that the R-value should be consistent throughout the entire wall assembly, and not just in a specific insulation layer. Building codes, energy codes, and local codes should be consulted for specific requirements in the area. Updated Building Codes are calling for continuous insulation on below and above grade exterior walls.

Common Insulation Materials


Insulation materials are used to increase the R-value of exterior walls. The type of insulation, the thickness of the insulation, and the design of the wall will determine the overall R-value of the wall. Some common insulation materials used for exterior walls include:

  • Fiberglass batts

  • Blown-in cellulose

  • Spray foam insulation

Each type of insulation has its pros and cons. Fiberglass batts are made of fiberglass fibers that are formed into batts or rolls and placed between the studs of a wall. They have an R-value of around R-3.5 per inch. Blown-in cellulose is made of recycled paper and blown into wall cavities using a machine. It has an R-value of around R-3.6 per inch. Spray foam insulation is a spray-applied insulation material that can be used to fill gaps and crevices in a wall. It has a very high R-value, around R-6.5 to R-6.7 per inch and also helps to prevent air leaks through exterior walls.

For High R-Values, Turn to Concrete via ICFs


Insulated concrete forms (ICF) are not just concrete. Blocks made from two sheets of insulation are held together with ties to form the block shape. The blocks are stacked on site to form a building’s walls. Rebar is placed in the hollow space formed in the blocks between the sheets of insulation. Finally, concrete is poured into the gap and allowed to set. The final structure is a steel-reinforced concrete building with both interior and exterior layers of insulation. R-values for an ICF building can be R-22 or higher. Since the double layers of insulation are continuous, no thermal bridging occurs through the walls.

The mass concrete, between the double layers of continuous insulation, moderates the temperature change through the wall assembly, assisting in the effective thermal efficiency. Codes recognize ICFs as a mass wall, with no thermal bridging and apply reduced R-value requirements for ICF wall assemblies.


Maximize R Value with ICFs from Fox Blocks

When looking for high R-value walls that also result in an exceptionally strong building, look no further than ICF blocks. Resulting in a durable, energy efficient, and easy to maintain building, ICF blocks can be hard to beat. To learn more about using ICF blocks to achieve exterior walls with high R-values, reach out to the team at Fox Blocks today.