You want to renovate your home and are compiling lists of everything that should be included in the renovating process. The revamping of your home’s old insulation – especially in your exterior walls – is high on the list. But every time you search online for more information about the “right” insulation for your exterior walls, you come across the term “R-value” and discussions regarding a good R-value for exterior walls. The questions you have are first, what exactly an “R-value” is, and then also, what is a good R-value for exterior walls.
The typical R value recommendations for exterior walls are R-13 to R-21. The R-value needed for walls depends on the climate zone you live in. Colder regions require higher R value while temperate regions require exterior walls with lower R-values.
In this article, I’ll not only provide a table indicating the recommended R-values for exterior walls but will also briefly discuss general aspects regarding R-values and how insulation works.
General aspects regarding R-Value
When you discuss and research the R-value for exterior walls, it is always a good idea to keep other insulation aspects concerning the exterior of your home in mind as well. Although I’ll mainly discuss the insulation of exterior walls, I’ll also touch on aspects such as the attic, crawl spaces and the floor.
R-value refers to heat-resistance
As mentioned above, the R-value is an internationally recognized measurement to indicate the resistance against heat the insulation material offers. Thus, the higher the R-value of the insulating material, the more resistance the material can provide against heat loss.
R-value can differ in the house
It is important to know that the R-value of all the insulation materials in your home is not necessarily the same. The R-value needed to insulate your attic, for instance, will most probably differ from the insulation needed in your home’s outside walls. And insulation with another R-value might be needed for the floor. Generally speaking, the typical recommendations for exterior walls are R-13 to R-21, while R-30 to R-49 is recommended for attics.
The region where the house is situated influences the needed R-value
The area where you live and the average temperatures in the area also influence the R-value of the insulation you have to use. For example, a colder climate requires higher R-values than a more temperate climate.
Other aspects influencing the R-value
Other aspects influencing the needed R-value of your insulation include the size of your home, the type of HVAC system that is being used in the home and the material the walls, floors and roof are made of.
Why is insulation needed?
Now that you know the R-value gives you an indication of the resistance heat will encounter to get into or out of your home, let’s look at why it is so important to keep heat in or out of your home.
Simply put, insulation is needed to keep the heat in your home (during winter) and out of the home (in summer) to help the HVAC air conditioner and/or furnace to keep your home at a comfortable temperature during the summer’s heat and the winter’s cold. The better the insulation, in other words, the higher the R-value of the insulation material, the more heat is kept in or out of the home.
Thus, insulation with the correct R-value saves you money on your energy bill. Your air conditioner and furnace don’t have to work so hard and continuously and use a lot of unnecessary energy if your home is well-insulated.
How insulation works and what to insulate
Ways of transferring heat
Heat can be transferred by means of conduction (transmitted through substances – electricity for instance), convection (movement of hot air or liquid rising and cool air or liquid dropping) or radiation (heat travelling in a straight line in the form of waves or particles).
Purpose of insulation
The purpose of your home’s insulation is to slow down the flow of conductive and convective heat. However, if, for instance, your exterior walls are well-insulated, but there is insufficient insulation in your attic, the heat will, in summer, move from warmer places in the house to the cold places in your house, such as the attic, until the temperature is the same everywhere.
In summer, the opposite will happen. Heat can come into your house from the insufficiently insulated attic causing your cooling system to work harder to remove the heat from your home.
Which other exterior parts of the home have to be attended to?
When you attend to the insulation of your exterior walls you’ll have to look at the following exterior aspects as well:
- Windows and doors opening to the outside.
- The roof.
- Floors – especially over an uninsulated basement.
- Foundations without barriers between the ground and the concrete.
- Crawl spaces.
What is a good R-value for exterior walls?
The R-value for your exterior walls varies depending on where you live. If you live in the northern parts of the US, you’ll need the highest R-value recommended and in the warmer regions, you’ll need insulation with the lower recommended R-values.
The major climate regions of the US and recommended external wall R values
There are 7 major climate regions or zones in the United States and each has its own weather pattern and temperatures. The seven regions are
- 7. Northwest Coastal,
- 6. High Plains,
- 5. Midwest,
- 4. Mid-Atlantic,
- 3. Southeast,
- 2. South, and 1. Southwest, including Guam, Hawaii, Puerto Rico, and the Virgin Islands.
- The separate 8th zone comprises boroughs in Alaska.
You can use the following table to find the recommended R-values for exterior walls;
|Zone||2 x 4 Exterior Walls||2 x 6 Exterior Walls|
|7||N/A||R-19 to R-21|
|6||N/A||R-19 to R-21|
|5||R-13 to R-15||R-19 to R-21|
|4||R-13 to R-15||R-19 to R-21|
|3||R-13 to R-15||N/A|
|2||R-13 to R-15||N/A|
|1||R-13 to R-15||N/A|
In summary: On average, the insulation R-values for exterior walls are between R-13 and R-21.
What insulation material is best for exterior walls to provide the right R-value?
Depending on the summer and winter temperatures in the area where you live, a good exterior wall R-value is between R-13 and R-21. (See the table above.) To achieve that, any of the following exterior wall insulation materials can be used.
- Foam boards.
- Cellulose-based insulation.
- Batt insulation.
- Closed-cell or open-cell spray foam.
Fiberglass batts are one of the most commonly used materials, but if you use them remember that a 2 x 4 wall can only hold batts providing you with up to R-15 and a 2 x 6 wall can only accommodate batts to provide R-21 insulation. If you live in an area with extreme temperatures and you want more than R-21, you’ll have to use another type of material.
How to use insulation material to get the required R-Value
It must always be remembered the R-value is directly linked to the thickness of the insulation material. Fiberglass batt, for example, typically has an R-value of R-3.7 per inch of thickness. If you use two batts on each other, the R-value will be 2 x 3.7 = 7.4. Thus, if you need an R-value between 14 and 15, you have to place 4 batts on each other.
The relationship between R-value and insulation is linear. So, the higher the R-value of the insulation you use, the less you will spend on heating in the winter and cooling in the summer. But you’ll have to find a compromise between the R-value, the thickness of the walls, and how much you can spend on insulation.
R-Value Rule in the U.S
Something to remember is that according to the FTC’s R-Value Rule you should know what the R-values of the insulation in your home are when you want to sell your house. The Federal Trade Commission (FTC) regulates this R-Value Rule. The full name is “Trade Regulation Rule Concerning the Labeling and Advertising of Home Insulation.”
It requires insulation manufacturers and installers, as well as home sellers, to provide R-value information, based on the results of standard tests, to consumers. The main purpose of the rule is to ensure that a possible home purchaser is informed about the insulation sufficiency of the home.
Q1: How much R-value makes a difference?
A1: Doubling the R-value cuts the heat loss in half. Thus, adding R-1 to existing R-1 insulation will make a big difference, but adding R-1 to existing R-30 insulation reduces heat loss by only about 3%.
Q2: Is R-value always per inch?
A2: Yes, insulation ratings are always measured in R-values per inch of thickness of the insulation material.
Q3: How do you increase the R-value of a wall?
A3: By adding more batt insulation between wall studs or installing foam-board insulation, you can increase the R-value of a wall – inside and exterior walls.
If your exterior walls and other exterior parts of your home are insulated according to the recommended R-values discussed in this article, you will save on your energy bill because the air conditioner and furnace won’t have to work continuously to keep the temperature in your home comfortable. Remember, a good R-value for exterior walls in the northern parts of the US is between R-19 and R-21 and in the warmer parts of the country, between R-13 and R-15.