R30 Vs. R38 Insulation: Which One Is Better?

Dennis Howard
by Dennis Howard

In some regions of the United States, home insulation is a very important thing. The quality of the insulation in your home can mean experiencing large heating and cooling bills. Your comfort may also suffer if you have the proper level of insulation. When comparing insulation, many homeowners get confused about R values. What is the difference between R30 and R38 ratings on insulation?

The R-value associated with insulation measures resistance to heat flow through the insulating material. The higher the number associated with the R-value, the greater the insulating value. Insulation with an R-Value of R-38 is about twenty percent more efficient than R-30. R-values are cumulative as you add insulation layers to your home’s attic or walls.

R-value is important when determining how much and what kind of insulation to install in your home. Understanding how your geographic zone affects your insulation project can impact your budget and material choices. There are many options for both materials and installation techniques warranting consideration.

How Are R-Values Calculated?

The R-value assigned to insulation measures the thermal resistance of the insulation material. In simpler terms, the R-value expresses the insulation materials’ resistance to transferring heat through the material.

The R-value of most insulating materials is calculated by taking the thickness of the material and dividing it by the thermal conductivity of the insulation. For example, a sheet of insulation that is two inches thick with a thermal conductivity of .25 BTU’s per inch equals an R-value of eight.

2 inches (thickness of the insulation) divided by .25 (thermal conductivitiy equals 8)

Consequently, the sheet of insulation will show R-8 on the labeling. The R-value is an important factor. The R-value on the insulation product is dependent on the thickness of the insulation. If you are installing batt insulation that rolls into place, the batt’s thickness is pre-determined. However, if you are using loose insulation, you must make sure the thickness meets the manufacturer’s specifications to achieve the advertised R-value. Insulation and R-Values

Insulation comes in many different configurations made from different materials.

R-values allow customers a means of comparing these different materials. However, there are some other factors to consider beyond just the R-value. Before you start to add insulation to your home, you should carefully consider these other factors.

Comparing insulation types should go beyond just looking at R-values. The installation requirements are very important as well. In some cases, the needed depth or thickness of the insulation required for your needs may be prohibitive. In other cases, the installation may require specialized equipment or training. Each type of insulation has its unique characteristics to consider.

The location and the type of construction can also impact which insulation is better suited for your project. For example, you may need insulation with an R-value of 38. However, the concrete block construction of your home makes installing many types of insulation impossible. The insulation you install must be appropriate for the location and type of construction.

The Advantages and Disadvantages of Popular Types of Insulation Materials

There is a wide variety of insulation types and materials available. However, some of these materials are not suitable for residential use. Others require specialized tools or equipment, making them better suited to a professional installation. However, many types of insulation materials are installable by a homeowner intent on improving the efficiency of their home. Each type and material has its advantages and disadvantages that you should consider before starting your project.

Blankets, Batts, and Rolls

A wide assortment of insulation materials come packed in blankets, batts and rolls. For an attic installation, these are probably the easiest and quickest types of insulation to install. Common materials found in these types of insulation include

  • Fiberglass
  • Mineral Rock Wool
  • Plastic Fiber
  • Natural Fibers

These types of insulation common use are in unfinished walls, during new construction where stud spaces are still open, and retrofitting attic spaces. The batts or rolls fit between rafters or wall studs sixteen inches on center.

Blankets, rolls, and batts of insulation are probably the easiest types of installation for do-it-yourselfers to install in attics. If the space to be insulated has exposed studs, the insulation material is quick and easy to install.

Rolls and batts usually rate at R-13 or R-15. Most roll and batt insulation has a foil or paper backing that also acts as an infiltration barrier when installed between rafters or studs. A few products offer ratings in the R-19 and R-21 values.

Foam Board or Rigid Foam Insulation

Sheets of insulating foam board can be used to insulate exposed concrete or concrete block walls. Basement or foundation walls are typical installations and are easy materials to provide at least some R-value to an otherwise uninsulated space. Installation is fairly straightforward and requires only basic tools. Foam board insulation is typically a manmade product such as

  • Polystyrene
  • Polyisocyanurate
  • Polyurethane
  • Phenolic

The exterior of unfinished walls and basement walls are the typical application for foam board insulation. In some cases, foam board insulation is applied to walls or ceilings before finish coverings are applied.

Foam board may be used in attics with minimal height under low slope roofs. If applied inside a structure, the foam board must be covered with ½ inch gypsum board. Suitable exterior finishes must be put over foam board.

Foam board insulation R-values vary from 3.6 to 8 depending on the material. One advantage of foam board insulation is its ability to mitigate thermal transfer from other materials such as concrete or steel studs.

Loose-Fill and Blown-In Insulation

Loose-fill blown-in insulation is a popular alternative for insulating attics in existing homes. The process involves a blower and hopper with an attached large diameter hose. This type of installation requires specialized equipment which can be rented from many home improvement stores. Blown-in or loose-fill insulation is very effective providing the proper dept of insulation is installed. Common materials used for loose-fill or blown-in insulation include:

  • Cellulose
  • Fiberglass
  • Mineral wool (Rock or slag wool)

Blown-in or loose-fill insulation works best on enclosed or existing structures. Wall cavities can be filled without doing extensive damage to open the wall. The shallowest attics can be effectively insulated by blowing in the insulating material. Usually, the blower equipment rental is relatively cheap where you buy the insulation.

The major problem with blown-in or loose-fill insulation is getting a consistent insulation depth over large areas. The hose can be difficult to control in small spaces. Obstructions in the attic space can create problems getting an even layer of insulation in tight spaces.

Most blown-in and loose-fill insulation have an R-value of 2.2 and 2.7 per inch. To achieve an R-value of 20, you must install at least 8 inches of loos-fill insulation in an attic.

Sprayed Foam and Foam-in-Place

A relatively new product in the residential insulation market is insulating foam. This material is usually applied using a power sprayer. This type of installation requires considerable skill to get the proper coverage and depth of foam with this method. In addition, the equipment is relatively expensive and requires attention to maintenance especially cleaning. There are several types of foam insulation currently in use.

  • Cementitious
  • Phenolic
  • Polyisocyanurate
  • Polyurethane

In general, foam insulation must be applied while wall cavities and the underside of the roof are uncovered. Not many homes use foam insulation. Commercial applications, especially in steel buildings, are the most common applications for spray foam insulation.

The R-value of spray foam insulation is between 3.6 per inch to 5.7 per inch. Most applications on stud walls fill the cavity giving you a four-inch depth. A stud filled with medium density foam with an R-value of 5.7 per inch gives you a total R-value of 22.8.

How Much R-Value do you Need?

Where you live is also another big factor in selecting the R-value and type of insulation you need for your home. The US Department of Energy publishes a map of the United States. The map depicts the US divided into zones that show the most appropriate insulation R-value. The chart shows different types of construction. In general, these are the recommendations made by the Department of Energy for each zone.

1R30–R49R19–R38R13R13 or R0 + R10 CI*N/A
2R49–R60R38–R49R13R13 or R0 + R10 CIN/A
3R49–R60R38–R49R19R20 or R13 + R5 CI or R0 + R15 CIAdd R5 CI
4 EXCEPT MARINER60R49R19R20 + R5 CI or R13 + R10 CI or R0 + R15 CIAdd R10 CI
4 MARINE AND 5R60R49R30R20 + R5 CI or R13 + R10 CI or R0 + R15 CIAdd R10 CI
6R60R49R30R20 + R5 CI or R13 + R10 CI or R0 + R20 CIAdd R10 CI
7 AND 8R60R49R38R20 + R5 CI or R13 + R10 CI or R0 + R20 CIAdd R10 CI

Table Courtesy of the US Department of Energy

More May Not Be Better

Under some circumstances, simply adding more insulation may not be a better choice. The reality is that at some point, you reach a point of diminishing returns where the cost of the insulation and the installation exceed what you can save on your utility bills.

Several factors work into this equation. No insulation is perfect. There will always be some thermal transfer happening. Spending more to gain a fractional advantage is uneconomical and inefficient.

If you are insulating an attic, the more insulation you add, the greater the weight. The lower parts of the insulation compact, reducing the effectiveness of the insulation.

The goal is to determine the most efficient amount of insulating material for the best cost savings. Using the insulation zone tables and doing some preliminary calculations can help you arrive at the optimal amount of insulation to achieve the best R-value.

R-38 or R-30 – It Depends

There is no one answer to this question. In some cases, R-30 is the optimal R-value for your home and the area in which you live. Other circumstances can make R-38 the better answer. In extreme cases, an insulating value of R-60 is recommended. You must look at all the variables before deciding on the best R-value for your situation.

Dennis Howard
Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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