R13 Insulation Thickness For Different Insulation Materials

When it comes to insulating a structure, you have to implement a certain amount of insulation material thickness for maximum blockage of airflow. This thickness is measured through the R-value measurement system.  Every material has an R-value, even if it’s not designed for insulation purposes. To determine a material’s capability of insulation properties, its R-value is calculated. In simple terms, the higher the R-value, the better the material would be in not letting heat energy through. Now, R-value can be further categorized into subdivisions such as R-6, R-13, R-30, and many more. Today we will be talking about R13-rated insulation.

The thickness required for R13 insulation varies from 2 to 5 inches depending on the insulation material used. 2-inch thick closed cell spray foam insulation can achieve R13, while it takes 5 inches of loose-fill fiberglass to achieve the same.

R13 thickness for fiberglass batt insulation is 4 inches.

Material Thickness Required to Achieve R-13

The following table will help show how much thickness an insulation product needs to offer an R-13 rating.

Insulation MaterialR13 Thickness (inches)
Fiberglass (batt)3.2-4 inches
Fiberglass (loose-fill)4-5 inches
Spray foam (closed cell)2-2.5 inches
Spray foam (open cell)3.1-3.7 inches
Cellulose (loose-fill)3.5-4 inches
Rockwool (roll)3.4-4.1 inches
Rockwool (loose-fill)4-4.5 inches
R13 insulation thickness for different materials

These are some of the most commonly used insulation materials. However, the R13 figure given in inches may vary slightly due to multiple factors.

Here are the common insulation materials and their R13 thickness;


Fiberglass is one of the most commonly used insulation products out there. This material is made up of puny glass fibers that are tangled together tightly. Fiberglass is widely available in the market in the form of batts and loose-fill. Batts are rolls positioned between joists and studs, while loose-fill can be blown on any surface. The specialty of the material is its ability to trap air flow within its fine fibers, making it a good insulation solution. One of the best parts about fiberglass is its easy installation. You’ll obviously need a blower for loose-fill, but for batts, a couple of tools would be sufficient to make it an enjoyable DIY project. 

R13 insulation thickness for fiberglass batts is 4 inches and for loose-fill fiberglass insulation that is 5 inches.

Spray Foam

Spray foam insulation is a liquid foam that is sprayed on walls, attics, and between studs. Due to the material being in liquid foam form, it can easily make its way into small spaces and miniature openings. This makes it one of the most effective insulation materials out there. Furthermore, spray foam neither becomes compressed nor loses its R-value for decades to come. Although it is a bit expensive, it can insulate your house, unlike any other material. Spray foam is commonly available in two types, open-cell, and closed-cell. The main difference between them is that the density of closed-cell spray foam is higher than open-cell foam.

R13 spray foam insulation thickness is 2 to 2.5 inches for closed-cell type, and 3.1 to 3.7 inches for open-cell type.


One of the oldest and most traditional insulation solutions is cellulose, which is comprised of recycled paper fibers. Cellulose has several similarities with fiberglass. It comes in the forms of both batts and loose-fill but the latter is not a popular choice in this age. Due to its unique composition, cellulose offers several other benefits than just blocking heat energy. Some of these include sound resistance, pest elimination, and fire-retardant properties.

Around 3.5 to 4 inches of cellulose thickness would be enough to make your insulation reach the rating of R13.


Rockwool hasn’t been around for that long, but its popularity seems to be increasing as we speak. As the name suggests, Rockwool is made up of natural rocks that are placed in a blazing hot furnace until they melt. After that, the liquid form is spun like cotton candy to make fiber components resulting in Rockwool. Later on, the wool-like fiber is either made into batts or loose-fill. It has several unique features such as high R-value, moisture resistance, and sound insulation. You’ll also find Rockwool to be a great insulation solution in terms of its longevity.

Rockwool in the form of batts would require around 3.5 to 4.1 inches of thickness to make it R13. If you decide to go for loose-fill, a thickness of 4 to 4.5 inches would be adequate.

You can also use my insulation thickness calculator to find out the thickness required for different insulation materials for your desired R-value.

When Should You Go for R13 Insulation?

Generally speaking, R13 is not far from the standard insulation rating. Most buildings in regions with temperatures that go slightly high in summers and winters typically require insulation of R6 to R20. To see whether R13 is your cup of tea, you’d have to consider several factors such as your region, your house, and the material you’re going for. If you already have insulation installed, you won’t have to go for R13. Instead, topping it up with enough material would increase the overall insulation rating to R13. This is applied only when your previously installed insulation is in good condition, and you’re looking to upgrade to R13.


There are several insulation materials out there that you can use to attain an R13 rating. We’ve given you a list of the most commonly used products and the minimum thickness required for each. Hopefully, this read made it easier for you to understand how R13 insulation can be reached.

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

Latest Posts