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. 

Material Thickness Required to Achieve R-13

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

MaterialThickness (inches)
Fiberglass (sheet)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

These are some of the most commonly used insulation materials. Bear in mind though that the R13 figure given in inches may slightly vary due to multiple factors.

If you’re getting R13 insulation from scratch, you’ll have to examine the list of common insulation materials and then choose one according to your budget and needs.


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 that can be positioned between joists and studs while loose-fill can be blown on simply any surface. The specialty of the material is its ability to trap air flow within its fine fibers that make it a good insulation solution. One of the best parts about fiberglass is that it’s easy to install. For loose-fill, you’ll obviously need a blower but for batts, a couple of tools would be sufficient to make it an enjoyable DIY project. 

When it comes to achieving an R13 insulation rating through fiberglass batts, you’ll need at least 3.2 inches and a maximum of 4 inches of thickness. If you decide to go for loose-fill, 4,5 inches would be sufficient.

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 high as compared to open-cell.

As far as spray foam’s R13 insulation is concerned, you won’t need more than 2-2.5 inches of closed-cell thickness to secure the rating. Whereas for open-cell, 3.1-3.7 inches of thickness would do the job.


One of the oldest and 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 3.5-4 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 3.5-4.1 inches of thickness to make it R13. If you decide to go for loose-fill, a thickness of 4-4.5 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 take several factors into accounts 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 make the overall insulation rating up 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 along with the minimum thickness you’d need for each. Hopefully, this read made it easier for you to understand how R13 insulation can be reached.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

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