Rockwool (Mineral Wool) Insulation R-Value Chart

Rockwool, aka mineral wool, is an insulation material that is commonly used for insulating and soundproofing structures. Commonly available in the form of both batts and loose-fill, it is made by putting natural minerals through extreme heating until they melt. Later on, the melted material is spun until it is formed into thread. But how much R-value does it have?

Rockwool insulation has an R-value between 2.5 to 3.85 per inch. Rockwool batts have an R-value ranging from 3 to 3.85 per inch, and loose-fill has its R-value ranging from 2.5 to 3.7. The R-value of loose-fill is lower because it has air gaps that will result in heat loss. (Source)

Today we will be discussing Rockwool insulation’s properties and some frequently asked questions regarding the material. Let us start with a table listing the required thickness in order to attain a certain R-value for Rockwool.

Rockwool (Batts)Required Thickness (inches)Rockwool (Loose-fill)Required Thickness (inches)
Rockwool aka mineral wool R-value chart

As you can see in the above table, the thickness required for Rockwool insulation increases with the R-value requirement. The R-value of a batt of insulation is calculated by multiplying its thickness with the R-value per inch of the Rockwool material. For example: Taking 3.65 as the R-value per inch, a 5.2 inch thick Rockwool batt has an R-value of 19 (3.65 x 5.2 = 19 approximately).

Ref: Insulation thickness calculator

Rockwool Recommended R-Value for US Climate Zones

The recommended R-value for Rockwool varies from area to area. For example, a region that has a humid climate has different insulation requirements as compared to a region with a dry climate. Choosing which R-value rating would work best for you is through having a professional come over to your house. For this decision, several factors are taken into account, including the condition of already-existing insulation (if there is any) and the area you want to be insulated. The professional would examine the house where insulation is needed and calculate the recommended R-value. To figure out the recommended R-value, one can analyze the US’ seven climate zones.

For instance, Zone 1 includes California and Hawaii, where the climate is humid due to the border meets the Pacific. Zone 7 mostly covers Alaska, where the winters are severe, and the summers are light. To make it simple, here is a table that would give you an idea of the required R-value for each climate zone.

Climate ZoneFor AtticFor FloorFor Wooden Wall
Rockwool R-value for different US climate zones

The condition and amount of existing insulation play a major role here. Note that compressed insulation does not deliver the required R-value rating. Insulation needs to fit in without having its pores flattened. Otherwise, it’s not going to do the job properly. This brings us to a frequently asked question regarding Rockwool insulation: 

Does Rockwool Slab Compress?

Compared to other insulation materials, Rockwool cannot be compressed much. This is because Rockwool batts already undergo compression during their manufacturing. After it is formed into batts, the insulation material is tightly packed into plastic before making its way into the market. Due to its rigid texture, you likely won’t be able to compress it any further. Due to this nature, the R-value of the insulation remains largely unaffected during the installation process. However, make sure you order the right fit.

Ref: Rockwool vs fiberglass insulation

Is Rockwool Affected by Moisture?

Since Rockwool is made of natural minerals, it boasts exceptional moisture-resistance qualities. The material is not affected by moisture at all. This is a major plus point for insulation since moisture can wreak havoc and boost the growth of mold and fungi. Rockwool insulation does a great job at resisting moisture due to its densely packed fibers. It does not absorb water and repels humidity in every form; therefore, it is free from the need for a vapor barrier, unlike most other insulation materials. Since Rockwool is effective against dampening, pests find it to be a bad place for reproduction as well. So, you’re also saved from insects and bacteria impacting the life of your insulation.

Another benefit worth mentioning of rock wool’s moisture resistance is that it makes the insulation an excellent choice for places where wetness might occur. For instance, bathrooms and kitchens have higher humidity levels and are more prone to experience pipe leaks. Therefore, having rock wool insulation in such places is a wise decision. Lastly, Rockwool’s quality of defying moisture is a key reason behind its extraordinary durability. The material can last for a good while, thanks to the mineral resources which brought it into being. It does not break down with time and ensures a safe investment for homeowners.

What is the Standard Size of Rockwool Batts?

As mentioned previously, rockwool comes in the form of both batts and loose-fill. The standard size of rockwool batts is 24×48 and 16×48. These sizes are perfect for fitting in standard wall sizes. However, Rockwool is also available in the form of rolls, meaning that you can cut the material according to your needs. Moreover, several layers of rockwool insulation can also be put up to achieve the required R-value. For instance, if you have an R-20 rating of insulation already installed and you intend to make it R-30, an addition of R-10 would get the job done.

Is Rockwool Insulation Soundproof?

Rockwool insulation is often used for soundproofing purposes as well. Due to its incredibly dense and tough composition, rockwool can effectively block out noise to a great extent. A cubic foot of rock wool holds around 1.5 pounds of density. Depending upon the applied thickness, it is capable of fully soundproofing a room. Soundwaves are either absorbed into the material or very few of them manage to get through. This is why you’ll often find rockwool insulation being used in studios and residential buildings where the traffic noise is too much to bear.

Final Thoughts

There’s no denying that rock wool insulation’s performance is way better than most popular materials out there. Even fiberglass does not come anywhere near its level. However, with decent insulation properties comes a heavy price tag. If you can afford the material, then rest assured it’s a safe investment. You can refer to our table for achieving certain R-values by applying different levels of thickness.

Further reading:

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

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