Do Not Use Rockwool To Soundproof Walls

FREE Soundproofing Workshop: https://www.soundproofyourstudio.com/workshop

Many people come to me saying they will use Rockwool to soundproof their walls. First, this is not really necessary. Second, if you build a normal wall with Rockwool it will only marginally improve the sound isolation. In this article I will argue why the cheapest insulation that provides adequate climate control for your location is the best choice for your wall. 

1) Soundproofing Is All About Systems

When we build a soundproof wall it is soundproof because of the sum of its parts, not a single material. Many people believe that adding Rockwool, which boasts enhanced acoustic properties will help improve the STC rating on their wall. The truth is that is will mostly hurt your wallet without adding any noticeable change in sound isolation. 

Below is a diagram of several different wall designs. 

Notice that the wall to the far right has the best sound isolation. This is due to the wall construction not the individual parts. To prove this interesting point, the wall the third from the left has an STC of 40. This involves the same 4 layers of drywall, wood studs, and insulation, however by moving the drywall to the two outside walls and leaving an airspace in the middle the STC rating improves by 23 points! 

My point is that the insulation is important, but not a huge game changer when it comes to soundproofing. What matters most is having some form of fiberglass insulation in the wall and building it the correct way so that you have a mass spring mass system. 

2) Safe N Sound Does Not Have an R Value

So the first thing that we need to do when properly insulating our walls regardless of soundproofing is to get the right R Value for our climate. Below is a chart for the USA for different recommended R Values depending on the region you are building in. Now this would be important for a stand alone structure build in your backyard, roof insulation, or any wall that touches the outside of your home or garage. 

For example, my studio needs insulation on all walls and in the ceiling for walls that touch that outside. According to this chart, I could use R38 in my attic and R13 to R15 in my walls. We actually used R30 insulation for my entire studio build, so be sure to confirm with your contractor what is best for your specific build. 

The key point is that Safe N Sound is meant for interior wall construction only and does not have a tested R Value. This means is is created for sound control, but not holding in heat and air conditioning. 

This is a huge flaw for many builds and is one reason I don't recommend Rockwool Safe N Sound to my soundproofing clients. 

3) Using Other Insulation Could Save You Hundreds of Dollars

The truth is that Rockwool is more expensive than most other insulations on the market. Now if you are not building a double wall or a wall using a hat channel system then by all means use Rockwool. It will help some with sound reduction. However, if you are building a true soundproof wall system then the Rockwool is a waste of money. Let's look at the costs comparison. 

Rockwool Safe N Sound - $0.95 per sq/ft (Home Depot in 2023)

Owens Corning R13 Kraft Insulation - $0.55 per sq/ft (Home Depot in 2023)

You save $0.40 per square foot which can add up. If you are building a 300 square foot studio with 10 foot ceilings then you would spend: 

Rockwool Safe N Sound = $1,045

Owens Corning R13 = $605

That is a savings of $440! 

Most people want to save money where they can during a big construction project. This is a place where that money could go towards another purpose. I always recommend spending more money on mass when you can. So putting that savings towards another layer of drywall would be far better spent than on Safe N Sound. 

4) Conclusion

Don't get me wrong, Rockwool is great for acoustic panels it just really doesn't help in a soundproof wall system. If you are building a wall in your home and you are not soundproofing that wall then use Safe N Sound. However, if you are building a recording studio or any serious soundproof room I do not recommend wasting money on Safe N Sound insulation.