How To Soundproof Over Existing Walls, Ceilings and Floors
Apr 08, 2024If you have followed me for some time you know I love to say you have to take it to the studs to properly soundproof a room. Now, while I still think this is one of the best ways to soundproof, there is another way that means you don't have to remove any drywall/gyprock/plasterboard.
This technique is especially helpful for those who want to soundproof apartments, houses and offices against outside noise like those pesky neighbors.
Okay let's dive into how this works.
1) Wall Design
Everything I am about to teach is from Philip Newell. He is a great studio designer and I would highly recommend his book: Recording Studio Design, if you want to dive deep on the subject.
Ideally your existing wall should have as much mass on it as possible. I like to shoot for 4.4 Lb per Sq/Ft (21.5 Kg/m2). That is the weight of two layers of 5/8" drywall.
For example if your existing wall is just 1/2" drywall I would add another layer of 5/8" drywall on top to get a bit more mass on the existing wall.
Next, we create our spring or decoupling system. This is done using 4" 5 Lb/ Ft3 (10cm 80 Kg/m3) of Rebond foam also known as reconstituted open cell polyurethane foam. This will act as the spring in our mass spring mass system. This is also what the air gap is doing in a double wall system. In that case the spring is air not foam.
To finish off the wall system we need to add two more layers of 5/8" drywall on top of the foam. All of this will be glued together to the existing walls with contact adhesive.
2) Ceiling Design
The ceiling is built the exact same way. You make sure you have enough mass on your existing ceiling and that your ceiling can hold the extra weight and you build your soundproof sandwich.
In our example above you would add the 5/8" drywall to the exiting 1/2" drywall, then the rebond foam and finish it off with two layers of 5/8" drywall. Again, everything would be held together with contact adhesive.
You might be wondering about wall penetrations from outlets and lights. You have two options here. First, you can use putty pads on the backs of all the lights, outlets and switches which requires pulling them down adding the putty and reinstalling the boxes in the new ceiling.
Alternatively, you could run the electrical through the ceiling and flush mount all your electrical inside the room. This is what most pro studios do to increase isolation.
3) Floor Design
Now that you have soundproofed right over your walls and ceiling it is time to do the floor. There are many ways to soundproof a floor or float a floor, but this design will work in most homes and apartments provided they can handle the extra load.
First, put down a layer of 1" 10 Lb/Ft3 of Rebond foam (3cm 160 Kg/M3) over your existing floor. Next, add a 1/2" layer of drywall (13mm). Then add a layer of 1/8" 1/2 Lb Mass Loaded Vinyl (5kg/m3). After that add another 1/2" layer of drywall. Then glue and nail together two layers of 3/4" plywood (19mm) and your final flooring layer on top of that.
This will give you a very heavy floated floor. You could also pour concrete over the foam or use paving slabs mortared together.
4) How Well Does It Isolate?
If you followed this design, Philip Newell says you should expect to get 20dB of isolation at 70Hz and 50dB of Isolation at 2kHz. That is pretty good and will work for voices, TVs, traffic noise and other common noise issues. It will fall short for loud bass from amps, bass drums or sub woofers and it will not be adequate for super loud sounds from rock bands and full drum sets.
However, for most people this could be an adequate way to soundproof if you really don't want to tear out your current walls. Is this easy and cheap? No, Rebond foam is more expensive than framing a new wall and you will still cover up your existing walls, ceilings and floors. However, this is just another option in the tool box for sound isolation.
Works Cited:
Philip Richard Newell. Recording Studio Design. New York ; London, Routledge, Taylor & Francis Group, 2017.
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