How To Soundproof A Metal Roof
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I recently had someone in our community reach out and ask how to soundproof a metal roof. In this article I will dive into the considerations and techniques involved in soundproofing a metal roof.
1) How much of the roof do you need to soundroof?
This would be my first question if this was my client. The reason is that soundproofing is not an isolated thing where you can just soundproof the ceiling, floor or walls. You have to approach sound isolation as a holistic system with each room or each structure.
For this reason, I trying to isolate sound from the roof in an entire house would be much more difficult than say isolating sound in a single room in that house. If you are trying to do the latter than your job will be easier. If you want to isolate the entire metal roof from the house than the job will be much more difficult.
2) Isolating the metal roof in a single room
The best system to isolate your ceiling in a specific room from your metal roof would be to remove your existing drywall and attach acoustic clips and hat channels in its place. Then you will add two layers of 5/8" drywall to those hat channels. You would mud and tape your ceiling and leave a 1/4" gap all the way around the ceiling where it meets the wall. Then you fill that 1/4" gap with backer rod and acoustic caulk.
This would be one step. It may not stop all the noise, but it should be a huge improvement over your original ceiling. To take your isolation to the next level you should use the same system on all of your walls as well. This decouples the drywall from the walls meaning less sound transfer to your room.
Lastly, you may need to isolate the sound from the roof coming through your window or doors. To do this I would recommend a window insert by a company called Indow. They can make custom plexiglass window inserts that are removable. They do not stop low bass frequencies below 250Hz, but can eliminate the sound of rain on a metal roof.
For your door you can replace the hollow core door with a heavier solid core door and seal up around the entire perimeter of the door with weather stripping or acoustic seals.
As you can see, stopping the sound of rain or hail on your metal roof could be a very big ordeal and costly too.
Picture from a studio build in Nashville. The acoustic clips and hat channel decouple the drywall from the ceiling joists.
3) Isolating the entire house from the metal roof
Now, if you are in the unfortunate position of wanting to isolate the entire house from the metal roof, things get harder. Option 1 is to isolate each room below the roof in the manner I described above. That would be costly and time consuming. The other option is to build a sound barrier in your attic. Now, this is a thought experiment, but I do have confidence that it could work.
Sound isolation needs three things. Mass, Decoupling and an airtight system. To fulfill each of those requirements you could build a floating floor in your attic to stop sound. Crazy right?
Let's assume for this example that your attic is unfinished. First, I would put down two layers of 23/32" OSB over the existing attic floor joists. I would overlap each layer so the seams don't line up. Then I would ensure that the OSB is air tight around the perimeter where the roof meets the walls of the house. This is important since sound can travel through even tiny holes in your system. I would use backer rod and acoustic caulk to seal the perimeter.
After, adding the OSB I would wait and test to see if that was enough to fix the sound issue. If not, I would then add a layer of Rockwool Safe N Sound over the entire OSB attic floor. Then I would add another two layers of 23/32 OSB over the Rockwool Safe N Sound. Again I would make sure this was air tight, but this time I would put a thin layer of backer rod and acoustic caulk between the top layer OSB and the inner roof so that technically they are not touching. This will help decouple sound vibrations from the roof to our top layer of OSB.
In this system let's say a piece of hail hits the metal roof. It reverberates through the roof and into the attic cavity. The sound hits our first two layers of plywood and is reflected back. Some of that sound continues into our safe n sound where it gets converted into heat from all the miniscule fibers. The sound also gets trapped in that cavity and bounces between the two layers of OSB. Then a small amount of sound will get through our plywood at which point it then must travel through your existing attic insulation and drywall at which point all but the loudest or lowest frequency sound would be heard.
Conclusion
Metal roofs are not ideal for sound. They create a reverberant surface from which sound travels easily. The methods mentioned above will stop the sound of rain or hail and even other sounds in your neighborhood making life with a metal roof much quieter.
