Is this enough to sound proof my ceiling?


After trawling through the many threads and links and professional websites I have gathered enough knowlegde and I am about to do this (well TBH I'm halfway though it!)

We have an extension to an old house, with the living room downstairs and my toddlers room above. It is only a few years old and the soundproofing is a joke. There is hardly any loss of sound when you stand above the TV in my daughters room. I don't think they put any insulation in :mad:

As I have the headroom, I have built another ceiling in the front room. It is 3x3 timber as the main support with 3x2 cross members. It is approx 40mm from the original (which it doesn't touch at all) and in the void I have screwed wickes high density blocks to the original ceiling. Leaving an air void of 10mm (this is where I am ATM). Next I intend to put 12mm plaster board up then get it skimmed.

Now, do people think this is enough? 2 more options I can think of, another layer of plaster board and rock wool in the rafters of the new ceiling. I don't want to do these if they are overkill or serve no real purpose, but I would be devastated if after all this work and cost there is still noise in my little princess room!

Peter Parker

Distinguished Member
I've done a lot of reading too, and it's certainly an interesting subject, and here's my 2ps worth: :)

Two layers of plasterboard and more rockwool will help - the plasterboard is mass and that will help to stop sound travel, provided that you seal all edges with silicon (or similar). Don't put the ceiling plasterboards right up to the walls - leave a small gap and seal with silicon rubber or similar. Use no more nails between the plasterboard layers for extra rigidity, improved transmission (of sound) loss and to stop any vibrations between them.

Where air can travel, so can sound, so you want to eliminate this as much as possible, so a good flexible sealer should be used at all edges. Silicon or builders caulk should do the trick.

When sound passes through something, it changes direction when it hits it, and gives off energy in the form of heat. The more you get it to do this, the more sound dissipation (transmission loss) will occur. The rockwool also helps to attenuate in-void resonances as well as some higher frequencies.

If you look at STC (Sound Transmission Class/Coefficient) values, you will see that the numbers increase the more layers of plasterboard and rockwool that you use.

A single wall with one layer each side is around 25STC. Add rockwool to the cavity, and it becomes 28STC IIRC, though this seems to vary from publication to publication (though not by much). The only way to stop bass is to use mass, or to decouple from transmission surfaces. By adding new walls and ceiling, you've gone a long way to do this, so that should help conciderably I would think. The existing floor and walls will still allow some vibrations to travel though.

If you had a sound presure level meter, you could take a reading now by playing a set piece of music or a movie sequence, and then repeat at the same volume when you've added the extra rockwool, added the first layer of plasterboard, caulked, added the second layer etc.

IIRC, a rough guide is that for every 4inch layer of normal rockwool inside a cavity, you will add approx 3 to your STC value. For every layer of 1/2inch plasterboard, you will add approx 4, so by adding two layers of plasterboard and another single layer of Rockwool, you could be improving your STC by 11. (I will have to check this though)

You'll find the STC values for the varuious types of construction for walls does vary, but the principal remains the same - the more rigid the wall, and the more mass it hass the better the losses - provided there are no leaks! A single 15mm square hole will allow an increase of around 15dbs of noise, so make sure you don't have any gaps. :)



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