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Blockwork verus rockwool

IronGiant

Moderator
I need to fill a doorway between what will become my son's bedroom and another bedroom. I'd like to plan for maximum sound proofing.

As it's through the original outer skin of the house I have a 12"wide gap to fill. My easiest option is to build two stud walls and pack it with 8"+ of rockwool.

Would a central wall of blockwork with a couple of inches of rockwool either side be better or worse for sound attenuation?

This is a DIY project so I'd prefer option a)...

Any thoughts?

Dave
 

Nimby

Distinguished Member
It depends on what the original wall material is and its thickness. Block (or particularly) brick would be best for blocking sound.

Density is everything. If you can't excite it in the first place it can't vibrate and transmit sound from the other side.

If you build a stud wall and fill it with rockwool noise will be conducted through the studs themselves unless you can build two spaced structures within the thickness of the wall with no contact between the two.

You only get one chance to do it right. Just make sure you fill all the voids between the blocks. (or bricks) Blocks are easy as long as your mortar isn't too wet and you don't rush to pile one on top of the other. Or get a personally recommended local builder in to do it for you. Provided you supervise (unobtrusively) and emphasise the need for sealing every gap.

Nimby
 

inzaman

Moderator
Nimby, are you saying that bricks would be better than plasterboard and rockwool. I am converting my cellar and have a wall that i wanted to soundproof (i did do a post but cannot find it on the search menu) and was going to batten the wall and plasterboard it then fill with rockwool.
Do you think though for better soundproofing i should just build another brickwall next to it/attached to it and that would give a better soundproofing than the plasterboard and rockwool at the same thickness. Thanks Inza
 

Nimby

Distinguished Member
inzaman

Bricks work best because they are so massive (heavy) that they don't vibrate in the first place. So they don't re-transmit the sound (or noise) out of the back like a flimsy partition would. Their weight is a serious problem though. You can't just build a brick wall off the cellar floor without checking load bearing capabilities of the existing floor.

Sealing round the edges also requires care to avoid completely bypassing the brick barrier. Floor joists can carry the noise into an adjoining wall when the floor above is vibrating madly to the subwoofer's output.

When you build a stud wall to soundproof a wall you should ideally have a layer of rockwool hanging free like a curtain behind the wall for best effect. The studwall stands in front of the curtain with multiple layers of plasterboard to dampen surface vibrations and increase the mass. The idea of the free hanging curtain is to avoid direct contact with either the stud wall or the wall behind. The problem with this idea is that you loose at least 8-10" of precious space in your HT Room. What you should not do is fix the studs direct to the wall. There should be some space behind the stud or brick wall.

I've added a link below which offers sensible advice for home studio builders. It applies equally to HT rooms though.


http://www.soundonsound.com/sos/jul00/articles/faqacoustic.htm

Nimby

Where's ACOUSTICE when you need him? He's the expert in this area.
 

inzaman

Moderator
Thanks for the quick response Nimby :thumbsup: i will have a read of the link later tonight.
 

inzaman

Moderator
Thanks again for that Nimby, it is very interesting reading and has hopefully really helped me out and should help severely reduce the noise that may potentially go to next door, so long as the buillder says its okay to build another wall two bricks deep next to the original wall.

I can also stop saving my egg boxes now :D
 

woody67

Novice Member
For a doorway, it may be no use trying to make it more soundproof than the walls it is adjacent to. If you currently have stud partition, then you may as well put the same in the doorway.

Unless you have a supporting wall or lintel etc under the doorway and the adjacent wall is also blockwork, then using blockwork infill is not recommended - as it could lead to differential movement.

There will always be some sound transmitted through the structure (bass) and reflected off the surfaces (higher frequecies such as talking). So whatever infill you decided on, it may be made worse if the room as bare plaster walls. If you are after soundproofing, then you must look at the room as a whole.

A timber stud, with any voids filled with rockwool, and 12.5mm plasterboard and skim, should be adequate for domestic purposes
 

woody67

Novice Member
inzaman said:
Nimby, are you saying that bricks would be better than plasterboard and rockwool. I am converting my cellar and have a wall that i wanted to soundproof (i did do a post but cannot find it on the search menu) and was going to batten the wall and plasterboard it then fill with rockwool.
Do you think though for better soundproofing i should just build another brickwall next to it/attached to it and that would give a better soundproofing than the plasterboard and rockwool at the same thickness. Thanks Inza
Whilst 'dense = good' is normal for sound proofing, its not always the best option for all circumstances.

A dense block wall will be better than brick, but if it is not independant to the wall behind it, then bass will travel through it. Also you have the floor loading to consider.

A lightweight, independant wall such as timber and rockwook, with a sound absorbant surface (paper or similar as opposed to bare plaster), could be a better option.

Better still, something like www.fermacell.co.uk may be usefull
 

IronGiant

Moderator
Interesting,

If you've ever lived in a victorian terrace you will realise bricks are almost accoustically transparent :D

I'm blocking off a doorway through the outer skin of the house, so I've got the best part of a foot of space to play with. So I was thinking of two unconnected plasterboard clad walls with a big gap in the middle, stuffed with air, high density rockwool or whatever...

This will now separate what will be my 9 year olds bedroom from our 2 year olds bedroom, so soundproofing only neeeds to be appropriate for this, not home cinema

Dave
 

Nimby

Distinguished Member
When it comes to noise production I'll take AV over kids any day. :devil:

With such a thick wall you might as well use two clearly spaced stud walls with doubled plasterboard either side & rockwool filler with no connection between the two structures. Leave the plasterboard surfaces slightly below flush so you can skim over for a nice finish.

After that you just have to pray they don't both take up the drums and/or electric guitar! :eek:

Nimby
 

avanzato

Active Member
Sound transmission between houses is part of the Building Regulations now.
You can download a free info book from the insulation manufacturers: Knauf, Rockwool etc. Look for the 'Part E' book. It'll be full of good information.
 

IronGiant

Moderator
Thanks people, I'll go down the two unconnected stud walls/rockwool approach

Dave
 

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