# Sound Insulation Rockwool or Hemp?



## Brigid (22 May 2011)

Hi, I wonder if anyone can give me some idea as to what is better as sound insulation - Rockwool or hemp?  Does Rockwool sag? does its quality deteriorate overtime?  Is hemp any better?  we have gone for first floor joists rather than concrete slab - while I don't mind there being muffled sounds between the floors I don't want to be able to hear conversations or the kettle being boiled etc.  Any suggestions on how to achieve a moderate degree of sound insulation would be appreciated.  Many thanks,  B


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## amh (23 May 2011)

Hi Brigid,

In regards to sound travelling from ground floor to first floor, I was advised by a carpenter friend that if you simply lay a layer of plaster board over the top of the joists before putting down the floor boards this will help to a fair degree in keeping the level of sound transfer down. 

Now this, I'm sure will not be advised by the most technical people on here, but in my experience it definately has helped a lot. It's not particularly expensive so as part of a solution, it's one I'd go for again.


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## onq (23 May 2011)

amh,

 I am astonished that the  carpenter would say that to you.

Did the carpenter not tell you what happens to plasterboard in an environment where moisture can come into contact with it of condense within it - i.e. under lino or tiles in a bathoorm?

Plasterboard is notorious for absorbing moisture and deteriorating.

It deteriorates  significantly if it actually gets wet.

Even timber sheeting may buckle, which is bad enough,  so you need to use a water resistant ply as a minimum, but even this  can give trouble.

Using plasterboard is also potentially disastrous because its crushing  strength is not good enough to use it as a support stratum.

Hit some ply with a hammer and then his a plasterboarded wall [between the timbers] to see this.


ONQ.

     [broken link removed]

     All advice on AAM is remote from the situation and cannot be relied                  upon                                                                                                as  a          defence    or                support   -         in          and     of                 itself    -                        should                      legal                        action              be                       taken.
     Competent legal and building professionals should be asked to      advise        in                                                                                                      Real      Life      with             rights      to                inspect         and               issue                       reports           on            the                                   matters         at                      hand.


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## Brigid (23 May 2011)

Thank you for those thoughts AMH and thank you ONQ for your considered response!


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## Satan's Bed (3 Jun 2011)

Rockwool/Hemp is not sound insulation but can be classified as sound absorption. It will provide practically nothing in terms of sound insulation.

S.B.


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## Brigid (5 Jun 2011)

Hi Satan's Bed,

Thank you for that, I wonder if you can elaborate?  What can one use that will create sound insulation - From my description of what I am looking for in my original post - is that sound absorption or sound insulation?


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## Satan's Bed (7 Jun 2011)

You'll need a combination of both sound insulation and absorption.

Hers's a sample build-up
Decouple ceiling using resilient bars. Fix a sound insulation material and layer of gypsumboard to the bars. Leave 5mm gap around perimeter of gypsumboard layer and fill with acoustic sealant.

Fill between joists with 100mm or more of suitable density mineral wool.

Lay 20mm ply. Then lay a resilient impact sound insulation layer followed by floor covering. Ask for flanking transmission detailing from sound insulation supplier.

S.B.


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## rockofages (11 Jun 2011)

Sounds like you're being baffled into going to a sound insulation supplier!


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## Brigid (12 Jun 2011)

Definitely baffled ...


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## onq (29 Jul 2011)

Brigid,

Unless you employ both sound insulation and sound absorption measures the effectiveness is likely to be limited.

http://en.wikipedia.org/wiki/Soundproofing

Both airborne and structure-borne sound require to be dealt with and the effects of harmonics must also be taken into account.

In a timber floor -

- impact noise needs an absorbent layer
- airborne sounds may need the ceiling to be decoupled and
- the whole floor may need to be stiffened to reduce the likelihood of harmonic transmission

If the floor timbers are undersized or marginal, the entire structure will "give" when someone moves across it, and this in itself will create and transmit noise.
If the floor isn't well braced, [and sometimes even if it is] the heading up and cooling down of the house may cause a lot of creaking noises - ours talks to us each day.
The only good floors for domestic use that I have used have been concrete or steel and concrete floors - I have specified them in three private houses and noise if not a problem.

Just remember when dealing with noise that addressing one source well may seem to exacerbate the next worse source, as sounds previously masked become more noticeable in the quieter house.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon        as a defence or support - in and of itself - should legal action   be      taken.
Competent legal and building professionals should be asked to advise in        Real Life with rights to inspect and issue reports on the matters   at      hand.


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## Brigid (5 Aug 2011)

Thank you for this ONQ.  I understand what you are saying but wonder how that translates into practical application - I was thinking of using rockwool between the joists and then put something like "Silentplus" (shown to me by a builders providers dont know anything about it really) on top of the WBP and then have a 'floating floor' above that.  We dont need complete soundproofness.  just wondering if there is anything more that we should be considering at this time. Thanks for your help.


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## onq (5 Aug 2011)

Brigid,

You're on site and you're thinking now about something that is better dealt with at the detail design stage - pre-tender stage.

For what its worth, I prefer -

215mm solid concrete blockwork supporting -

circa 200mm composite steel and cast concrete flooring

or 

200mm PC units with 75mm loading screed.

You could drop a hammer on the floor above and probably wouldn't hear it if all the (tight-fitting) doors were closed in the house.

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If you want to build in timber that's a whole other technology, but you start with oversizing joists and keeping your spans down to 4.0-4.5M and putting in twice as many cross braces as usual to stiffen the floor.

Then you could install wire netting and fill the spaces between the joists with Rockwool.
Then you could lay absorbent strips along the tops of the joists and install a floating floor of 25mm boards or you some something similar to what you're suggesting.

Unless you're exposing floorboards you could consider an absorbent layer on top of the floorboards to deal with impact noise (hammers, stilletto heels, toys thrown out of prams, etc.)

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Alternatively you may find a house which is well soundproofed using different methods and employ their technology their details.

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The thing is, you have to balance all the regulations, not deal with them piecemeal.
Recessed downlighters and MVHR systems can both contribute to or cause risk in an emergency.
The ducting for MVHR also seems to transmit sound.
Both are relevant to what you are considering.

The whole current movement towards air-tight living seems to be a hugely retrograde step but its "out there".
Here is a link you may want to take a look at although I haven't read all of it myself.

http://comment.veetech.org.uk/index.htm

None of the issues raised therein come as a surprise to me, but its one  of the first places I've seen them all grouped together in this manner.
I'm currently undertaking research into this and discussing same with a  colleague and a building control officer I know and its raising more  concerns than allaying them.


ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon         as a defence or support - in and of itself - should legal action    be      taken.
Competent legal and building professionals should be asked to advise in         Real Life with rights to inspect and issue reports on the matters    at      hand.


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## Brigid (6 Aug 2011)

Thank you for this.  We were advised regarding the benefits of a concrete first floor and we opted for a timber one.  Your thoughts on what to do are appreciated.


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