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Housing - New Build: Sound insulating properties of dense block party wall

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  1.  
    Dear all,
    I'm hoping for some thoughts on party wall construction
    I'm overseeing the build of a pair of semis one of which will become my home. The outside walls will be made of 365mm Durisol blocks rendered inside and out with hemp lime render. For the party wall my builder is suggesting a single 215mm high density concrete block on the flat with a thick hemp lime render on either side. I'm wondering would it be better to use the blocks on their edge to form a cavity with maybe some insulation in the middle?
    My main concern is noise but obviously a bit of insulation is no harm for when they go away at Chritmas etc.

    Putting aside issues about concrete and Durisol blocks has anyone any comments about the sound insulating properties of these proposed solutions or any better ideas that would be equivalent in price?
    (I intend to post more about Durisol soon)
    Thanks in advance,
    Mike
    • CommentAuthormarktime
    • CommentTimeMar 2nd 2010
     
    Got on any idea what the density of those blocks will be? If you are using a single skin you will need mass but don't you have a building reg that you must follow with regards to acoustic performance that will act as your guide?

    I'd think you'd be looking at 250 - 300 kg/m2 per unit mass to get somewhere near 45 - 50dBA.
    • CommentAuthortony
    • CommentTimeMar 2nd 2010
     
    If it was mine I would build two 215mm solid concrete block walls with a 100mm fully filled cavity (batts) and no wall ties.

    I can explain why if necessary
  4.  
    marktime, I'm finding out what density the blocks would be.

    The more I think about it the more I think that by standing the 215X100 mm block on its edge I'm covering 7.5% more area with the same number of blocks or more relevantly I can cover the same area with aprox 7.5% less blocks and labour. This would go some way to offset the cost of insulation and wall ties. By doing so I would have lowered the density of the wall but incorporated a cavity, this is where I'm not sure which is better.

    But Tony are you saying you would do 2x 215 on the flat plus a cavity ie a wall that is 530mm wide? What would you use for the batts? Yes I'd really appreciate you explaining why.

    Thanks,
    Mike
  5.  
    See http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir693/ir693.pdf and also http://www.mikeholmesfanforum.com/phpbb3/viewtopic.php?f=10&t=28997&p=200853#p200853 - "There are 4 elements to soundproofing. Decoupling, Absorption, Mass and Damping. Insulation does the absorption, and is the least contributive of the 4 elements. In a standard wall or ceiling, the National Research Council of Canada has a quoted opinion that insulation all by itself as a soundproofing measure is almost not worth doing. I believe this is light of the large expense associated with insulation. The key is 'all by itself.' When used in conjunction with a decoupled system (clips+channel, staggered or double studs) insulation provides a much better return on investment.

    Hope these help.

    Paul in Montreal
    • CommentAuthortony
    • CommentTimeMar 2nd 2010
     
    I wouldn't do blocks laid flat -- only cowboys do that but I would build two 215mm walls with a 100 cavity fully filled with glass and no wall ties.

    the more mass you have between you and next door the better --- better sound deadening

    wall ties carry noise across so omit them and two 215 walls most likely wont need wall ties if restrained by floor(s) roof, front and back (back inside wall not to bridge cavity either

    The insulation is crucial to stop thermal bypass

    The insulation will assist in deadening sound and help keep you thermally isolated from them next door

    If it is gable wall I would stop mine below the ceiling insulation and let theirs go on up :bigsmile:
  7.  
    Mike

    Will any joists or beams be penetrating the wall? Will there be stairs against the wall? If so, you need to ensure they don't cause noise to be propagated from one side to the other.

    David
    • CommentAuthortony
    • CommentTimeMar 2nd 2010
     
    Isnt that the usual thing in semis? joists or trimmers in wall, stairs against party wall and noise sent through to next door.
    • CommentAuthorTimber
    • CommentTimeMar 2nd 2010
     
    215 mm solid is ok, in an ok kind of way.

    I wouldn't bother using 2x 215 leaves with a 100 mm cavity. That is WAY overkill, however it all depends how concerned you are with noise.

    I would build 2x 100 mm leaves of dense aggregate block with a 75 mm fully filled cavity (to prevent thermal bypass).

    Please watch out for flanking. The durisol blocks may allow flanking sound via the inner leaf of the wall. I would get an acoustic consultant to check out the details to make sure they will work.

    You could always go for timber framed wall! 2x leaves of 89 mm studwork with a 50 mm cavity. Fill the whole lot with insulation to prevent thermal bypass and then line with 1x 15 mm wall board and 1x 19 mm plank.


    Penetrations of solid party walls can be a problem, but then they can also be a problem with cavity walls!

    Timber
  10.  
    Thanks for the links Paul.
    There are no stairs or joists going into the party wall and where possible I have designed store rooms and bathrooms to be against it keeping living rooms and bedrooms away. In the one bedroom that has a party wall there will probably be a fitted wardrobe (possibly both sides). However what I had not considered is that the cooker hoods will be back to back on this wall in the kitchen.

    I'm checking with my builder to get the density and dimensions of the block he is intending to use. I should have clarified this before starting the post....

    Mike
    • CommentAuthorchuckey
    • CommentTimeMar 2nd 2010
     
    I would be careful of using glassfibre batts, they need to be 100% tight against each other on all faces, roll insulation punched down (16" width) in a continous length would be better though slower to install. Likewise how are you going to install the floor joists, which ever method you use it is imperative that there are no air leak holes through the skin(s). I would think that a trimmer bolted along two sides of the house with joists hung of them would be the least leaky (or run them front to back).
    Frank
    • CommentAuthortony
    • CommentTimeMar 3rd 2010
     
    I talked to an acoustics consultant at Ecobuild and he said 2 x 140mm dense block walls with a 75mm filled cavity --- I would still go for 215 so that wall ties can be omitted.
    • CommentAuthorsinnerboy
    • CommentTimeMar 3rd 2010
     
    Can you plan your elecs so that there are points on the party wall ? Would be a shame to see the acoustic seperation compromised by cables and boxes chasing .
  14.  
    Ok sorry to take so long getting back to this. My builder is prepared to do a cavity wall of 2 x 100mm dense blocks (1800kg/m2) with 75mm rockwool in between and 20mm hemp lime render for the same price as the Durisol 250mm solid block with 30mm of hemp lime either side. Durisol state a dB value of 63dB which is presumably even better with the hemp lime on top.

    Could anyone help me estimate the likely dB value of the cavity with insulation option so that I can compare?

    I'm aware that the Durisol is not insulated as such having a u value of 0.82W/m2K but with addition of the render and the fact that the other side even if not heated won't be freezing I'm ready to go with the best noise insulation. I would imagine that using Durisol for the whole job rather than changing materials might yield some advantages when it comes to avoiding flanking as the concrete will be continuous between the outside and party walls.
    Thanks in advance as usual
    Mike
    • CommentAuthortony
    • CommentTimeMar 8th 2010
     
    I talked to an acoustics consultant at Ecobuild and he said 2 x 140mm dense block walls with a 75mm filled cavity -- most old semis have what you are thinking of and sound insulation isnt great.

    Workmanship is crucial -- point and fill all perps.
    • CommentAuthormarktime
    • CommentTimeMar 9th 2010 edited
     
    I don't agree with tony. 63dBA is the spec for a high performance acoustic dry-wall and more than adequate for airborne noise attenuation. You'll not hear conversations or music through that wall. However, make sure that the construction follows the detail (method) that was employed for the sample wall from which the measurement was taken. As a solid wet wall construction it's improbable that you'll have sound flanking but as tony points out, the perps MUST be full-fulled.

    edit: ensure the sample wall wasn't cement mortar rendered because that would make a significant difference to unit mass.
    • CommentAuthortony
    • CommentTimeMar 9th 2010
     
    It wasn't so much me as me asking an acoustics consultant about a house that I was going to live in 100mm is OK for everyone else but for his own house I would go better

    It is difficult to upgrade the sound insulation of a party wall and the marginal cost of 140 over 100 is small

    If it were mine I would go 200mm.
    • CommentAuthormarktime
    • CommentTimeMar 9th 2010 edited
     
    But isn't that what is specc'ed i.e. 1 x 250 Durisol dense block?
    • CommentAuthortony
    • CommentTimeMar 9th 2010
     
    no I would do two walls separated by a filled cavity with no wall ties. very different
    • CommentAuthormarktime
    • CommentTimeMar 9th 2010
     
    But tony you are answering a different need and yes, there's an argument to be had in thermal terms but as mike has pointed out, the thermal demands of an internal party wall are much lower than an exterior wall.

    I put great store by staying with one skillset throughout and if the builder is comfortable laying 250 blocks and a 250 block answers the acoustic demand, then that would be my preferred solution.

    It really boils down to the 90% rule, the last 10% is going to cost a lot more than the previous 10% so it's a cost/performance balance ranged against all the other elements in the construction.
    • CommentAuthortony
    • CommentTimeMar 9th 2010
     
    Would that pass building regs?
    • CommentAuthorTimber
    • CommentTimeMar 10th 2010 edited
     
    Danger danger!

    I bet the durisol value is NOT in the correct format.

    The format for a site test (and for compliance with Bregs) is DnT,w + Ctr.

    I would suggest that the durisol figure is Rw. This is a lab test result.

    On site the DnT,w is usually 5 - 10 dB worse than lab, PLUS the Rw figure doesn't take into consideration the negative Ctr correction. for that kind of wall i would estimate a negative correction of 3 dB (ish)

    So the 63 dB Rw figure COULD end up being a 50 dB DnT,w + Ctr on site. That still pass Breg of 45 dB DnT,w + Ctr or more. Its ok in an ok kind of way.

    The two leaves of 100 mm block with a 75 mm cavity and some mineral wool will give between 50 and 55 dB DnT,w + Ctr which is ok. If you get to 55 dB that is pritty good, but some timber frame walls can get up to 65 dB which is a HUGE improvement over Bregs.

    2x 140 walls will give you up to 60 - 65 dB DnT,w +Ctr, but is a lot thicker than a timber frame wall reaching the same spec.

    It all depends on your expectations!

    Timber
  23.  
    Posted By: Timber
    It all depends on your expectations!

    Timber


    .... and the frequency.

    At most frequencies I believe the Mass law means that denser materials [such as concrete blocks] out perform less dense one [such as timber frame] Here's Rockwool's slant on it http://www.international.rockwool-marine.com/applications/sound+insulation/sound+and+noise+theory/sound+theory/acoustical+mass+law

    I suspect the concrete boys will spin it the other way
  24.  
  25.  
    Dear all,
    I should probably plough through the very interesting information from the rockwool link above before posting but since I started the post I want to get something back up as soon as I can. I found a link from the Durisol site to an acoustic test done by an independent tester on a block of flats using Durisol. I actually phoned the tester and talked to him because I just thought that in addition to the test results as someone testing all the time he probably has a good 'feel' for acoustic properties of various options. He told me that he was amazed at how well the Durisol worked and really hopes he gets to test more houses made of it in the future. I asked him directly what would I expect to get with a 2x100mm dense block cavity with 75mm rockwool and he guessed at about 55dB. Well above regs but well short of the 62dB that the Durisol got.

    I have attached the sound test results. Interestingly they are only one dB down on the lab results but this is because of the addition of the plasterboard so the danger warning by Timber above is valid even though the figures are for genuine field test results and in the correct format.

    As a result of this and coupled with the fact that I'm using Durisol for the outside walls I'm pretty sure that I'm going to go with the Durisol.
    • CommentAuthorLizM
    • CommentTimeMar 13th 2010
     
    Excuse my ignorance of the matter - but aren't there standard "robust details" for this kind of thing? http://www.robustdetails.com/
  27.  
    Hi Liz. Yes there are robust details but none of them match the systems that I was trying to compare ie solid masonry wall, cavity filled with rockwool or Durisol.
    The nearest I could find would be at http://www.robustdetails.com/Robust-Details-for-Part-E-separating-walls-or-floors-sound-insulation-and-testing-Robust-Details-Limited-65d22b1#frame-0 but there is no way to compare different thicknesses of the different options to see which is the better and non of the examples even mention rockwool in the cavity which was suggested as the way to go here. Unless I missed something but for sure there will be nothing on Durisol in there.
    Mike
    • CommentAuthortony
    • CommentTimeMar 14th 2010
     
    Robust details are not that great in green terms as they allow thermal bypass, others recon sealing a skirting to the floor is a good thing -- closing the door after the horse has bolted to my way of thinking.

    Often they consider one area in isolation when a holistic view is needed. long way to go as yet.
    • CommentAuthordstart
    • CommentTimeMar 28th 2011
     
    Hi - there. Sorry to reopen the discussion!

    We are trying to separate tow old houses (600 mm stone walls) by block up the interconnecting doorways on all floors). We are keen to achieve very high sounds insulation (~55-60dB) and would like to use dense block (sorry about greenness...)

    Which would be best sound insulation

    215mm dense concrete block (i.e.laid sideways), with dense render both sides
    OR
    2x 100mm dense concrete block with 50mm cavity plus rendering

    Also not sure if we should fill the cavity with acoustic mineral wall or not

    Can you help?

    Thanks so much

    Daniel
    • CommentAuthortony
    • CommentTimeMar 29th 2011
     
    2x single skins so long as the perp end joints are full of mortar and pointed up with rockwool batts in the cavity

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