Do I have a three-leaf ceiling problem?

I'm ready to finish the ceiling of my recording space using (expensive!) acoustic clips and fireline drywall boards (one 1/2" plus one 5/8"). But before I do I want to make sure I don't waste my time and money (having read a lot about the three/four leaf effect in walls). What I am already working with is illustrated in the diagram below. My question is, if I leave it as is and go ahead with installing my new ceiling, am I likely to end up suffering from a three-leaf effect? And if so, what can I do about it? Will it help to fix additional layer(s) of drywall directly beneath the celotex sheet before installing the ceiling (as recommended by Rod Gervais in his book)? Or will this compound the problem? For reference, I am trying to minimise sound transmission from my recording space up through the ceiling. More information on my project is posted in the Design section: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=9431 All and any comments welcome! Chris

mandragora wrote:

I'm ready to finish the ceiling of my recording space using (expensive!) acoustic clips and fireline drywall boards (one 1/2" plus one 5/8"). But before I do I want to make sure I don't waste my time and money (having read a lot about the three/four leaf effect in walls).

First a few observations/comments: The way you present this makes it sound like you are doingroom witha room construction. Is this true? If the answer is "Yes"=- then why are you using acoustic clips - if the answer is "No" - then please provide a sketch indicating exactly HOW you are using this assembly. FWIW - you would be better suited to use double 5/8" rather than 1/2 / 5/8......... the added mass is worth much more than varying the coincident frequency ( which is such a high frequency that it get's dealt with in the process). The added mass will help with low frequency - which isn't an issue of coincidence - just mass.

My question is, if I leave it as is and go ahead with installing my new ceiling, am I likely to end up suffering from a three-leaf effect? And if so, what can I do about it? Will it help to fix additional layer(s) of drywall directly beneath the celotex sheet before installing the ceiling

Yuo don't explain exactly what you are attaching your new ceiling to - so I have no way of answering the question.

(as recommended by Rod Gervais in his book)?

I don't recall ever speaking about a situation such as this - never mind making a recommendation about it - perhaps you were thinking about something different.

Or will this compound the problem?

Again - I (we?) need more info - seeing as I don't know what you're building yet........ ANd I did not get a warm fuzzy feeling from your other thread - and still not any more sure about exactly what you're doing. Sincerely, Rod

Hello Rod Thanks for your reply. Your comments suggest that I have a lot to learn about communicating what I'd trying to do - in addition to learning about the best way to do it. So thanks for your patience, while I will try and explain myself more clearly! My primary intention is to create a space in which myself and my acoustic rock band can make some noise without incurring the wrath of the neighbours. Having achieved a reasonable level of sound insulation I then intend to try and condition the space so the noise sounds as good as possible (accepting that others' interpretation of "good" may be at odds with our own!) My comments about finishing the ceiling are made in connection with my first intention of achieving sound insulation and the diagram is what I currently have to work with: a ceiling comprising a floor covering and underfloor heating installation serving the room above (which has no music-related function) with unfinished joists visible from the room below (which is the band practice room I am trying to insulate). Just to be clear, I am not building a room within a room (though maybe I should consider this option?) and my intention was to counter-batten the existing exposed joists in the ceiling using acoustic clips and hat channel product spec: http://www.cmsacoustics.co.uk/pdfs/IsoMax.pdf) and then fix two layers of drywall to this. I am attaching an amended diagram to illustrate this. Also in the new second diagram I have tried to illustrate (in green) what I meant regarding the recommendation in your book - namely adding additional drywall within the joist space before finishing the ceiling - although of course I accept that this circumstance is quite different from what you describe in your illustration on page 67 of your book. I hope this will help to clarify what I'm asking. Thanks very much for your interest (and for your book, I am reading as much as I can between posts!) Chris

if the celotex isn't currently in place, swap the position of the celotex and drywall position (put the drywall on the 10mm ply).

Thanks Glenn, I can see that makes sense - and I guess from your reply that you strongly advocate the installation of that extra drywall. However I am afraid the celotex was put in place some time ago, before I planned the space as a studio. But I am prepared to cut it out if that's the only way to get a top result... Chris

Rod, I re-read your initial reply and with regard to your comment about not understanding what my intentions are, it occured to me that you may not have picked up on the original thread I posted in the Studio Design section: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=9431 In that I tried my best to outline what I want to achieve, but I subsequently started posting in the Construction section because I realised I needed to ask specific questions in order to get meaningful replies that would help me move forward... If you have the time - and the interest - to check out that original post and let me know what else you need from me to help you feel "warm and fuzzy" about the project, I would be most happy to oblige. Thanks Chris

i would think that if you can pull out the celotex, put in the drywall layers, then put the celotex back in (and some pink insulation) you'll do better than going with the layers as you have shown in your drawing. also, before doing all this work, have you done any measurements to determine what you need in terms of isolation?

The answer to your question about measurements is no, I have not done any. I am not expecting to sound-proof the room, just to achieve the best result I can without rebuilding the entire ceiling, in a bid to minimise disturbance to my (reasonably tolerant) neighbours. Compared to the walls and floor, the ceiling is the obvious weak spot, which is why I am concentrating my efforts on it. From what I have read, and what you have said, I am guessing that it is only worth installing the additional drywall (green in my diagram) if I first remove the celotex. That's going to be messy fun, as it has been firmly glued into place! After the celotex goes back, you have suggested adding pink insulation - however the supplier of the acoustic clips told me that leaving the space void would be the best solution... But I am inclined to take your advice rather than his... Chris

Actually - the celotex forms a part of the 2nd (of 3) leaves - adding drywall to the bottom of it would only add mass to that 2nd leaf. I don't think I would proceed in that manner, right now the celotex itself isn't doing much to either help or hurt you - and I don't believe that the single layer of 10mm (3/8"?) plywood is doing much either........ BUT - if it were me - I would take the money for the 2 layers you were going to put there - and add one them to the ceiling below all of this....... and then consider using a layer of green glue between the inner mostr (room side) layers........... BUT - I caution you - I still believe that the walls - and flanking around them to the upstairs is going to be your biggest weakness......... Rod

Help me out here. After the pipes are installed for an underfloor heating system, isn't a screed poured into this void? That doesn't make, from the tile down to the Celotex, one leaf? I mean, if the screed is in there, it isn't a void but additional mass on the upper leaf. 'Course if it is nothing but air, I guess I'm about to get my head handed to me:)

xSpace wrote:

Help me out here. After the pipes are installed for an underfloor heating system, isn't a screed poured into this void? That doesn't make, from the tile down to the Celotex, one leaf? I mean, if the screed is in there, it isn't a void but additional mass on the upper leaf. 'Course if it is nothing but air, I guess I'm about to get my head handed to me:)

That would be very unusual in any new construction situation. perhaps in a retro-fit - but I'ver never seen it in new......... Rod

generally - if the heater is directly under the tiles it would be covered by the thinset or cement, if its under wood floors its usually left with air space and (as shown) has an insulator underneath to ensure it goes up... maybe another good reason to follow Rod's suggestion to ignore this middle leaf and add the additional drywall to the lower ceiling - it may cause the upper heating system to operate differently (such as soaking up heat into the drywall instead of being reflected back...)