2-leaf wall system question

Hi everybody...i started a topic in the design section about the new studio i'm planning to build this summer in my basement.I'm still in the designing progress and i must say that finding this forum was one of the best things that happened to me lately!!! back in my question now....I've been reading Rod Gervais book and i realised how important the "2 leaf system" is....i'm planning to follow this plan!! My idea is: 4x125mm gypsum board on 2x4 steel frame with 5cm of rock wool, 5-10cm of air gap and then again 5cm of rock wool on a 2x4 steel frame with 4x125mm gypsum board. I'm going to build a floating 15cm concrete floor on 10cm of high density rockwool, so the separating walls between the rooms will have each leaf standing on the room's floating floor exept for the outer wall system where the first leaf(inner) will stand on the floating floor and the second leaf(outer) will stand on the existing concrete floor. Here is my main question: can i use(where possible) the existing concrete walls as the outter leaf of the wall system? i mean if mass is the important factor....these 30cm concrete walls have quite a mass!!As i said this is a basement and behind these walls is the ground. I made a sketch up model of this design and i have uploaded a jpg of it but if you think that uploadink the skp file will give you a better idea please let me know... Well as you can underestand my main problem is that i'm not sure if i got the "Mass-air-mass" concept correctly....so please....i need your advice!! The thing is that English is not that good and i could very easily got some things wrong... Thanks for your time reading this... Nikodemos

Welcome to the forum Nikodemos. Yes you can and should use your existing concrete walls as the outer leafs. Basically you can add the "ground outside" to the equation of the mass of your 30cm walls. Even if the ground outside does not come to the top of the walls AND whether the concrete walls are solid concrete or hollow concrete blocks does not really matter... they will make a great outer leaf... that is presuming you've described and I understand correctly. I don't know your sound isolation goals however if this is a basement and there is ground underneath the existing concrete floor building a floating concrete floor may NOT be needed. It's expensive. You will loose height in the rooms and have a harder time with acoustics... we always want as much cubic feet/meters in the room as we can get. You will have a harder time getting building permits. You will make much more of a mess building. Most floating floors (not all) are best suited for studios not on the ground floor where sound isolation to spaces below studio is critical. Also you will (I think) have to examine your existing concrete floor to make sure it can take the weight of all materials you want to put on it. With no floating floor life will be easier. Marc

Mark thanks for your reply!!! Well that's what i thought about the 2 leaf system but asking is allways the best to find the way.....You see here in Greece constructing a studio(even a comercial like the one i'm planning to) is a weird story full of "urban legends". I already have a recording and rehearsing studio in the same basement and my ideas and designs are based on avoiding the mistakes i've done in the past (...and even look at some of the good points in my older designs!!!) That's where the floating floor comes.....I have 2 recording rooms in my old studio: one with a floating concrete floor and one without....we had big noise problems with the neighbours on the first....even the second floor with the "no-floating" room (and remember that the ground floor is an empty unused parking slab) and we had no problem at all with the floating room...so we ended up using the one room just for vocals or acoustic instruments :( I've read the topic about wether a floating floor is a real need or not and i think i understand the concept.....but reality in our building is totally diferent. i think it probably has to do something with the way concrete is build with it's steel reinforcment probably going all the way up to the building providing a great path for impact noise and low frequences to travel through...So i think in my case the floating floor is a must do. I've talked to some arcitects and engineers and they assumed that since this is the lowest slab of the building there is no question on the weight the existing floor can support......still i'm willing to search all possible sollutions with or without floating floors!! You can check this post http://www.johnlsayers.com/phpBB2/viewtopic.php?t=8898 where i put my main design idea i have another question regarding the 2 leaf system: how much space must be between 2 "2 leaf systems" in order not to be considered as a 4 leaf one....i mean i want to have a rehearsal room attached to the other rooms but need as much isolation as possible (i don't want a heavy metal band practising to be on tape in my new cello recordings!!!!) I thought that leaving an air space of about 80cm between two completely different 2 leaf systems will provide the maximum possible isolation between the two rooms.....or am i wrong? I wish Rod could read this..... Thanks again and pleace check my other post in the design section Nikodemos

Nikodemos wrote:

i have another question regarding the 2 leaf system: how much space must be between 2 "2 leaf systems" in order not to be considered as a 4 leaf one....i mean i want to have a rehearsal room attached to the other rooms but need as much isolation as possible (i don't want a heavy metal band practising to be on tape in my new cello recordings!!!!) I thought that leaving an air space of about 80cm between two completely different 2 leaf systems will provide the maximum possible isolation between the two rooms.....or am i wrong? I wish Rod could read this..... Thanks again and pleace check my other post in the design section Nikodemos

Nikodemos, you are not correct ("80cm between two completely different 2 leaf systems will provide the maximum possible isolation between the two rooms") but then again are not far off either. MAximum isolation would be more tan that - there will be some 4 leaf effect at this distance - BUT - you need a corridor anyway - (this is a corridor, right?) and so we live with what we get.......... Besides which - it will probably be flanking (if you take extra care with iso details) that will determine your true isolating values. Sincerely, Rod

thanks so much for your reply Rod!!! well actually that's not a corridor :oops: :oops: :oops: I just thought tha leaving some air between the 2 rooms would be a good idea...so it is just "dead space". Then again i could re-design the whole thing and add a corridor there and even make it wider, let's say about 1,20m :) :) :) So will that work....or even better, can you tell me what would be the ideal width for this corridor? thanks again Rod Nikodemos ps your book is great and a real help!

Nikodemos wrote:

well actually that's not a Corridor :oops: :oops: :oops: I just thought tha leaving some air between the 2 rooms would be a good idea...so it is just "dead space".

If that's the case - then you would be better off with a 2 leaf system - a 3 foot dead space will (itself) give you almost an additional 6dB of isolation. The 3' with a 4 leaf will actuallky decrease it slightly. BUT - if you need a corridor anyway - then I always tell people to live with what they end up with - and then it's a 4 leaf system - just the nature of the beast and all that. Sincerely, Rod

thanx so much for sharing your knowledge Rod I thought of this: If i just build an iso booth between the 2 rooms to act as a sound lock? I was thinking of 1,50m on its narrow side and 2,50m on the other wide.....and all the walls 2-leaf built. Would this work? I mean will i have increased STC in my live room from the noise in the rehersal room?(My english suck...i know).... I have posted this jpg allready on my design post....sorry about that :oops: Actually this is the link http://www.johnlsayers.com/phpBB2/viewtopic.php?t=8898 So i'll keep it all there....till i start construction anyway!!