slab or floating floor?

jeffjazz wrote:

here is the garage door wall wrapped n packed w. insulation and vapor barrier

External image, not preserved — original: http://www.johnlsayers.com/phpBB2/files/12306pics_002_176.jpg

Are you sure you want to use a vapor barrier, and not a vapor retarder?

One of the problems in the building industry is that we have a spreading "cult-like" mentality that worships at the "church of polyethylene". This cult views the answer to all moisture problems as the installation of a polyethylene vapor barrier condom on the inside of buildings. This cult is responsible for many more building failures than building successes. It's time that the cult deprogramming started. (Source)

Jeff, on pic's 4 and 13, can you describe what you've used for a window header - complete with sizes, methods, etc - you may be undersized, can't be sure from the pix... Steve

hey there steve! i actually called in a framer for this and he was very familiar with this sliding glass door framing. what he did was use a 2x4 laying flat 2 2x4s on their sides next to each other to create a square-ish beam 2x4 laying flat so basically it is a sandwich using 4 2x4s on the header going across the top of the sliding glass door. how does that sound to you?

Are you sure you want to use a vapor barrier, and not a vapor retarder?

this barrier is on the inside (i am in zone 6-7), just before the drywall. there is no kraft facing on the insulation and there is no vapor barrier or retarder other than this. behind the barrier is: -unfaced r19 insulation -2' foamboard insulation -garage door & exterior wall of house the exterior of the house can breathe and i will have a dedicated air handling system for the interior. i have not suffocated anything here. with that said, no i am not sure! at this point i am really not sure about much except that i need to finish this thing and start making music! :)

Looking good Jeff! Can you tell me more about that stuff you painted on the garage door. I need to do something like that. Thanks! :)

thanks dan!!! you too! it is called Quiet Coat or Quiet Car. it is car body undersealer, or viscoelastic compound. it transfers vibrations to heat or something... check out their website. i bought a gallon online here: www.quietcoat.com then i bought a measuring cup and a paintbrush from the dollar store... poured some compound into the cup so it is an easy hand-held dispenser and painted it right on there. but it was approaching winter so i had to wait for the temperature to be above 50. let it dry and painted another one on there. that's about it... it applies like a very thick paint. pretty easy but very effective in damping metal and lowering resonance. 8)

thanks Jeff! did you use the whole gallon? my door is a 2-car size, i wonder if i would need 2 gallons of the stuff ...

dan i totally recommend 2 gallons for 2 coats on a 2 car garage. who knows, you might even want to do 3 coats. i have very little left over that i can use to paint something small maybe the size of a stage box or some conduit, bottom of my engineer chair... whatever! maybe i'll find a good use for it somewhere along the line. :D must... sleeep... good luck with it dan!

Hmmmmm... Made by Quiet Solution...

hey jeff, what is up with your project. just re-read your thread from start to finish. i'm contemplating buying some of that Quiet Car stuff. i'm wondering, did your garage door isolation turn out as hoped. dan

hey there dan! i have been mia due to a busy schedule. anyway here is an update... two layers of 5/8" sheet rock are now up in the tracking room. the garage door is far behind me now! on every intersection of drywall layers, the seams are offset and each layer was both glued with grabber drywall adhesive (www.grabberman.com) and screwed into the wood studs with course thread drywall screws. all drywall was cut 1/8" - 1/4" short at the corners, and was caulked... we really caulked this thing together like crazy. i used the acoustical sealant from grabberman (www.grabberman.com) in all the corners and major seams. it wipes very smooth very easily with a wet sponge. each layer got mud & tape on the innards of the walls. right now i am going to sand the second layer smooth and go to town rocking up the control room. we still have a lot of work ahead. it is a VERY strong room, but i won't know the stc until everything is finished. more to come!

cool man ... i just received 2 gallons of that quiet car stuff. i might have to buy a 3rd but we'll see ...

Hey I'm baaaack! ok, now the control room has 2 layers of drywall and we're ready to pop in the heating/cooling system! regarding room treatments, i have searched but cannot find a definitive answer... I want to build slat resonators which are by your definition, a sealed cavity. -is it ok for the wall of the tracking room to act as the back of the slot resonator as long as the sides and top are sealed? -is it also ok for the ceiling to act as the top? -my ceiling is very high and on a slope for 2 of the resonators. is there a recommended method for capping a slat resonator with some plywood while still using the wall as the back of the SR? -is there a recommended method to mounting electrical boxes on top of the SR? -is there a recommended method to running the audio cabling to a panel mounted on the SR? many thanks!

jeffjazz wrote:

....on every intersection of drywall layers, the seams are offset and each layer was both glued with grabber drywall adhesive (www.grabberman.com) and screwed ...

I had thought that the layers of sheetrock should NOT be glued to each other? thanx, K

yes i see where that is written, but i have put up 2 layers of 5/8" sheetrock. my interpretation is that the layers are not a different density and are not supposed to act as 2 independent layers anyway. if i had put up one layer of 1/2" on top of a layer of 5/8" then i think the 2 layers would purposely have 2 distinct properties and are supposed to act independently. therefore you shouldn't glue them or you would take away the distinct properties. i have glued them so i hope for the best. either way, they aren't coming down! this is one extremely strong monolithic structure.

Jeff, sorry but that's not quite the case - what happens when you glue two layers together, whether they are the same thickness or not, is that you LOWER the coincidence frequency of that panel and make it so there is only ONE coincidence frequency - by doing that, you make the wall's weakest frequency LOWER, so it then takes more MASS to compensate in order to maintain the same TL. The coincidence frequency of 5/8 gypsum is around 2500 hZ; two layers GLUED together lowers this to about 1250 hZ; exactly 1 octave lower, which makes it 6 dB less effective when following straight mass law (as in, one solid mass for your wall instead of a m-a-m construction) The only type of adhesive that doesn't cause this (that I'm aware of) is a CLD material such as Green Glue; the constrained layer damping actually makes two layers of gyp work almost as well as 4 layers WITHOUT the GG. If this seems like it may become a problem, you might want to hold off on painting the inner layer til you do some isolation tests; if necessary, an additional layer of 5/8 gyp NOT glued should at least bring you back to where you would have been with two layers just screwed onto the studs... Steve

The coincidence frequency of 5/8 gypsum is around 2500 hZ; two layers GLUED together lowers this to about 1250 hZ; exactly 1 octave lower, which makes it 6 dB less effective when following straight mass law (as in, one solid mass for your wall instead of a m-a-m construction)

Steve, i'm not entirely sure i understand. so if the wall is twice as thick and twice as heavy, the coincidence frequency is one half lower? i don' t understand why it is better to have 2 separate layers of 5/8 than it is to have one monolithic layer of 10/8? i thought mass = isolation? I also don't understand why if the coincidence frequency is lower, then why is the isolation worse and the wall weaker? is it because the wall will now resonate at 1250 AND the octave at 2500 whereas before the fundamental was 2500? my studio is based on m-a-m construction. how does gluing the layers together defeat that? is it because it is thought that the layer of glue would create air gaps between the two layers of drywall? does it change things that both layers of drywall are screwed into the wood studs? how does it change things that the first layer of drywall is also glued to the wood studs? so far, isolation for my purposes and setup is very good, if not excellent so i doubt there will be a need for a third layer. however i am thirsty for this knowledge and would like to understand. thank you! I am at this point considering interior treatments so if anyone can contribute to the discussion regarding my questions on slat resonators i would be most appreciative! thanks again!!!

Jeff, I'll see if I can clear this up for you - First, let's take a fairly normal (for studios, anyway) double-framed wall as an example - Let's start with using two layers of 5/8 gypsum on the outer side of each frame, so it looks like the famous "63 dB wall" shown in several places in this forum, including here http://www.johnlsayers.com/phpBB2/download.php?id=1819 Now, if we break down what's happening in this wall we find that the critical, or coincidence frequency of 5/8 drywall by itself is roughly 2530 hZ; this is the frequency a single drywall panel would resonate at on its own. This is also one of the frequencies that will pass through such a panel easiest, because it's resonant at that frequency. IF you put more than one such panel on each side of the wall, but don't bond them together, the critical frequency is STILL 2530 hZ, whether you use 1 panel per side or 10. It's only when you BOND more than one panel together continuously, that you create a NEW type of panel with a higher mass, and therefore lower critical frequency. Double the mass and you will halve the frequency. This means that, by itself, the new, bonded, double-weight panel would have one octave lower resonance than a single panel - Mass law states that although a double weight SINGLE panel would have higher TL by 6 dB at all frequencies EXCEPT near resonance, it also has one octave lower resonance and so would be weakened (show a dip in isolation) 1 octave lower than a single weight, single panel - Now, we combine panels and frame and insulation into a complete, double-framed wall - if each side has two NON-glued 5/8 drywall panels, its total mass is double what it would be with only ONE such panel, but its critical frequency is STILL THE SAME as if only one panel were used, IOW it's still 2530 hZ for each side of the wall, even though there are more than one panel on each side. Now, let's assume we have two 2x4 frames spaced 1 inch apart in this wall - this decides the air gap, which would then = 8 inches, or 200mm. If we place a single, 1-1/4" thick drywall panel on each side of this frame, using standard household fiberglass insulation, prediction software shows that the resulting coincidence/critical frequency occurs at 1265 hZ and causes approximately 8 dB lower TL at that frequency than at surrounding ones - change the panels to two SEPARATE 5/8 drywall panels, which moves the coincidence dip up to 2530, and although you STILL get that 8 dB dip in the TL curve, it happens an octave higher - This does three things - one, it places the resonance at a higher frequency which isn't as close to the "weighted" center frequency used by the STC curve (500 hZ); two, the higher resonance frequency gets a 6 dB "helping hand" by mass law, since we now have the same mass but TWICE the coincidence frequency, therefore 6 dB better TL, and three - the coincidence frequency is an octave further away from the mass-air-mass resonance of the complete wall structure, so they will have somewhat less interaction (so one loss doesn't exacerbate the other) I've done a few calculations on this, and if it weren't such a pain in the ass to build, we could get even better results by using 4 layers of 1/4" drywall per side instead of two layers of 1/2", or (even worse) one layer of 1" drywall per side. (This is because 1/4" drywall has an even HIGHER coincidence dip, over 6 kHz - it also assumes NO GLUE.) I'm about ready to crash, but I hope this helps explain what I meant earlier... Steve

steve, thank you so much. you made a lot of sense in your explanation. non glueing would add mass without lowering the resonant frequency of the wall. so this affects isolation, and the weakest point will be around 1265 hZ. The STC for the rest of the walls will be around 63 but around 1265 hZ the STC will be around 55. is this correct? how should i factor this in when building in the room treatments? does it also affect room resonance?