MASS-AIR-MASS Question

A mix of heavy and "normal" insulation will work fine; do you have anything in mind to use for your outermost layer on the outside wall? Gypsum won't work for that layer, it needs to be more weatherproof... Steve

For the outer layer i´m planning to use 18mm gypsum board and attached to it, a layer of wood (similar to pine) treated to be weatherproofed... That´s the idea i came up to have the mass of the gypsum and the weatherproof capacity of wood... what do you think?

Should work fine with good sealing - does your place get heated or cooled at different seasons? We may need to talk about air/vapor barriers... Steve

Yes, since the studio will be exposed to weather changes, i´m planning to use a vapour barrier... right now i´m searching different brands here in Argentina, so i can ask you if i don´t understand anything... BTW, where should i put the vapour barrier? In which frame -inner or outer-?

Steve, before getting into the vapour thing... I found this... http://www.usg.com/USG_Marketing_Conten ... 63-003.pdf from USG... The seller told me that i can use it with basecoat and it´s 100% weatherproof. Do you think it´s a good material for the outer layer? I´m planning to use 50kg/m3 mineral wool on the frame...

Depends on the "Shear" strength required - if your outer walls will be supporting roof or anything, then probably not a good material. If not, then it should be fine - see their "FAQ" page on this material here Note their comments about keeping this stuff DRY until install, and Their comments about replacing OSB From your latitude and marine influence, I would think your climate is rather warm and humid - do you intend to air condition this space, or heat it in winter, etc? What's your typical relative humidity in different seasons? All these q's are to help figure out what/if an air or vapor barrier will be needed... Steve

My roof is already supported by columns, so i will probably use Fiberock... Here´s the pic that dealer send me (which includes the vapour barrier - Tyvek-)... I won´t put the that layer of gypsum on the inside, but that´s the way i´m making the panels... Any other thing to have on mind? I´m not sure if i´m creating enough mass...

So is that just the fibe-rock for the outer mass, or is that a stucco finish outside? Will you be using steel studs, or wood? Total air space between masses again? Also, can you finish answering my previous questions on climate? Steve

Julián Fernández wrote:

Here´s the pic that dealer send me (which includes the vapour barrier - Tyvek-)...

FWIW........ Tyvek is not a vapor barrier - it breaths...... Tyvek only helps to stop the passage of free air........ which has a much larger molecule than water vapor. So if you really need a vapor barrier find something else to use. (Polyethelene Sheets work quite well). Rod

So is that just the fibe-rock for the outer mass, or is that a stucco finish outside? I´m planning to use some kind of render. I´m not sure if it´s stucco, but it´s something similar... Will you be using steel studs, or wood? Steel. I know that´s not ideal. But i´m doing it myself and it´s cheaper and easier. Total air space between masses again? 300 mm. The inner mass is a steel frame -filled with fiberglass- + 2 layers of 5/8 gypsum. "From your latitude and marine influence, I would think your climate is rather warm and humid" Yes, you´re right. I not sure about the typical relative humidity, but since the studio will be in direct contact with weather changes i think i´ll need a vapour barrier...

Once more - do you intend to air condition this space, or heat it in winter

No...

OK - one of the down sides of using steel in insulated walls with gypsum, is that it only takes 1/100 as much water retention to cause problems (mold, rot, etc) as it does with masonry; wood studs and wood paneling is in between in the amount of moisture that can be retained without problems. Where you won't be heating or cooling the space, there should be virtually NO moisture traveling through the wall, so just an outside air barrier (tyvek) should be all you need. What I WOULD do, however, is to get some Zinc Chromate primer in a spray can; when your steel framing is up, but before you put any panels on, spray all the joints and screw penetrations and places that were cut in any way, and let it dry; this will minimise corrosion where the insulation keeps moisture against the steel... Steve

Suppose Julián changes his mind in the future and decides to heat or cool the room... Wouldn't it make sense to construct with that possibility now? Upside, a little bit of effort and expense installing a vapor barrier. Downside, mold problems that will be nearly impossible to address.

If only ONE of the two choices were added back into the question, it would be fairly easy to say if (and where) such a barrier should be placed; where it's presently not under consideration, and BOTH choices (heating AND cooling) are added into the question, you can't win. If you heat the room, you will drive moisture OUTWARD through the wall. If you COOL the room, you will pull moisture INTO the room. IF you paint the inner wallboard with an OIL base paint, that would act as a vapor barrier which should ONLY be done if HEATING the room. In that case no OTHER vapor barrier should be in place. At least with NO vapor barrier, the wall would have a chance to breathe and DRY if it ever DOES get wet inside... Steve

Steve... after some research of availability of products here , i have 2 choices... http://www.eternit-ap.com/product/multi ... rd_nav.htm It´s not exactly this product, but is from Eternit too and is 15mm thick. Pretty much the same. The other option is the already-talked hollow bricks wall (unfilled and rendered only on the outer side). What should i do? If i go with the Multiboard -i planning to put some render on it- with steel frame, i can fill the frame with high density wool and achieve a 300mm air gap. The only reason i have to not forget about the hollow brick wall is, even that i know the theory of stay away from multiple leafs walls, i don´t know if using the Multiboard it would be enough to be my outer mass. IF using the room within a room system, which one should i choose? Hollow Bricks or 15mm Multiboard? I would like to play my drums without thinking about my neighbours.

I would like to play my drums without thinking about my neighbours. Julian, with your second floor terrace thing and without a high-mass floated floor to go along with a complete floated room, that's not gonna happen unless your neighbors are either hard of hearing or quite a ways away... Steve

Steve, i´m planning to float my entire room! (Following John´s SAE design) The outer wall (the one with Multiboard) is the weakest link of my chain... I would like to know your advice on my options... (described below) Anyway, i will do it -even if i can not play drums all day long-, so i´m trying to get the best of it... Thanks again!

Actually, your weakest link will probably be the floor; where it's not able to support enough weight to float a concrete inner floor, the low frequencies will tend to pass through the lighter floor that can be supported by your terrace. I checked out the Multiboard stuff, it sounds like what we call "Durock" or "Wonderboard" - it's heavy, which is good for sound. I think I'd use that plus the render for your outer leaf, with a 300mm air/insulation gap and 2 layers of 15mm gypsum you would see something like STC 70, with low frequency TL of around 40 dB. Keep in mind that any and all these are just "estimates", and will be severely affected by quality of construction - airtight is assumed in all cases... Steve

Thanks Steve! I just like to know how can i "translate" STC to real life. I think a drum can produce 100db... Does it mean that i´m dumping that sound to the half? It´s hard to me to imagine the final result... :?

"STC" does NOT translate to today's version of "real life" - it was developed for SPEECH isolation, not MUSIC, so it doesn't even CONSIDER anything below 125 hZ, and is centered around 500 hZ. Drums and bass have their main energy at or below the lowest frequency band that's even mentioned in STC calculation. The human ear requires approximately 45 dB to hear frequencies at 50 hZ; (this value changes depending on whose study you look at) http://www.phys.unsw.edu.au/~jw/dB.html Scroll down to the heading, Loudness, phons and sones Just below that, there is a chart of equal loudness values - note the lowest curve on the graph, called "Threshold of Audibility" - so 40 dB of TL at 50 hZ means that your sound level inside the room would have to be 85 dB at 50 hZ before a person standing right outside the wall would hear it at all. 110 dB (inside) at that low frequency would be a fairly low level sound outside, and probably wouldn't be audible by the time it gets to the property line, unless the houses are crammed together within 5-10 feet of each other; even then, if windows are closed in the neighboring houses I doubt they would hear anything... Steve

Amazing! Thanks StevE! I can´t believe how much knowledge you havE (and SHARE!) :wink: By far, the greatest forum i´d ever seen. Amen. 8)