Helping a mate

[JohnGardner]

I have a friend who is part way through constructing a practice room and he wants to use 13mm "soundline" gypsym board. This retails at $40 per sheet. I have told him he is far better to use 1x10mm standard gypsm board and 1x13mm standard gypsm board, total combined cost $38.
He will save a few bucks, get thicker leaf (23mm verse 13mm) in his construction and better isloation if all joins are sealed.

Am I correct in the above?
Should he glue and screw or just screw these togeather?

His existing wall he is attaching this board too is 13mm cladding on the outside and a 2x4stud filled with R18

JohnG

[cadesignr]

$40 a sheet? HOLY MOLY At that price it should keep out the sound of a 747 50' away and install itself BTW, what makes "soundline" any different than standard gypsum drywall? I think your suggestion is good though, unless the STC or whatever rating the "soundline" uses, is equal or near the use of two seperate panels. If it does, saving $2 for the same square meters doesn't make sense, because of all the extra labor it takes to install, caulk, and tape a second layer. But if the rating is way below the use of 2 layers, I'd say go for it. My .02 only though.
fitZ

[knightfly]

I've seen spec sheets on several different versions of this "designer" gypsum - I've yet to see any reason for spending that much money. As to your pricing on the standard gypsum; have you shopped around, or is that REALLY how expensive gypsum is in NZ? Sorry, but 15mm runs $6.70 USD per 4' x 8' sheet at my local building supply, so I'm always dismayed at costs elsewhere.

As to "magic bullets", the main thing you want for sound wall construction is MASS, pure and simple; more mass, more isolation. Wider air/insulation gap, more isolation.

If your mate wants decent isolation, I'd suggest more like at least 1 layer each of 12 and 15mm on each side of a 2-leaf wall; if that's just too expensive, maybe the wall's inner and outer leaves can be separated more? This would help the thinner wallboard do a better job of isolation.

Fasteners - screw each layer separate, use half the normal schedule on fasteners for the base layer then use full schedule for the face layer. You can download this

http://irc.nrc-cnrc.gc.ca/irc/fulltext/ir761/ir761.pdf

For a good guide to fastener spacing - this is covered at the first of this report, followed by tests of 350 different wall assemblies done over a few years.

If your mate wants much isolation, he should NOT fasten the new wallboard directly to the studs assuming it's a single frame wall; instead, first putting Resilient Channel on the frame and THEN the two layers of wallboar will give better results -

Make SURE you get REAL Resilient Channel though; I just had to tell a member in another forum that he'd paid for RC and got plain HAT channel, once he posted pix of the work in progress; I recommended he get a lawyer, as this is making him crazy; he's getting at least 9-10 dB worse performance than if it had been done right. It pays to ask us on things like this BEFORE you close everything up and finish the job.

Hope this helped... Steve

[JohnGardner]

Steve,
thanks again.
Gypsm prices do suck down here, thats what you get being two small islands in the middle of nowwhere! .5/8 is $45US equivilent a sheet, thats why I keep asking questions about 10mm and 13mm, thats our standard and the cheapest by far!!
I let him know about the RC and he thinks he will go for that option.
Thanks again
JohnG

[knightfly]

Jeez, Louise; $45 a sheet - I'm gonna buy a big boat and smuggle gypsum...

Do you have any OTHER building materials there that are high mass but REASONABLE? How much is concrete per cubic yard/meter, delivered? What about concrete blocks, bricks, etc? Man, there must be SOMETHING that's cheap mass for you guys... Steve