Littlewater Studio - Norway (Europe)

[ask]

"A" is better, for sure. But Rod has pointed out that you might not be allowed to do that, due to the quirks of some building code regulations.

Cool, thanks! I'll check with my local code then

Btw, did you see my post and questions from June 17th regarding the Fermacell gypsum-fibreboards? Do you have any experience using other types of drywall like this?

Basically it's drywall made from 80% gypsum and 20% wood fibre and has a density of 1150 kg/m3. They come in 12,5mm and 15mm and are said to be equally good or better than two gypsum boards together.I'm thinking I could go for one layer of 12,4mm fibre gypsum and then a layer of 15mm fire rated plasterboard for the inner shell. Would that do the job? Does it matter in what order I place the two materials considering their density and weight?

Here's some more data if you're interested: http://www.fermacell.com/en/docs/130606 ... amends.pdf

Thanks!

-Andreas

[Soundman2020]

Basically it's drywall made from 80% gypsum and 20% wood fibre and has a density of 1150 kg/m3.

That's pretty good density. I think that should work fine.

- Stuart -

[ask]

That's pretty good density. I think that should work fine.

Ok, thanks. They do however only come in 2400mm x 600mm. Won't that be a problem when attaching them to the wooden studs 60 c/c considering that I should avoid seams overlapping for the second layer?

What would you consider good density? Would a 15.4mm thick fire rated plasterboard of 780kg/m3 also work okey?

Also, does the size of the drywall plates matter for better sound isolation? Is bigger plates better or does smaller plates mean less flanking across studs and more "freedom" for the plates to vibrate and absorb energy?

Thanks,
Andreas

[Soundman2020]

Ok, thanks. They do however only come in 2400mm x 600mm. Won't that be a problem when attaching them to the wooden studs 60 c/c considering that I should avoid seams overlapping for the second layer?

Turn the boards sideways for the second layer, and/or offset them by one stud. OR change your studs to 40cm OC instead, and offset by one stud.

What would you consider good density? Would a 15.4mm thick fire rated plasterboard of 780kg/m3 also work okey?

Yep, that would be OK too. But if you want to be certain, then you should do the math: calculate the MSM resonant frequency of your wall, and the isolation.

Also, does the size of the drywall plates matter for better sound isolation? Is bigger plates better or does smaller plates mean less flanking across studs and more "freedom" for the plates to vibrate and absorb energy?

The size of the panels makes no difference to how well they isolate. What matters is the density and the thickness. Thin drywall (less than 15mm) is too flexible for good isolation, the surface density is too low, the resonant characteristics are not so good, etc. As long as you are above about 10 kg/m2 on each layer, you should be fine. Use the equations to figure out how many layers you need, or rather, how much total mass you need. Other options include OSB, plywood, MDF, and even fiber-cement board.

- Stuart -

[ask]

Turn the boards sideways for the second layer, and/or offset them by one stud.

Great. Bought 2400x900x15.3mm plasterboards and will put them sideways.

What do you recommend to put between the separated windows in that 3cm gap between the frames? I guess it's a question of estetics while avoiding to create a flanking path between the two systems.

between windows.jpg

I guess the same goes for the space between the frames for the double doors?

in between doors.png

Thanks,
Andreas

[Soundman2020]

What do you recommend to put between the separated windows in that 3cm gap between the frames?

That's where you need to put your desiccant! At the bottom, at least. One way is to make a light-weight "tray" with Homasote and put the beads in there. Or you could try to cut a small "bed" out of a piece of OC-703, or something similar. You then wrap that with black cloth, and fit it across the gap. For the sides and top, just 703 wrapped in black fabric.

Some people glue those to one of the frames, and leave the other side floating freely, to avoid any possibility of flanking, but if you do it with 703 cut carefully to just the right size so it is a snug fit, then there shouldn't be any problems.

Same concept for the gap between the doors: 703 wrapped in black fabric, press-fitted into place, or glued on one side.

- Stuart -

[ask]

That's where you need to put your desiccant!...For the sides and top, just 703 wrapped in black fabric.

Good stuff!

So, hopefully a quick and easy question; I've made these back boxes for the electrical boxes in order to seal them as airtight as legally possible. Should I fill the air within this box with something (like fiber glass or hardening foam)?

back box.jpg

Thanks,
Andreas

[Soundman2020]

Should I fill the air within this box with something (like fiber glass or hardening foam)?

Naah, that's fine. But do put some insulation in the ends of the conduit after the wiring is in, then seal that with caulk. And also make sure to caulk the front face of the framing around that box just before you put the drywall on, to make sure you have a good seal there to, around the edge of the box.

- Stuart -