Two layer drywall thicknesses

[archive]

From: ron_v0@y...
Date: Tue Mar 6, 2001 4:36 pm
Subject: Two layer drywall thicknesses

For a wall using RC channel mounted on studs, is it
better to have 5/8 and 1/2 inch drywall mounted or
5/8 and 5/8 inch drywall mounted. The first being
"unbalanced", the second having more mass.
I was hoping to block lower frequencies so, I'm thinking
the second a better option... maybe it doesn't
make much diffence?

Thanks.

[archive]

From: SRF7@a...
Date: Tue Mar 6, 2001 4:51 pm
Subject: Re: [acoustics] Two layer drywall thicknesses

In a message dated 3/6/01 11:38:41 AM Eastern Standard Time, ron_v0@y...
writes:

> For a wall using RC channel mounted on studs, is it
> better to have 5/8 and 1/2 inch drywall mounted or
> 5/8 and 5/8 inch drywall mounted. The first being
> "unbalanced", the second having more mass.
> I was hoping to block lower frequencies so, I'm thinking
> the second a better option... maybe it doesn't
> make much diffence?
>
> Thanks.
>

Hardly seems worth the trouble to have two sizes of drywall on a small job
... I'd just do it all in 5/8ths, less waste ... my $0.02

Scott R. Foster

[archive]

From: sjoerd@n...
Date: Tue Mar 6, 2001 7:27 pm
Subject: Re: Two layer drywall thicknesses

--- In acoustics@y..., SRF7@a... wrote:
> In a message dated 3/6/01 11:38:41 AM Eastern Standard Time,
ron_v0@y...
> writes:
>
>
> > For a wall using RC channel mounted on studs, is it
> > better to have 5/8 and 1/2 inch drywall mounted or
> > 5/8 and 5/8 inch drywall mounted. The first being
> > "unbalanced", the second having more mass.
> > I was hoping to block lower frequencies so, I'm thinking
> > the second a better option... maybe it doesn't
> > make much diffence?
> >
> > Thanks.

Scott seems to know the size of the job, I don't! So for what it is
worth, its better to use 2 different thicknesses, or the same
thickness but different densities, like for instance one layer of
"normal" drywall, one layer of fire rated drywall

[archive]

From: SRF7@a...
Date: Tue Mar 6, 2001 10:48 pm
Subject: Re: [acoustics] Re: Two layer drywall thicknesses

In a message dated 3/6/01 2:29:37 PM Eastern Standard Time,
sjoerd@n... writes:

> Scott seems to know the size of the job, I don't! So for what it is
> worth, its better to use 2 different thicknesses, or the same
> thickness but different densities, like for instance one layer of
> "normal" drywall, one layer of fire rated drywall

Not really ... I'm guessing ... its imaterial really ... I'm just commenting
on how things go wrong on the job when you give the installer too many
choices and too many ways to run out of something.

sjoerd is correct, differential materials work better .. that's a given ...
but since our choices were either both sides 5/8ths or 5/8ths and 1/2 I'm
not so sure that differentiation would offset the loss of mass, particularly
if LF loss is considered more important.

That said, even if the different flavor combo did work marginally better, if
we are cutting it close enough to worry that two layers of 5/8ths with one
row of RC won't do the job unless we switch to 1/2" on one of the layers ...
I'm thinking we need to beef the whole thing up ... because at best, changing
to 1/2" isn't going to help much.

Differential materials is a proven general design rule but I suspect the
effect would be small in the example cited (perhaps even a loss for LF
damping). Maybe we should think about adding a layer of OSB, or plywood
(well caulked) underneath the RC .. then the two sides are very different and
we've added quite a bit of mass for little cost.

You are stuffing this wall with insulation aren't you? Maybe you should give
us the run down on the entire wall system ... what kind of studs, insulation
scheme, etc.

Do you have a target STC?

Good Luck

Scott R. Foster

[archive]

From: ron_v0@y...
Date: Wed Mar 7, 2001 5:01 am
Subject: Re: Two layer drywall thicknesses

--- In acoustics@y..., SRF7@a... wrote:
> In a message dated 3/6/01 2:29:37 PM Eastern Standard Time,
> sjoerd@n... writes:
>
>
> > Scott seems to know the size of the job, I don't! So for what it
is
> > worth, its better to use 2 different thicknesses, or the same
> > thickness but different densities, like for instance one layer of
> > "normal" drywall, one layer of fire rated drywall
>
> Not really ... I'm guessing ... its imaterial really ... I'm just
commenting
> on how things go wrong on the job when you give the installer too
many
> choices and too many ways to run out of something.
>
> sjoerd is correct, differential materials work better .. that's a
given ...
> but since our choices were either both sides 5/8ths or 5/8ths and
1/2 I'm
> not so sure that differentiation would offset the loss of mass,
particularly
> if LF loss is considered more important.
>
> That said, even if the different flavor combo did work marginally
better, if
> we are cutting it close enough to worry that two layers of 5/8ths
with one
> row of RC won't do the job unless we switch to 1/2" on one of the
layers ...
> I'm thinking we need to beef the whole thing up ... because at best,
changing
> to 1/2" isn't going to help much.
>
> Differential materials is a proven general design rule but I suspect
the
> effect would be small in the example cited (perhaps even a loss for
LF
> damping). Maybe we should think about adding a layer of OSB, or
plywood
> (well caulked) underneath the RC .. then the two sides are very
different and
> we've added quite a bit of mass for little cost.
>
> You are stuffing this wall with insulation aren't you? Maybe you
should give
> us the run down on the entire wall system ... what kind of studs,
insulation
> scheme, etc.
>
> Do you have a target STC?
>
>
> Good Luck
>
> Scott R. Foster
>
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]

Thanks for the info thus far!

I'm attempting to reduce the sound coming from an exterior wall
in a room in my house. Not too far away is a railroad track -thus
the desire for a low frequency barrier.

I'm hoping to get an STC of >55.
Thus far the wall system consists of:

siding(LP)/OSB(1/2")/MineralWool(5")/2x6studs/RC channel/drywall(5/8)

It's already much better than the orignal wall, but I was going for
the maximum possible with this setup. I'm going to have to replace
the siding in the near future. Should I have another layer of OSB
added to the outside?
Any other hints are appreciated. Thanks.

Ron

[archive]

From: SRF7@a...
Date: Wed Mar 7, 2001 5:05 pm
Subject: Re: [acoustics] Re: Two layer drywall thicknesses

In a message dated 3/7/01 12:04:17 AM Eastern Standard Time, ron_v0@y...
writes:

> in a room in my house. Not too far away is a railroad track -thus
> the desire for a low frequency barrier.
>
> I'm hoping to get an STC of >55.
> Thus far the wall system consists of:
>
> siding(LP)/OSB(1/2")/MineralWool(5")/2x6studs/RC channel/drywall(5/8)
>
> It's already much better than the orignal wall, but I was going for
> the maximum possible with this setup. I'm going to have to replace
> the siding in the near future. Should I have another layer of OSB
> added to the outside?
> Any other hints are appreciated. Thanks.
>
> Ron

Is the wall your weak link at this point? LF rumble is notorious for taking
flanking paths ... like through your slab and through the frame of the
building into the ceiling. Would a beefier ceiling or a slab decoupler help
more than adding to the wall?

If you are sure your your wall is the weak link, are you considering a new
exterior for only acoustic purposes, or is it a job that must done anyway
(due to rot or termites etc.?) .... If the existing siding is in good shape,
it might be cheaper and easier to focus on the interior. Adding improvements
to the exterior is tough because you don't want two vapor barriers to create
an unvented space which could trap water vapor .. thise means exterior of the
VB you must vent to the soffet / attic ... this factor doesn't come up on
the inside where you can seal air tight to your heart's content.

If you must do work on the exterior siding however, you might as well make
the most of it. I'd do this job first in that case and see what kind of
results I got before doing more to the inside (after beefing up the outsdide
of the wall you may find that your floor or ceiling is the weak link.

If this is to be an outside job, then the first thing I'd think about (after
ripping the rotten siding off) is sealing every crack and cranny in that
existing OSB layer and putting some form of highly effective vapor barrier to
make sure that the wall was aboslutely air tight ... if feasible a bit of
mechanical decoupling betwixt the OSB and the new siding would be a good
thing also.

I might use a closed cell foam board like Tuff-R which has a tough plastic
outer skin so when the edges are well caulked its pretty well sealed ... I
won't say air tight, but pretty darn close ... it also has a foil inner skin
which serves as a radiant heat barrier. The stuff is easy to work with and
reasonably priced, I used simplex nails (the ones with washers attached that
like to lay around the job pointy side up so you can step on them) to nail it
up. I also put a bead of caulk along each board edge after it was tacked up,
and then butted the next board to it to insure a good seal ... a bit messy
but it worked.

On the exterior I would look for a material with mass that could be easily
sealed ... a board and batten approach might work well. You might consider
putting RC or hat channel horizontally on the outside and hanging the panel
siding on that .. caulk the gap then cover the seam with a 1x batten .. stain
to tatse. You would need to seal the bottom well to make it work ... maybe
a pressure treated 2x at the bottom just a hair thinner that the channel that
you can double bead caulk as each panel goes up. Always use a caulk which
does not get stiff so that the seal can flex, acoustic caulk is best.

Sealing the top would be problematic as you would want the air gap exterior
to the VB to vent through the soffet into the attic to keep it from trapping
water vapor in the wall.

Is the old siding shot? Could you install something over the existing and
build a new soffet? That might be the cheapest way to get the wall density up.

Good Luck

Scott R. Foster

[archive]

From: ron_v0@y...
Date: Thu Mar 8, 2001 5:49 am
Subject: Re: Two layer drywall thicknesses

--- In acoustics@y..., SRF7@a... wrote:
> In a message dated 3/7/01 12:04:17 AM Eastern Standard Time,
ron_v0@y...
> writes:
>
>
> > in a room in my house. Not too far away is a railroad track -thus
> > the desire for a low frequency barrier.
> >
> > I'm hoping to get an STC of >55.
> > Thus far the wall system consists of:
> >
> > siding(LP)/OSB(1/2")/MineralWool(5")/2x6studs/RC channel/drywall
(5/8)
> >
> > It's already much better than the orignal wall, but I was going
for
> > the maximum possible with this setup. I'm going to have to replace
> > the siding in the near future. Should I have another layer of OSB
> > added to the outside?
> > Any other hints are appreciated. Thanks.
> >
> > Ron
>
> Is the wall your weak link at this point? LF rumble is notorious
for taking
> flanking paths ... like through your slab and through the frame of
the
> building into the ceiling. Would a beefier ceiling or a slab
decoupler help
> more than adding to the wall?
>
> If you are sure your your wall is the weak link, are you
considering a new
> exterior for only acoustic purposes, or is it a job that must done
anyway
> (due to rot or termites etc.?) .... If the existing siding is in
good shape,
> it might be cheaper and easier to focus on the interior. Adding
improvements
> to the exterior is tough because you don't want two vapor barriers
to create
> an unvented space which could trap water vapor .. thise means
exterior of the
> VB you must vent to the soffet / attic ... this factor doesn't
come up on
> the inside where you can seal air tight to your heart's content.
>
> If you must do work on the exterior siding however, you might as
well make
> the most of it. I'd do this job first in that case and see what
kind of
> results I got before doing more to the inside (after beefing up the
outsdide
> of the wall you may find that your floor or ceiling is the weak
link.
>
> If this is to be an outside job, then the first thing I'd think
about (after
> ripping the rotten siding off) is sealing every crack and cranny in
that
> existing OSB layer and putting some form of highly effective vapor
barrier to
> make sure that the wall was aboslutely air tight ... if feasible a
bit of
> mechanical decoupling betwixt the OSB and the new siding would be a
good
> thing also.
>
> I might use a closed cell foam board like Tuff-R which has a tough
plastic
> outer skin so when the edges are well caulked its pretty well
sealed ... I
> won't say air tight, but pretty darn close ... it also has a foil
inner skin
> which serves as a radiant heat barrier. The stuff is easy to work
with and
> reasonably priced, I used simplex nails (the ones with washers
attached that
> like to lay around the job pointy side up so you can step on them)
to nail it
> up. I also put a bead of caulk along each board edge after it was
tacked up,
> and then butted the next board to it to insure a good seal ... a
bit messy
> but it worked.
>
> On the exterior I would look for a material with mass that could be
easily
> sealed ... a board and batten approach might work well. You might
consider
> putting RC or hat channel horizontally on the outside and hanging
the panel
> siding on that .. caulk the gap then cover the seam with a 1x
batten .. stain
> to tatse. You would need to seal the bottom well to make it
work ... maybe
> a pressure treated 2x at the bottom just a hair thinner that the
channel that
> you can double bead caulk as each panel goes up. Always use a
caulk which
> does not get stiff so that the seal can flex, acoustic caulk is
best.
>
> Sealing the top would be problematic as you would want the air gap
exterior
> to the VB to vent through the soffet into the attic to keep it from
trapping
> water vapor in the wall.
>
> Is the old siding shot? Could you install something over the
existing and
> build a new soffet? That might be the cheapest way to get the wall
density up.
>
>
> Good Luck
>
>
> Scott R. Foster
>
>
> [Non-text portions of this message have been removed]

I believe the wall is the weak link in my case. I mentioned the
exterior since I have LP siding (Louisana Pacific) which is has
know problems here in the West. Many class action suits have forced
LP to replace siding at their cost. The house is only 5 years
old with LP LAP siding. The siding is showing signs of problem
so I'll be replacing it in the near future. I appreciate your
suggestions and will look into some of them to see if they
might work. One possible problem is that the room is on the
second floor which will make it a bit more tricky (or expensive).

Thanks,
Ron

[archive]

From: SRF7@a...
Date: Thu Mar 8, 2001 1:02 pm
Subject: Re: [acoustics] Re: Two layer drywall thicknesses

In a message dated 3/8/01 12:50:11 AM Eastern Standard Time, ron_v0@y...
writes:

> I believe the wall is the weak link in my case. I mentioned the
> exterior since I have LP siding (Louisana Pacific) which is has
> know problems here in the West. Many class action suits have forced
> LP to replace siding at their cost. The house is only 5 years
> old with LP LAP siding. The siding is showing signs of problem
> so I'll be replacing it in the near future. I appreciate your
> suggestions and will look into some of them to see if they
> might work. One possible problem is that the room is on the
> second floor which will make it a bit more tricky (or expensive).
>
> Thanks,
> Ron
>
>
>

Ah yes the old LP curl ... we've had similar cases here in Florida. If there
is insurance / settlement money involved you want to look at "Hardy Board" or
something similar ... it's a cement board that can be had factory primed,
painted or stained ... most examples I have seen are lap siding, but I think
there is variety in the product line ... the stuff aint exactly inexpensive,
but if there is to be cost participation your expense might be fairly
reasonable. If you could figure a way to get it sealed up tight it ought to
work great.

It's very high density and if facotry painted comes with something like a 30
year guarantee not to need repainting. Come to think of it Cement board does
come in sheets ... its used as backer board in shower stalls etc ... very
high density ... bitch to cut ... but might just be the ticket for you use
... sold under brand names like Durarock, etc.

Good Luck

Scott R. Foster

[archive]

From: SRF7@a...
Date: Thu Mar 8, 2001 1:49 pm
Subject: Re: [acoustics] Re: Two layer drywall thicknesses

In a message dated 3/8/01 12:50:11 AM Eastern Standard Time, ron_v0@y...
writes:

> One possible problem is that the room is on the
> second floor which will make it a bit more tricky (or expensive).
>
> Thanks,
> Ron
>

Another thought ... brick.

Scott R. Foster