Soundproofing Over an Old Wood Floor?

If height and cost is no issue, then I would put down a rubber mat (or other resilient product intended for sub floor sound control), two layers of OSB with a green glue sandwich floated on top of the rubber. Then a layer of flooring sound control underlayment intended for hardwood floors and then the new hardwood. Not an expert just a guess. I do know that Green Glue between MLV and plywood is not an appropriate use of GG.

My understanding of MLV is that it works best hanging in an airspace, but there are other cheaper methods.

Zina, per your request, I've reposed my reply from that other thread:


Plywood: No - use MDF instead - same cost, but MDF is more dense, and is better at assisting in transmission loss.

MLV: Bad for a flooring application. It is substantially more costly than other solutions. MLV has its place - but constrained in the floor is not one of them.



EASY: Place a layers of QuietWood on the existing floor, then your new wood flooring.

but Cheaper and probably more effective than quietwood: Use green glue over the existing hard floor, then a layer of 5/8" MDF, then Acoustitech underlayment, then your new wood floor.

Looks like this:

wwwwwwwwwwww Shiny new wood floor
--------------------- Acoustitech underlayment
XXXXXXXXXXXXXX 5/8" or thicker MDF
________________ GREEN GLUE (3 tubes per 4x8 sheet of MDF)
[[[[[[[[[[[[[[[[[[[[[ EXISTING FLOOR


Acoustitech: http://www.finitec-inc.com/EN/floating.asp


However, you need to consider that much of the sound transmission is NOT through the floor, but flanking, thought the walls - the structure borne sound from below radiates not only through the floor, but your walls as well.

Consider applying greenglue and a layer of drywall over your walls as well.


Good luck,

ANdy

before doing any work I'd be making sure the floor joists can support the excess weight..

The project requires a reduction of airborne noise from below, however you can only treat the floor above.

Clearly treating the ceiling below would be much more effective, since that would reduce the vibration entering the original framing. Once in the floor framing, vibration will be entering your walls, since that floor framing is holding up your walls.

This is an airborne concern, so a resilient mat and MLV have much less utility. Decoupling isn't the goal in this case. Also, you'll essentially be introducing a small Triple Leaf. This isn't at all an optimal situation, however I'd focus on simply adding as much damped mass as possible.

In my opinion, MDF in a floor could be asking for trouble, as it can swell considerably more than standard OSB if soaked in water. Consider layers of cement board if there is a practical limit on the height you can add.

No, foam is not particularly good for suppressing transmission. MDF is a high mass, rigid solid, which is damped using green glue. To suppress transmission, you need MASS and DAMPING.

Foam is a low mass, and will do next to nothing in terms of transmission loss.



The "Acoustitech" I mentioned is a rubber mat, intended for sound control.

I prefer MDF over OSB - MDF is denser, stiffer.

One of the selling points of OSB is that it is lightweight - this is NOT a good thing for sound transmission - you want MORE WEIGHT - MORE MASS, not light-weight materials.

And yes, MLV and GreenGlue are NOT a "correct" combination of materials.

GreenGlue is a viscoelastic material for developing a "constrained layer damping" configuration. For this confirmation, you need two still layers of mass, and the green glue between them - the green glue damps the mechanical vibrations and turns them into shearing forces, where they dissipate as heat energy.

MLV is most certainly not "stiff", so I don't see it working correctly - also, MLV is SUBSTANTIALLY more expensive per pound than other mass types, like drywall or MDF.




Floors - even old ones - are designed to handle *dynamic* loads, such as people walking around.

A single layer of MDF underlayment is a static load, and a static load of only 2 to 4 pounds per square foot ( depending on thickness).

A person standing still represents a much greater static load - a typical 170 pound person standing on a 1 square foot area represents 170 pounds in that square foot. Lets say the floor joists are spanning a 14' wide room, and are spaced 16" apart, such that a single person would represent a load over the area of 16"x14' (about 19 square feet) then that single person represents a static load of about 9 pounds per square foot.

However, that is static. people walk, meaning that a floor needs to withstand a dynamic load, which is substantially greater. And in fact, a dynamic load of several people which can easily exceed 100 lbs per sq ft (depending on floor stiffness). As such, the addition of a couple pounds of MDF is not significant to the total load carrying capability of the floor.

In fact, the addition of a green glue layer will add dampening, which will actually INCREASE the ability of the floor to withstand dynamic loading. (more damping means greater deceleration means lower dynamic loading.)

See also:

http://www.nrc-cnrc.gc.ca/obj/irc/do.../nrcc26485.pdf



I wouldn't be too concerned about green glue seeping - it will dry to a rubbery compound. If you really want to dampen noise, you could go further by using 2 layers of MDF and acoustimat (note you only need 2 tubes of green glue per sheet in this configuration):


wwwwwwwwwwww Shiny new wood floor
--------------------- Acoustitech underlayment
XXXXXXXXXXXXXX 1/2" or thicker MDF
________________ GREEN GLUE (2 tubes per 4x8 sheet of MDF)
XXXXXXXXXXXXXX 1/2" or thicker MDF
- - - - - - - - - - - - Acoustimat (A cheap thin foam underlayment)
[[[[[[[[[[[[[[[[[[[[[ EXISTING FLOOR



Quietwood is good for airborne noise as well - but you will see it is more expensive than the GG/MDF plan I outlined.



Cheers

Andy


EDIT: Looking at the relative costs of OSB to MDF, I see the value of using OSB - though I might mention that looking at prices for 1/2" wonderboard cement board, that is looking more attractive - 56 cents a sq ft, vs OSB's 43 cents a sq ft - and Wonderboard is much denser, stiffer.

If footfall noise isn't an issue (it isn't in this case) then I would avoid compressible layers. Any compressible layer, whether an air cavity or a foam or solid rubber mat, will create a bit of a triple leaf effect. The compressible layer will have a new resonance point we don't want.

If footfall noise were an issue, then the slight decoupling associated with a resilient mat layer is an acceptable trade. If no footfall noise, then no need for a compressible layer. Stick you damped mass as Andy suggested.

There seems to be some controversy on this point.

OSB does itself swell. And particle board swells up like a sponge - yet particle board is routinely used as underlayment.

MDF is superior to particle board in terms of water resistance. And water resistant and sealed grades of MDF are available.

The OP mentioned he was putting down hardwood flooring on top, and so I mentioned using acoustitech on top of the MDF, and this is a moisture barrier.

I suppose I like MDF simply because it is two to three times as dense as OSB for a given thickness.

When using MDF as flooring, I'd see using a rubber caulk at all edges and seams, partly for decoupling, but also for sealing the edges. I should think that covering the mdf with a primer sealer will prevent moisture based problems.


On the other hand I see the modulus of elasticity for MDF is lower than OSB - so OSB is stiffer. But both OSB and MDF are less stiff than concrete, and I was just looking at the specs for cements boards like AQUABOARD, DUROCK, and PERMABASE

interesting: Similar density to MDF, yet as it is cement board, it is substantially stiffer - and Aquaboard or Permabase can be cut with a "score and snap" method.

And as the costs for these boards seems to be in the same ball park as OSB or MDF, well, it seems like it's a better way to go...

Certified underlayments are not standard particleboard for that reason. Standard particleboard is used in cabinetry, etc, but not floors. OSB will swell far less than MDF, and so is used as standard underlayment.


If compressible, it's not optimal in this application, but really, a moisture barrier isn't necessary IMHO.


I believe OSB is dramatically less than MDF. But if it were the same price, I'd certainly use it, since it is denser as you say.


7/16" OSB has been seen at $4 a sheet. I'm not thinking that MDF and cement boards close to that, but I haven't done a shop on either MDF or cement board lately.

In any event, the added mass is great if affordable and durable.

myndex, it don't matter how good the floor is, if the floor joist's rotten under the current floor boards you don't want to be having the floor fall out from below you with the excess load of new flooring and so forth...

being it is a 100+ year old building I would expect some damage to the floor joists..

which will likely need replacing before construction starts..

At $4 a sheet, that's a great price - The pricing is/was substantially higher at a few outlets here in LA - I'll shop around some more - I have not seen anything even remotely that cheap here. If the price is that much lower, then indeed I'd go with 2 layers of OSB and GG instead.

As always, thanks for your insights.


A

RE: OSB vs MDF vs WONDERBOARD


I was just at Home Depot, checking out supplies - I see their current prices on OSB vs MDF has OSB at about half the price of MDF (though with OSB being about half the density, I suppose it is a wash in terms of dollars-per-mass).

But interestingly, they had 1/2" wonderboard at nearly the same price as OSB. And wonderboard cement board is dense and stiff.

Andy


See also:

http://www.kineticsnoise.com/arch/pdf/soundmtt.pdf

An underlayment resilient mat, used in conjunction with wonderboard.

Does anyone have data or rationale why a mat would have value incorporated in a floor system where footfall noise is not an issue?

The specific mat I mentioned in the above post is a viscoelastic from kinetics, which they are promoting as a damper - i.e. as an "instead of" green glue.

I should have been more clear on that point.

Andy

Thanks for that clarification. Many mat / MLV suppliers contend they are visco-elastic. Sort of a trendy buzz phrase. While most things could be defined as viscous and elastic, their capacity to damp is what's relevant. Pads don't damp nearly as well as a semi-liquid paste.

The reason is the pad damping layer is too thick and not intimately bonded to the panels. A liquid seeps into the panel pores to dry very bound. This yields higher sheer force and therefore damping.