Author Topic: Impact noise from above and cannot touch underlayment. Never used hat or RC-1  (Read 3553 times)


  • Guest
I live downstairs in a ~90 year old house in Western NY in which I bought in 2015, and thankfully the house is decently quiet for its age and construction.  I am getting a good amount of noise (not bad by any stretch) but I'm willing to put down the effort the make sure noise is never a problem.

The floor in both units is original tongue & groove subfloor (tongue nailed to studs) and hardwood over it (nailed to tongue and groove).  It is far more valuable as a property to keep the hardwood and add area rugs which will help but they'll never have the muffling capacity of a solid underlayment.  I know this, but it limits my options.  I get lots of squeaks from either wood to wood contact or more than likely the nail to moving wood and then footfalls.

My ceiling is lathe and plaster.

I'm an engineer, and have been in plenty of plants where we hang VLM curtains around pumps and other noisy equipment in large open areas to control decibel level.  So I understand VLMs benefit for high frequency sounds.

My tests so far
So I went to Home Depot and saw what they had and picked up a package of rock wool (accoustic, no R value 3" thick) and shoved the bats up between the floor joists below my bedroom on one section of the room and then used construction adhesive at the top edge of the joist to try and "lock" it to the tongue and groove.

Results were as expected - the adhesive made almost no difference and the rock wool was AMAZING and cutting down music & speech.  I can still hear every footfall and the overwhelming majority of squeaks.  There is no ceiling in the basement.

My questions for the experts
I've heard one layer of rock wool vs 2 has a slight but noticed difference.  It's not major, but with 1 layer you either place the rock wool against the subfloor or against the ceiling below (better to have it against the subfloor?) while two layers nearly fills the cavity, eliminating pockets of air to vibrate.  Is this correct and the better choice?

I can then find RC1 locally.  I haven't found hat channel yet.  The only reason to use any channel is to isolate the drywall from the joists, and supposedly hat & clips works better, but I haven't seen any demos or videos comparing them.  No real world references or a "its x% better", just "it's MUCH better trust me".  Are there any good comparisons that I can show the wife?

RC1 isn't rated for two layers of 5/8 drywall from what I can see, nor is it certified from a manufacturer standpoint which makes me question its structural integrity in the first place.  Even if I used hat & clips, would two layers of drywall make that much of a difference over 1?  I haven't seen data or comparisons that convinced me it's worth it.  I understand the raw benefit of more mass, just no quantifiable data, and 5/8" drywall is pretty heavy.

I have heard of using "green glue" between two layers of drywall and somehow it performs better.  I could understand stud-clips-channel-VLM-drywall due to the mass of the VLM and higher density, but I can't see how a squirt of "magic caulk" works any better than any other to a quantifiable and repeatable result.  I've also seen plenty of complaints that green glue and two layers didn't work any better than a single layer of 5/8 drywall.   Has anyone tried putting VLM between the channel and drywall?

The room has a ceiling fan & light in the center.  As that's solidly mounted to the joists, is the best bet to leave a 1/8" gap around the penetrating electrical box (dropping the height of the box to meet the lowered ceiling) and then fill it with soft silicone when doing tape & mud (don't mud drywall to the box as it'd create a solid structural connection)?  Is there a product that's recommended for this purpose?  It'd get covered by the fan "medallion" that goes against the ceiling anyway, so an open gap would be hidden.  Is there any recommendation for the medallion and keeping it from becoming a hard structural connection?  I want to keep the fan & fixture there, so I'd be willing to replace the ceiling fan in this process...  the cost of a fan is nothing compared to the job as a whole.

I'm also in Western NY so I haven't found things like "quiet rock" or other pre-fabricated dual-layer 4x8 sheets at Home Depot or Lowes.  I'm not sure it's worth the benefit either as 5/8" is like $12 per sheet and the pre-fab stuff is like $50 per sheet if you can find it.

I plan to rip down the lathe & plaster and put up rock wool myself but I'll be paying someone to hang the drywall and do tape and mud cause it's a pain in the butt.  I know to tell them to NOT tape & mud to the walls and to leave an 1/8" gap along the walls and then have it filled with silicone.

Am I missing anything?

Randy S

  • Guest

You are pretty close to the money on this , give me a call and I will send you the data you are asking for and provide you with options that will improve the value of reduction.

Randy S.