Sound deadening in floor

[akpolaris]

I am building an apartment above my shop. The floor joists are 2X10. I intend to use rockwool batts in the joists and cover with sheetrock. The joists have an assortment of plumbing and electrical connections running thru them. I cannot find rockwool 10" thick. Is it effective to use 2X8 or 2X6 material and leave a cavity against the floor or stuff insulation up against the flooring and leave a cavity against the sheetrock? Previous posts have commented on the expense of the product but also on the effectiveness. This will be on an interior application so there is no need for ay vapor barrier, correct? Thank you

 

[mike93lx]

Vapor barriers are used when you have a differential in heating/cooling. If the shop is kept at ambient and the apartment is climate controlled, you would want a barrier to prevent condensation.

I don't think filling the cavity will help. I'd use the largest size you can source and run that

 

[Denwood]

No vapour barrier needed. You could also blow in cellulose. DIY, much cheaper, and just as effective for noise, if not better if you dense pack. You can purchase insulation netting/fabric that you would fasten over the joists, then blow in.

If you want to take things up a considerable notch, use resilient channel and 5/8" type X for the ceiling. Or use two layers 5/8" type X (with or without resilient) with green glue between.

I've used a combination of these methods on several projects (with comparative sound reduction tests) and they work extremely well. Cellulose is very effective for noise attenuation..denser packs are better.

 

[Rusted Nut]

If you want sound deadening, hang the shop ceiling drywall on hat channel. Even better sound deadening would be two layers of drywall, with hat channel between the two layers. I would skip the rock wool and use fiberglass.

 

[RaisedByWolves]

If you want sound deadening, hang the shop ceiling drywall on hat channel. Even better sound deadening would be two layers of drywall, with hat channel between the two layers. I would skip the rock wool and use fiberglass.

Something like this.

You need to decouple the two surfaces (ceiling and floor) like you would if building a theater room or sound/listening room.

Staggered joists with the floor connected to the existing joists and additional joists between these with a 2" gap from the floor to suspend the ceiling.

 

[dfiler2]

I found 10" fiberglass at Menards and it has worked very well, however the area above is not heated. I used those little wires to hold the insulation in place until I got the ceiling in, several months later.


insulation

https://www.menards.com/main/building-materials/insulation/insulation-rolls-batts/r-30-ecobatt-reg-unfaced-fiberglass-insulation-batt-16-x-48/5001631/p-1444437014472-c-5780.htm?tid=-246518658720364909&ipos=8&exp=true

Wires

https://www.menards.com/main/building-materials/insulation/insulation-accessories/robinson-tech-insulation-support-wire/1611760/p-1444421524998-c-5776.htm?tid=6345655923624594657&ipos=2&exp=true

 

[billconner]

I'll assume you want to limit shop noise below getting into appartment above. Denwood and Rustednut have it. Not sure 8" Rockwood will do more than 4" but the double 5/8" gwb on resilient channels or on furring hung on result hangers (slightly better than channels) will help a lot. Also as much absorption in shop - tough in an "industrial" area but there are products.

Take it to extreme, double floor above. Subfloor, homasote, and subfloor (or carpet on homesite).

Also important, watch out for flanking patches. Any penetrations for conduit or pipes sealed with a non-hardening resilient caulk - butyl or an acoustical caulk. Try to avoid plastic drain pipes and especially ducts or flues.

 

[akpolaris]

So I am at the point that I will be insulating the floor next. I can't double up the flooring or do any structural or framing modifications. Doubling up on the sheetrock is a possibility but I don't know that I have the headroom for a "hat channel". The questions that I may not have articulated well is if the unfilled cavity between the floor and the insulation that I do stuff in there, is it a problem? Is there an echoe (of footsteps) above due to this cavity or how does the air cavity affect the transfer of noise from below? The rockwool is denser and provides a fire retardancy allowing the use of 1/2" rock rather than 5/8". I was opting for the rockwool rather than fiberglass for those reasons. Which goes back to the cavity of unfilled space in the floor joist. Stuff the joist full? Can I use a combination of fiberglass and rockwool to pack the space? of just use the 8" rockwool leaving a cavity up against the floor, or stuff it up to the bottom of the floor and leave the cavity against the sheetrock? There is plumbing and electrical throughout the framing so it isn't' just a matter of laying the batts in there. Dense cellulose may be an option but I need to rent the equipment and I am 120 miles from my supplier

 

[Rusted Nut]

Most of noise transfer comes through solid framing members, such as floor joists. Sound batts in the joist cavities will help, but you’ll get way more effect by decoupling as RaisedByWolves said. Hat channel is usually 7/8”. So if you add hat channel and an extra layer of 5/8”, you’re only loosing 1 1/4” of head room.

 

[mike93lx]

Even with resilient channel, you'll still hear some stuff.
I renovated a basement room in my last house at the beginning of the pandemic. Filled the cavities with rockwool (double layer) then resilient channel and two layers of drywall separated by a case of green glue. I was expecting a really quiet room and while I couldn't hear as much voices/TV noise, the kids banging toys on the floor still came through pretty well. Definitely an improvement, but I was not super happy, although my expectations were likely too high

 

[Zeke]

I wonder if that thin engineered flooring foam sheet placed between drywall sheets would be effective. One thing I know from windows is different thicknesses (Glass in this case) stops sound transfer better than like for like. IOW, use 1/2" drywall., foam and then 3/8ths.

 

[billconner]

Whether the cavity is stuffed full or only 4", Rockwood or fiberglass or cellulose, not sure you could hear the difference. Measure it probably. Resiliently mounting the drywall will be noticeable. It's just like 2 tin cans and a string. Pull it taut and you can hear. Slack and no sound transmits.

 

[theoldwizard1]

Rock wool is probably the best sound barrier there is, but it is expensive. A couple layers of 4" would be fine.

 

[billconner]

I wonder if that thin engineered flooring foam sheet placed between drywall sheets would be effective. One thing I know from windows is different thicknesses (Glass in this case) stops sound transfer better than like for like. IOW, use 1/2" drywall., foam and then 3/8ths.

If you could glue the drywall, sure, but driving screws into joists couples it rigidly.

 

[mike93lx]

I wonder if that thin engineered flooring foam sheet placed between drywall sheets would be effective. One thing I know from windows is different thicknesses (Glass in this case) stops sound transfer better than like for like. IOW, use 1/2" drywall., foam and then 3/8ths.

I bet a foam layer would help a ton

 

[mike93lx]

If you could glue the drywall, sure, but driving screws into joists couples it rigidly.

Use adhesive between the layer and screws to clamp then go back and remove the screws.

Bonus of no nail/screw pops to contend with down the road!

 

[Denwood]

No. Don’t glue or hard fasten a single layer to the joists. Think drum skin.

If you don’t have 1/2” to spare for resilient, hard fasten one layer of 5/8 type X drywall, then add another with Green Glue in between. HD stocks it. Code will likely require this fire separation anyway. Green glue does not dry, forming a viscoelastic dampening layer, similar to how acoustic drywall works. These are well tested and well documented methods.

As Bill has suggested, homasote on the floor above works. Underpad and carpet is very effective as a damp ending layer as well.

If you blow in cellulose (again every bit as good as rock wool and likely 1/4 the price) it will flow around wires and duct etc. HD does rent equipmemt but you’ll have to play a bit to approximate dense pack. In any case, fiberglass would be your last choice over cellulose or rock wool.

I posted progress and sound testing results of my theatre build here: https://www.avsforum.com/threads/measured-before-after-results-with-green-glue.2929668/

We are 100% happy with the results..and the basement is open to our first floor via an open stairwell. That build used rock wool, resilient and 2 layer drywall with Green Glue. My film studio (2nd floor, commercial space) , about 900 square feet, used dense pack cellulose 16” in the floor truss cavity. The entire ceiling of the main floor (4500 sq/ft) used 5/8” type X and cellulose which gave us the commercial fire rating. That was full of ducting, wire etc. cellulose was cheap and required far less labour. That studio was extremely quiet along with double walls, isolated HVAC etc.

Are there any HVAC connections between the spaces? If so, they will require some work first before you even think of ceiling work.