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Help! Isolation Possible Between Basement Ceiling Joists?
Old 1 week ago
Here for the gear

Help! Isolation Possible Between Basement Ceiling Joists?

Please help! Reaching out to your collective expertise to please tell me I'm not wasting a collosal amount of time and hard work.

I've read over 30 threads on this forum topic and while some have come close to containing a solution to my situation – I fear in my derivation and interpretation, I'm likely to get it wrong.

I have a confined 500sf music area in my basement of a 1950's house I just bought. I am doing all the remodel myself. Nothing professional level, but we do record and rehearse in this space - and watch TV and listen to music over surround speakers. My daughter's room is directly above, and I can talk to her straight through the ceiling, and she yells (mocking an old person) "turn down that racket down there..." lol So my immediate ASAP focus is minimalizing sound transmission through the ceiling - is that 'isolation'? I don't know, I am overwhelmed in terms on this topic and don't want to assume. I am not trying to cancel out things like the drumkit or amplified guitars, all bets are off there-- I'm strictly focusing on sounds produced when listening to moderate volume of music from the surround speakers or watching a movie with surround sound system on. Had I more ceiling headroom to sacrifice, I would jump straight into MSM with decoupling approach which seems to be the overwhelming winner of a solution, but I don't, so I can't. I need next best alternative for maximum efficacy *between* the joists. Hence the problem. No firm answer on that. And maybe because the answer is that without decoupling, achieving a reduction of 30-40dB's is a pipe dream.

Using what I'm sure is a fairly inaccurate approach, I used a phone app called "SoundMeter" that uses my phone mic to measure in dB(spl) -and the level of sound I wish to cancel out in both bedrooms above the music room measures between 35 and 45 dB -- first of all, does that equate to STC 35-45? Or some other STC level? I read somewhere on this forum that before you devise your isolation system, you should first measure and quantify what it is that you need to achieve. So I interpret this reading as saying that I need to find a way to prevent 35 to 45dB from escaping the room below - is this accurate to say? So I have no idea if that means a constructed system rated at an STC equivalent to the dB readings from my measurements of sound escaping to the upper/ground level? I know STC measures how well a product/system prevents sound from leaving a room - but I don't understand how to traverse from dB measurement>>>> to adequate STC design.

I am not concerned with noise reaching outside of the house. The basement is thick concrete and solid brick foundation/walls, and right now, if I stand directly outside the basement window well, I could barely hear an electric guitar wailing at 11. Not to mention my new next door neighbor is a drummer and so we both have the hand-shake agreement not to call the cops on each other. ;-) So this is all focused on internal noise transmission loss.

The room is roughly 500 sf-- 15 foot by 30 ft. rectangle. It is partitioned off from the rest of the basement by 1/2” solid pine wood paneling. When I close the door to the room, it's not open to any other room. The outer/foundation walls are concrete but two exterior walls are lined with 2x4 wall studs that separates the foundation walls from the ½” solid pine wood paneling. No drywall, no insulation.

**Here are the ceiling details: I removed TWO layers of acoustic ceiling tile, both layers damaged in various sections. The lowest layer was 5/8" suspended USG acoustic tiles rated at .55 NRC (water stains, broken rails) and then a 2nd layer of 1950's (no asbestos/tested negative) 1/2" thick cellulose acoustic tiles at .50 NRC that were stapled to furring strips going across the bottom of the studs.

Not only was the ceiling layer damaged, it was LOW! LOW! Like "Gandolf-Crouching-In-Bilbo's-House" LOW! When I removed the 1st layer of ceiling, you can see 4" of ceiling height gained from the paint line above. Now I feel I can breathe in this room. The height from floor to the bottom of the studs is 7' 1" and 7'11" to the ceiling/floorboard above. I'm very tall and now that I finally feel comfortable standing up in the room, I can't sacrifice any head room to do RC clips or decoupling. The ceiling now is 2 layers: 1" x 6" solid oad wood boards/subflooring and finished off with 1/2" solid oak hardwood flooring. The hardwood is original and was installed in the 50's with no liner in between subfloor and hardwood above. The ceiling studs are 2" x 10" wood joists spaced 16" on center.

The first thing I have done after removing electrical fixtures (and temporarily capping off wires) is to wrap any exposed pipes with 1" thick foam, including any PVC pipe. The PVC I then intend to wrap with an additional layer of MLV because I read many reviews that said doing so effectively killed the PVC water drain sound dead in their tracks. The 1" foam wrap has already made a huge difference. Then I have "filled the gaps" as many of the threads here have recommended. I have recently just finished filling EVERY single crack between EVERY single baseboard across the entire space with Sashco Big Stretch sealant. first I filled gaps exceeding ¼” with Backer Rod foam strips because backer rod is WAAAYYYY less expensive than filling sealant into 900 linear ft worth of 1/2" thick gaps (30 boards that are 6” wide with 1/2" gaps that are each 30ft long) at $6-7 per tube. The job required 18 tubes of Big Stretch and 5 bags of small backer rod. I also sealed the perimeter. So basically, if there was a joint, I sealed it. I can't do anything about the two heating vents. Tried both the white and clear formulas of Big Stretch. The white is less 'drippy' and stays in place (a relief when applying something inverted over a carpet) the advantage of the Clear however, is that it applies milky white but then dries clear as the bond finally starts to form. The cool thing about that is that I can monitor the progress of the bond setup -- and right now it's taking about a 4 days for the sealant to turn 100% clear. So the last section of ceiling I just finished last night won't be ready for my "next steps" until this upcoming weekend.

***NOW*** here is my question. The only place I even came close to gleaning a recommended solution for BETWEEN the joists (meaning- not to the end of the studs, but rather up in between the joists) are bits and pieces of 1 or 2 topic threads on this forum. So two posters on this forum mentioned affixing two layers of gypsum 5/8" drywall DIRECTLY to the floorboards of the ceiling between the joists. THEN loosely filling the gap next with an R- layer of pink fiberglass insulation. I shopped Owens R-13 fiberglass faced batts which is 3.5" thick. From what I read I should apply the insulation so that it does NOT pack in up against the 2-layer drywall, but rather leave an inch or two of air space between the drywall and the insulation. Then beneath the insulation I should install a THIRD layer of 5/8" drywall. Since I need a way to fix the final/outer layer of drywall in place, I intend to re-purpose the furring strips I salvaged and nail them to either 'inside' of each joist as a "cleat" so that I can screw the drywall into the bottom of each furring strip. ALL of this layered system will exist between the joists and will not exceed 6" from the floorboard ceiling. I am seriously considering cutting into 15" strips the 72 boards of 2ftx4ft 5/8" thick USG acoustic boards I have salvaged since they seem to have a decent NRC/sound absorption rating of 0.55 and adding that as the final outer layer as a sound absorption layer.

So here is my question -- is this all a colossal failure???? I mean, if I still have exposed studs and don't have a decoupled MSM system is this basically like adding a Twin outboard motor to a boat with a 5-foot hole in the hull? Can I achieve my goal of severely reducing the level of music that can be heard above the basement in the bedrooms above?* In other words, can I still find a way to muffle out those 35-40dB's without a decoupled system? Should I add a layer of MLV to the ceiling? Is there any hope? Many many thanks for any thoughts, corrections, recommendations
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Old 1 week ago
Lives for gear
Jason Foi's Avatar

I skimmed your post quickly and did not take in all the details of your situation, but i will give some advice based upon what i did read.

What you propose, just beefing up the floor between joists will leave you at the mercy of the mass law. Basically, for every doubling of mass, you gain a 6db reduction in noise levels. So, if your floor was one layer of drywall, and you wanted to gain an additional 30db of isolation you would have to double the mass 5 times. Thats 33 total layers of sheetrock thick. Not gonna happen.

Your best bet would be to add several layers between the joists, add insulation, add hat channel with isolation clips, and another few layers of drywall. This will only work with airborne sound transmission. If the sound is traveling through the walls and into the structure, all bets are off. So, decouple all sound sources before they can transmit energy to the structure.
Old 4 days ago
Here for the gear

Thank you Jason, you are always helpful in your replies. I will take your advice on most points. On the RSIC clips, I can't devise a way (yet) to incorporate them, but I am looking into of design catalogs online for different floor/ceiling assemblies. They must go above the stud line or none at all.

Started researching some very interesting articles on CLT ceilings and Mass Timber construction and soundproofing, along with a good link to the ceiling/floor assemblies in case anyone is interested. Acoustics and Mass Timber Construction. The article contains a link to CLT assemblies and STC ratings. I am interested in this because several of the challenges of what I face are mentioned in Mass Timber design.

It mentions decoupling in the form of certain membranes. This notion sparked an a-ha moment as I am DIY light construction person and have flipped many homes and have done all the foor tile work myself. Out of roughly 20 rooms I have tiled, i have used an amazing uncoupling membrane called Schluter Ditra. It is marketed as an uncoupler mechanism and I can vouch in floor applications it is very effective. It is a waffle system and it is very expensive but always worth the investment.

It dawned on me that if I cannot find a place for RSIC clips/hat rail, that I might incorporate the Ditra uncoupler membrane in its stead. I know this is not an equivalent, but I do feel it will be better than zero decoupling mechanics.

I plan to just start layering up and take my dB readings between each step.

Right now, I am considering an "inverse" design of assembly between the joists:

-Ditra uncoupler membrane between the floorboards/ceiling and the double-drywall layer

-double 5/8" drywall

-R-13 insulation

-potentially a layer of MLV (depending on where the readings are) attached to the insides of the studs between joists and allowed to remain limp between joists

-3rd layer of drywall which I will support with cleats (furring strips on either inside of each joist)

-outer layer of the 5/8" USG acoustic tiles that I salvaged when I removed the suspended ceiling.

So since I don't see many results posted on this (exposed ceiling design), I will update this thread as I progress. If it is a failure, hopefully I can provide results for others to assess in their own research.

Last edited by LauraAnna; 4 days ago at 03:17 PM.. Reason: Typo
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