Author Topic: Ceiling (with cans). Spend soundproofing $$$ below or above?  (Read 4959 times)

Bill F

  • Guest
Ceiling (with cans). Spend soundproofing $$$ below or above?
« on: September 23, 2008, 09:51:14 PM »
Lots of great info on this site, but one comment (that I'm basically screwed if I have light cans) prompts me to spell-out my situation:

1) House is a single family home, built in '30s. 

2) I will be renting out downstairs as its own unit. 

3) Both upstairs and downstairs have million-dollar views, and I believe that I will get better rent downstairs if I can provide a reasonably "clomp-proof" environment.  (Note: My wife and I are not heavy, and we have no kids.)

4) Two-thirds of the home is in the midst of a massive remodel, and thus has no sheetrock, insulation or flooring in place, so the timing is right to do the right thing.

5) I do have, downstairs, 14 light cans nailed to the joists.  All are insulation-contact, but only 4 are airtight.  (Yes, from reading other posts, now would be the time to replace them with track-lighting, but I don't want to - the cans look classy.)

6) The ceiling between our living rooms is 2x8 joists supporting a 1x12 subfloor (with plenty of plywood patches).

7) Ceiling height both upstairs and downstairs is important to me.  I could see the solution from underneath being 2 sheets of sheetrock, and I've allowed for about 1 1/2" of flooring "stuff" upstairs.  Right now my upstairs flooring solution might be 1/4" plywood (to tie together the gapping planks) + 1/2" inch of rubber or cork or (   ?   ) + an 11/16" floating engineered wood floor.  (Floating engineered because we want the look of real wood and a flooring guy said that "floating" was a way of isolating sound...

8) At the risk to too much detail, there are actually 3 floor/ceiling situations.  Upstairs, 1/3 of the (gutted) floor is over a downstairs crawlspace adjacent to their living room; 1/3 of the floor is over downstairs' gutted living room ceiling; and 1/3 is over their bedroom bathroom, whose ceilings I am not opening.  I mention this because A) part of the solution might involve spending a bit less on the floor that is adjacent to their living space (yeah - I know... Sound will carry.), and B) at this time, for a portion of the house, the only solution is from the top.
== == == ==

So... There is no existing noise problem that I am trying to specifically eliminate, but the timing is right to do the right thing, so that I can get - and keep - the best tenants.  What pointers / recommendations do you have? (e.g., "Use 11mm of Privacy Ultimate Underlay and life will be great."

Bill in the SF Bay Area




  • Guest
Re: Ceiling (with cans). Spend soundproofing $$$ below or above?
« Reply #1 on: October 16, 2008, 11:47:30 PM »
Hi Bill,
What a fortunate circumstance you have - being able to work with exposed floor/ceiling joists from the floor above.  Remember, the first element in soundproofing is to decouple any vibrating surfaces (like the to-be-installed sub flooring) from the structural's they are attached to.  By using isolation tape on top of the floor joists before screwing down the sub floor you will eliminate 60-80% (this % was provided to me by a construction inspector with the city of Los Angeles) of the impact sound at the source of resonance.  Here is a link which discusses this material
If you apply MLV in continuous layer to cover the floor area first (stretch and staple to joist tops, tape seams with lead foil seam tape - then put the isolation/padding tape on top of the MLV continuous where joists run) then you also block air-borne sound from both directions.  Of course you will want to fill the cavity with insulation (bonded coton insulation is best for both absorbing and blocking sound - see this link for info ) before you do the MLV and isolation tape.  To finish the assembly from the top you can add a second layer of sub flooring with Green Glue to further damp any impact vibration.  This second (top) sub floor layer with Green Glue needs to stop 1/4" short of any adjoining wall framing (sill plates) and then this gap is filled with acoustic caulk (this prevents any vibration transfer into the walls).  To see how effective this step is review the Green Glue data at
This is a long explanation for a simple and highly effective solution my customers have used with outstanding and satisfying results.

Bill F

  • Guest
Re: Ceiling (with cans). Spend soundproofing $$$ below or above?
« Reply #2 on: October 30, 2008, 05:24:45 AM »
Sorry for the lag in replying... lots of things going on right now. 

First, a major clarification: I stated that flooring was gone, and it is.  But I've still got the subfloor in place.  So isolation tape on top of the joists is not an option.

Then your reply confused me. I can't figure out at what point you're recommending the MLV.  Let me reiterate, I've got old and gapping 1x12s resting on 2x8 joists. 

In my first email I indicated that I had room for 1 1/2" of flooring stuff, but let me be more specific.  My lowest door swings over the current subfloor with a clearance of 1 7/8 -2.0"

I am a fan of green glue, but one question was whether I could put it directly on the nicked, notched and gapping 1x12s, then cover with plywood underlayment.  If too much GG would slip out of place into the cracks in the old subfloor, one idea I have is to lay on top of the planks some heavy-duty vapor barrier I have left over from the foundation work.  Thoughts?

As of today, I'm thinking that my ply underlayment will be two half-inch sheets of CDX, nailed and glued to each other, but floating on the GG (i.e, not nailed to the planks underneath.)  My top engineered wood floor will be only 1/2", and floated.  That leaves me just over 1/4" for a rubber, cork, or vinyl sound/vibration barrier right underneath the engineered wood.  Anyone interested in convincing me which material is the best at blocking footfall under the scenario I've just described?



  • Guest
Re: Ceiling (with cans). Spend soundproofing $$$ below or above?
« Reply #3 on: November 07, 2008, 05:27:06 PM »
Green Glue sandwiched between all the layers is best for reducing foot fall noise.  Use it at the rate of 3 tubes per 4'x8' sheet of whatever (do not use with pourous sound board - only rigid sheets of building materials like dry wall, ply wood, OSB, cement board, MDF).  In fact, multiple layers of Green Glue with multiple layers of . . . works best.
MLV works best when it is attached to structutals (studs, joists) with open bays behind it - not sandwiched flat between sheets (the only exception is existing sub floors and existing walls when you use two layers of MLV - then it works well for stopping air-borne sound).