AVS Forum banner
Status
Not open for further replies.
1 - 3 of 3 Posts

·
Registered
Joined
·
659 Posts
Discussion Starter · #1 ·
I have some 3/4" PVC pipe that runs throughout my basement ceiling, so I need to basically "lower" the entire ceiling at least that much. My plan is to just screw 2x2's to the joists throughout most of the ceiling. My question is, is there any benefit to attaching them perpindicular (forming a grid), as opposed to directly on the joists? I figure running them directly along the joists would be much easier, but if there is an acoustical (or structural) advantage to doing them perpindicular, I will do it that way.
 

·
Registered
Joined
·
287 Posts
This came up a long time ago earlier this year, and possibly several times since then (and probably before)


There didn't seem to be an overwhelming consensus, but if it were me I would go wtih the perpendicular installation if you have any of the following conditions:


- dimensional lumber joists that aren't level with each other to enough of a degree that the variance will show in the final ceiling. By running perpindicular you can find your lowest point and shim from that point at the other intersections which are significantly higher, and get a much more level ceiling with no bowing anywhere. It is much harder to shim when running right on the joists and keep up with attaching the 2x2 to the joists every 16" as you should. If you joists are manufacturered, or haven't checked or twisted at all and are in great shape, or if you don't care about your ceiling having an occasional bow in it, don't worry about this.


- joists that are not 16" OC. You can sometimes find up to 24" OC joists depending on region, when the structure was built, etc. If the joists aren't 16" OC, I would definately install the strips perpindicular and space them 16" OC.


- You are trying to elminate sound transfer to the room above (or vice versa). While I have no measuredc data to back it up, I have to think that a perpindicular ceiling due to the much less are of contact would have less sound transferrance. In fact, if I recall there are clips made which allow you to attach a ceiling like this which are design to specifically reduce sound transferrance. However, I don't think you have to use these.


From my experience, I know that simply putting 1/8" to 1/4" of medium-density rubber between the two, even with a screw going through it, definately helps dampen the sound transfer. However, it may create a diaphram effect on the ceiling which would be undesirable (I'm no expert in acoustics, but it is a possible concern).


Just 2 weeks ago in my garage (HT going upstrairs), I wanted to quiet down my already quiet garage door openers (belt driven Chamerlain Whisper Drives) even more so they couldn't be heard upstairs (I could care less if the HT can be heard down in the garage, but when somebody comes home I don't want to hear the openers upstairs). Since they are attached through a 2x6 directly to the joists, I simply removed the lag bolts holding the 2x6, placed 2 layers of a pair of truck mud flaps I bought at a garage sale, and re-attached the 2x6, through the hard rubber, about 1/4" total. The same was done for the front plate holding the track. I learned this trick on Ask This Old House on DIY, believe it or not. :)


The results were fantastic. First, the hand vibration test where I rested my hand on the side of the joist about 4" away from the opener reveled a difference in night and day. With no dampening I could feel a ton of vibration, and where there is vibration there is noise. In the after case, I could barely feel the opener running.


From above the garage in the HT, the sound of the opener went from fairly audible to barely audible. While I don't have a SPL, there was definately greater than a 50% reduction in audible sound, because it was quite clear that two openers running after the mod were considerably quieter than one running before. I would estimate a 60% to 80% total attenuation of the opener noise. Once I add my second layer of subfloor, plus carpet, plus a movie running, I don't even think you will be able to hear them at all.


Now, I'm sure that if you put a piece of rubber like this between the intersection points of the 2x2 strips and the joists they are running perpindicular to, it would definately reduce sound transferance to a certain degree, but how much I'm not sure. In my case above, a vibrating device was physically anchored to the ceiling joists, which is definately a special case, so that was a prime case to get great results. The whole ceiling would now have a tiny bit of give to it, but no more than a RC wall would (my understanding is it is this give that absorbs the sound energy, thereby reducing transferance). I'm not sure of the overall acoustical impact of this, but I know it will make things quieter above if you care about this.


The really nice thing is by purchasing thin rubber, say 1/16" or 1/8" thick (the softer cove moulding would work great here I bet), you can use that as your shims by simply stacking it up, and you kill 2 birds with one stone. You would plan on putting at least 1/8" everywhere, and where the joists are a bit high, you could add additional layers in increments so everything is nice and level. If you don't have one, by renting a SOLID laser level (not something like the Craftsman Laser Trac POS which is off by 1/2" over 30'), this would actually make the shimming phase go very quickly.
 

·
Registered
Joined
·
659 Posts
Discussion Starter · #3 ·
Wow! Thanks for the great info, Ryan. I was actually planning on using some sort of rubber acoustical treatment on the ceiling, but my plan was to put it directly under the drywall (below the furring strips). Is there any real reason to putting it in between the joists and the strips instead?
 
1 - 3 of 3 Posts
Status
Not open for further replies.
Top