Floating Ceiling construction opinion wanted

I suspect you'll have no problem. I spanned a ~13' section with 2x8's to do that very thing, although I was only hanging a 25lb projector, and it was at one end of the span, and not the center. However, I was able to do pullups on the projector backing, and I'm a a bit over 200 lbs.


I did some online searching for joist loading, and was able to find ratings charts for typical lumber at span lengths. For just 5/8's rock, 2x8 was plenty.


Here's a couple of shots of my framing in between the existing joists. They were resting on a framed wall at one end, and an I-beam on the other end:





More pics HERE.

Rats.... this is more difficult that I had hoped.


I get the part about not removing the crossbracing but I have seen other rooms built with this type of construction.... yet, I have similar concerns as you have raised. I looked into using Rsic clips that have the strap on them so that they could be hung below the existing floor joists... but man are they expensive to do a whole room. It may be my only choice.


So I could do RSIC clips, resilent channel and then use the biggest EJ I can fit to span the area where the projector will mount. My thought there is that I could drill a hole in the EJ for the horizontal strap bracing to pass through.... as long as it meets the specs for the EJ.


I'm struggling because if I go the RSIC route it will lower my ceiling which affects the layout of my wall panels.... so I really need to find a usable solution now.


Thanks for the valuable info.


Frustrated in PA. - Bud

Bud,


One way or the other you're going to have to lower that ceiling if you want heavy isolation. Using RC Channel, RSIC clips, or the (best isolation) floating ceiling all drop the theater ceiling below the bottoms of the original joists. A floating joist system will eat up available space for ceiling cans, but then again, if you're considering this route you likely won't want to compromise isolation with ceiling can holes...


Klindy is right about the cross braces. Drilling a hole through the floating joists and running a pipe, strap or some other item for bracing has been done successfully by others.


This "floating" type of system will be significantly better than resilient channel, however. The floating ceiling is analogous to a double stud wall, which is completely decoupled with no contact. Resilient channel could very well fail (badly) and is not completely decoupled.

Be careful of mis-information. Do research before making major changes to your design.


Cross bracing is not required by many, and in fact provides very little (if any) reduction in the deflection. Cross BLOCKING is a little different, but still not required by many. I removed mine years ago to put in radiant heat, 2x10 with a 13'+ open span.


If you have the cheesy metal straps, toss 'em.


Framing in a floor does not take into account any bottom ceiling attachment for structural purposes. This should be obvious from all the unfinished basements around. Quality lumber from a contractor supply (NOT the big box stores) should not warp. KD means kiln dried...so unless the material was not properly stored in it's path to you this is a non issue. No need for any engineered lumber.


Draw up a plan, and talk to your building official about your intentions - specifically ask about the x bracing....make sure you detail your current span and framing detail.


Framing a room-with-a-room is the best way to go, so make sure; 2nd is RSIC, and a very very distant 3rd is just RC.


IF you have to go the RSIC route, there are ways to frame it so you loose only about a 1/2" of headroom (the same as if you did the room-in-a-room). I had to do this in a section of my ceiling because the opposing wall is unable to support the ceiling joist. You simply add a cross brace in the framing out of 2x4 and set it up in the joist bay about 1 7/8" (for my situation) and the RSIC/hat channel (running parallel with the floor joists) sits just below the floor joists. This is SLOW compared to framing, but if you have no choice time becomes the compromise.


So, don't just base your plans on newsgroup banter, including posts like this one



Quote:
Originally Posted by budk /forum/post/12819495


Thanks again. I know that the ceiling as to be lower, although if I go the floating route it can be higher than the RSIC/resilent channel route.


I need to talk to the lumber yard, but I'd like to use top quality 2x8 and just put a hole in them to run the bracing through.... I think that will be my plan. I am also hoping to vary the spacing some so that I can fit can lights put in boxes (as described in other threads) in the floating ceiling. I'm thinking that as long as I don't leave a span of greater than 24" I should be okay. There will even be some areas where I may want to double them up like in the area of the projector possibly.


Still learning, but getting tons of great opinions. Thanks one more time. Bud

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5/8" drywall is about 2.8 lbs per sqft so two layers is just over 5-1/2 lbs per sqft. That's not a lot of load compared to your floor system above (or compared to any typical span charts you've seen for wood joists). Point is your selection of a 2x8 would be overkill anyway so a plan to drill a hole (or even notch the bottom edge - although that generally would not be recommended.


According to this span calculator a 2x8 can span more than 16'-3" (that would be from inside of bearing to inside of bearing). I say "more than" since the minimum live load I can use on the calculator is 10#/sqft and you have zero and the minimum dead load is 10# which is probably somewhere close to reality. Incidentally I used Spruce-Pine-Fir #2 spaced at 24" O.C. which L/360 as the deflection limit. Using the same criteria but changing to a 2x6 I get 12'-10" max (again inside of bearing to inside of bearing).


Also if you use a 2x10 SPF #2 floor joist with 40# live load and 10# dead load; 24" o.c. (typical residential floor loads for living space). The calculated deflection at an 11'-0" span is somewhere close to L/700 - significantly 'stiff' compared to the code limit of L/360. Of course if the spacing is actually 16" (which I would more likely think it is) the performance will be even better.


The point here is even with a 2x8 you have a lot of 'strength left over' to work with. Of course I suspect you've already looked at some span charts and discovered most of this. If the 11' reference in your first post is accurate and you have accurately identified the bearing wall condition (so you know the floor above is only an 11' span too), I'd suggest your thoughts of a 2x8 as a ceiling member is fairly conservative. If it were me, I'd be more concerned with the performance of the floor system above since the ceiling should be well over designed.


If you're doing this work yourself you could always dip your toe in first by removing the cross braces from the floor system above and see if you can tell a difference - the difference would be vibration and a 'sense' the floor feels 'spongy' to walk on above. If that seems unchanged or at least is acceptable to you, I'd suggest you'll be ok with the 2x8's in between as ceiling joists below. Since it's your house, your perception is all that matters. Even with the cross bracing removed that floor above isn't going to fall down or anything it would just tend to vibrate more. Although it appears to be over built enough to not cause a great concern. You could even add a strap to the bottom of the joists (use screws to remove it again to install the joists) and test that performance. If all this works acceptably to you, then move forward with the ceiling joists.


***None of this should be viewed as engineering advice - Use at your own risk*** I am not an engineer but have been in the structural building products business long enough that this is similar situation I've run into many times in the past 20+ years. My belief is you'll have no problem and your perceived performance will be the same as you have currently.



Quote:
Originally Posted by budk /forum/post/12825780


I'm still leaning towards 2x8's in the area of the projector since the projector weighs in somewhere around 180 lbs. How does doubling up the joists improve the weight handling? i.e, should I run a couple of 2x8's screwed and glued together in the area of the projector?


Thanks. Bud

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In theory doubling the joist double's it's carrying capacity. It's essentially the same as halving the spacing between joists. In reality two pieces lumber will have some opposing grain etc so it may even out perform it. Glued and screwed/nailed is fine. That said remember that deeper is better when carrying a load.


Note that doubling it's carrying capacity does NOT mean doubling its span. There are other slenderness issues and deflection issues that come into play that prevent that.


Depending on where the projector is located (near the end or near the middle) you may not have anything to worry about. If it's in the middle of the span you might want to double it for your own piece of mind.