The infamous floating floor

[fuzzybunny]

I hope I'm not being a moron here. I spent a good hour or so searching the forum for this answer but didn't find it spelled out so that the dumb kids could understand it, so I'm gonna ask it.

The way I understand a floating floor is that joists are laid on rubber (or similar) isolators upon which flooring materials are then laid, and between which insulation is laid. Obviously this is only ONE method, but I think it comes closest to my budget.

So then, given that, am I to understand that the floor joists rest on the isolation material (e.g., rubber) held in place by gravity and weight only? Is it common to then put crossmembers in (as one normally would)?

In cross-section pictures I see, floor joists are listed as 2x4 (50x100mm), which is different than the 2x6 construction I would have expected. The shorter joists are acceptable? Or would 2x6's increase a floor's "deadness"?

Most designs I see for this type of floor show insulation in the gaps between joists, flush under the flooring (plywood, etc.). Is there a reason this insulation is drawn "suspended" above whatever subfloor exists, or is this just an idiosyncracy of drawings I've seen and the presence of absence of a gap on either face of the insulation isn't as important as the presence or absence of the material itself. And, does what I just typed make ANY sense at all?

I also read that floating the floor is a waste of time and money if one does not float the walls around it. In my normal construction experience, a wall is built onto the floor, I understand that this is a no-no in the studio world. Should, then, the floor joists and anything sheathed onto them be isolated from the walls by rubber/felt/whatever, and if so, what is the method for "finishing" the joint for appearance?

I hope this isn't too many questions from a rookie, but since you guys seem so helpful and smart, I figured I'd let fly. I appreciate any help in advance.

Thanks--
FB

[knightfly]

Man, what an appropriate screen name considering the time of year :=)

OK, I'll see what I can do here, somewhat in order - keep in mind that I've yet to build a floated floor - any and all of what I say here comes mostly from research over the last 10-15 years, in preparation for my own goal of having a separate and high quality facility to replace the area(s) I've been using all this time.

First Q - You're right, there are several ways/brands/schools of thought on floated floors, walls, etc - on a budget, a high mass, multi-layer floor over conventional joists, rested (by gravity) on rubber isolators seems to be the preferred method. If ceiling height allows it, deeper joists will slightly improve isolation, all other things being equal. The fiberglas (or rockwool) is there to break up standing waves in the joist cavities - the most common reason to suspend it would be to combat moisture absorption, which would be less of a problem if you have an adequate vapor barrier laid down first.

I've read in a couple of places, that picking the type of rubber and spacing can be hard to get right - rubber works best for isolation when it is compressed the right amount, and not restricted laterally so that it can compress vertically. In order to achieve this "right amount", which I'm not sure I even found, much less retained, you would need to know the Durometer rating (hardness) of the rubber (most available neoprenes seem to hover around a Durometer of 60) - Then, you need to know the ENTIRE weight of the structure to be floated, and how much weight per square surface area of contact will achieve the best amount of compression of the rubber isolators, etc - All in all, it appears that doing it right is a real ball-buster.

Some companies offer products and guidelines to make it simpler, if more expensive - kineticsnoise.com is one of them. They offer several different materials for floating floors, and for semi-floated isolation. One of their products is a 4 foot wide, 50 foot roll of compressed fiberglas pucks spaced out on softer material, that you just unroll, put plywood and plastic over, add reinforcing and pour a 2" concrete floating floor on top. They also offer isolation materials to sandwich between harder floor materials.

Auralex offers their "U-boats", but considering that they push the acoustic foam, which is 4 times as expensive and half the effectiveness of rigid fiberglas, I'm not sure if they've done their homework on spacing, etc, of the U-boat type isolators.

Floated walls - I've seen both methods of floating walls - either free-standing, with floor entirely INSIDE the perimeter, using soft soundboard between floor and walls, with moulding around the wall about 1/4" above the floor, caulked with acoustic-rated caulk - Kinetics shows this method on their site. Using their isolator mat and a 2" concrete float most likely bypasses the need for figuring out Durometer vs spacing vs weight, and might be easier in the long run because of that.

Or, building the walls on TOP of the floated floor, using 1/4" neoprene between the floor surface and the wall plates. Doing it this way, you would need to take into account the weight of all the walls, and put the floor isolators closer tobether around the perimeter. Don't ask me how MUCH closer, I already mentioned I'm still learning too...

Either way, if you're using Resilient Channel to mount wallboard on, the RC needs to fall short of the intersecting wall by at least a half inch, so it doesn't couple one wall to the next. Then you would stagger the wallboard joints so that the cracks between edges form a Z pattern, caulking each joint as you go, for best sound containment and wall isolation.

I've seen ceilings done different ways - one way is to rest a conventional framed ceiling on neoprene (between the cap board and joists) and do staggered wallboard joints, as I described the wall intersections above - Another way, is to use isolators like the ones kineticsnoise.com sells, and suspend a timber-framed sound wall-type construction (but HORIZONTAL) INSIDE the walls, sealing the gaps inside and out with acoustic caulk. This wouldn't be cheap, nor would it be a one-man job. Yet another way, depending on the situation, is for an existing structure where there are already joists in place from the floor above - it involves beefing up the mass layer of the above floor with 2-3 layers of wallboard (cut to fit between the joists, caulked and cleated to retain) then heavy insulation, with RC on the bottoms of joists and at least 2 more layers of wallboard.

I hope this answered some of your questions - I'm sure it will also prompt some more, since in my own travels along this path every question answered causes me to ask at least two more :=)

Personally, in my case the jury is still out as to whether I think floated floors are necessary where there are no railroad tracks close - other than that, as near as I can tell the main value in floated floors is room-to-room isolation, primarily in lower frequencies... Steve

[giles117]

Here I am late to the game, but in my humble experience having floated 4 floors, insulating properly and improperly, I have noticed a difference in the Bass response of the room.

That is all I can offr.

Bryan

[knightfly]

Bryan, by a "difference", I'm assuming you meant a decrease? The general concensus is that (assuming wood floor, at least) floating contributes somewhat to bass trapping... Steve

[giles117]

Sorry, I should have elaborated. Yes it lends to bass trapping. And a reduction of that hollow you sound you get when you've done everything else but float your floor.

I messed around got cheap and did not insulate one I did and hear it all day long. Not grossly noticable, but I knew it was there. When I ripped it all apart, re did it right and put it ALL back together (very tedious and tiring.) I no longer heard the hollownes I was hearing before. Not to mention was the bass tighter. I am no physicist, but it is amazing how these small things make such a BIG impact on your mixes.

Not technical, but my ears did not lie to me.

Bryan