Did my room-in-room fail the "jump test"???

Hi there! I've now completed the insulation og my ceiling with free standing ceioling joists, resting on free standing walls (room-in-room). I've filled the space between the joists with 10 cm fibreglass and 15 cm Rockwool. The total airspace between the joists is about 24 cm. I've been trying not to squeeze in place the insulation, but to cut is in widths so that it just keeps in space and do no fall down. This amounted to about 1 cm more than the air space for widths about 25-28 cm. So what's the prblem then? Well, last night I made my wife jump up and down in the middle of the living room, right above the room-in-room. I stood on a chair and held one hand against an (existing) floor joist and one hand on one of the new ciling joists. I expected to feel next to nothing of vibrations on the ceiling joist (which by the way is a 2x8, while the floor joists are 3x9). But I felt a lot of vibrations. Surely not in the same class as the earthquakely vibrations of the floor joists. I was surprised and disappointed about this. As the ceiling joists are completely mechanically insulated from the existing construction I would expect them to not to be vibrating at all... The only explanation I come up with is that it is the insulation that is transporting the sideways vibration of the floor joists and setting the ceiling joist into motion. I'm blaming the 15 cm Rockwool for this, because it seemed stiffer than the fiberglass insulation. I guess the $50.000 question is this: Should I worry about this? I mean "bare" 2x8's isn't exactly difficult to set in motion. I'm about to put 3 layers of gypsum boards in the ceiling (with 2 layers of GG between). Will this stiffen/stabilize the 2x8 so that this story will have a happy ending

Hi Rune, If you want to check if the 703 is transporting the vibrations, remove it and try your jump test again, it's never nice to have to undo good work but it is good to have a definite answer. Adding the gypsum will stiffen your ceiling joists as they will be providing cross bracing which is not there at the moment. I would think as mass is the key to soundproofing, along with decoupling and sealing, that 3 layers of gypsum will absorb a lot of the vibrating energy be for they reach the joists. Just my two cents... Joe

kie wrote:

Hi Rune, If you want to check if the 703 is transporting the vibrations, remove it and try your jump test again, it's never nice to have to undo good work but it is good to have a definite answer. Adding the gypsum will stiffen your ceiling joists as they will be providing cross bracing which is not there at the moment. I would think as mass is the key to soundproofing, along with decoupling and sealing, that 3 layers of gypsum will absorb a lot of the vibrating energy be for they reach the joists. Just my two cents... Joe

I'll grateful for your two cents, kie! Any amount appreciated! I'll surely try the "jump test" again without the insulation. But who knows? Maybe this kind of behavior is normal (and I do not mean jumping up and down in the living room, but the movement of the "bare" ceiling joist wile a person jumps on the floor above). I guess the "jump test" isn't a test normally performed???

RuneW wrote:

But who knows? Maybe this kind of behavior is normal (and I do not mean jumping up and down in the living room, but the movement of the "bare" ceiling joist wile a person jumps on the floor above). I guess the "jump test" isn't a test normally performed???

Actually it's performed quite often - by me anyway......... It's called (in the construction industry) the "Feelgood" method of engineering. I would be very surprised to have any real movement being caused by the rockwool - there might well be another short somewhere causing flanking. Get yourself a mechanics stethescope - (they aren't at all expensive) - and have someone tap on the existing joist lightly with a hammer - check the new joist to see if you can hear the tapping. Make sure to check each member - if you can hear the tapping at all - that means there is a physical connection between the 2 structures. Rod

Just curious and slightly OT, was there any cross-bracing between the existing joists that you removed? Are you going to put any cross bracing between the new joists?

rod gervais wrote:

Actually it's performed quite often - by me anyway......... It's called (in the construction industry) the "Feelgood" method of engineering. I would be very surprised to have any real movement being caused by the rockwool - there might well be another short somewhere causing flanking. Get yourself a mechanics stethescope - (they aren't at all expensive) - and have someone tap on the existing joist lightly with a hammer - check the new joist to see if you can hear the tapping. Make sure to check each member - if you can hear the tapping at all - that means there is a physical connection between the 2 structures. Rod

Thanks Rod, I'm not sure where to get such a stehescope, but I'll do some ear-to-joist testing and see (hear). BTW, there actually IS another possible culprit here and this is the HDMI-cable shown below: As can be seen from the picture, the cable is only very loosely hung over the ceiling joists with some insulation under to eliminate mechanical shortcuts. I've not felt especially good about having this cable here, but it was too short to put around and I didn't want to carve notches on the underside of the ceiling joists. As said, the cable is very loosely hung over the joist, but if somebody actually jumps on the floor above, they may tighten up and transfer the vibration to the ceiling joists... If this cable is a No, NO, NOOOO (and red lights flashing), I'll surely remove it faster than you can say H-D-M-I. Event if the cable is a $200 waste of money (by not using it) I wouldn't even blink cutting it down (if it comes to that), if it's any chance at all that it's gonna break my sound proofing!!!

wmtunate wrote:

Just curious and slightly OT, was there any cross-bracing between the existing joists that you removed? Are you going to put any cross bracing between the new joists?

No there wasn't any cross bracing. For some reason cross bracing isn't that much user here in Europe, or in Norway at least. I'm not sure why. Maybe we use slightly thicker joists?

Don't be scared by the jump test. Sound will not come close to creating that kind of energy. I speak from experience. I built a true room within a room on an isolated concrete slab. Even with no physical connection between the two rooms, I could hear someone coming down the stairs. Yet, they can't hear my drumming from inside the room. So don't worry about it too much... Try playing some music from a loudspeaker instead.

Yesss! Tonight I had a guy (that is a home theater consultant) over and we did a test where we tapped one (floor)joist with a hammer while listening to another (ceiling)joist with a screwdriver (pointy edge into the joist and round edge "into" the ear). I'm extremely happy to tell that there were no indication of a acoustical shortcut between the outer and inner room, thank God! Personally I thought I could hear some deep frequency sound through the screwdriver, but the consultant said this was nothing to worry about. There were absolutely no tapping type of sound, if you know what I mean.

what is that (appears to be) triangle wood between the floor and inner ceiling joist? it looks attached... another source of flank could be through the structure itself - down the side walls through the floor and up the inner walls. maybe feel the side walls and floor to see if any vibration is making it. if not, then maybe its just sympathetic from being relatively loose at this point.

RuneW wrote:

I'm extremely happy to tell that there were no indication of a acoustical shortcut between the outer and inner room, thank God!

In your second picture, right hand side below where the red circle is, is that a block connecting the existing and new framing? Or does it just look like it is touching both members? edit...durn Glenn...I was looking at that too, my bad :)

gullfo wrote:

what is that (appears to be) triangle wood between the floor and inner ceiling joist? it looks attached... another source of flank could be through the structure itself - down the side walls through the floor and up the inner walls. maybe feel the side walls and floor to see if any vibration is making it. if not, then maybe its just sympathetic from being relatively loose at this point.

Ok, I can understand your concern... These triangles were part of a construction to fasten the video projector tp the ceiling. Because it's very annoying when projectors vibrates even so slightly (the picture on the wall vibrates "somewhat" more). Therefore, when adding a wood plate to be placed above the gypsum (so that I could screw into some "real wood"), I added some bracing for just the two joist on either side of the projector. As can be seen from the pictures below, there should be plenty of air and no direct contact between the triangles and the existing joist:

Rune, maybe the vibration is going down thru the exterior wall into your floor and that is going back up into your framing. did you ever notice that if someone jumps up and down on a slab you can feel it move? i bet that's what is happening. but probably nothing to worry about.

Hmm... I've now put one layer of gypsum in the ceiling (no caulking or such and no gypsum on the walls yet), hoping that the gypsum would somehow stiffen the ceiling joists. I redid the jumping test and the ceiling still very noticeably vibrated (and I had no problem hearing the jumping either, thank you very much). I'm not too worried about the sound, though, because the current gypsum layer is all cracks (between the sheets) right now. But I was a little but disappointed about the vibration, though. So, as far as I can judge: A) Sounds made by tapping one structure with a hammer (even not-so-lightly) was clearly not transmitted to the other structure (I tried several places). B) Jumping on the floor above clearly does transmit vibrations to the inner structure. Rod advised me to du the hammer/stethoscope test. I did, and my ceiling joist passed the test. But still jumping on the floor clearly sets the ceiling in vibration. I'm extremely unsure at this point. Should I take down the gypsum again? It's not a job I look forward to to say the least... I'm thinking that this jumping thing makes the floor move in its natural frequency with a energy that's never gonna happen from sound alone. Am I on to something? What can I expect in difference from my current one layer, non-caulked gypsum sheets and the planned 3 layers of caulked gypsum sheets, with 2 layers of GG in between?

Dan Fitzpatrick wrote:

Rune, maybe the vibration is going down thru the exterior wall into your floor and that is going back up into your framing. did you ever notice that if someone jumps up and down on a slab you can feel it move? i bet that's what is happening. but probably nothing to worry about.

At this stage I'm willing to believe anything. I didn't think this was possible though. The existing floor joists rest on a 25cm Leca wall. When the concrete slab (on which the inner room is built) was poured, we put a 30 mm thick EPS along the boundaries. When the concrete was hardened, we removed (as best as we could) the EPS and used a foam backer rod + caulk to fill the space (see attached picture). All this is an effort to mechanically insulate the slab from the rest of the house. The slab really IS somewhat insulated from the rest of the building. I've been running a noisy compressor on the slab, and the amount of vibration on the upper hand side of the boundary is dramatically less than on the slab itself. So having the above in mind, I'd never thought that the vibrations could travel down through the walls an into the slab in such a "unattenuated" manner. But, as I said, at this point I'm willing to listen to every suggestion!!! Is there a way to determine if this is what really happens?

RuneW wrote:

I'm thinking that this jumping thing makes the floor move in its natural frequency with a energy that's never gonna happen from sound alone. Am I on to something?

You are more than on to something. You are correct! Andre

AVare wrote:

RuneW wrote:

I'm thinking that this jumping thing makes the floor move in its natural frequency with a energy that's never gonna happen from sound alone. Am I on to something?

You are more than on to something. You are correct! Andre

Thank you. But what I don't understand is why the ceiling joists/gypsum layer "plays with" the floor like it does, since it's highly unlikely that is has the same natural frequency?

Rune, from what I see in your pictures - the lack of barcing for the existing floor joist is a big part of your problem. In my book I tried to point out just how important a properly braced floor was - and some methods to acheive this. Your new ceiling joist are installed much to high to allow you to do thid in your case. Bracing that runs from joist to joist not only stops the joist from being able to roll under load (which concerns me a bit in your case) but it also makes the deck that much stronger and stiffer by transfering part of the floor load above to adjacent joist. Without the bracing your floor joist are allowed to move independently of one another, and this is neither a good thing - nor is it code compliant. As to why it can make your independant ceiling below vibrate? Have you had someone jump while you carefully watched (I mean with your face right up inside where you could see if the upper joist ever touched the cross piece passing under it? There doesn't appear to be much more than a 1/4" space between the 2 - and a 16' long joist (with a design deflection of L/360 - which is the most common design deflection used) can deflect around 9/16" to 5/8". That would be enough to touch your cross member. Perhaps you should look into that. Rod

rod gervais wrote:

Rune, from what I see in your pictures - the lack of bracing for the existing floor joist is a big part of your problem. In my book I tried to point out just how important a properly braced floor was - and some methods to acheive this. Your new ceiling joist are installed much to high to allow you to do thid in your case. Bracing that runs from joist to joist not only stops the joist from being able to roll under load (which concerns me a bit in your case) but it also makes the deck that much stronger and stiffer by transfering part of the floor load above to adjacent joist. Without the bracing your floor joist are allowed to move independently of one another, and this is neither a good thing - nor is it code compliant.

Thanks for your concerns, Rod. Yes, I'm aware of the lack of bracing and it might very well be the source of my current problems. Actually I have thought about the (lack of) bracing problem a lot (the wood triangles, remember?). None of the construction consultants that I've contacted recommended bracing, however, so I skipped them (and we don't have codes requiring cross bracing between joists in Norway). But I bet neither of those building consultants have made any studios... I'm probably going to take down the gypsum again to get to the root of this...

rod gervais wrote:

As to why it can make your independant ceiling below vibrate? Have you had someone jump while you carefully watched (I mean with your face right up inside where you could see if the upper joist ever touched the cross piece passing under it? There doesn't appear to be much more than a 1/4" space between the 2 - and a 16' long joist (with a design deflection of L/360 - which is the most common design deflection used) can deflect around 9/16" to 5/8". That would be enough to touch your cross member. Perhaps you should look into that. Rod

I haven't looked closely, no. The air space between the overside of the ceiling joists and the underside of the floor is about 35-40mm. My hope wsa that this, in addition to the fact that 3 layers of gypsum would bend down the ceiling joist with a few mm, would be more than enough. But it might not. My own private theory is that it's the relatively stiff Rockwool + the lack of bracing that is the culprit. The jumping makes the floor joists roll, which in turn pushes the Rockwool against the ceiling joists. Even if the Rockwool isn't solid as such, it's actually quite stiff and when the whole length of the joists are being pushed this way... I tried to cut the Rockwool so that it only was wide enough to just keep in place, but it probably got too tight anyway. Maybe cutting the Rockwool so that there would be an airspace (so that it didn't tough any joists at all) would have been better? I regret bitterly that I didn't remove the Rockwool and redid the jumping test before putting up the gypsum layer. I was so relieved by the tap-with-a-hammer test that I forgot all about it. Hope someone else can learn from my mistakes, though...

RuneW wrote:

Thanks for your concerns, Rod. Yes, I'm aware of the lack of bracing and it might very well be the source of my current problems. Actually I have thought about the (lack of) bracing problem a lot (the wood triangles, remember?).

It's the upper joist that have me concerned - and that type of block won't do what I am talking about - which is the load transfer.

None of the construction consultants that I've contacted recommended bracing, however, so I skipped them (and we don't have codes requiring cross bracing between joists in Norway).

That must be a lack of familiarity with wood frame construction on their part. Any joist (floor or ceiling) which has a load on it can actually rotate at the center of the joist - lay down on it's side - and collapse. I am very suprised to hear that Norway doesn't have any bracing requirements for unbalanced joists. If you have plywood on top and drywall on the bottom - that constitutes bracing - (although it still doesn't take care of the transfer of load - which makes the deck MUCH stronger than the individual joist do by themselves). I would be very suprised if there isn't something somewhere in the Codes about dealing with that situation - even if it's obscure and buried somewhere. Rod But I bet neither of those building consultants have made any studios... I'm probably going to take down the gypsum again to get to the root of this...

rod gervais wrote:

As to why it can make your independant ceiling below vibrate? Have you had someone jump while you carefully watched (I mean with your face right up inside where you could see if the upper joist ever touched the cross piece passing under it? There doesn't appear to be much more than a 1/4" space between the 2 - and a 16' long joist (with a design deflection of L/360 - which is the most common design deflection used) can deflect around 9/16" to 5/8". That would be enough to touch your cross member. Perhaps you should look into that. Rod

I haven't looked closely, no. The air space between the overside of the ceiling joists and the underside of the floor is about 35-40mm. My hope wsa that this, in addition to the fact that 3 layers of gypsum would bend down the ceiling joist with a few mm, would be more than enough. But it might not. My own private theory is that it's the relatively stiff Rockwool + the lack of bracing that is the culprit. The jumping makes the floor joists roll, which in turn pushes the Rockwool against the ceiling joists. Even if the Rockwool isn't solid as such, it's actually quite stiff and when the whole length of the joists are being pushed this way... I tried to cut the Rockwool so that it only was wide enough to just keep in place, but it probably got too tight anyway. Maybe cutting the Rockwool so that there would be an airspace (so that it didn't tough any joists at all) would have been better? I regret bitterly that I didn't remove the Rockwool and redid the jumping test before putting up the gypsum layer. I was so relieved by the tap-with-a-hammer test that I forgot all about it. Hope someone else can learn from my mistakes, though...[/quote]

rod gervais wrote:

It's the upper joist that have me concerned - and that type of block won't do what I am talking about - which is the load transfer.

rod gervais wrote:

That must be a lack of familiarity with wood frame construction on their part. Any joist (floor or ceiling) which has a load on it can actually rotate at the center of the joist - lay down on it's side - and collapse. I am very suprised to hear that Norway doesn't have any bracing requirements for unbalanced joists.

I guess I was too fast with that one. Grilling one building consultant anew, it turns out there are bracing requirements for unbalanced joists here after all, but these are dependent on the dimension of the joists (and he still claims there's no need for joists with my dimension). Well, I'm not so sure anymore...

rod gervais wrote:

If you have plywood on top and drywall on the bottom - that constitutes bracing - (although it still doesn't take care of the transfer of load - which makes the deck MUCH stronger than the individual joist do by themselves). Rod

I see. So from your point of view, is there a point putting triangles in place at all? If I carefully connect the two triangles with a piece of wood (and screw them in place with "a tension"), I was hoping to achieve a kind of load transfer (see attachment below), but this might be a stupid dream from my part... --- Anyway, for those whose interested I went as far as taking off the middle gypsum board and the insulation above it to analyze what really happens during a jump test. This I did with a (admittedly) compact camera in video mode and a DIY instrument to clarify the movement of the joist. I started the camera and hurried up one floor and jumped from a chair on the middle of the floor and TRIED to jump in a similar manner for all the tests... Measurement of the movement of the upper joist (1 mb) On this video it's quite clear that the joist has a sideways movement (as Rod actually predicted!). This can be seen from the black dot on the "instrument" moving with a sideways component. What's strange is that from this video, the ceiling (joists) doesn't seem to move much at all... Measurement of the movement of the lower joist (1 mb) Here we see that the lower joist isn't exactly static... But it also (it's really difficult without to see with this low resolution video) seems like the sideways movement is limited.

Somebody claimed that it was the air pressure from the floor above that was the cause of the ceiling to move!! I find this hard to believe as I would expect the air to evacuate nicely through the insulation and to the sides (I haven't closed the walls yet). And addition I hadn't caulked/mudded anything of the gypsum layer so there were plenty of places for the air to escape between the gypsum... Is the air pressure theory just BS?

I tried to remove all of the insulation from one "gypsum board strip" (240 cm wide strip). Then I put a piece of wood (horizontal piece) between two of the lower joist to compare the movement of the lower vs upper joist (vertical piece of wood): video In the video I jump as hard as I'm capable of on the floor above and then try to "swing" the floor by "not quite jumping...". I notice two things: 1. The floor actually doesn't move all that much. The two horizontal lines on the vertical piece of wood is 10 mm apart. The movement of the upper joist is about 2 mm, which I think isn't too bad for a non-braced joist, or does anybody think they still need additional bracing? I really don't know. 2. The important part: The lower joists now appears to move MUCH LESS and the movement seems to be a lazy, natural frequency motion. With 3 layers of gypsum this kind of motion will be no problem. So what was the porblem? I really don't know. For all I know the problem will be back when I put up the insulation and gypsum again, but I have a 5 point plan: 1. Reduce the height of the insulation with 5 cm (so now it will NOT have contact /pressure against both the floor and the ceiling at once) 2. Reduce the width (with a cm or so) so that sideways motion of the joists will not be transmitted) 3. Remove the insulation that were above the lower joists 4. Add bracings to the ends of the lower joists (they were only screwed in place from below at the ends) with angle irons. 5. Remove the HDMI cable Then at least I've done my best.

RuneW wrote:

1. The floor actually doesn't move all that much. The two horizontal lines on the vertical piece of wood is 10 mm apart. The movement of the upper joist is about 2 mm, which I think isn't too bad for a non-braced joist, or does anybody think they still need additional bracing? I really don't know.

The test isn't valid - and therefor we can't comment on movement. I'll try to explain - joist take all different types of loading - and I certainly would not expect one human being doing anything to drastically impact a joist's movements. I don't know your codes - but here in the US we have design requirements like this - Live Loads - Bedrooms, bathrooms, corridors - 30 psf (pounds per square foot) .......... Living rooms, family rooms, kitchens, dining rooms - 40 psf. Dead Loads........ 10 psf in either case. We also have maximum deflection to meet - in most general cases it would be L/360 (That being maximum deflection equal to the total length of the joist divided by 360) although in some cases it's L/240 and as much as L/480 if installing floor tile. We use all of that to determine what species, size, spacing to pick for our floor joist. We also have a general requirement that cross bracing is required on any joist with a span greater than 8'. Now - that is all intended to create safe situations not for you jumping on your deck - but for the times where it's a holiday - and all your friends and family are over - and you're kicking back listening to your favorite music - and everyone starts dancing and having a good old time - and now you have what is referred to as "sympathetic impact" - with the sum of the whole acting on the members from a number of different perspectives - one being bending - another being shear - another being roll-over, etc. It makes me nervous that you can see any roll over movement with just one person jumping - and I shudder to think what would happen if you had 20 or 30 doing the same thing. or even 20 or 30 people just walking around up there - especially long term - because each time it hasppens it weakens the joist - so in the end it takes less energy to cause a collapse than it does in the beginning.

2. The important part: The lower joists now appears to move MUCH LESS and the movement seems to be a lazy, natural frequency motion. With 3 layers of gypsum this kind of motion will be no problem.

Nope - the important part is above - you have your priorities crossed. Sincerely, Rod