Quick Ceiling question for Steve

[JohnGardner]

Steve,

As you know I will have a height problem (7feet) in my tracking room if I build a new "floated" ceiling on the new walls.

Another member sugessted adding two new layers of wall board to the existing 10mm plasterboard ceiling however you commented that because my control room shares this same ceiling (trusses and 10mm plasterboard) I could run into problems will flanking noise.

I am building the standard double wall between these two rooms that will have a 50mm air gap between the studs.

If I cut the existing 10mm plasterboard ceiling away in this 50mm air gap (think long thin line) with a sharp craft knife how far do you think it will go to helping the possible flanking noise between the rooms?

I also realize that three layers of board (10/13/13mm) in my new tracking room is still only one leaf and not that great for over all isolation of the room but If I can reduce the flanking noise and make sure all joins are well sealed it may be a good compromise between isolation and room height.

Thanks and look forward to your thoughts - general idea showen below.

[sharward]

I'll take a stab at this...

I'm assuming your illustration is a side view -- which actually is not obvious because the studs are showing as horizontal rather than vertical.

Slicing away a strip of ceiling gypsum probably won't suffice, because both ceilings are attached to the same structural members (ceiling joists or trusses). In order for a true room-within-a-room design to function properly, there would be no firm contact between the loud place and the quiet place. If your loud room ceiling is attached the ceiling joists which is attached to the quiet room ceiling, your quiet room won't be very quiet at all.

Have you considered removing the gypsum on the ceiling altogether, then staggering new ceiling joists parallel to the existing ceiling joists? This would allow you to, in theory, have a ceiling that has the benefit of decoupled ceiling joists but you could tuck the majority of each joist into the space between your existing joists, thus saving probably at least 4"/10cm of headroom. You might have to increase the mass of the floor above (assuming there is one) by inserting strips of gypsum between the joists, sealed, and held in place with cleats. This thread covers that approach in some detail.

I hope that helps, and that I haven't made life more difficult for the real brainiacs around here... (If a bunch of contradictory advice comes at you, you'll know that I did!)

[JohnGardner]

Thanks for your help on this one
Will lookminto removing the original board and report back
JG

[knightfly]

John, what's the unsupported span on your ceiling, what's the existing joist size? Could be that you may be able to put your outer leaf on top of the old joists, set new joists up below these as Keith mentioned, and your new INNER leaf on the NEW joists; this WILL eat into your headroom MORE than Keith thought, however; you will need some cross-bracing of the old joists to keep them from twisting in the mid-span (and therefore weakening support) - so best you'd get is dropping the new joists to about half their width below the existing joists. Note the red "X" in the middle of this sketch -

This still doesn't provide any twisting control for the ceiling joists, only for the upper ones; on any span longer than about 12 feet, this could also cause problems; only way around that is to NOT "interleave" the joists as much, leaving enough room for cross-bracing between the new, lower joists in the same manner... Steve

[JohnGardner]

Hi Steve,

thanks for the details provided.

I am trying to find a compromise between isolation and ceiling construction.

My problems are:

I can't do a false ceiling as I need the headroom. - just not an option. I will hate wotking in a room with a 7ft ceiling.

My tracking room and control room share the same floor and ceiling

I can semi isolate the floor on pucks and new framing floorboards

Walls I can do on this new floor therefore isolating them from the floor.

Ceiling is where I am stuck.

I totally understand the mass air mass thing but what I am asking is , as a compromise between isolation and height, what is the best way to go?.

If I add two new layers of board to the exisiting ceiling (36mm in total) and cut the gap in the existing ceiling to help flanking noise between the rooms - as in the above diagram - what kinda STC/TL can I hope to acheive to the outside world. I maybe able to live with 50, or even forty. I reckon the existing ceiling has about 40 now so surly to more layers will help.

Thanks for you help, I know you don't want me to regret the build but there is always middle ground. I am not a pro facility just a hobby guy that wants to keep the neighbours happy.

I can always add more gib board once the room is done or even a false ceiling if I really had to but i just need a basic ceiling upgrade as a starting point.

[knightfly]

John, I'm not remembering what's ABOVE your ceiling; a vented attic, or what?

You can get SOME improvement in isolation between rooms, by using Resilient Channel to mount each inner ceiling's wallboard layers separately from the other inner ceiling - however, if you rely on strictly mass law for iso, that will pretty much suck. even 3 layers of 15mm gyp board will barely keep up with a single, 44mm solid slab exterior door; maybe around STC 35 or so at best, and not that good at lower frequencies.

Doing the ceilings that way will require maybe a foot of loose fiberglass insulation over the ceiling, for damping and wave control.

Is there a pic or drawing up yet on your building? Thanks... Steve

[JohnGardner]

Thanks Steve,

Heres the building.

The VIP's are:

(1)There is no access to the attic/ceiling space.
(2) If I build a new false ceiling I have a 7ft room, I am only starting with 2.4m - that will suck big time

What I need to do is somehow bulk up the existing ceiling.

any magic bullets out there in cyber space!!

[knightfly]

OK, no access to the attic (I could make access )

Is the attic vented in any way, anywhere along the perimeter or at roof peaks, etc?

Check out this document, and let me know which (if any) comes close to yours

http://www.buildingscience.com/resource ... Design.pdf

Also, is there anything UNDER the "iron roofing", or is it placed right on the framing?

No magic bullets, but I've not given up on finding something usable... Steve

[JohnGardner]

Hi Steve,

Thanks for reply:

(1) The roof has no venting at all - It is not normal practice to vent iron roofs in New Zealand. I walked around the building again last night and can see no vents at all. I suppose the ceiling cavity is not totally airtight and has it's on "natural:" venting to some degree. Our climate hear is fairly moderate 0-18degrees in winter, 20-30degrees in summer. Figure one from the PDF looks like me except it is an iron roof with building paper and there is no "continuous sofitt venting" under the eves.

(2)The iron will have building paper underneath it between the top of the truss and the iron.

(3) I contaccted the architect that built/owned the place before us and he is sure that he put insulation (R2.2) in the ceiling cavity on top of the existing plasterboard (95%sure). I have a sparke coming around this week to take down existing flouresant lighting and disconnect the power so I can confirm this for sure later this week.

Thanks

JohnG