Trying to understand ceiling gap (photo)

[edenorchestra]

Greetings Studio Fans . . .

Ok . . here's my newest issue. I have the outer and inner wall frames up. I have of course a gap between the two walls that goes to the ceiling. My question is do I fill the void above the walls (as shown inside the green elipse) between the two leaves or do I simply allow the insulation to go up through into the ceiling insulation area?

Regards,

[AVare]

My question is do I fill the void above the walls (as shown inside the green elipse) between the two leaves or do I simply allow the insulation to go up through into the ceiling insulation area?

The wording of your question makes it difficult to understand what you mean by "fill the void."

Treat the the space as if the top plates are studs on their sides. That is the same amount and depth of insulation as you have in the rest of the wall cavity.

Hope that is clear.

Soundly;
Andre

[edenorchestra]

I THINK I understand . . filling the void was the wrong syntax. The gap between the leaves at the top plates, does it have to be covered with a leave as if to say the leaves would:

Start at the floor on the inner leave . . go up the wall . . across the top . . over to the outer leave and then back to the outside grade.

If I understand you correctly I do not have to do this but only have the insulation fill the area between the leaves up through the gap between the leaves into the insulation above the ceiling.

If the ceiling is to come only over to the inner leave, I was concerned that the area between the leaves would be compromising the wall.

Also I was planning to put RC on the ceiling and use 2 layers of 1/2" with the gypsum coming up close to the inner leave but allowing a gap to which I would caulk . .

Being that the ceiling has no upper floor is this the best method? I see alot about ceiling with floors above, but little on an attice space. I guess my concern is that my walls have plenty of mass . . but above the ceiling is a lot of space and a 4:12 pitch truss roof.

Thanks for you reply

[John Sayers]

leave it void - the idea is for the inner wall to NOT touch or be connected to the outer wall.

cheers
john

[AVare]

I was planning to put RC on the ceiling

The RC is of no value in your ceiling. It may even degrade sound isolation. The rest of it sounds about right.

Andre

[knightfly]

Mark, if I understand your question correctly you're wanting to know how to get a double leaf barrier where your ceiling will be?
If so, since you can't seal your outer roof (the 4/12 pitched part) without causing moisture problems, that needs to be vented - this means that it can't provide your outer leaf of mass for the ceiling.

So, for good isolation in your ceiling you need to find a way to make your outer wall leaf continue across the ceiling, then leave an insulated gap and make your INNER wall leaf ALSO continue across the ceiling, but without any hard coupling between your inner and outer leaf -

If your trusses are strong enough (only the company who built them can tell you this, these are calculated by engineers for specific loading at time of manufacture) you could conceivably put 2 layers of wallboard on TOP of the horizontal chords of the trusses, sealing each layer with caulk where the wallboard is penetrated by the web chords of your trusses - this is a major pain in the ass to do, and by the time you then add RC to the underside of these trusses and 2 more layers of wallboard (insulated) in order to get your 2 leaves, you will very likely EXCEED the ratings of your trusses and create an UNSAFE construction.

A better way would be to put your ceiling's OUTER leaf UNDER the trusses - then, build your inner wall frames so there is room for new ceiing joists to rest on top of those inner frames, and size your new ceiling joists so they will support the necessary weight of the inner layers of wallboard.

If you need any help calculating joist size, we can do that no problem - I know this method will reduce headroom, as will a floated floor if you want maximum isolation; the alternative is upset neighbors and not being able to use the space at all.

So to recap, your outer leaf would consist of the layers of paneling on the outside of your existing wall frames, sealed to two layers of wallboard fastened to the INSIDE of your ceiling joists (the bottoms of your trusses) - then, your INNER leaf would consist of new wall frames resiliently braced at the top, in order to keep from hard contact; you would build inner ceiling joist frames resting on top of these wall frames, and ONLY put layers of wallboard on the INSIDE of each of these frames. All air gaps filled with insulation, or as close as possible.

Anyplace you might need fireblocking, this can be to code by using mineral wool/rockwool insulation batts, same as the rest of your walls should have; this material meets code for fire blocking but will NOT compromise the isolation you need between inner and outer leaf.

The final goal is to have two complete but separate envelopes of mass wrapped entirely around you and your toys, with no gaps and no weak spots. This is rarely easy to do, but necessary for good isolation... Steve

[edenorchestra]

Steve,

Thanks for the detailed advice. I am going to bite the bullet and take down what studding I have installed and rethink this construction (its only $150 worth of wood and I can reuse most of it).

Your suggestion of covering the lower side of the existing rafters as my outer leaf is the best method, as I have no idea who designed the trusses nor do I want to try to fill in the gaps from above. The building is 24' X 36' with the trusses running across the 24' length. Ultimately I will be adding another 16' to the length and will end up with a 24' X 52' facility, but I stopped constrution on the addition for the winter here in Western Pennsylvania.

My issue now will be to find a way to span the 24' in a safe manner, which may entail some pillars or some creative thinking as I want to make the studio open with no separate control room (RE: http://johnlsayers.com/phpBB2/viewtopic.php?t=2706 The working height at the moment is 9'6". The addition will have an open scissor truss with an additional 2 feet added to the wall height for a "live area".

I would be happy to send more pictures if you have need of more detail. Here is what the inside looks like right now and of course those new studs will be taken down in lieu of our discussions.

Best Regards,

[edenorchestra]

Oh did I mention that I have trains . . neighbors aren't much of a problem but the trains are about 500 yards away .

[knightfly]

I resized your pic so we wouldn't have to scroll sideways - it's better if you resize before posting, down to about 750 pixels wide -

Are your block half-walls hollow, or filled, or just a few cavities filled for re-bar reinforcement? If they're NOT completely filled, you will need to do that before continuing - especially with low frequency crap from trains being a concern.

Also, it's a good thing you're taking down the new studwork; just furring out like I see on the pic will cause a couple of problems, depending on whether the blocks are hollow or filled - if they're hollow, they already make up both leaves of a mass-air-mass barrier and would be seriously compromised by another air gap and another leaf of mass. If they're filled, then that air gap is about 12" short of doing much for your isolation potential.

By keeping your span so long AND floating a floor, you're going to run into some SERIOUS loss of headroom - the ceiling will cost you about 13" total, and if you're getting rumble from the trains as well as the other squeaks, groans and crashes trains tend to make, a floated floor that actually WORKS for you will cost you about 9 MORE inches of headroom - I'm thinking 3-1'2" concrete floated on 3/4 ply resting on vertical PT 2x4's floated on 1" EPDM or Sylomer blocks -

There's more, but I've got to go dig a hole and put down my oldest dog before going to night shifts - he's in too much pain to wait any longer, sorry... Steve