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post #1 of 45 Old 07-19-2009, 07:56 PM - Thread Starter
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I am beginning my theater construction and would like to keep a separate thread for all my questions and uncertainties. I am trying to keep my room as isolated as possible and hence i have a few questions. the theatre consists of 3 walls that share an exterior concrete wall and are placed approx. 1" away from the concrete. there is only 1 wall that will be an interior wall which will be 2x6 staggered construction.

1.) i have built the exterior walls of the theater room 1/2" short of the main floor joists. i was planning to use dc04 clips to attach them but right now i have used 1 nail every 3-4 feet to attach the wall to the floor joists. i will be installing a new, independant ceiling for the theater completely decoupled from the main floor joists. this includes having new ceiling joists for the theater. as we stand, the wall is very secure even with only 1 nail every 3 feet. is this method okay and can i omit using the rsc-dc04 clips?

2.) in regards to hvac, i would like to have 2 supplies and 2 returns for the room. room size is 15'x21'. i am flexible with placement as this is a new construction home, so what is the best advice for placement? should i have 1 supply and 1 return low wall, and 1 supply and 1 return high wall?

3.) i will be using dd and gg for the entire room, in addition to 1 staggered wall that joins the bar area which will have dd and gg on the other side as well. is using 2 sheets of 5/8" with gg in between sufficient or will i gain anything by using a 3/4" sheet, followed by gg and then another 5/8" sheet?

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post #2 of 45 Old 07-19-2009, 10:49 PM
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I am no pro but here's some of my limited insight to your questions...

1) Could you expand a little on your future ceiling's construction? Are you planning on installing a completely separate set of ceiling joists, that will be fastened to your interior walls?

Assuming that is the case, may I suggest you fore go the use D/GG/D and instead use OSB/GG/D. With the added shear support the use of a OSB layer will give you, I don't see the need to connect your new internal walls to the exsiting floor joists. To be very clear... I am not a structural engineer, and/or building inspector, so my opinions are just that, and are not meant to imply that what I suggest is an acceptable way to do things according to building code. However, I am getting the impression that you are planning a room within room build, and I feel using anything to couple your efforts to the existing structure will hamper the end result.

With that said... What I am suggesting is exactly how I plan on to handle my room within room build.

2) If your build is a truly dedicated HT, I think you should concentrate on removing heat from your room. So that lends me to believe a high location for your returns would be best.

3) I think everyone here agrees that the more mass you have the better off your are. Where diminishing returns start to come into play...I don't know.
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post #3 of 45 Old 07-20-2009, 04:12 AM
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Quote:
Originally Posted by Anthony A. View Post

3.) i will be using dd and gg for the entire room, in addition to 1 staggered wall that joins the bar area which will have dd and gg on the other side as well. is using 2 sheets of 5/8" with gg in between sufficient or will i gain anything by using a 3/4" sheet, followed by gg and then another 5/8" sheet?

If I recall correctly part of the equation that makes DD+GG work is that the two layers should be the same thickness. Different thicknesses of Drywall have different flex characteristics and it was always my understanding that in order for the green glue to work efficiently you needed to make sure the two layers were the same thickness. I believe 5/8" drywall was always the recommended thickness just due to the cost and availability side of things.

-Rick
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post #4 of 45 Old 07-20-2009, 04:58 AM
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Not true. You can use different thickness's of drywall but thicker means more mass. More mass is what you want. Having said that... most use 2 layers of 5/8" although some have gone to 3 layers!

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post #5 of 45 Old 07-20-2009, 05:04 AM
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Quote:
Originally Posted by sr20rocket View Post

If I recall correctly part of the equation that makes DD+GG work is that the two layers should be the same thickness. Different thicknesses of Drywall have different flex characteristics and it was always my understanding that in order for the green glue to work efficiently you needed to make sure the two layers were the same thickness. I believe 5/8" drywall was always the recommended thickness just due to the cost and availability side of things.

-Rick

Not really, Rick. There are two schools of thought on this.

One says you should always used the max thickness for both layers to give maximum mass, and therefore maximum isolation.

The other says you should use two different thicknesses, e.g. 5/8" and 1/2", to circumvent a potentially nasty sound isolation problem called "concidence effect." The latter is a dip in the isolation curve which occurs at 2-3 kHz, due to the bending sound waves in the sheet of drywall coinciding with the speed of sound in the sheet. This frequency changes with the thickness of the drywall sheet, so if you use two different thicknesses, the coincidence dips don't coincide, and the isolation from one sheet fixes the coincident dip of the other.

I tend to favor the latter approach, particularly after I have come from the lab and seen some rather extreme measurements of coincidence dip. But the thing is, the real-world severity of this effect is hard to predict. Two walls, built ostensibly the same, can exhibit different degrees of coincidence dip. I don't know why.

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post #6 of 45 Old 07-20-2009, 07:08 AM
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Mass:
TL = 20 log10 (ms*f) - 48
Effectively means doubling the mass reduces transmission by 6dB. There's a point at which doubling the mass becomes a poor economic choice.
---
Coincidence Dip
While thickness plays a role, stiffness (modulus of elasticity) plays a larger role. At BNR and another secure but undisclosed location, the elasticity of common building materials (drywall, plywood, mdf, etc) were significantly inconsistent from sheet to sheet. Further, variations in method of construction would also alter boundary stiffness. For example, mounting drywall horizontally over 2x4 framing, 16" O.C. would produce significantly different results than when mounted vertically. Two layers of drywall, say 3/8" + 5/8" will behave similar to a 1" layer of drywall when those two layers have been glued together. Two layers of drywall, as above, will more closely mimic two individual layers with a viscolastic agent between layers.

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post #7 of 45 Old 07-20-2009, 08:20 AM - Thread Starter
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so dennis, are you saying that using a 3/4" and 5/8" is better than 2 5/8" simply because there is more mass? would you recommend i do this instead or just go ahead and use the same 5/8" all around.

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post #8 of 45 Old 07-20-2009, 09:45 AM
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Quote:
Originally Posted by Anthony A. View Post

so dennis, are you saying that using a 3/4" and 5/8" is better than 2 5/8" simply because there is more mass? would you recommend i do this instead or just go ahead and use the same 5/8" all around.

I don't think you'll find 3/4" drywall. 5/8" is about as thick as I've ever seen it.

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post #9 of 45 Old 07-20-2009, 01:17 PM - Thread Starter
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okay, i guess i'll just do double 5/8" then. i have also figured out the hvac portion of the theater and will have 2 low wall supplies at the rear of the room, and 1 high wall at the front. i will have 2 returns as well, 1 high and 1 low.

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post #10 of 45 Old 07-20-2009, 02:19 PM
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Quote:


i have also figured out the hvac portion of the theater and will have 2 low wall supplies at the rear of the room, and 1 high wall at the front. i will have 2 returns as well, 1 high and 1 low.

Nah...don't think so. You'll want two supplies (typically in the front of the room, high mounted) and two returns (high mounted) in the back of the room. You do not want air flow directly on any seating location. You do not want a velocity of more than 250 FPM through any vent (diffusor). You want the HVAC system to maintain a temperature of 70 degrees F with an outdoor temperature range of -30 to 100 degrees F and to maintain a relative humidity of not less than 25% nor greater than 50%. You want six air exhanges per hour and 15 CFM of fresh air per person.

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post #11 of 45 Old 07-21-2009, 04:04 AM
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Quote:
Originally Posted by Terry Montlick View Post

Not really, Rick. There are two schools of thought on this.

One says you should always used the max thickness for both layers to give maximum mass, and therefore maximum isolation.

The other says you should use two different thicknesses, e.g. 5/8" and 1/2", to circumvent a potentially nasty sound isolation problem called "concidence effect." The latter is a dip in the isolation curve which occurs at 2-3 kHz, due to the bending sound waves in the sheet of drywall coinciding with the speed of sound in the sheet. This frequency changes with the thickness of the drywall sheet, so if you use two different thicknesses, the coincidence dips don't coincide, and the isolation from one sheet fixes the coincident dip of the other.

I tend to favor the latter approach, particularly after I have come from the lab and seen some rather extreme measurements of coincidence dip. But the thing is, the real-world severity of this effect is hard to predict. Two walls, built ostensibly the same, can exhibit different degrees of coincidence dip. I don't know why.

Regards,
Terry

Thanks for the clarification of the science involved Terry I appreciate it.
Maybe I have been reading to much on here and its time to start my own theater already.

-Rick
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post #12 of 45 Old 07-26-2009, 07:33 PM - Thread Starter
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i would like to know if my current setup is sufficient. this is in regrads to foregoing the use of dc04 clips tp decouple the exterior walls of the theater to the ceiling joists. right now, i constructed my walls 1/2" short of the ceiling joists and there is 1 nail every 4' around the perimeter of the room holding the walls in place. so total number of nails in the theater is like 20. so the only coupling of the exterior walls would be the nail that connects it to the floor joists. is this an okau practice or will it make all my efforts of double drywall, greenglue and independant floating ceiling futile?



another question is in regards to filling the stage with sand. below is a pic of my setup.



note the area at the bottom of the pic where it shows a large sub box. this is where the sub will be housed. could i make this small area (its about 4'x6') detached from the stage and fill it with sand and forego having to fill the rest of the stage with sand? the lcr speakers (which will be klipsch ultra 2's) will be installed and bolted to the wall and there will be nothing actually resting on the stage. what are your thoughts on this?

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post #13 of 45 Old 07-26-2009, 07:52 PM
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Quote:
Originally Posted by Anthony A. View Post

i would like to know if my current setup is sufficient. this is in regrads to foregoing the use of dc04 clips tp decouple the exterior walls of the theater to the ceiling joists. right now, i constructed my walls 1/2" short of the ceiling joists and there is 1 nail every 4' around the perimeter of the room holding the walls in place. so total number of nails in the theater is like 20. so the only coupling of the exterior walls would be the nail that connects it to the floor joists. is this an okau practice or will it make all my efforts of double drywall, greenglue and independant floating ceiling futile?

The nails will not provide wall to joist decoupling. If you want this, you should replace them with the RSIC-DC04 clips. It is exactly what they were designed to do.

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post #14 of 45 Old 07-27-2009, 07:26 AM
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The front wall wall is shared with the stairwell. Stairwells will communicate sound vibration very well. It's advised not to incorporate that stairwell wall into the build.

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post #15 of 45 Old 07-27-2009, 09:32 AM
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Hello Anthony,

I noticed a post of yours in another thread, that kinda sent up same red flags for me...

http://www.avsforum.com/avs-vb/showt...5#post16884895

Are you really planning on using 2x4 for Joists, as your independant "Floating Joists"? Spanning 15' unsupported, then hanging 2 layers of Dwall.

Not only will this not pass inspections, but you can expect some serious ceiling sagging in the future.

I didnt take the time to look it up, and I'm no structural engineer but even at only a 15# dead load, i would bet you need a min of probably 2x8, to span 15'.

If you dont have the ceiling height below or the room between your current joists because of mechanicals, for larger joists then you would be better off with clips / channel / current joists to decouple your ceilings. IMHO

If I misunderstand what you mean by floating ceiling or i read your intentions wrong then I apologize and disregard this post.

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post #16 of 45 Old 07-27-2009, 10:06 AM
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I don't mean to hijack, but I have a question that probably serves the thread well.

For a basement theatre, what is the best course of action for the ceiling?

1. Z-Channel and 5/8" drywall
2. Z-Channel and doubled up 1/2" drywall/green glue
3. Doubled up 5/8" drywall without the channel (right onto joists).

I am going to use pink QuietZone all round the room and in the floor (basement ceiling) joists. I am trying to not go too expensive so these are the best options for me I think.

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

Thanks guys
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post #17 of 45 Old 07-27-2009, 10:13 AM
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Quote:
Originally Posted by slider33 View Post

I don't mean to hijack, but I have a question that probably serves the thread well.

For a basement theatre, what is the best course of action for the ceiling?

1. Z-Channel and 5/8" drywall
2. Z-Channel and doubled up 1/2" drywall/green glue
3. Doubled up 5/8" drywall without the channel (right onto joists).

I am going to use pink QuietZone all round the room and in the floor (basement ceiling) joists. I am trying to not go too expensive so these are the best options for me I think.

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

Thanks guys

I would not use Z-Channel. Too stiff. Here's what is recommended starting from the top and working down in terms of performance:

#1 a Floating Ceiling. Best, most complete decoupling. Uses simple lumber

#2 Use Resilient Clips and Drywall Furring Channel

#3 Use the Drywall Furring Channel attached directly to the joists. Attach drywall to the channel. Channel is 24" on center

#4 Attach drywall directly to the joists.

In the joist cavities use dtandard (cheap) R19 fiberglass. Shop for the best price.

Use double 5/8" drywall. It's too cheap no not use 2.

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post #18 of 45 Old 07-27-2009, 10:19 AM
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Quote:
Originally Posted by Ted White View Post

I would not use Z-Channel. Too stiff. Here's what is recommended starting from the top and working down in terms of performance:

#1 a Floating Ceiling. Best, most complete decoupling. Uses simple lumber

#2 Use Resilient Clips and Drywall Furring Channel

#3 Use the Drywall Furring Channel attached directly to the joists. Attach drywall to the channel. Channel is 24" on center

#4 Attach drywall directly to the joists.

In the joist cavities use dtandard (cheap) R19 fiberglass. Shop for the best price.

Use double 5/8" drywall. It's too cheap no not use 2.

Pardon my ignorance, but what exactly is a resilient clip? Is the furring channel the same thing as a Z channel? I only have an 8' ceiling down there so I don't think I'll have the space for a drop ceiling.
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post #19 of 45 Old 07-27-2009, 10:21 AM
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Quote:
Originally Posted by slider33 View Post

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

If you mean "resilient channel," fugetaboutit. It used to be an option for sound isolation, but has proven:

1. Unreliable to install, because of the likely possibility of installers shorting it out with long screws.

2. Unpredictable, due to product change/variation and lack of testing for new versions.

The replacement for these are RSIC -- Resilient Sound Isolation Clips, distributed by PAC International.

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post #20 of 45 Old 07-27-2009, 10:22 AM
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Great question. A Z-channel is used for other things, but not ideal for this application. Distinctly different animal from a Drywall Furring Channel. See various clips and applications here: http://www.soundproofingcompany.com/products/clips/

My apologies for the commercial nature of this link. You can see various types and how they are applied

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post #21 of 45 Old 07-27-2009, 10:52 AM
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Thanks for the help guys
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post #22 of 45 Old 07-27-2009, 11:36 AM
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Just a little interesting tidbit. Holmes on Homes episode this weekend had the big man using hat channel. In his explanation he said that they only fastened it on one side so that it would hang down and act like a spring for sound proofing.

Kind of a poor man's Z channel if you ask me. Also struck me as a little risky to use it in a manner it wasn't intended.
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post #23 of 45 Old 07-27-2009, 11:43 AM
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Wow. What a liability

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post #24 of 45 Old 07-27-2009, 07:46 PM - Thread Starter
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Quote:
Originally Posted by Terry Montlick View Post

The nails will not provide wall to joist decoupling. If you want this, you should replace them with the RSIC-DC04 clips. It is exactly what they were designed to do.

how much flex do the dc04 clips have in terms of measurements? (ie. can i push the wall 1/4" in)

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post #25 of 45 Old 07-27-2009, 07:48 PM - Thread Starter
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Quote:
Originally Posted by Ted White View Post

The front wall wall is shared with the stairwell. Stairwells will communicate sound vibration very well. It's advised not to incorporate that stairwell wall into the build.

what would be your suggestion ted? that wall is a 2x4 bearing wall resting on concrete, but i can add a 2x2 plate on the bottom and top and use more 2x4's to make it a staggered wall. this is will be covered with dd and gg on the theater side, but single layer on the stair side. or would you recommend resilient clips, etc?

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post #26 of 45 Old 07-27-2009, 07:52 PM - Thread Starter
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Quote:
Originally Posted by KNKKNK View Post

Hello Anthony,
Are you really planning on using 2x4 for Joists, as your independant "Floating Joists"? Spanning 15' unsupported, then hanging 2 layers of Dwall.

Not only will this not pass inspections, but you can expect some serious ceiling sagging in the future.

Brad

i thought so too until my carpenter advised me that it is standard practice to use 2x4's vertical and then use either 1 or 2 perpendicular pieces to tie them together. i asked an engineer who is a friend of mine, and he said that will be much stronger than if i were to use 2x6 verticals. aparently the span is by code as well, so we'll see tomorrow how it goes. if i find i can't hang from them , then i'll beef it up with something bigger. this method is used when reinforcing roof trusses and is quite solid when completed braced and nailed together.

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post #27 of 45 Old 07-28-2009, 05:58 AM
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Quote:
Originally Posted by Anthony A. View Post

i thought so too until my carpenter advised me that it is standard practice to use 2x4's vertical and then use either 1 or 2 perpendicular pieces to tie them together. i asked an engineer who is a friend of mine, and he said that will be much stronger than if i were to use 2x6 verticals. aparently the span is by code as well, so we'll see tomorrow how it goes. if i find i can't hang from them , then i'll beef it up with something bigger. this method is used when reinforcing roof trusses and is quite solid when completed braced and nailed together.

Sounds like engineered web joists... in which case yes these are stronger and can span farther than dimensional lumber of "=" size.

Quote:
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in regards to insulationg a ceiling, i need some help. i have 2x10 joists, followed by a 6" air space, and then a 2x4 independant floating ceiling for my theater. so total joist air space is about 20". other than the fact that anything more than r12-19 is sufficient, is it advisable to stuff this entire 20" air space to avoid resonance, or can i simply put up r19 at the top of the 2x10 joists and have about 15" of airspace in the cavity? will this act like a drum and should i competely insulate this space?

Your earlier posts describe walls build within 1/2" of your existing joists, at first I thought you were going to rest your new ceiling joists on top of the walls you built (with new joists Weaved between existing joists) to create your decoupled ceiling. Then I read this post that describes the bottom of the new joists being ~ 10" below the existing joists.

Are they using joist hangers off of the walls to carry the new "floating ceiling"?

If you could post some pictures that would be great.. I'm having a hard time wrapping my head around the construction of what you are describing. (maybe i shouldnt post until i have 6 cups of coffee in me ) sorry about being so dense, but now I'm curious.

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post #28 of 45 Old 07-28-2009, 06:24 AM
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Quote:
Originally Posted by Anthony A. View Post

how much flex do the dc04 clips have in terms of measurements? (ie. can i push the wall 1/4" in)

This turns out not to matter, Anthony. The issue is with mechanical decoupling of the walls to the ceiling.

Another option is to use sway braces to hold the walls. But these are not designed to support the walls -- only stabilize while mechanically isolating them. And they tend to be rather expensive compared to the DC04 clips, which provide support as well.

I don't know the details of your configuration. But if you follow the PAC International's installation recommendations on number of DC04 clips, or speak to an engineer there (they are excellent), your wall will also be guaranteed not to fall down.

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post #29 of 45 Old 07-28-2009, 06:27 AM - Thread Starter
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you're right, i haven't been too clear, but basically the exterior walls have been built 1/2" short of the existing floor joists. the interior wall that i will be building (staggered one), will be about 10" lower than the existing floor joists' bottom. so the new independant ceiling will be resting on the staggered partition, but the other side will have a ledger nailed to the wall and then joist hangered for support. i hope this is clear, if not by tomorrow night the basement will be finished framing and i'll post some pics in my build thread.

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post #30 of 45 Old 07-28-2009, 06:27 AM
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Anthony, I would strongly encourage you to build a new wall system in front of the old theater stairwell. Any contact with that wall will diminish your results.

You really cant contact any existing framing, especially the stairwell framing. Everyone wants to, but not a good idea at all

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