Low ceiling theory and thoughts

[Nick Boyd]

Hello all,

I'm working on a basement studio which has a height a 6'5" from the slab to the bottom of the first floor joists.

I'd like to humbly submit an idea for a ceiling and hear people's thoughts.

It most likely has been suggested before and I apologise in advance for the probable redundancy.

I'm aiming for maximum transmission loss and a ceiling cloud in as shallow a sandwich as possible. A pretty common objective ...

I'm including 2 images ...

There are a few variations on the low ceiling image floating around.

I've built a few basement rooms like these and have always found TL to be less than satisfactory in the low-mids to low range. This is hardly a surprise as I've never seen this structure touted as anything more than a deeply compromised way to get both cloud and isolation while losing as little overhead as possible.

With good sealing practices I have been able to get rooms like these to contain most of their high frequency emissions but a good deal of low frequency content always pass trough. This is likely caused by the bottom of the joists being exposed in the sound room ... a major flanking by mechanical transmission path.

I apologise deeply for my pityfull ceiling idea drawing and really hope folks can manage to decipher it ... I've have absolutely no skills whatsoever at computer assisted imaging of any kind. My girlfriend saw my "windows paint" experiment this morning and let out a solid laugh... Next time I'll make sure I ask my 2 year old nephew to draw this for me good n' proper in autocad .

Essentially my idea is a take-off on the backer box (as seen in this document):

SIM Backer Box Installation Guide | Soundproofing Company

The basic plan is to build 8' long backer boxes between the joists to house a ceiling cloud and join them in a continous surface that passes an inch below the first floor joists. Finish in burlap ... you get the idea.

It assumes one is using false joists (but boxes could be suspended with hangers) to house high density mineral wool. It assumes also that no cross bracing is in the way though one could conceivably have 2 boxes on both sides of bracing and join them below the bracing.

Assemble it all in plywood, laminate drywall with green glue, seal it up and go for a cheeseburger.

It seems to me that a complete high-mass, fully decoupled, sealed envelope could be built this way with minimal overhead loss ...

This creates a good number of outside corners the likes of which could be done with standard backer rod and caulk practices (like any wall outside corners) Care would be taken where this assembly meets the walls so as not to break the envelope ... it goes without saying also that this would need to remain in place and never come in contact with other framing members etc ... Standard studio building practices would apply fully of course.

I'm about to give this a try in my own basement ...

Does anybody see something that I might have missed ?

Any blatant reason why this would lead to an epic fail worthy of a youtube video ?

If I'm wrong set me right unashamedly.

If it's already a practice (though I read a lot and I've never seen it) apologies for re-inventing the wheel ...

Any recommandations on materials ? How would you build it ? I went with plywood on the first layer to keep it all together and laminated drywall with green glue on top.

Would you use triple materials for more mass ?

Watcha think ?

Nick

[MichaelH]

I'm not expert enough to make a real comment one way or another, but your design is definitely intriguing!! I'm sure someone "in the know" will weigh in. It does look like an awful lot of work, and might be hard to hang them, but, yeah, definitely very interesting.

-Mike

[gullfo]

#1 will have a lot of flanking due to the joist exposure and the compressed insulation. #2 looks like an inside-out ceiling that using nested joists. It should be functional but will be quite a bit of work. Are these boxes resting on the inner isolation walls and joined using lag bolts?

[Nick Boyd]

Originally Posted by gullfo

#1 will have a lot of flanking due to the joist exposure and the compressed insulation.

Precisely the point of this thread ...

I've built a few personally and indeed they flank like bast#$%& but at below 7' what other options have we got ?

Originally Posted by gullfo

Are these boxes resting on the inner isolation walls and joined using lag bolts?

Yes they sit on inner walls. Not sure where you see lag bolts ... Fastened like any other false joist sitting on a top plate.

Way I see it:

1- Build an 8' long (flower type box) box on the ground an seal it
2- Stick it on the inner wall on one end and locate between joists, fasten to top plate.
3- Rest the other end on a wall, beam or suspend with a decoupling hanger... etc ... framing application dependant.
4- Proceed to next boxes.
5- Mesure and rip necessary plywood strips to join them below the other joists.
6- Laminate drywall with green glue
7- Backer rod and caulk

Sure it's some work but in a studio build what isn't ?

One could do that just over drum and mix area as well ...

In my case I'd do the whole room because at 6'5" I want as little contribution from the ceiling as possible anywhere in the room...

Given the number of low ceiling threads on here ... I'd say there is a need.

What I want to know is: Is there anything in there (the plan) that could compromise or defeat the isolation ?

In actual application it (like any thing else) depends on the guy who's putting it together...

To me it would be easier to execute then some cathedral ceilings with multiple skylights I've built ... It wouldn't be that bad really ...

Nick

Also my drawing is completely out of proportions which certainly doesn't help to read it ... Apologies again.

[johndykstra]

it is intriguing.

I wonder, is the drywall layer necessary as drywall? I mean, all that mud and tape... all corners. yuck.

It's all covered anyway with the fabric. I wonder if it wouldn't be easier to install a second mdf layer, and caulk the joints.

I would leave plenty of wiggle room for uneven joist spacing, and make the thing "one cut fits all" rather than individually measured custom cuts.

[Nick Boyd]

Originally Posted by johndykstra

it is intriguing.

I wonder, is the drywall layer necessary as drywall? I mean, all that mud and tape... all corners. yuck.

It's all covered anyway with the fabric. I wonder if it wouldn't be easier to install a second mdf layer, and caulk the joints.

Hello John !

I put in drywall cause it's your classic cheap mass ... but indeed mdf and caulk should perform the same right ? Constant mass and airtightness being the objectives ...

Originally Posted by johndykstra

I would leave plenty of wiggle room for uneven joist spacing, and make the thing "one cut fits all" rather than individually measured custom cuts.

Couldn't agree more with the wiggle room and one-size-fits-all ... It is a system that could be easily shorted.

My feeling is that getting this caulked and properly airtight would be the main challenge here ... And to have the assembly remain as such for the future. Also I'm thinking that the bottoms wouldn't be anything more than an horizontal version of an outside corner on a wall ... A procedure we're familiar with.

Couldn't agree more on the wiggle room.

While it would affect the ratio of exposed absorbant to reflective materials in the room ... I think I'm gonna aim for no less than a full inch all around.

I'm also considering adding another complete layer of 1" 703 at the bottom of the assembly to pass below it all and treat the additional plywood facing down in the room. Trying to maximise the amount of exposed absorbant material.

My joists here are on 24" center ... so the cavities are fairly wide.

Thanks for you thoughts !

Nick

[once a roadie]

This idea looks very interesting to me - unfortunately, I'm no pro can't say if it will work or not!

[MichaelH]

I suppose, if you just build 1 size box that you know will fit between all your joists, like say, a 14" wide box, you could easily rip all you mdf to size, and do cabinet type assemblies that wouldn't take too long. What about doubling up the mdf on top of the box for more mass? What kind of a span do you think you could run before the boxes sag if they are resting on your new walls? I suppose a pretty good distance, really cool design idea!

[Rod Gervais]

Nick,

The 2nd application should work pretty well (no real way to determine the actual TL value without testing though).

If it was me doing the work I would probably go for drywall rather than MDF for the subsequent layers.

I would do three layers total - not the 2 you have indicated.

The cost would be much cheaper, and, seeing as you are caulking the corners anyway (and then hiding everything behind fabric so there isn't a finished surface to deal with) taping would be at a minimum.

I would add some fluffy insulation above the rigid insulation before installing the fabric.....

Not only will it increase your level of absorption, but it will also help to damp the surface of the lower assembly.

Good Luck, keep us posted - and remember - "pics or it didn't happen"

Rod

[Mofo]

This thread is very close to my situation. I also have a have very low basement ceiling. Right now it's exposed and has terrible sound transmission (I can hear my cats walking on the floor above). I was thinking of framing walls and new joists with metal studs to hang the ceiling so as not to produce flanking through the existing joists (which are so old I don't trust attaching a ceiling to anyways).

Now the OPs plan to emboss the ceiling in between the joists is very appealing and would like to know if this can be accomplished without attaching at least the ceiling to the existing joists? I understand that the sub-floor should have some mass glued and or screwed...not sure how to do that...

BTW, I have read Rod's book and have a few questions as to his comments here regarding going for 3 layers of drywall...do you mean with green glue in between them all?

Thanks so much!

[Nick Boyd]

Rod,

I hadn't seen your reply (Been away for a few days).

I will incorporate all your recommandations ...

Thanks a million for weighing in !

I've already got a 7-8 boxes built and test fitted in place.

Pictures coming up today or tomorrow !

Nick

[Nick Boyd]

Originally Posted by Mofo

This thread is very close to my situation. I also have a have very low basement ceiling. Right now it's exposed and has terrible sound transmission (I can hear my cats walking on the floor above). I was thinking of framing walls and new joists with metal studs to hang the ceiling so as not to produce flanking through the existing joists (which are so old I don't trust attaching a ceiling to anyways).

Now the OPs plan to emboss the ceiling in between the joists is very appealing and would like to know if this can be accomplished without attaching at least the ceiling to the existing joists? I understand that the sub-floor should have some mass glued and or screwed...not sure how to do that...

BTW, I have read Rod's book and have a few questions as to his comments here regarding going for 3 layers of drywall...do you mean with green glue in between them all?

Thanks so much!

Mofo (great name !)

Think of the boxes as a glorified false joist. It really is no different. As such it needs to sit on decoupled walls resting on damped concrete (your typical basement slab).

Wth standard sheet good sizes you'll be limited to a run of 8 feet, at the ends of which you'll need either a decoupled wall, a decoupled beam or isolation hangers hanging from the ceiling to support the boxes.

I'm going with the later. It goes like this: Figure out the finished weight of the box (including all layers of drywall, plywood, insulation etc ...) and get an isolation hanger company to spec a product for that weight.

As per Rod's recomandation to go with 3 layers total (which I will do with Green Glue myself) I suspect it has to do with the huge amount of 90 degree bends this assembly produces. And adding mass which is never bad ...

I should have mine up within the next month or two (if time allows) and I'll be sure to report with pictures.

Nick

[Nick Boyd]

Here are some pictures of my ceiling build.

Naturally the 2X4 blocking which are holding the walls plumb will be replaced by DC-O4 clips ... And the octogonal light boxes will be surface mounted properly ...

This is a test fit !

Feel free to comment !

[Nick Boyd]

So I'm moving along with the construction of the ceiling. The fear I have with what I'm doing is that this assembly creates a small airspace of 1" at its bottom (around the first floor joists).

I know small airpaces are rather costly in terms of transmission loss ... I'm hoping it won't degrade performance too much.

That 1" air cavity at the bottom of the flange has direct connection to a good 6" airpace over the top of the box ... Maybe performance will be an average of both air spaces ...

Damn you low ceiling .

Anybody got any thoughts to add ?

[gullfo]

maybe too late - but capping the space across the joist with an MDF/plywood/OSB layer could seal that and would improve it a lot versus leaving the air gap...

[psykostx]

I was under the impression that a small air gap between the finish material and the insulation was a good thing in reducing vibration, and maximizing the bandwidth of reflection (enabling you to control the bandwidth of reflections with a cloud of some sort). In your situation I would stuff Roxul between the joists, then use a fabric or cieling tiles over that, leaving the cieling completely dead, and then using the walls for your reflections. My 2 cents.

[Nick Boyd]

Originally Posted by gullfo

maybe too late - but capping the space across the joist with an MDF/plywood/OSB layer could seal that and would improve it a lot versus leaving the air gap...

Yes absolutely ...

A lot has happened since these pictures ...

Obviously a flange connects the boxes across (underneath) the joists. (as explained earlier/above). I stuffed in some light fluffy in there around the joist as well ... Being carefull not to compress anything as compressed mineral wool can couple/transmit vibrations.

This structure is fully decoupled ... One end on a studio wall, one end suspended via mason HD-A-Green.

Plywood layer is fully caulked and I'm starting drywall layer 1 (with green glue tomorrow).

Even with a single plywood layer in place (given that it's decoupled) I can't hear my nail gun compressor from upstairs ... Dramatic transmission loss.

I'm confident once I get the additional 2 layers of drywall with Green glue I'll get satisfactory isolation.

Then fill those nested boxes with roxul to create a cloud, staple fabric, trim and away I go ...

I'm quite happy with the system ... It wouldn't suit everybody but it gets the job done for a personal writing room ...

The space is my basement in an urban area where space is expensive ...

I've got a few threads lying about which pertain to various aspects of this build.

I should probably start a build diary.

Not too long ago I got Jeff Hedback involved.

There are reverberent volumes coupled to the drum area in there as well ...

The walls are combination membrane/porous absorbers AND isolation.

Slats ... space couplers ... Nested clouds.

Fun stuff really !

[Nick Boyd]

Originally Posted by psykostx

I was under the impression that a small air gap between the finish material and the insulation was a good thing in reducing vibration, and maximizing the bandwidth of reflection (enabling you to control the bandwidth of reflections with a cloud of some sort). In your situation I would stuff Roxul between the joists, then use a fabric or cieling tiles over that, leaving the cieling completely dead, and then using the walls for your reflections. My 2 cents.

Hey there thanks for the comments.

Not sure if I'm reading you right ...

You seem to reference the old classic "fill the space between the joist with thick fluffy and cover with fabric"

While this works well for a cloud it does nothing for isolation.

This ceiling is the same as a double drywall decoupled ceiling AND a 6" cloud.

It's just that the cloud is embedded/nested between the first floor joists.

I'll add more pictures tomorrow !

Thanks for the comments !

[psykostx]

I got you, I thought you were just going for the cloud...try vinyl with MDF on top perhaps... or HDF if you can afford/find it... just wrap it around the whole ceiling construction, joists and all then put the fluffy clouds in between perhaps?

[Nick Boyd]

Originally Posted by psykostx

I got you, I thought you were just going for the cloud...try vinyl with MDF on top perhaps... or HDF if you can afford/find it... just wrap it around the whole ceiling construction, joists and all then put the fluffy clouds in between perhaps?

Well plywood/osb/mdf plus 1 layer of drywall is how most soffits are built ...

Plywood + 2 layers of drywall (my case) is cheapest and necessary to meet code (fire) in my area ... Inside the boxes I'm just caulking ... not taping.

I'm not covering the whole ceiling in fabric either ...

I'm plastering the bottom horizontal layer ... then I'll staple fabric over the cavities and add trim to hide the staples.

The way it looks now is like a continuous surface with 6" recessed cavities everywhere ...

My finished surface will be 2 1/4" below the first floor joists. Not bad !

Not sure were you'd see HDF but this stuff is not too great with screws ... Actually I detest screwing in the sides of plywood ... So I glued and screwed the bottom pieces all around and drilled pilot holes not to split the ply ...

I'll add pictures today !