Floating Floor on top of Second Floor (wood joist) - Help!

I have read every topic I could find on this site and others on the subject of floating floors (pro's/cons, etc.), and given the situation I am in, am thinking that a floating floor may be my only hope of any semblance of isolation, but am looking for suggestions and frankly am stuck on whether it would be a good idea or not. There is a decent amount of traffic about 50 feet from the wall of my garage, and sound seems to carry right through the garage via flanking and airborn through the floor. On a second floor, the mass loading options are limitet, but in the design I have tried to max out the load bearing limit of the floor joist underneath (have a 20 PSF dead weight, 40 PSF live load weight limit on the structure) The floor is already torn up exposing the 2x12" floor joists (I had to do this as part of the engineering specifications... the former owners didnt build the floor correctly), so costs to remove and replace the floor have already been factored in the project. Attached is a sketchup file of the proposed build up of layers of the 2nd floor structure. On top of the proposed floating floor, I would build walls for the room within a room (2 layers of 5/8" drywall sandwiched by green glue), and the ceiling greenglue/drywall sandwich hung from iso hangers (rather than built on top of iso walls). Am I crazy for even considering this?

you might want to read up on JohnH thread where he is building an awesome control room in his barn which has a problem with trucks driving by. why the perpendicular joists? to spread the load? you're likely to get the same load capacity by cross bracing the 2x12 and using 29/32" plywood subflooring. then add a layer of 2" 3lb/ft3 rigid insulation with 2x MDF w/ GG and finish flooring. if you can add the concrete board ($ and weight) that would even be better. build the isolation walls (which support the isolation ceiling?) on their own supports- consider Rod Gervais' approach using ND-1 isolators on the frame, or just neoprene.

Thanks for the tip on JohnH's post. I think I read it awhile ago before beginning this project (if I am thinking of the right post), but will re-read. The purpose of the perpendicular joist is two-fold. First, I need a structure built on top of the 2x12 with the height of around a 2x8 to meet the existing bathroom floor (outside the acoustic isolation zone but in the same room), and the entry threshold height. The entry to the studio above the garage opens up to the flat roof (foam/sealed) which is used to traverse in order to get to a set of stairs. The second reason was to distribute the load better accross the structural 2x12" floor joist and for bracing purposes. I wasnt planning on attaching this secondary floor structure in any way to the surrounding structure, but rather using isojoists from the sound isolation store (http://www.soundisolationstore.com/jois ... ators.html) placed either underneath the secondary 2x8" floor or on top. My framing experience is limited and I never thought of cross bracing. Thanks for the idea. To clarify, were you suggesting the cross bracing structure above the 2x12"s that I would in turn build the isolated walls on? Wouldnt I need to attach these to the 2x12's (and/or the outer walls) to make this structure effective? As far as the ceiling, I hadnt planned on having the isolation walls support the ceiling, but rather have 2 layers of drywall with greenglue sandwiched in between hung from the existing ceiling joist with RSIC-1 clips. The existing ceiling joist is supported by the outer walls of the studio. Ideally, i would have these completedly isolated like the walls, but I am getting close to the 20 PSF dead load limit on the 2x12's (spans and species rated at/near 40 PSF live load, 20 PSF dead load), and only have a ceiling height of 8 feet to work with. I will have to check out the weight of the concrete board. I would love to use it, but not sure I can do it without going into my live load allowance. Attached is a floorplan of the entire space. The closet next to the bathroom is gone down (I decided to demo it along with the floor), and I havent yet determined the design for the control room/tracking room within yet (any layout suggestions are welcome). First just trying to ensure that I have 100% confidence in the design (and structural integrity) of the floor.

Tell you what - just looking real quick at your assembly - you might want to recheck your deal load numbers...... I have you at about 12 psf without including your inside walls, the new floor joist and the existing floor joist (can not account for the joist due to lack of knowledge on the spacing) Also - what is the span of the 12x12 joist - you not only have to concern yourself with dead load - but also with the shear load at the ends of the joist Rod Gervais GIK Acoustics Director of Education http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

Thanks Rod. Are you the same Rod Gervais who wrote the book on home recording studios? I misplaced the book (had the first edition) about a month ago, and just ordered the second edition... I suppose the loss gave me a great excuse! Cant wait to get it. I really appreciate your response. Some details on the construction of the house (sorry in advance for so long, but I tend toward too much detail)... The walls of the garage on top of which 3 walls of the studio are built on are concrete block (2 walls on the side with no openings, 1 wall with main garage opening). These walls extend upward about 2 feet beyond the roofline to for a parapet. The studio outer walls are frame construction built on top of these walls with the ceiling joist supported on the concrete wall with the garage door opening (front) on one side and on what I am calling "the problem child" (back) wall on the other. This "problem child" is fully framed, load bearing to the flat roof above, and is resting right on top of the roof bitimen. The entire length of the garage from front to back is about 21 or so feet. The entire length of the existing room itself is only 16+ feet. The net result is a number of structural issues... eccentric loading being one of them. An engineer designed a glulam/beam structure to cut the long span and clear up the eccentric loading. It will be placed directly underneath that "problem child" in the garage... complete with new footings inside the garage and all. They also recommended a larger lentil to support the wall above the garage door (it was undersized). Both of these projects are fairly well defined, scoped by an engineer, permitted and ready for construction. The sheer load issues that you bring up and some additional blocking issues under the "problem child" were physically covered up when the engineers did their initial "as-built" evaluation. This week I completely opened up the floor upstairs, took down all the drywall upstairs, and cut a few spots of drywall in the garage to understand exactly what I was dealing with so that I could move forward on the design. With that out of the way, to answer your questions. The span is 16.9 feet. It anchors on one side to a 4x12 girder (same Douglas Fir grade B species) with joist hangers (not sure of type, but with 8 nails each), which is in turn anchored to the concrete block outer wall of the garage with redheads or similar about 2 feet apart. The other side of the span will be resting on a steel glulam/beam - the 2x12 actually extends beyond the beam, unbroken at least to 21.5 feet (and beyond from what I can see) where it rests on top of the backside concrete block wall of the garage. The 2x12 is braced laterally every 6-8 feet and is 16" OC. I completely agree with your concern about sheer load, at least on the side of the joist anchored to the block wall. I was just sharing the concern with a contractor I am working with on part of the construction. If I can't determine the manufacturer of the hangers to know the sheer strength of them, I am considering anchoring an additional 5x5 under the girder/joists and anchoring it to the concrete wall to provide additional sheer strength, and checking with a structural engineer on the exact numbers of what the additional support would provide. Attached are the load tables I pulled on the species and spans for 40/20 and 40/10 loading. 40/20 allows 16.5 feet of the span. At 16.9 feet, I am a bit over for 20 PSF dead load, so am checking with the engineer on exactly what dead loads the 16.9" span could carry maximum. Also attached is the worksheet I am using to estimate loads. It is an inventory of everything in existance + proposed that would add load to the floor, its weight (in the case of bathroom items estimated after discussing with a plumber), and PSF calculated by dividing its weight by the square footage of the room. Not sure if this is correct, but I am trying to be conservative in my estimation.

Pro, Yes I am the same Rod, and glad you liked the book (the 2nd edition is much better - lol) Some questions, comments I have on your loading spread sheet...... To begin with - the bathroom load cannot be distributed based on the full room size - it's load has to be allocated to the joists that are carrying it. Once you are one joist bay away from it, it it will not create a loaded condition there. You really need to break the loading down into area components...... The same goes for walls that are running parallel with the floor joists - their load will not be carried in the middle of the room either...... These are (even with the crossed joists you plan on installing to help distribute the load) eccentric loads that will not transfer throughout the deck....... Forget any calculations that deal with actual live loads - these give you no breathing room in the design........ the design requirement is the capacity to carry 40 psf....... I believe you are misunderstanding this - there is not a limit of 40psf live load - there is a requirement that the design will provide a minimum of 40psf live load. I do not see the load calculations for drywall on the bottom of the existing 2x12 floor joists in the garage space. or are you planing on trying to accomplish your isolation levels using a one sided isolating assembly? That is a huge challenge. I do not see the insulation that should be in the joist bays. Please recheck the drywall load for your room within the room walls...... assuming double 5/8" on the studio side of the bath room walls my take on that is the following...... 2 walls 16'+/-, 2 walls 20'-6"+/-, (you don't lose the wall lengths at the bath they still have to get the drywall) that's 73 lf of wall - wall heights are 7'11 3/4" - call it 7'-11" just for ease of the calcs...... That just about 577.6 sf - 2 layers of drywall run about 5.2psf - so that would put you somewhere around 3,000 pounds of drywall - not just shy of 700.... or am I missing something? Please check your numbers again. Rod Gervais GIK Acoustics Director of Education http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

Answers below... To begin with - the bathroom load cannot be distributed based on the full room size - it's load has to be allocated to the joists that are carrying it. Once you are one joist bay away from it, it it will not create a loaded condition there. You really need to break the loading down into area components...... The same goes for walls that are running parallel with the floor joists - their load will not be carried in the middle of the room either...... These are (even with the crossed joists you plan on installing to help distribute the load) eccentric loads that will not transfer throughout the deck....... Makes sense. I will isolate the loads in sections. I imagine this will make areas where isolated walls are parallel to joists (especially near the bathroom) overweight. Thanks for the advice. Forget any calculations that deal with actual live loads - these give you no breathing room in the design........ the design requirement is the capacity to carry 40 psf....... I believe you are misunderstanding this - there is not a limit of 40psf live load - there is a requirement that the design will provide a minimum of 40psf live load. Yeah... I had this very backwards on the live loads in my mind (and in my calcs). Dead loads are treating as limits though correct? I do not see the load calculations for drywall on the bottom of the existing 2x12 floor joists in the garage space. or are you planing on trying to accomplish your isolation levels using a one sided isolating assembly? That is a huge challenge. Oops... yes, I missed it. There is 5/8" fire rated below. I hadnt really even though about doubling up on it or green glue between. I will add it in. I do not see the insulation that should be in the joist bays. There is no insulation in the 2x12" joist bays (before construction or in tentative design), but there is Roxul AFB (listed as Rock Wool 4" + 4") in the 2x8" proposed decoupled joist bays figured in. Will add it in. Please recheck the drywall load for your room within the room walls...... assuming double 5/8" on the studio side of the bath room walls my take on that is the following...... 2 walls 16'+/-, 2 walls 20'-6"+/-, (you don't lose the wall lengths at the bath they still have to get the drywall) that's 73 lf of wall - wall heights are 7'11 3/4" - call it 7'-11" just for ease of the calcs...... That just about 577.6 sf - 2 layers of drywall run about 5.2psf - so that would put you somewhere around 3,000 pounds of drywall - not just shy of 700.... or am I missing something? Nope, you are right on. I am missing the bathroom walls and the second layer. Please check your numbers again. Let me try that again and repost.

protechtor wrote:

Yeah... I had this very backwards on the live loads in my mind (and in my calcs). Dead loads are treating as limits though correct?

in load design - all of the numbers are minimums....... If the design calls for 20#DL/40#LL - then the design has to have the capacity to handle 20 lbs of deal load and 40 lbs of live load. A design capable of handling a 100#DL and 400#LL would be compliant....... one capable of 19.5#DL/40#LL would not. On the other hand - an analysis by an engineer determines capacity......... If your engineer is telling you that the maximum dead load on your existing joists is 20 psf - then you cannot exceed that (which is different from any code requirements) in short your design can always exceed any code requirements - but you can never exceed your capacity....... And you cannot swap out what you might consider excess live loads to make up for dead loads that would exceed the capacity of the members. Rod Gervais GIK Acoustics Director of Education http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

Ok, from a design perspective... I get it. As a novice, I was trying to impart the floor joist members min's onto what a structure built using those members could hold up safely. I know this isnt a structural engineering forum, but after thinking about it, if a ran a floating (with rubber iso joists) wood flooring assembly above the 2x12 primary structural framing assembly, but perpendicular to the 2x12 assembly, and then built my decoupled walls on top of that, wouldnt the loads of the walls be spread over the span of 2x12"s supporting the new floating floor/wall assembly?

protechtor wrote:

Ok, from a design perspective... I get it. As a novice, I was trying to impart the floor joist members min's onto what a structure built using those members could hold up safely. I know this isnt a structural engineering forum, but after thinking about it, if a ran a floating (with rubber iso joists) wood flooring assembly above the 2x12 primary structural framing assembly, but perpendicular to the 2x12 assembly, and then built my decoupled walls on top of that, wouldnt the loads of the walls be spread over the span of 2x12"s supporting the new floating floor/wall assembly?

No they would not necessarily....... You need to get your head around the way things actually work when loaded..... So let's just look at one joist placed across a number of other joists to make it simple to picture....... Let's suppose (for a moment) that you were to build this with a full joist spanning 13 joists - If you put just one isolator at each end - you would impart no load to anything but the 2 ends of the new joist, and thus to the outer most existing joists......... Joist loads work like this - basically everything from the 1st 1/4 of the joist transfers the load to the end they it's closest to (not really 100% but close enough to that so that we can use this for the purpose of discussion) This is eccentric loading. As you begin to shits the load towards the opposite end you gradually transfer a greater load to the unloaded end of the joist - a concentric load is reached when the bath is dead center, and then you gradually load the opposite joist as you continue in moving in that direction. I know you already understand all of this - but I am going through the exercise regardless...... With your layout you are probably loading the existing joist in that case with 80% of the bath at one end - 20 percent at the other... Now lets picture what happens if we add a support over the center joist below That joist is now going to become a beam - and it is going to pick with 1/2 of the load between the 2 outside walls........ So it decreases the load at the wall with no bath by 1/2 - and transfers about 1/2 of the bath load to the center - so now you have just 1/4 of the unloaded deck bearing on one existing end joist, 1/2 of the bath, plus 25% of the unloaded deck load bearing on the other existing end joist...... and 50% of the unloaded deck load - plus 50% of the bath loading up on the center existing joist (which is probably overloaded because it is just a joist not a beam.) There is no longer any of the load being transferred to the wall furthest from the bathroom - all of that structural load is being borne by the new center point and the end wall closest to the bathroom. Now - lets add 2 more bearing point to the equation - one on the joist directly beneath the end wall of the bathroom - (let's call that the exact 1/4 point of the total span just for ease of working through this) and one more equal distance on the opposite side of the center-point. So you now have the new joist being carried on 5 points - the 2 ends - the center - and one each at the 1/4 points. If we picture this left to right - with your bath located on the left...... Point 1 is carrying 1/2 of the bath room - point one is also carrying the 1/2 of the unloaded deck load between 1 & 2 - or 1/8th of the unloaded deck load........ point 2 is carrying 1/2 of the bath load - plus 1/4 of the deck load, point 3 is carrying 1/4 of the deck load - point 4 is carrying 1/4 of the deck load - and point 5 is carrying 1/8 of the deck load. Notice that the more supports we install the less load we impart to the ends - at the same time the we consolidate the load making it much more localized to the joists beneath. The walls are still going to (for all intent and purpose) still just load up the joists they are directly above......if you place an isolator over each and every existing joist - in the end it is exactly the same as if you just framed the member in that position without the isolator....... Rod Gervais GIK Acoustics Director of Education http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

Thanks for straightening out my thinking Rod. Vertical loads are vertical loads. Isolators certainly dont change the nature of gravity and load bearing characteristics of the structural material... I get it now. My very nature is to learn and does not allow me without great effort opposed to that nature to take shortcuts especially if I do not understand fully the implications of those decisions... and now with a baby set to arrive soon in the house, safety and getting the structural design right first is paramount to success. I want the best reasonable acoustic solution for my needs, but would never sacrifice safety. I spent some time on updating the loads worksheet and breaking areas out into specific sections. The process really helped me to think through how many gaps there are in the specifics of the design, so thank you. I am resolved to work through them and appreciate all the help I have recieved in the information on this board. The 2x12 structural joists are running east to west (ie. from the wall with all the windows to under the wall with the main studio door), so I broke out the loads of the proposed walls (room inside a room) that would run parallel to the 2x12 joists underneath. I also broke out the main studio into two overlapping sections that are very close in sq ft footprint. The first with just the interior space of the room within a room studio, the second including the footprint of the entire room within a room (including walls not parallel to joists). The former is probably not needed, but it was easy to break out. Also, I recalculated the surface area of the walls in the room within a room. It is significantly less than in your previous posts estimate because of the windows and doors. I used sketchup to calculate the area based on actual dimensions and then rounded up. Whenever you get a chance, take a look and let me know if it makes more sense.

Pro, you are still missing the weight of the existing 2x12 joist themselves...... remember that they have to carry all the other loads imparted to them - PLUS their own....... their weight is always a part of the dead load that they have to carry. can you post a sketch of the existing floor joist layout - as well as the over lay of the new joists you have in mind? Rod Gervais GIK Acoustics Director of Education http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

Rod - Updated Load sheet attached. Also, a few quick graphics files as requested (sketchup files are too big). I overlaid it on top of the floorplan I am working on to give you an idea of spacing. Its not complete, but hopefully it gives you an idea. You can see the joists butt into a 4x12 girder on one end. On the other, they continue on. They are blocked together every 6-8 feet (didnt show on the pictures).

I'm (thinking out loud) why not reinforce under the perimeter of the 2x12 and add another beam underneath between the corner of the bath room and the left hand wall (looking at your original plan)? You have a 9' span in the short run and a 16' span in the other. Adding the additional beamp and support posts would cut that down to a 9' or less span all around with a lose downstairs of about 4" of wall space. This assumes the foundation underneath (perhaps with some additional work) can handle the 4000+ lb you're going to add...

Glenn - We are thinking similarly. I am having an engineer look into maximum loading on the structure and should have an answer Monday. A glulam/post supporting the 2x12's under the girder/joists and splitting the span at the bathroom with an additional glulam/post is an option. I could also look at adding 2x12 joists to take the 16" OC condition to 8" OC and a 5x5 ledger under the girder/joists. From a flooring design perspective, I am concerned about the result in building a wooden deck over a wooden deck isolated by neoprene/rubber pads. Cons - It is adding more weight without the weight helping structurally, or acoustically. In order to build properly would have to create a 3 leaf structure (drywall on ceiling of garage, plywood on top of 2x12's, then flooring layers on top of 2x8's) Pro's - It gives me more space to add more layers of insulation. It allows me to level the finished floor of the studio to the existing bathroom and outer doors. I am seriously considering killing the 2x8" floating joist option and instead focusing on using the 2x12's as the subfloor and adding weight - gypcrete or hardibacker, and a layer of OSB and Plywood with a max application rate layer of green glue in between. Install ND isolators on the studio interior walls or RSIC-1 clips. This would give me a finished floor height about 7 3/4 inches lower than my outer door and bathroom door height... the max riser height by code on stair steps. By default, the height of the ceilings on the room would also increase. I am going to work up some sketches on the concept...

protechtor wrote:

Glenn - We are thinking similarly. I am having an engineer look into maximum loading on the structure and should have an answer Monday.

That's great - there are too many variables here to deal with this at a distance...... Rod Gervais Director of Education GIK Acoustics http://www.gikacoustics.com (USA) http://www.gikacoustics.co.uk (Europe) Tel.(US)[removed] Tel.(UK)+44(0)20.7558.8976

"I am seriously considering killing the 2x8" floating joist option " I think you will find that hard to get past code anyway...

xSpace wrote:

"I am seriously considering killing the 2x8" floating joist option " I think you will find that hard to get past code anyway...

Certainly not without an engineering stamp of approval on it.

[quote="That's great - there are too many variables here to deal with this at a distance......[/quote] I'll report back on what the limits are, but I expect some reinforcement will be needed to add the mass needed.

protechtor wrote:

xSpace wrote:

"I am seriously considering killing the 2x8" floating joist option " I think you will find that hard to get past code anyway...

Certainly not without an engineering stamp of approval on it.

Won't matter since I would find it on the far side of difficult to get a stamp on basically a floating room that is going to push a wooden structure with no modifications saving the mild sway braces, to the brink of what it was designed to do. Any engineer will say a few things in respect to this and the first will be "how is it secured"? And that may be even with a stamp...everything is negotiable. And yours isn't and cannot be as it exists at present. The room construction is one thing but the existing structure cannot maintain it based on friction and gravity alone. And to be fair, I do not even know where in the world you live...and you can bet your 150K that it will make a difference. But if your guys come up with something to the contrary...

Some good news and bad news. The engineer finally got back to me today. This is the firm who designed the beam/post and additional lentil designed support the 2nd floor structure about a year ago when we were first looking at the adequacy of the structure to support the existing loads + some additional weight for heavier materials used in a remodel. The design is based on a load of 16 PSF (dead) and 40 PSF (live), but they did not do a study on maximum loads for the design. Also, the study was primarily concerned with the design and sizing of a beam/posts/footer and an additional garage door lentil (as the existing structure was inadequate to support the loads it was even carrying before construction as-is).The spans of 2x12's were also included, but again only using the min loads above. They can perform a maximum load analysis on the existing structure (2x12's, joist hangers, beam/post/footer, lentil) for a fee of $150, but am considering holding off on hiring for additional scope until I nail down the design of the studio. From the exercise in calculating loads last week with Rod and others, I think I can safely assume that there will be some work required to support a structure that has enough mass to affect flanking and airborne sound levels to any significant degree. Building additional beams/posts/footers underneath the floor structure (in the garage) isnt a problem. I have the headroom to do it, just need to know the loads from the new design for the right sizing, etc.. Still working on the sketches for a different design. Had to shift gears this weekend and get some painting done in the kitchen for the Mrs., so had to put design work on hold for a few days.

Hi All! It took me a few days (had another project to work on), but I spent some extra time this weekend studying up on Rod's book (I did find that think there are some important additions in the 2nd edition), but below you will find a new version of the studio design. Before I post it... Just to recap on the engineering/load capacity status - After a number of conversations with a structural engineer, a home inspector, a GC, and my own reasearch, I am confident that a supporting structure will be able to be put in place to support the loads that I might need for the second floor studio. However, since the loads I have been using are estimated loads (thanks Rod and others for your input in helping me calc them), I am going to nail down the design in a much more detailed plan in order for the engineer to be able to create a more specific load analysis (and design if/when retrofitting of assemblies are required) to meet my needs. So, here is an updated "in progress" floorplan. I have nailed down the rough walls/layers (2 layers drywall with green glue sandwiched), rough window locations, interior and exterior door details and locations, listening position (and speaker locations), and primary furniture locations. Next steps are working on exterior window details (including exterior windows in listening room and window between tracking/listening) and HVAC. A few questions: 1) Layout - Any suggestions on the layout before I move forward? Just a reminder that the blank room is the bathroom. 2) HVAC - This one has me really stumped... I have a mini-split system with the capacity to cool/heat the entire square footage of all 3 rooms, but it has (#2 only a single wall unit. I am considering creating the listening room as an "exchange chamber" similar to what Rod describes, with a return and supply to the tracking room, and another set to the bathroom. I am concerned though of sound traveling between rooms through the short ducting runs required. Any thoughts on the detail of how to pull this off without short circuiting my isolation between rooms? Thanks! Have a great week!