Material for "Beefed up" Subfloor

Greetings! I need to get some suggestions on some type of material (acoustically friendly :) ) that comes in 1/8" size to use as a fill-in material for my beefed up ceiling. The upper and lower supports on my "I" joist is 1 & 3/8" in height each. If I put 2 sheets of 5/8" drywall below my subfloor, that will = 1 & 1/4" so I'm 1/8" shy to make it flush with the bottom of my upper "I" joist (see drawing 2 & 3) By having all the "mass" flush with the bottom of my upper "I" Joist support, I can support the weight of my drywall by having wood braces screwed into the upper "I" Joist support. (see 4th drawing) These strips will be spaced apart and spanning the cavity length. I have already had a structural engineer to tell me my "joist" will support 4 sheets of 5/8" drywall. (drawing 4) However, by knowing here that it's recommended to have the drywall "screwed" into the subfloor, I need to know that my subfloor can handle the extra weight. I may be "waiting a while" from my structural engineer to get a response concerning this issue, so I'm asking this now in the event my subfloor can't support the weight. I have to admit, I'm not too keen about screwing into my subfloor, but as long as there's ample room for a screw to "secure" itself in the subfloor (without coming close to coming through my floor! :shock: ) along with supporting the weight of the drywall, I'm ok. I'm going to check other houses they're constructing in my area to see just how thick the subfloors are. I also need suggestions for a "strong" thickness of wood for the braces supporting the drywall. 1/4"?? 1/2"?? 3/4"?? And also how far do the screws need to go into a subfloor to secure the weight of the drywall? (Sure hope my subfloor is thick enough!!) There may be other suggestions on how to do this, so if there are, I'm all EARS...er, I mean EYES... :D Thanx!

camistan wrote:

Greetings! I need to get some suggestions on some type of material (acoustically friendly :) ) that comes in 1/8" size to use as a fill-in material for my beefed up ceiling. The upper and lower supports on my "I" joist is 1 & 3/8" in height each. If I put 2 sheets of 5/8" drywall below my subfloor, that will = 1 & 1/4" so I'm 1/8" shy to make it flush with the bottom of my upper "I" joist (see drawing 2 & 3) By having all the "mass" flush with the bottom of my upper "I" Joist support, I can support the weight of my drywall by having wood braces screwed into the upper "I" Joist support. (see 4th drawing) These strips will be spaced apart and spanning the cavity length. I have already had a structural engineer to tell me my "joist" will support 4 sheets of 5/8" drywall. (drawing 4) However, by knowing here that it's recommended to have the drywall "screwed" into the subfloor, I need to know that my subfloor can handle the extra weight. I may be "waiting a while" from my structural engineer to get a response concerning this issue, so I'm asking this now in the event my subfloor can't support the weight. I have to admit, I'm not too keen about screwing into my subfloor, but as long as there's ample room for a screw to "secure" itself in the subfloor (without coming close to coming through my floor! :shock: ) along with supporting the weight of the drywall, I'm ok. I'm going to check other houses they're constructing in my area to see just how thick the subfloors are. I also need suggestions for a "strong" thickness of wood for the braces supporting the drywall. 1/4"?? 1/2"?? 3/4"?? And also how far do the screws need to go into a subfloor to secure the weight of the drywall? (Sure hope my subfloor is thick enough!!) There may be other suggestions on how to do this, so if there are, I'm all EARS...er, I mean EYES... :D Thanx!

Why don't you just do 3 layers instead of 2 - and gain a little more mass in the process? 2 layers of 1/2" plus one layer of 3/8" would flush you up perfectly - and give you a wee bit more isolation in the process. Sincerely, Rod

Great suggestion Rod... :D I'll include that with info I'm emailing to my structural engineer! Thanx

Great news & So-So news... The great news is my Structural Engineer called me today to let me know my subfloor could handle the "beefing up" drywall. The so-so news is that he would only approve 2 sheets of 5/8" drywall attatched to the subfloor instead of 3 sheets. ( 1/2"-1/2" & 3/8" drywall) I can live with the 2 sheets of 5/8" though... :) The official approval document should be here in a few days. Now, all I need to know is what is the minimum depth the screws need to be inserted into the subfloor to secure the 2 sheets of drywall. My subfloor is 3/4" thick. (How about a 1/2" insertion depth into the subfloor...that too much? too little?) I don't want to have the screws sticking through my carpet (on the top of my subfloor) to get the correct insertion depth :x . I will be installing the "beefed up ceiling" drywall like the drawings below with it hopefully looking "something" like the 3rd pic below that (minus the drywall support cleats/wood strips in the 3rd pic) Thanx ya'll! :D

Just checking back to see if anyone has suggestions as to the correct insertion depth for screws to support two 5/8" sheets of drywall on my subfloor. The subfloor is only 3/4" thick. I read this post http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3726 Paul mentions to go ahead and screw the dywall, (and I was considering inserting screws 1/2" into the subfloor) but I'm wondering if a 1/2" insertion is enough to support the weight of 2 sheets of 5/8" drywall. I plan to folow PhiloBeddo's plan about cutting the drywall into 4' long sheets. Also, I believe in the FAQ area... http://www.johnlsayers.com/phpBB2/viewtopic.php?t=598 it stated that the 1st sheet would have screws spaced every 8" on the drywall edges. I believe it's recommended not to screw anything in the center of the drywall. I'll also take Paul's reccommendation about putting up 1 sheet, caulking, then putting up the other sheet. (Seems like you have to do it like this in order to overlap the drywall joins) Thanx for any and all help.

Did I see "Steve" lurking on here tonight??????

Yeah, you did; I'd go for 5/8" penetration into your subfloor to be safe; I'd also use full schedule along both edges of EACH layer of "beef", (8" O.C.), and offset the second layer's screws so you have no "collisions" - so the first layer would get screws along each edge (and a couple across each end of each piece) spaced every 8", and the second layer would get the same spacing but offset by 4". Only got 3,872 more projects and I'm caught up... :? Steve