REBAR Concrete Pad Question

I have read on here, and during the research have seen that Rod suggested putting Rebar 16" on center for under/in the concrete pad. Also I understand that he says it should be 1/3rd up in the concrete. Here is my question: I met with my building consultant friend (who builds houses, NOT Studio's) anyway I met with him yesterday to go over the plans one more time, so I can get this project moving, and when he saw the Rebar graph I had made up (with the rebar 16" OC) he said it was WAY Overkill. :cry: He said that we do not get earthquakes here, and their company does pads for garage floors all the time, and they only do 1/2" Rebar 4FT On Center :shock: :shock: in their pads, and thats even when they are poured on unsettled ground (over a bed of stones of course). He said he has yet, to his knowledge, ever had any of his floors, in his 15 years of doing this, crack. He said he dosent even use Fibermesh (which I know dosent prevent cracks, just keeps them small). He did agree that the Rebar MUST be pulled up into the concrete 1/3 of the way, and I was to make sure that was done. So, for here in Pennsylvania where we dont get earthquakes etc, is 16OC overkill,,,,,or can I back that down to maybe 24" on center? (I do think 4FT on center is too wide, but again thats what they use successfully.) Any input?? Thanks, its much appreciated. AJ

In the spirit of overkill :twisted: I did my rebar 12" o.c. Point out that garage floors are inferior to structural slabs and that the walls you'll be building will be heaaaaaaavvvvyyyyy. Then tell him, "I really appreciate your concern for my budget, but I'm not budging on this. Rod has spoken... That's good enough to me." If he continues to press the issue, ask: "How many books have you published?" ;-) --Keith :mrgreen:

In the spirit of overkill I did my rebar 12" o.c.

WOW...so in other words you didnt even put down any concrete because you now have an all metal floor :lol: :lol: :lol: (kidding Keith) :wink: But seriously, dont you live in an "earthquake zone"? I think what he is saying that since we dont, that much Rebar isnt needed. :?: I totally agree with you and the fact the Rod is a master in building Studio's, I think he (my builder) was just asking the question reference overkill. (also said its $200.00 vs $400.00 in Rebar that may not be actually needed) I was thinking of maybe going 20" OC at most, but if thats going to seriously or possibly compromise my floors overall strenth, I will just stay with the 16OC. :evil: I know Top Class Studios are expensive to build, but again this is just my Home Studio, and I do have to follow somewhat of a budget. So I just ask about cutting costs whenever or wherever possible. If cutting certain costs is going to seriously compromise the project, I wont cut them. :wink: Just trying to cross my "T"s and dotting my "i"s as I go. I do have to ask,,,how is the construction of this/a Studio going to be that much "heavvvvvier" then if it were just going to be an ordinary addition to the house?? Wont bascially the walls and roof weight, be the same ?? Recording gear thats goign in here wont weight any more then most appliances in a house>?>? Just curious.. :oops: (again I am not a builder, so I am just asking & learning as I go) And finally, as an update, Codes was here again last week. Said I can NOT build the 2nd floor Loft as planned if I am planning on using Scissor Trusses. the interior wont have the needed headroom. He said after looking it over, that I will need minimum 7ft headroom over 50% of the floor space on any floor. Sooooo, once again, another change. So I could either "Stick Build" the loft roof, or, (what I decided to do) is,,, I am just going to make a complete 2nd floor on the Studio. The first floor walls with be 10Ft high and the 2nd floor will be 8ft high. :oops: :roll: :D Also the tracking room will still be room within room and totally uncoupled from everything (except the concrete floor), but the rest of the building (control room, 2nd floor, etc) will be a regular constructed building. Another day,,,,,another lesson learned! :roll: Thanks :wink: AJ

Aj, You have a lot of the basics correct here. Have not seen your design so not privy to how many walls you will have. My assumption would be you are doing doubles wall const. through out. So yes you will have some added weight. double layer sheet rock and so forth. So 2 times that of a house. The difference beteen the floor and the buildig is the building will be built on your footings that will bear most of the load for the structure. Again I have not seen your drawings so I am Ass-uming. Most garages that are built here in the NW are footings first structure built and then the floor is poured. So the outside strudcture is not atop the slab. People drive cars on these every day. some minimal cracking some extensive. and 90% do not have rebar.. But they do have expansion/construction joints installed or cut to compensate for thermal and drying of shrinkage cracks. You show me a piece of concrete and I will show you a crack. So to answer your question from the NW where we have had some quakes. Garages almost never get rebar...but they have saw cuts or const. joints. Commercial... depending on floor loads are tpically 16"-24" OC 1/2" rebar with saw cuts and const. joints Overkill is good thing if you can afford. Standard or better is where you should start from Tom

Hi Tom,,,,and thank so much for the response. My building is going to be basically a standard built 32ft X 21ft building (2X6 walls over the exterior footers) except for the 18ft by 21ft tracking room which will be 10ft double walled, single story construction with 2 layers of drywall in interior walls. (it will have a 2nd floor over top of it thats totally uncoupled) I totally understand the weight difference there, which makes sense. I guess I was just thinking of the whole building in weight overall, and not just the tracking room area. So with the response from you and Keith, I understand "overkill" is good, but I was looking at it as "is it really needed" the same as my builder friend was. OR,,,, is maybe "more then standard", but not quite "overkill" enough. (where does one draw the line) :shock: For conversation sake, wouldnt it be the same as then saying a 4" or 5" concrete pad is thick enough for a floor, but why not make it 20" thick instead just because more is better? :lol: I guess I am just trying to find the justified and most appropriate figures so I budget and build properly Plus I like to learn as much as I can about things I get involved in, and this site obviously offers that opportunity. :wink: I appreciate the responses as always. Thanks AJ

For conversation sake, wouldnt it be the same as then saying a 4" or 5" concrete pad is thick enough for a floor, but why not make it 20" thick instead just because more is better

Kinda sort of. I would consider a 20" slab way over kill. :shock: From what I have seen in old builds 60-100 years old concrete will withstand quite a bit. I have seen basement slabs @ 2" and still functioning. Granted they where not loaded with heavy walls. And look at what the Romans did. :lol: Part of a concrete floor is the sub grade. Proper compaction and gradation are important for the the slab itself. Less settling less cracking. Better compaction better stability. Lower water content in your mix stronger concrete (however its harder to work with ) More sack count in your mix also harder concrete. To much it gets weaker. too much water also makes it weaker. With a minimum of 4" slab, 4' OC rebar and work up from there. Saw cuts or construction joints 10'x10' grid. Footings will be determined by your building size. The worst that will happen is the slab will crack. If your compaction and soil base are good and your drainage is handled properly you should have minimal if any settling. Basic rules of construcion apply. Hope that helped Tom

studio911 wrote:

I have read on here, and during the research have seen that Rod suggested putting Rebar 16" on center for under/in the concrete pad. Also I understand that he says it should be 1/3rd up in the concrete.

Hang tight for a second here...... my recommendation for a structural slab is a minimum Grade 60 #4 drb @ 16" centers in the bottom 1/3 of the slab when I have cause to not trust the substrate..... But when I am talking strictly about shrinkage cracks (which is what your builder is) then it is #3 drb (Grade 40 or 50 doesn't matter) @ 1' - 6" centers and that is installed in the top 1/3 - not the bottom 1/3 of the slab.. I (personally) wouldn't construct anything with a 4' square mat for shrinkage control - although I do see a lot of engineers specify 24" centers ea. way for that. But then I figure that my way is only a 33% increase from their design - and it's worth it to me for the comfort zone....... But I have never seen anyone install or design at 4' centers. But then again - I have never built in PA - driven through on a few occassions - but never built there. I don't know what to say.......... if your concrete man will warrant his work for 10 years - with an assurance in writing that he's fix any cracks with a high pressure epoxy injection - then what the heck - save a couple of hundred bucks and go for it. I hope this helped. Sincerely, Rod

Another possibility. If you're going to lighten up on the reinforcing, you'd probably be better off doing that by using welded wire fabric (mesh). Typically used for non-structural slabs as you're describing to control cracking from shrinkage or minor settlement. Generally 6x6 or 4x4 mesh would be used in this type of application. As with the rebar, you should use chairs or small pieces of brick/block to raise the mesh up into the slab. The mesh is not going to do you any good laying on the backfill when you pour.