rlackore Posted September 30, 2015 Share Posted September 30, 2015 It has to do with the "slab" being placed on an inappropriate layer. But is it? Why? If a wood subfloor is placed on the Floors Surfaces layer, why wouldn't an interior slab be placed there? Both components act as a base for a finished floor system. I'm not saying that interior slabs don't deserve their own layer, but I think the current system is logical, if not convenient. Link to comment Share on other sites More sharing options...
Joe_Carrick Posted September 30, 2015 Author Share Posted September 30, 2015 Here are a couple of details. The 1st is simply taken from the Chief CAD Details Library. The 2nd is the same detail modified to what a true Mono Slab Foundation would look like. That's how it would be built, with the footing offset to the exterior of the forming. This could/should have been done with some tweaks to the Foundation Wall Footing dbx to free up the settings. There are Check Boxes that are disabled and tied into code that acts more like Radio Buttons. It's a mess and any good programmer knows that Check Boxes are not supposed to disable other Check Boxes. This limits the flexibility to set dimensions, etc. In fact, many of those Check Boxes actually change the values in other fields when they shouldn't. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted September 30, 2015 Share Posted September 30, 2015 But is it? Why? If a wood subfloor is placed on the Floors Surfaces layer, why wouldn't an interior slab be placed there? Both components act as a base for a finished floor system. I'm not saying that interior slabs don't deserve their own layer, but I think the current system is logical, if not convenient. I'm not saying its totally stupid or anything. There's some logic to it, just not a whole lot. There's a slab layer for a reason...its because concrete slabs are unique and structurally quite different from most other "Floor Surfaces". I think most anyone in the industry would place subfloor of any kind in a different category than slabs. Regardless though...having control over what layer various components are placed on would be a huge plus. Not only for this situation but for many many many others. I guess until that time there should maybe be a check box in the foundation room dbx. to "Display Floor Structure As Slab" or something along those lines. Link to comment Share on other sites More sharing options...
rlackore Posted September 30, 2015 Share Posted September 30, 2015 There's a slab layer for a reason...its because concrete slabs are unique and structurally quite different from most other "Floor Surfaces". I think most anyone in the industry would place subfloor of any kind in a different category than slabs. Regardless though...having control over what layer various components are placed on would be a huge plus. Agree. Link to comment Share on other sites More sharing options...
Joe_Carrick Posted September 30, 2015 Author Share Posted September 30, 2015 But is it? Why? If a wood subfloor is placed on the Floors Surfaces layer, why wouldn't an interior slab be placed there? Both components act as a base for a finished floor system. I'm not saying that interior slabs don't deserve their own layer, but I think the current system is logical, if not convenient. Robert, A "Slab" - even with a footing - is on the "Slabs" Layer. A Mono Slab Foundation has the Slab on the "Foundation Layer" A Slab as a part of a Foundation Wall System doesn't even have a 3D Slab - Why not? These things are inconsistent and should be unified - but there should probably also be a "Patio Slab". Link to comment Share on other sites More sharing options...
HumbleChief Posted September 30, 2015 Share Posted September 30, 2015 Here are a couple of details. The 1st is simply taken from the Chief CAD Details Library. The 2nd is the same detail modified to what a true Mono Slab Foundation would look like. That's how it would be built, with the footing offset to the exterior of the forming. This could/should have been done with some tweaks to the Foundation Wall Footing dbx to free up the settings. There are Check Boxes that are disabled and tied into code that acts more like Radio Buttons. It's a mess and any good programmer knows that Check Boxes are not supposed to disable other Check Boxes. This limits the flexibility to set dimensions, etc. In fact, many of those Check Boxes actually change the values in other fields when they shouldn't. Never designed, nor have had built a mono slab with an offset like in the above detail - in 15 years. Just sayin'. Link to comment Share on other sites More sharing options...
rlackore Posted September 30, 2015 Share Posted September 30, 2015 A "Slab" - even with a footing - is on the "Slabs" Layer. Makes sense, only because it was created using the Slab tool. CA isn't guessing how you're going to use the slab as a building component - so it sticks it on the Slab layer. A Mono Slab Foundation has the Slab on the "Foundation Layer" Because it's a foundation. A Slab as a part of a Foundation Wall System doesn't even have a 3D Slab - Why not? It does - but it's on the Floor Surfaces layer. I agree - this is the part that makes the least sense, and should be fixed. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted September 30, 2015 Share Posted September 30, 2015 Never designed, nor have had built a mono slab with an offset like in the above detail - in 15 years. Just sayin'. You know...I wouldn't knock it but I've never built (or even seen) a mono slab that way before either. Not even sure how one would go about pouring it in a single pour. I can see why it wasn't contemplated when developing the foundation tools. Link to comment Share on other sites More sharing options...
dshall Posted September 30, 2015 Share Posted September 30, 2015 You know...I wouldn't knock it but I've never built (or even seen) a mono slab that way before either. Not even sure how one would go about pouring it in a single pour. I can see why it wasn't contemplated when developing the foundation tools. Imagine your 2x12 form boards are 8" above bottom of footing trench. The concrete will ooze under form boards by about 3" to side of trench. Note that trench for footings was dug @ 12" wide. I need a minimum 12x6 footing with bottom of footing 2" into grade. thus we have a "stem wall" that connects the footing to the slab. Note the "stem wall" needs to be between 6"-8" wide (not s wide as footing), The point being, big time developers who are building a 1000 homes is looking to cut costs where they can, so by using a narrower "stem all" he can save on concrete materials. think about how you would dig the trench for the footing (a bit wider thane the perimeter of house), put in form boards..... think about it.... the concrete oozes under the form boards. Link to comment Share on other sites More sharing options...
Joe_Carrick Posted September 30, 2015 Author Share Posted September 30, 2015 Really guys, that's the way they are actually built. The trench is excavated (the width of the footing) about 4-6" to the outside of the edge of the slab. Then forms are installed on the outside with the "footing thickness" open to the outside of the trench. Rebar, Sand, & Membrane are placed and then the whole thing is poured. As the concrete seeps out under the forms it's typically back-filled just enough to prevent the concrete from coming up outside the form boards. Later when the forms are removed, if you were to cut thru the foundation that's what you would find. For a 3' deep foundation on a 40' x 60' building the savings in concrete is about 10 cubic yards of concrete. That's a lot of money to just put in the ground. btw, Even if you don't show it that way in your drawings - I would be willing to bet that your builders do it as shown in my detail. IAE, if you use the Materials List - and I know that most of you don't - you would find a huge difference in the amount of concrete. 1 Link to comment Share on other sites More sharing options...
HumbleChief Posted September 30, 2015 Share Posted September 30, 2015 Imagine your 2x12 form boards are 8" above bottom of footing trench. The concrete will ooze under form boards by about 3" to side of trench. Note that trench for footings was dug @ 12" wide. I need a minimum 12x6 footing with bottom of footing 2" into grade. thus we have a "stem wall" that connects the footing to the slab. Note the "stem wall" needs to be between 6"-8" wide (not s wide as footing), The point being, big time developers who are building a 1000 homes is looking to cut costs where they can, so by using a narrower "stem all" he can save on concrete materials. think about how you would dig the trench for the footing (a bit wider thane the perimeter of house), put in form boards..... think about it.... the concrete oozes under the form boards. Cool, just never seen it and I think on my smaller jobs will not use it but nice to have in the tool box if ever needed. Link to comment Share on other sites More sharing options...
HumbleChief Posted September 30, 2015 Share Posted September 30, 2015 Really guys, that's the way they are actually built. The trench is excavated (the width of the footing) about 4-6" to the outside of the edge of the slab. Then forms are installed on the outside with the "footing thickness" open to the outside of the trench. Rebar, Sand, & Membrane are placed and then the whole thing is poured. As the concrete seeps out under the forms it's typically back-filled just enough to prevent the concrete from coming up outside the form boards. Later when the forms are removed, if you were to cut thru the foundation that's what you would find. For a 3' deep foundation on a 40' x 60' building the savings in concrete is about 10 cubic yards of concrete. That's a lot of money to just put in the ground. Never come up against the same parameter. Actually never had to pour a 3 ft. deep perimeter ftg. nor have I ever seen one spec'd even on the most complex house designs, but again nice to know and have in the tool box. And of course that's not the way all mono slabs are designed or poured guys, really, but I can see it for larger more complex jobs. My remodel jobs never need a design like that but they might benefit - not sure. Joe, what do you do with that design using Chief's tools, just add a detail? Or too complex an answer to go into here. Link to comment Share on other sites More sharing options...
Joe_Carrick Posted September 30, 2015 Author Share Posted September 30, 2015 Larry, I don't use the Mono Slab for exactly that reason. I use a standard "Footing Wall" and offset the Footing. Since the "Slab at Top of Stem Wall" doesn't work very well, I just add a Slab at the correct height inside the Stem Walls. The depth of the footing varies a lot depending on soil conditions and freeze problems. Where you have less than perfect soils the footings often need to go quite a bit deeper. This is particularly true where there's a lot of top soil or clay. The bottom of the footings need to be deep enough (to avoid expansion/contraction due to freeze/thaw) and wide enough to support the loads. Link to comment Share on other sites More sharing options...
Joe_Carrick Posted September 30, 2015 Author Share Posted September 30, 2015 Even for a 1 story building without a soils report you would have the bottom of the footing 18" below grade and the overall depth from top of slab to bottom of footing would be 24". That means a distance of 18" from top of footing to the top of slab. Same 40'x60' house with a 4" offset is about 4.5 cubic yards of concrete. Link to comment Share on other sites More sharing options...
glennw Posted October 1, 2015 Share Posted October 1, 2015 Joe, Is the plan you posted giving you what you want or are there still deficiencies with that system? Since the "Slab at Top of Stem Wall" doesn't work very well, I just add a Slab at the correct height inside the Stem Walls. Why do you have to draw a manual slab, why doesn't Chiefs slab work for you? A Slab as a part of a Foundation Wall System doesn't even have a 3D Slab - Why not? This is incorrect, I have no problem getting a slab on (or inside) foundation walls. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted October 1, 2015 Share Posted October 1, 2015 Imagine your 2x12 form boards are 8" above bottom of footing trench. The concrete will ooze under form boards by about 3" to side of trench. Note that trench for footings was dug @ 12" wide. I need a minimum 12x6 footing with bottom of footing 2" into grade. thus we have a "stem wall" that connects the footing to the slab. Note the "stem wall" needs to be between 6"-8" wide (not s wide as footing), The point being, big time developers who are building a 1000 homes is looking to cut costs where they can, so by using a narrower "stem all" he can save on concrete materials. think about how you would dig the trench for the footing (a bit wider thane the perimeter of house), put in form boards..... think about it.... the concrete oozes under the form boards. I guess I should have said I don't see how it could be done cleanly or "right". That all sounds very messy to me. What do you attach the exterior from board to? Are stakes permanently left in the footer? How do you make sure sure concrete actually fills that little horizontal footing extension? Its hard enough even with a straight wall to avoid "honeycombs". If Joe is right that they just backfill that exposed horizontal area during the pour, that sounds sketchy at best and could result in concrete that continue to ooze out and settle after the pour is complete. It could also very easily result in compromised concrete (with the introduction of dirt into the mix) and would more likely than not end up resulting in a "valley" between the concrete erupting from the footer and the main exterior foundation wall. I don't really want to get into it. Just mentioning the few things that come to mind. Suffice it to say I can see how someone would be at least entertained by the idea it could save money. I'm sure its different elsewhere, but we typically only use mono slabs in 2 situations around here... Frost protected shallow foundations (rarely if ever deeper than about 24") or for unheated detached structures (also rarely if ever deeper than about 24"). Both of which we find most efficient to pour with essentially just a thickened edge. If its not that shallow, we go straight to a full depth block or poured wall foundation to get below the frost line and everywhere except garages gets a crawlspace (sometimes even garages but I also think that is a sketchy practice). Any slabs are poured after the walls. Aside from commercial structures I for one don't see any benefit to a deep mono slab. I'm sure a lot of it is a climate thing though. Anyway, I'll stop now. Just my ramblings based on that design I've never seen before (and can't imagine we would ever use here in Alaska). Link to comment Share on other sites More sharing options...
RGWhite Posted October 1, 2015 Share Posted October 1, 2015 I pour this way (per Joe's sketch) sometimes. There are different ways to do this kind of pour. If it is shallow (12"-18") I will start at one corner with a pump mix and just fill to top of the footer. By the time I get back to where I started the concrete in the footer has set up enough so as to not bleed through the back side of the form. I have a concrete design mix for this. For deeper foundations the forms are somewhat different. But getting back to the original post I agree CA should give us more control over the foundation/slab DBX. Link to comment Share on other sites More sharing options...
rlackore Posted October 1, 2015 Share Posted October 1, 2015 I have a concrete design mix for this. There it is. It's all in the mix, the slump, and the pour sequence. However, by the time you get back around to the corner that is "set-up", are you confident the concrete is still plastic enough to avoid a cold joint? If not, then you're pouring a footing, and a stem wall - not a mono slab. Granted, if you've got vertical hooks then it isn't much of an issue. Link to comment Share on other sites More sharing options...
HumbleChief Posted October 1, 2015 Share Posted October 1, 2015 I don't think the field set up would be that difficult and if your crew had a lot of experience it would go fairly smoothly I would suspect (soil type would matter as well it seems), but for a one off situation I would think it would come close to a break even situation with the over dig and additional labor versus concrete costs. I work in San Diego and have designed/remodeled a few really large homes and have never seen this detail on any house ever (talking about the original as-builts) but still nice to have in one's tool box. Link to comment Share on other sites More sharing options...
JLDrafting Posted October 1, 2015 Share Posted October 1, 2015 Similar footing that ties footing to slab. COASTLINE SHEETS-SECTIONS.pdf Link to comment Share on other sites More sharing options...
Joe_Carrick Posted October 1, 2015 Author Share Posted October 1, 2015 It's very interesting to me that there's anyone that hasn't seen this. It's been done this way for as long as I can remember. In fact, if you look at a full Stem Wall Foundation detail you will find a similar condition - but on both sides of the wall. The Footing itself is wider than the Stem Wall. It really doesn't matter how it's done - the reality is that the Stem Wall portion of the foundation is almost never as wide as the footing.. Link to comment Share on other sites More sharing options...
dshall Posted October 1, 2015 Share Posted October 1, 2015 ...... In fact, if you look at a full Stem Wall Foundation detail you will find a similar condition - but on both sides of the wall. ..... Agree, not sure what the mystery is. Link to comment Share on other sites More sharing options...
JLDrafting Posted October 1, 2015 Share Posted October 1, 2015 It really doesn't matter how it's done - the reality is that the Stem Wall portion of the foundation is almost never as wide as the footing.. Joe is correct. In my area, block is the typical stem wall choice due to the forming required for a concrete wall. This example was used because of the existing grade for this project. We do not have a frost line in Florida. The footing is designed for the psf required for the perimeter based on the soil load capacity. Same would apply for a mono-slab. Link to comment Share on other sites More sharing options...
rlackore Posted October 1, 2015 Share Posted October 1, 2015 It really doesn't matter how it's done - It matters if you have large gravity loads, poor soil, unbalanced fill, etc. Link to comment Share on other sites More sharing options...
JLDrafting Posted October 1, 2015 Share Posted October 1, 2015 It matters if you have large gravity loads, poor soil, unbalanced fill, etc. Robert, Most of my work has been commercial and any construction requires a certified soil report that includes the recommended foundation as part of the Soil Engineers Report that is submitted along with the CD's. The Engineer of Record will not review plans without it. This has been a guideline for submitting for several years now.I am not sure about residential as most of my residential has been additions and repair to existing structures. V-zone structures along the coast always require the soil reports with piling design recommendations. Link to comment Share on other sites More sharing options...
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