Floating Slab Foundation

[Draftsman-don]

Hello all, 

I am a former user of AutoCad and also of Turbo CAD. I finally made the switch to Chief Architect Premier X9 about a month ago. I decided to start the switch with a fairly simple plan. I also recently purchased "Residential Design Using Chief Architect X9" by Terry Munson last week. Although this book has been helpful I still haven't found what I'm looking for. I am trying to create a floating slab foundation that is common in Southwest Oklahoma. I believe IRC refers to them as ground supported slabs. I have a screen shot of one of the details that was created in a previous CAD program. I have also attached the plan in question. All I can seem to manage is a monolithic slab which is used in some localities, but not where this home will be built. Any help is greatly appreciated.

[Draftsman-don]

OK follow up question, I am unable to upload the plan file so maybe I should begin with asking how to accomplish this? The file size is 18.3 MB but the forum is blocking it. Any suggestions?

[johnny]

You can zip the file - some may want to help you right in your file, but what you provided as an example is generic enough in my opinion to get help on.

[Draftsman-don]

Great Idea, Thanks Johnny. Here's a zip file of the plan in question. Again, any help is greatly appreciated.

1703plan-6.zip

[Draftsman-don]

Wow that is it, How do I accomplish that in Chief Architect?

[rlackore]

Here's another method:

1. Replace the interior grade beams with Slabs, and put them on the Footings layer:

 

2. Select the Level 0 room and set the Stem Wall (I) value to 16". (You already have the other two critical settings correct: Floor>Room Supplies Floor for the Room Above, and Floor Structure (L) set to 4"):

 

3. Select all four Foundation Walls and set the Foundation>Footing values to 16"x20". Also uncheck Center Footing on Main Layer so you can set the Footing Offset to -1":

 

These few setting should give you what you're looking for: 1703plan-6.plan

[dshall]

I think the best method is to ZERO OUT floor assembly at LEVEL 1 and then put the SLAB ON LEVEL 0.

 

Using this method,

 you can control elevation of the slab independent of everything else on level 0 or level 1

you can control height of conc stem wall independent of everything else on level 0 or level 1

you can control the width of all footings separately but of course the top of footing will be a constant for all stem walls.

 

give it a try.  No manually adjusting height of stem walls.

 

 

 

[rlackore]

1 minute ago, dshall said:

I think the best method is to ZERO OUT floor assembly at LEVEL 1 and then put the SLAB ON LEVEL 0.

 

Doesn't Room Supplies Floor for the Room Above accomplish this? It allows independent control of the slab elevation using the Level 0 structure dbx, control of the stem wall height in the Level 0 structure dbx, and the width of footings in the wall dbx.

[dshall]

1 hour ago, rlackore said:

 

Doesn't Room Supplies Floor for the Room Above accomplish this? It allows independent control of the slab elevation using the Level 0 structure dbx, control of the stem wall height in the Level 0 structure dbx, and the width of footings in the wall dbx.

 

Yep,  I guess so,  I did that the first time and it seemed like I had less control.  

[DRAWZILLA]

of course you still need a cad detail for rebar and exact condition, Chief doesn't do that.

[rlackore]

1 minute ago, DRAWZILLA said:

of course you still need a cad detail for rebar and exact condition, Chief doesn't do that.

 

You know, that's a good point. We can specify a lot of the rebar conditions in the Foundation Defaults>Options dbx. It wouldn't take much more for Chief to expand that tab of the dbx a bit, then include the rebar in the Auto Detail tool.

[DRAWZILLA]

Yes, that would be great, if possible.

[GeneDavis]

It's gonna take some manual work to get that dropped slope bottom slab edge, right?  P-line solids, get everything on right levels, white-out joint line in section view, yadda yadda yadda.

 

Unless there's a trick I don't know.

[rlackore]

9 minutes ago, GeneDavis said:

It's gonna take some manual work to get that dropped slope bottom slab edge, right?

 

Gene, that's the gravel base, not the slab.

[GeneDavis]

Thanks, Robert.  Took to quick a look at the OP's detail.

[Draftsman-don]

I know it's late, and I am really burning the midnight oil on this project. I tried each of these suggestions and worked on each to try to understand what is exactly happening. Solver's suggestion to "Check Hang Floor Structure Inside Foundation Wall (in the build foundation dialog)" was a useful key to understand why I couldn't get the slab inside of the stem wall as I need. rlackore's suggestion looks correct, and I really appreciate uploading the plan file so that I can see what you did. I'm not sure I fully understand what's happening there though. I think it must be a little advanced for me just yet.

 

Again, bravo and thank each of you for the help. I'm taking the plunge and using a client with a simple form home and a long deadline to learn the new software. 

[Draftsman-don]

Yes Sir, 

Thanks again,

I may have more questions before I'm through.

[dshall]

An advantage to building the slab on level 0  and not on level 1  (not using floor supplied by floor below) .....  is you can auto put a sill plate on the foundation stem wall and still get a sill plate for the wall.  I usually do not build it this way,  but it is an option if you want the additional sill plate.

 

 

 

[Ridge_Runner]

13 minutes ago, dshall said:

An advantage to building the slab on level 0  and not on level 1  (not using floor supplied by floor below) .....  is you can auto put a sill plate on the foundation stem wall and still get a sill plate for the wall.  I usually do not build it this way,  but it is an option if you want the additional sill plate.

 

 

 

Good point, Scott. Your example is exactly the way we build garages here. Almost all of the designs I do are on crawlspaces or basements for the main house. However, slabs are becoming more popular, mainly on "Barndominiums."

[rlackore]

36 minutes ago, dshall said:

An advantage to building the slab on level 0  and not on level 1  (not using floor supplied by floor below) .....  is you can auto put a sill plate on the foundation stem wall and still get a sill plate for the wall.  I usually do not build it this way,  but it is an option if you want the additional sill plate.

 

 

 

 

What's the construction advantage to double-plating this condition? I'm not arguing, I'm curious.

[parkwest]

Double sill plates help if the foundation is out of level... you can shim between plates to make it right.

[Alaskan_Son]

45 minutes ago, rlackore said:

 

What's the construction advantage to double-plating this condition? I'm not arguing, I'm curious.

 

I for one always frame that way for the sake of framing efficiency.  In order to frame and sheath that wall while it is lying down, you need a bottom plate.  In addition to the issue Parkwest mentions above the problem with using the 2x8 sill as the bottom plate is 2 fold...

1. Tipping it up onto the anchor bolts is a huge pain.  Not only do the bolts themselves get in the way and hang up the wall while it is getting stood up, but they can also be very difficult to line up after the wall is stood up.  The fact the wall has to be up above the anchor bolts in order to slide down over the top of them also makes doing it this way a lot more dangerous as the bottom of the wall has to be pretty well completely disconnected from anything while performing this part of the operation.  I won't go into all the details and problems involved but suffice it to say that it can really be a messy pain.
2. In order to frame the wall properly and to tip it up in the safest and most effective manner, the bottom of the 2x8 bottom plate would need to be lined up with the inside of the foundation wall.    This gives a person no really good place to pop a straight line or to temporarily fasten that bottom plate in order to ensure the bottom is straight and secure before sheathing and standing it. 

If the 2x8 sill is installed first, most all of the problems are reduced or completely eliminated.  Actually, about 12 years ago I started adding one extra step.  I would install the sill plate, tighten down all the nuts, and then I would run around with a cut off tool and cut off all the excess anchor bolt.  I would then install some 3/4" plywood or common pine strips that ran from nut to nut.  This would completely eliminate the need to drill out and line up the bottom plate of the wall.  It also had the advantage of allowing us to use standard studs and even build a single continuous wall between the living space and garage if we were building a zero entry foundation.

 

Anyway, there are just a few reasons why the multiple plates can be a good thing.

[rlackore]

30 minutes ago, parkwest said:

Double sill plates help if the foundation is out of level... you can shim between plates to make it right.

 

I'd consider that less than ideal. If you're forced to shim, you need to shim between the concrete and the first plate so the loads are transferred as evenly as possible. shimming between the plates may level the top of the wall, but you're not taking care of the root problem, which is the gap between the concrete and the plate.

[parkwest]

This article might help you find the answer to your question...

 

http://www.jlconline.com/how-to/foundations/framing-fix-for-a-faulty-foundation_o

[rlackore]

I understand some of the advantages mentioned by Michael, though it may complicate incorporating braced wall panels using any methods that require exterior wall panel sheathing, and ensuring a continuous load path for uplift. But, it's all in the details.