Residential Slab Foundation 1

[TRAK.Structural]

I'm reviewing some drawings by others (see below) and wondering if this type of detail for a slab foundation is common for residential construction. More often I've seen a monolithic turndown at perimeter walls, i.e. no construction joint/separation between the thickened edge foundation and the interior slab. Which way do you see this detail most often? Are there pros/cons between this approach and the monolithic approach?

 

[kissymoose]

We haven't used it, but it's becoming more common for energy conservation. The insulation provides a thermal break between the interior slab and exterior exposed foundation. I still haven't seen any sort of quantitative check/test/reasoning for it, just inclusion due to the idea "thermal break good."

Pros: Decreased thermal transfer from interior slab to exterior exposed foundation, of unknown quantity
Cons: Harder to build/easier to mess something up

 

[Thomas_T]

I'm in Georgia. Nobody insulates anything here.... but that detail is also in the foundation handbook

 

[JoshPlumSE]

I think keeping the slab and the wall footing separate can be a good thing. It allows for some differential movement / settlement that will not be as likely to cause damage with brittle interior flooring.

 

[SE2607]

I'm reviewing some drawings by others (see below) and wondering if this type of detail for a slab foundation is common for residential construction. More often I've seen a monolithic turndown at perimeter walls, i.e. no construction joint/separation between the thickened edge foundation and the interior slab. Which way do you see this detail most often? Are there pros/cons between this approach and the monolithic approach?

View attachment 15541

What annoys me most about this details is "..BY OTHERS". What does this mean? Is the GC supposed to exclude this item from his/her bid and the owner will provide this or what?
Another one is "...@xx" O.C."This is redundant and unnecessary (clever, right?). Although I've let go of this a long time ago, I still refuse to use this, even when I get a plan check comment on this issue. My response is (always), for the plan checker to cite a code reference. I don't care if they are at xx" O.C., xx" ON EDGE or any other point of reference. What would be more accurate is "@xx" on average". I just use "@xx"".
Another one is "...PROVIDE 90^o STD. HK @ LOWER END". Where else would it be? The detail clearly shows it at the lower end. What would make the detail clearer is spelling out "hook".
Another one is the use of "TYP.". This adds nothing to the detail. This is a typical detail, so, of course those plate washers at the anchor bolts are typical.
Compacted Subgrade.
Sigh...
To 90%? To 95%? Per soils report? What is the criterion for acceptance?
The depth of the footing is shown at 1'-'6" from finish grade. The grade is shown as sloping. At what distance is that measurement taken? 5 feet from "daylight"? H/3? Again, not clear.
EL = 0'-0" shouldn't even be on this detail. If taken literally, that means the top of slab is at sea level. Aren't there other drawings which shows the datum elevation?
Arghhh.,
Some may say that, if these are the things that bother me, I'm doing pretty good and they would be right.

 

[Aesur]

What annoys me most about this details is "..BY OTHERS". What does this mean? Is the GC supposed to exclude this item from his/her bid and the owner will provide this or what?
Another one is "...@xx" O.C."This is redundant and unnecessary (clever, right?). Although I've let go of this a long time ago, I still refuse to use this, even when I get a plan check comment on this issue. My response is (always), for the plan checker to cite a code reference. I don't care if they are at xx" O.C., xx" ON EDGE or any other point of reference. What would be more accurate is "@xx" on average". I just use "@xx"".
Another one is "...PROVIDE 90^o STD. HK @ LOWER END". Where else would it be? The detail clearly shows it at the lower end. What would make the detail clearer is spelling out "hook".
Another one is the use of "TYP.". This adds nothing to the detail. This is a typical detail, so, of course those plate washers at the anchor bolts are typical.
Compacted Subgrade.
Sigh...
To 90%? To 95%? Per soils report? What is the criterion for acceptance?
The depth of the footing is shown at 1'-'6" from finish grade. The grade is shown as sloping. At what distance is that measurement taken? 5 feet from "daylight"? H/3? Again, not clear.
EL = 0'-0" shouldn't even be on this detail. If taken literally, that means the top of slab is at sea level. Aren't there other drawings which shows the datum elevation?
Arghhh.,
Some may say that, if these are the things that bother me, I'm doing pretty good and they would be right.

Are you ok? Seems like you kind of lost it there on that detail based on your ranting (we all get there at some point). Please remember we provide construction documents, not a construction detail, there is also more information in the plan set that answers many your frustrations above, specifically compaction and distance to daylight requirements for finished grade etc. You seem to also be wanting less information in the detail but more of other information which is typically in other locations on a plan set, for instance do you write the compaction requirements on every detail, I sure don't, in fact I don't put it on any details, it's in the GSN and sometimes on the slab callouts on plans.

TYP is often needed because unfortunately the industry has headed in the direction of incompetence where people will try to change order for anything. In fact we have started having to add a note on every sheet that details are typical and may not be cut in every location because contractors started only installing something like a column cap to support a beam only where specifically cut on a plan; this actually happened and wasn't caught until all 5 stories were built that they only installed the column caps at one end of the beam and not the other end, and these are massive custom caps because they insisted on large wood transfer beams on smaller columns to avoid steel members. You can imagine the fun or jacking up 5 stories to fit these in there after the fact. Therefore I believe TYP is a great note to keep, but more due to liability and lack of people being able to think now days.

 

[Aesur]

Now back to the OP's question: I am starting to see this more and more often in both cold and hot climates, I believe mostly due to the energy codes being more and more difficult to meet. I'm not a big fan of this detail, but have used something sim a few times when required. It appears that there are still hooked bars tying the slab to the stem, which would restrain some of the movement potential. I have always gone back and forth on tying slabs into stems and haven't really come up with a preference yet. Seems if I show one way, the contractor wants the opposite. Another item I don't like if when doing this, your stem gets thinner usually to the point that you need a longer anchor to get proper concrete cover for transfer of forces, this is often missed in the details/designs from what I have seen.

 

[Tomfh]

These thermal details are becoming a real pain here in Australia, where the climate is pretty mild. Suddenly there’s this pedantic obsession with thermal bridging, every architect and “green” consultant acting like a simple facade bracket is some catastrophic design flaw.

“Oooh no, can’t have that steel clip, it’s a thermal bridge!” Give me a break.

 

[Brad805]

Tomfh, do you have energy model consultants in AU? Wow, does that slows down a project.

 

[SE2607]

Are you ok? Seems like you kind of lost it there on that detail based on your ranting (we all get there at some point). Please remember we provide construction documents, not a construction detail, there is also more information in the plan set that answers many your frustrations above, specifically compaction and distance to daylight requirements for finished grade etc. You seem to also be wanting less information in the detail but more of other information which is typically in other locations on a plan set, for instance do you write the compaction requirements on every detail, I sure don't, in fact I don't put it on any details, it's in the GSN and sometimes on the slab callouts on plans.

TYP is often needed because unfortunately the industry has headed in the direction of incompetence where people will try to change order for anything. In fact we have started having to add a note on every sheet that details are typical and may not be cut in every location because contractors started only installing something like a column cap to support a beam only where specifically cut on a plan; this actually happened and wasn't caught until all 5 stories were built that they only installed the column caps at one end of the beam and not the other end, and these are massive custom caps because they insisted on large wood transfer beams on smaller columns to avoid steel members. You can imagine the fun or jacking up 5 stories to fit these in there after the fact. Therefore I believe TYP is a great note to keep, but more due to liability and lack of people being able to think now days.

Yeah, I kinda lost it.
Regarding the issues you mention:
1. The only place where I mention compaction is in my GSN which reads "see soil report for compaction requirements".
2. In the use of "TPY", where does it end? In the detail submitted by the OP, it either has too many references to "TYP". Again, in my GSN, I address this by saying similar details have similar requirements, paraphrasing of course. Putting too much information on a detail can invite conflicts.
3. Depth of footing with respect to slope is covered in job specific details as my "standard details" show only level grade.

 

[Euler07]

The projects I've seen that had under-slab insulation also had large cracking. I wonder who takes liability for the large cracking when the engineer is forced to include the insulation, even when we know it will reduce the performance of the slab?

 

[Tomfh]

Tomfh, do you have energy model consultants in AU? Wow, does that slows down a project.

Yes on some projects. It can be a pain.

 

[XR250]

TYP is often needed because unfortunately the industry has headed in the direction of incompetence where people will try to change order for anything.

I agree. I use it just for that liability.
I get crazy shit all the time like I call out (2)jacks and (2)kings at one end of a header and they just assume it is for that end only. Now I call it out on both ends.

 

[canwesteng]

Using a dummy elevation for TOC is pretty common I would think. Using 0 is pretty bad practice because you have negatives on the drawings now, but it's best not to put an elevation on the drawings until you have a known survey.

 

[dauwerda]

Another one is "...@xx" O.C."This is redundant and unnecessary (clever, right?). Although I've let go of this a long time ago, I still refuse to use this, even when I get a plan check comment on this issue. My response is (always), for the plan checker to cite a code reference. I don't care if they are at xx" O.C., xx" ON EDGE or any other point of reference. What would be more accurate is "@xx" on average". I just use "@xx"".

I disagree with you on this bit. If I saw this detail called out and it just said @12" I would interpret that as 1 item 12" away from some reference point. Not an array of items spaced every 12". But, maybe that's just me (and some plan checkers I guess)?

 

[phamENG]

Yeah - what if it's 12" clear? If I need to specify that's it's a clear distance, I should specify that it's a center-to-center distance, too. There's more than one way to dimension something, and it's not a good idea to assume the person reading it is going to interpret it correctly.

Standard practice here is to call first floor 0'-0", and everything is referenced from that. In the general notes I'll state that and refer the contractor to the civil drawings for what that is relative to the survey datum. This way, the framer isn't having to to figure out the floor to floor height between 246.7 and 237.6. First floor is at 0'-0", second floor is at 9'1 1/4". Easy.

Nobody does concrete stem walls around here. It's a CIP footing, CMU stem wall, and a slab. Most residential construction uses a hollow header course so the slab ties into the wall. Commercial floats the slab next to the block. Most architects are okay with the 2" of block showing - by the time you add drywall and baseboard and some sort of shoe, you're out past it anyway - but those that don't will usually accept a 6" course at the top so the joint becomes a non-issue. Insulation schemes always get interesting, but most can be dealt with.