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Features Of A California Slab Foundation. What Are They?

 
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Old 04-10-2010, 02:03 PM   #1
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Features Of A California Slab Foundation. What Are They?


What features are in a no-basement slab foundation for single-family homes built in California, and what needs to be shown on the foundation prints, to satisfy both plans reviewers and the contractors that form and pour the foundations?

I am asking this about the class of slab foundation that is done on a lot with reasonably flat topo, where the foundation slab has thickened edges, maybe drops for room or garage stepdowns, curbs around the garage, maybe shower drops, footings under partitions and bearing walls integral to the slab, and more.

A slab-type foundation. Not one with stemwalls, deep grade beams, piers and beams, and all the stuff we do when going onto a steep hillside lot. Just a slabber. The edge thickenings might step a little to deal with a little terrain, but again, I'm just looking for what happens in a slab poured monolithically. In the big state with the big stiff codes and tight plans review.

I am looking to see what goes on, because I am participating in a dialog on the website forum where we discuss Chief Architect software, which is used to design and draw house plans. Chief's tools for addressing monopour slab foundations is weak and needs to be improved.

For reference and to get a common terminology, I have included a sketch. I'm just guessing at what might go on, so don't misread the drawing. It's just here for terminology.
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Old 04-10-2010, 05:46 PM   #2
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Re: Features Of A California Slab Foundation. What Are They?


Hi Gene, 4" slab, 12" x 12" footings, 2 of #4 re-bar continuous one top one bottom, 1/2" hold-downs 48" O.C. typ. #3 re-bar 24" O.C. both ways in slab bent into footings or 10 ga. wire mesh, 2500 PSI conc. typ., top surface 8" above grade. No thickened slab under non-bearing interior walls. Int. walls shot to slab.
Probably forgetting a couple other things but that covers most of it.

30mil. vapor barrier, 4" sand all under the slab.

Andy.

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Old 04-10-2010, 08:29 PM   #3
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Re: Features Of A California Slab Foundation. What Are They?


Sounds pretty routine, Andy. Thanks.

Funny how things go. You hear about how ridiculously tough California building codes are, but maybe it relates more to how things go from the anchors up, than the 'crete in the ground.

Would what you just describe work from Barstow to San Diego, then all the way up to Fresno, and even up into the wine valleys NE of SF?

What about when the tracts go up and over the hills. Do they just shelf out for each house footprint, and then put in what you have described, for a foundation?
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Old 04-10-2010, 10:59 PM   #4
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Re: Features Of A California Slab Foundation. What Are They?


What I described is pretty much the prescriptive design for all of California, every city and jurisdiction has to comply with the latest 2007 CBC. Some of course can require bigger or deeper footings like the city of Fullerton requires 24" deep footings because they have a very expansive soil and require the rigidity a deeper footing offers.
Mountainous areas are different as you know, but the above pretty much describes the whole state (for a single story SFR in earthquake zone A B C or D). Personally, I hate slab foundations, I much prefer a raised foundation.

Andy.
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Old 04-11-2010, 12:41 AM   #5
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Re: Features Of A California Slab Foundation. What Are They?


Good reply Andy

Hey UpNorth, Your engineering may add some more specific hold downs depending on what you are doing. There is getting to be more framing hardware, plate to plate mechanical connections & lots of shear wall showing up. There are alot of raised foundations done in the hills. Some higher end tracts will advertise a raised foundation.
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Old 06-18-2010, 08:53 PM   #6
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Re: Features Of A California Slab Foundation. What Are They?


I pour foundations in so cal,and every blue print has to be drawn by an engineer.there are pads and hold downs between all windows and doors,anchor bolts often at 24" oc,all bolts must be in place for inspection before the pour.4x post will be used at ends of shear walls and most have a set of hold downs.
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Old 06-18-2010, 11:04 PM   #7
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by erikm View Post
I pour foundations in so cal,and every blue print has to be drawn by an engineer.there are pads and hold downs between all windows and doors,anchor bolts often at 24" oc,all bolts must be in place for inspection before the pour.4x post will be used at ends of shear walls and most have a set of hold downs.

I think you mean that ever print must be approved by an engineer.
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Old 06-18-2010, 11:07 PM   #8
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Re: Features Of A California Slab Foundation. What Are They?


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Originally Posted by framerman View Post
I think you mean that ever print must be approved by an engineer.


Correct,ever print is designed by the architect and than the s pages are added to the floor plan by the engineer
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Old 06-19-2010, 01:48 AM   #9
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Re: Features Of A California Slab Foundation. What Are They?


Hi Erik, I have done some "engineering" for some of my clients as long as the build is not too complicated and falls under the prescriptive or "Conventional Construction" requirements of the CBC and I am not an engineer.
This doesn't happen too often anymore though, so many cities want an engineer's stamp and approval. I think because the engineer then takes some or the bulk of the liability if an earthquake, tornado and hurricane all hit the house at the same time.

Andy.
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Old 06-19-2010, 02:09 AM   #10
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by ScipioAfricanus View Post
Hi Erik, I have done some "engineering" for some of my clients as long as the build is not too complicated and falls under the prescriptive or "Conventional Construction" requirements of the CBC and I am not an engineer.
This doesn't happen too often anymore though, so many cities want an engineer's stamp and approval. I think because the engineer then takes some or the bulk of the liability if an earthquake, tornado and hurricane all hit the house at the same time.

Andy.

Dang it,

Most the remodels I am doing are on 6000 sq foot lots and have homes that were built just after ww 2.and are about 1300 sq ft single story.
Raised foundation.We go in and fill 13 dumpsters,and leave just some stem wall.next is a hand dig and under pinning.most 2 story add ons have 30 or 40 pads with hold downs.next we drill over 100 anchor bolt holes in the existing foundation wall.At the end of the day we pour over 40 yards into the new foundation.
Than the straps and clips and post bolts.takes longer to seam the place up than it did to frame the walls.

ps...maybe you can draw something up for us in the future.

Erik
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Old 06-19-2010, 05:39 AM   #11
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Re: Features Of A California Slab Foundation. What Are They?


I am going to build a small extension on our house (about 11ftx14ft) on the end of an existing extension done in the 70's. Because we might be on medium shrinkable clay and there 4 Lalandi and a Hawthorn tree within about 4 ft of the foundations the Building Inspector is talking about me using a raft foundation, which I would guess is similar to a California slab foundation.
Features of a California slab foundation.  What are they?-im13.jpg
This will cost about 700 to be designed by an SE, but I think that the raft could move the extension away from the existing and cause some cracking between the 2. Rafts are fine for detached houses.
I would prefer to use a tradional strip footing, although it means digging down 10 feet.
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Old 06-19-2010, 11:08 AM   #12
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Re: Features Of A California Slab Foundation. What Are They?


Hi Erik, I think your guy is over engineering your stuff but that is just my opinion, I am not an engineer so I am not taking on the liability he is.
I have worked with many different engineers and what I look for is some one that will "value" engineer my projects.
By "Value engineer" I don't mean I look for the cheapest guy I look for the engineer that will produce calcs. and solutions that will not put an overly high burden on the cost of the project just because he wants to cover his a$$.
Hold-downs on 24" centers is just way over-kill and wastes the clients money.
If you talk to the plan checkers in your city they can not recommend any specific engineers or engineering companies but they informally give you their opinion on which engineers get their plans through plan check with the least cost to the client.

Andy.
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Old 06-19-2010, 09:15 PM   #13
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by ScipioAfricanus View Post
Hi Erik, I think your guy is over engineering your stuff but that is just my opinion, I am not an engineer so I am not taking on the liability he is.
I have worked with many different engineers and what I look for is some one that will "value" engineer my projects.
By "Value engineer" I don't mean I look for the cheapest guy I look for the engineer that will produce calcs. and solutions that will not put an overly high burden on the cost of the project just because he wants to cover his a$$.
Hold-downs on 24" centers is just way over-kill and wastes the clients money.
If you talk to the plan checkers in your city they can not recommend any specific engineers or engineering companies but they informally give you their opinion on which engineers get their plans through plan check with the least cost to the client.

Andy.

I was not saying hold downs @ 24" oc...12"x 5/8" ab on 24" oc.
The hold downs are used at the full sections of wall between the opennings.The hold downs are on top of a concrete pad.

I agree,the engineering sometimes goes way out of the way to over build.
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Old 06-20-2010, 12:37 AM   #14
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Re: Features Of A California Slab Foundation. What Are They?


[QUOTEI was not saying hold downs @ 24" oc...12"x 5/8" ab on 24" oc.][/QUOTE]

Ah I see, sometimes I slip and use the incorrect term, funny thing is I understood it as anchor bolts at 24"O.C. which is just way over-kill.
Even the prescriptive is 10" long (7" embedded), 1/2" wide, with a 3" sq. steel washer w/slot if desired. And that is at 6' O.C. in seismic category D.
Even seismic cat. E is 5/8" 72" O.C.

I wanted to ask you what you mean by pouring 30 or 40 "pads" Are these footings with hold-downs? I have done that for a couple homes in Orange myself when I was doing the GC thing. I found it to be a good solution for some homes.

Andy.
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Old 06-20-2010, 01:34 AM   #15
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by UpNorth View Post
I am asking this about the class of slab foundation that is done on a lot with reasonably flat topo, where the foundation slab has thickened edges, maybe drops for room or garage stepdowns, curbs around the garage, maybe shower drops, footings under partitions and bearing walls integral to the slab, and more.

A slab-type foundation. Not one with stemwalls, deep grade beams, piers and beams, and all the stuff we do when going onto a steep hillside lot. Just a slabber. The edge thickenings might step a little to deal with a little terrain, but again, I'm just looking for what happens in a slab poured monolithically.
would like to help but can't make heads or tails about what you are asking.
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Old 06-20-2010, 03:35 AM   #16
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by ScipioAfricanus View Post
[QUOTEI was not saying hold downs @ 24" oc...12"x 5/8" ab on 24" oc.]
Ah I see, sometimes I slip and use the incorrect term, funny thing is I understood it as anchor bolts at 24"O.C. which is just way over-kill.
Even the prescriptive is 10" long (7" embedded), 1/2" wide, with a 3" sq. steel washer w/slot if desired. And that is at 6' O.C. in seismic category D.
Even seismic cat. E is 5/8" 72" O.C.

I wanted to ask you what you mean by pouring 30 or 40 "pads" Are these footings with hold-downs? I have done that for a couple homes in Orange myself when I was doing the GC thing. I found it to be a good solution for some homes.

Andy.[/quote]


each section of shear panel is rated say from 300-700,and each length of shear panel is termenated at a post and hold down,depending on the value of the hold down the pad size nd anchor size get bigger with added value.these areas are tied all the way to the roof/via straps of different lengths/and each area of shear is nailed off at different spacing and nail gauge.
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Old 06-20-2010, 11:54 AM   #17
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Re: Features Of A California Slab Foundation. What Are They?


Quote:
Originally Posted by ScipioAfricanus View Post
4" slab, 12" x 12" footings, 2 of #4 re-bar continuous one top one bottom, 1/2" hold-downs 48" O.C. typ. #3 re-bar 24" O.C. both ways
30mil. vapor barrier, 4" sand all under the slab.
Andy.
5/8" AB are typ. because that is the requirement for hold downs. #4 @24" OC, #3 @ 18" OC. 6-6-10-10 works out to be equal to #4 @ 24" OC. 2" is maximum depth for sand. Too much sand and it looses it's ability to self compact.
Quote:
Originally Posted by erikm View Post
I pour foundations in so cal,and every blue print has to be drawn by an engineer.there are pads and hold downs between all windows and doors,anchor bolts often at 24" oc,all bolts must be in place for inspection before the pour.4x post will be used at ends of shear walls and most have a set of hold downs.
Anchor Bolts are required with-in 2' from corners and splices, plus accurately placed for hold downs and 6' OC in the field.
Quote:
Originally Posted by erikm View Post
Most the remodels I am doing are on 6000 sq foot lots and have homes that were built just after ww 2.and are about 1300 sq ft single story.
Raised foundation. 30 or 40 pads with hold downs.next we drill over 100 anchor bolt holes in the existing foundation wall.At the end of the day we pour over 40 yards into the new foundation.40 yards concrete sounds like too much for a SFR on a 6,000 sq ft lot.
Erik
Quote:
Originally Posted by erikm View Post
anchor bolts at 24"O.C. which is just way over-kill.
Even the prescriptive is 10" long (7" embedded), 1/2" wide, with a 3" sq. steel washer w/slot if desired. And that is at 6' O.C. in seismic category D.
Even seismic cat. E is 5/8" 72" O.C.
I wanted to ask you what you mean by pouring 30 or 40 "pads" Are these footings with hold-downs? doing the GC thing.
Andy.
Pad Footings are SOP for second story add ons.
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Old 06-20-2010, 05:20 PM   #18
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Re: Features Of A California Slab Foundation. What Are They?


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5/8" AB are typ. because that is the requirement for hold downs. #4 @24" OC, #3 @ 18" OC. 6-6-10-10 works out to be equal to #4 @ 24" OC. 2" is maximum depth for sand. Too much sand and it looses it's ability to self compact.
Anchor Bolts are required with-in 2' from corners and splices, plus accurately placed for hold downs and 6' OC in the field.

Pad Footings are SOP for second story add ons.

ab's are required 12" from corners and splices/hold downs vary depending on the hold down/some are 1 1/8"

sometimes 3" pt is required on heavy duty walls/sometimes #5 rebar is called out/depends on what the old engineer wants on that house

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