Author Topic: Cinder Block Foundation 20 x 30 with 1.5  (Read 8910 times)

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Offline Steve_B

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Cinder Block Foundation 20 x 30 with 1.5
« on: July 25, 2012, 09:47:32 AM »

A few questions about building a cinder block foundation as I have never done it before, and considering working with this and concrete, I really need to get it right the first time!

I've watched a few videos and read a few articles about doing it yourself, and keeping in mind constant checking of level and height, it does not seem to hard, very labor intensive, but that does not scare me

Keep in mind it must be built at or above code for inspections, and this is for the 20 x 30 plan with 1.5 stories....


Here in the midlands of SC, it is sandy and clay type soil, do I need aa concrete footing to build, or starting from the ground laying them is ok?

How and where do I put drainage in around the wall, and is this needed for code?

Is one cinder block width, which is 8" wide, strong enough to support the house, and meet code?

Building the foundation 4 blocks high, roughly 300 cinder blocks, how much concrete mix would be needed in terms of 50 pound bags?

Building it 4 cinder blocks high, should require rebar for extra strength I am guessing, so how much rebar, what #, and where to put it in space wise?

For code, do I just need to have concrete where all blocks meet each other with a 3/8" thickness, or does the entire hollows of the blocks need to be filled with concrete?

How do I cement in the "J" bolts that stand up that go through the bottom beam of the wall... do I just fill in the hollow area of a block?



All beginner questions, as I am myself, but this thread could be helpful for all that follow me in building a first house

Specifics or links to articles or videos will be greatly appreciated!




It's all about the kiddies I tell you...

Offline Squirl

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #1 on: July 25, 2012, 10:45:40 AM »
Ok. I learned a few things doing my block foundation this way.

First, don't be worried if you make a few minor mistakes, taking you time to keep it level and square are most important.  A sledge hammer, or hammer and chisel can fix many small mistakes.  The most you are out is the $1.25 block, the mortar, and the time you spent putting it in place.  Sometimes you aren't even out of the block, just the mortar you have to chisel off.  I did a short list of lessons I learned along the way that were not outlined in any of the books or videos I read and watched.
http://countryplans.com/smf/index.php?topic=10998.msg143361#msg143361

Yes you need a full footing.
The important thing with almost all foundation is unbalanced fill.  It is the amout of force from the soil on the outside of the wall pressing against the inside.  As you can tell from the name, you only have to worry about when there is no fill on the inside to counterbalance that force.  As far as compressive force (downward), almost all foundation systems in the code books can handle up to a 3 story house.  You should be fine with 8".  If you go with solid blocks or fill in the hollow blocks with grout, you can even use 6" under some circumstances.  The only time you usually have to worry about the downward force is when it is concentrated to point loads like posts for a structural ridge beam.

Drainage is not usually required by code.  It is good practice depending upon soil, slope, etc.  I was not as worried with a vented, crawlspace, without any utilities.

You would need no concrete.  Mortar.  10 blocks per bag of mortar according to quikrete.  I think that is bull.

Rebar is only required by code if you are in a seismic zone D or if you have over 4 ft of unbalanced fill (4 ft of soil piled against the wall).  Even though it is not required, it is common practice amongst contractors.  #4 every 48" is most common.  I did not use it for my own and passed inspection. 

You just need to mortar the blocks together.  They are not required to be filled, depending upon size.  You usually have a choice, like 6" blocks solid or filled with grout, or 8" hollow.

How to do the J bolts?
http://countryplans.com/smf/index.php?topic=10998.msg147130#msg147130
I changed from paper to plastic because I was concerned about mold and I had an old tarp I had to dispose of.  You can "Top" (filing the top of the blocks with mortar) the blocks the same way.

Sorry it is not as detailed as I would like.  I will post a walkthrough of how to read the code charts as soon I have some free time from work.
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec004_par001.htm

Offline Don_P

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #2 on: July 25, 2012, 02:50:59 PM »
The bottom of the footing needs to be at or below the local frost depth OR a minimum of 12" below grade. For an 8" block wall I usually pour an 8" thick x 16" wide footing with 2 rows of 1/2" rebar on "chairs".

You can buy ready to mix with water mortar, this is the quickrete way or you can buy masonry cement (as opposed to portland cement) and a truckload of mason's sand. The excess is good spread under the plastic in a crawlspace.

The short lesson on the lingo; you'll never see another new cinder block, these are cement blocks, CMU's, cement masonry units.

Cement is portland cement, available in 94 lb sacks (1 cubic foot)
Masonry cement is a mixture of portland, lime, and different admixtures to improve workability.
Concrete is a mixture of portland cement, gravel and sand... try not to confuse the terms cement and concrete.
Grout is a pourable mortar (masonry cement and sand) or concrete (cement and aggregate). It is used to fill the cells in a reinforced block wall. You can build a wall either reinforced or unreinforced depending on heights and loads.

Unbalanced fill; I think Squirl typo-ed, that should read the unbalanced fill can be pushing from the outside in, as in a basement OR it can be higher inside pushing the walls out. A garage on a slope often has unbalanced fill under the floor slab. We had a furniture plant under construction, football field size and built up above grade at tractor trailer deck level then backfilled and compacted. The floor pour was scheduled for a couple of days out, the gravel plumbing and vapor barrier needed to go in yet. The heavens opened up. The saturated fill became heavy and juicy. About 10 am the next morning 200' of wall laid over. Those were some unhappy masons.

Off the top, the only other thing I see is the anchor bolts need to be 1/2" x 12" HDG (hot dipped galvanized)min. Read your state's anchor bolt placement codes, those do vary quite a bit.

Do install an exterior perimeter footing drain to daylight, cheap insurance. I prefer at least some reinforcement in a wall. We likely just added a row to your guesstimate.

Offline Steve_B

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #3 on: July 26, 2012, 08:29:17 AM »


As for the concrete footing....

If I were to go with what is suggested at being 12" deep by 16" wide and an 8" thick layer of concrete

Is it just poured into the trench I make, or must it be poured into a squared off wood retaining wall that has to be put into place in the ground?

It's all about the kiddies I tell you...

Offline Squirl

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #4 on: July 26, 2012, 08:36:10 AM »
As long as your soil is firm, trench is fine.  Check your local frost depth, I am assuming because you are in South Carolina 12" is probably deep enough.

Offline Erin

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #5 on: July 27, 2012, 08:03:56 AM »
You might also check into surface bonding your cement blocks.  I'm drawing a blank right now, but one of our members has a good blog where he details how he did his surface bonded cement block foundation. 

It's what we did with our house, too.
ETA:  I don't know if SBC is code compliant, though...
« Last Edit: July 27, 2012, 10:54:42 AM by Erin »
The wise woman builds her own house... Proverbs 14:1

Offline davidj

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #6 on: July 30, 2012, 10:56:41 AM »
We did a concrete block foundation on our cabin - there are some pictures a couple of pages in.  I'd never done anything like this before but it wasn't too bad, although it is a lot of hard work.

We used wooden forms for the footings as our soil is pretty sandy.  Putting the forms in was a fair bit of work and I'd avoid doing it if you can.

We used the "speed blocks" with no ends.  This requires that you fill with rebar and grout.  I'd recommend this approach as it's easier if you don't have to "butter" the ends of the blocks.  However it does mean you need to fill it which costs a bunch to bring a concrete truck in.  However, what you end up with is really strong - I've seen them build 30' high walls in the Bay Area with this method (admittedly with wider blocks) and we've got some of the toughest engineering requirements in the world.

One place where it does get tricky is if you have to do non-trivial openings but that doesn't sound like it's an issue for you.

PS And having a wife that doesn't mind mixing mortar makes a huge difference!

Offline zion-diy

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #7 on: July 30, 2012, 02:23:55 PM »
I didn't see anyone mention the types.
Be sure to get the proper mortar mix.  probably type N. maybe type S for below grade. Just be sure you don't try to use something like type O.
Just a 50-ish chic an a gimp,building thier own house,no plans,just--work,work,work,what a pair :}

Offline Squirl

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Re: Cinder Block Foundation 20 x 30 with 1.5
« Reply #8 on: July 31, 2012, 08:41:02 AM »
Sorry I did not post the other topic link.

http://countryplans.com/smf/index.php?topic=12374.0

"Mortar shall be Type M or S"