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Old 01-30-2011, 03:10 PM   #1
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rebar in foundation


in a crawlspace block foundation do you put veritcal or horizontal rebar?

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Last edited by bluebird5; 01-31-2011 at 12:00 AM.
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Old 01-30-2011, 06:12 PM   #2
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rebar in foundation


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in a crawlspace block foundation do you put veritcal or horizontal rebar?
what about a basement if you were to have an 8 to 10 foot block foundation?
Yes, you put rebar in any foundation walls...both horizontal and vertical. The next question you should be asking is the size of the rebar required, the spacing of the rebar required, for both the vertical and horizontal bars.

Lack of proper rebar won't always cause the structure to fail per say, but it can lead to sinking, cracking walls, leakage, and a myriad of other problems. You'd be better served to get a structural PE to give you some advice based on your area.

What works in Florida doesn't work in Maine, different soil conditions can seriously affect the rebar size and placement

Often you can find a PE to write a letter discussing the instructions for a nominal fee based on a simple review of your plans. This would be minimal in cost and could save you a ton in the future

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Old 01-30-2011, 06:15 PM   #3
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rebar in foundation


It is code specific, but here there are very clear tables that give you rod dia., spacing & placement within the cell depending on wall width, height, unbalanced fill height, etc.... All of the tables call for vertical rod only. Generally the only time we see horizontal rebar (bond beams) in resi block walls is if a commercial architect drew the plans.
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Old 01-30-2011, 06:40 PM   #4
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rebar in foundation


In the northeast, I generally see horizontal rebar and ties in the footings. The rebar in the footings will resist sagging in the center of the wall..but only if placed properly. If it's at the top of the footing, it's worthless.
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Old 01-30-2011, 09:46 PM   #5
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rebar in foundation


I do agree Steeler, I just took the question as pertaining to the block walls themselves. I may have been mistaken in what his question was.
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Old 01-30-2011, 10:33 PM   #6
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im in tennessee and i see 2 number 4 rebar in the footings on chairs but don't see rebar in the block but i was thinking with no vertical rebar would it be possible for the whole structure to shift without rebar tying the block to the footer?
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Old 01-30-2011, 11:05 PM   #7
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rebar in foundation


The walls can shift if rebar isn't placed properly, but more importantly, they can buckle due to the wall in effect being a retaining wall. Any retaining wall over three feet high should in theory be reinforced in some way.

You don't need it in every cell, but usually it'll be at 24" or 48" o.c...and there's a bunch of variables in deciding it's size and placement.

In the footing, there'll usually be ties at 12" o.c. along with three bars placed evenly at the bottom of the footing...keeping at least three inches of concrete from the sides and bottom.

In the footing, there will be "L" shaped rebar that are spaced so that they can be lapped and tied in with the vertical rebar. Even the lap should be determined by an engineer.

Keep in mind, I'm not a PE and my recommendations are general in scope and apply in common building applications.
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Old 01-31-2011, 09:48 AM   #8
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Here's a link to WI code to give you an idea on reinforcement:

http://legis.wisconsin.gov/rsb/code/comm/comm021.pdf

Go to page 30 to see the tables I was talking about. The first table is used to determine allowable wall width. The next three show diameter, spacing, and placement of steel in regards to the walls outside edge, all based on wall width, height & unbalanced fill height.

Note that there is no inclusion for walls 4' and under. These should still get pilasters at the anchor bolts IMO. Especially necessary if the wood walls above are part of a shear wall, typically on garage OH door wings, narrow corner walls, etc....

Hope this gives you an idea, but you really should still determine what your own code requires.
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Old 01-31-2011, 10:14 AM   #9
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Block foundation reinforcing is different from poured concrete reinforcing. Block foundation is typically placed with the hollows facing upward. Vertical reinforcing may be placed if the blocks are filled with concrete after placement. This is commonly done in cases where the block is resisting soil load, or in seismic areas, or if the wall is over 4 feet tall, but may be required by the local building inspector. The rebar is typically #4 spaced 32 inches on center, however this varies by the region, check with your local building inspector.

As for horizontal rebar, it is difficult to place horizontal rebar in a block foundation using standard block because you would need a large joint. It is possible to place thin steel mat reinforcing (NOT rebar) between block courses, and this is sometimes done in commercial use, but rarely in residential use. The horizontal reinforcing is known as steel wire, and comes in a variety of patterns depending on the specific application.
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Old 01-31-2011, 12:52 PM   #10
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Block foundation reinforcing is different from poured concrete reinforcing. Block foundation is typically placed with the hollows facing upward. Vertical reinforcing may be placed if the blocks are filled with concrete after placement. This is commonly done in cases where the block is resisting soil load, or in seismic areas, or if the wall is over 4 feet tall, but may be required by the local building inspector. The rebar is typically #4 spaced 32 inches on center, however this varies by the region, check with your local building inspector.

As for horizontal rebar, it is difficult to place horizontal rebar in a block foundation using standard block because you would need a large joint. It is possible to place thin steel mat reinforcing (NOT rebar) between block courses, and this is sometimes done in commercial use, but rarely in residential use. The horizontal reinforcing is known as steel wire, and comes in a variety of patterns depending on the specific application.
I believe you can also add in bond beams periodically throughout the coursing as specified, Daniel can probably add more about this subject than I can.
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Old 01-31-2011, 01:53 PM   #11
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I believe you can also add in bond beams periodically throughout the coursing as specified, Daniel can probably add more about this subject than I can.
That's really the only effective way to add horizontal rebar to a CMU wall, other than by using an "Ivany" style block. Rarely done in residential, other than odd situations like large window openings, pre-cast concrete planking above, etc... Very common in comm. work though. The construction methods are two completely different "animals" though, as the basement generally see much more lateral pressure as well as benefits from the weight of the house above.

The wire Dan refer's to has the trade name of "Dur-o-Wal" and comes in two basic styles: Ladur & truss. Really just used as a mortar joint reinforcement to control cracking in long walls in this application. Again, rare to see in resi work, although it is used on occasion.
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Old 02-01-2011, 07:38 PM   #12
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rebar in foundation


well the frostline is only 12 inches where i am and foundations generally do not hold back any earth maybe 18 inches max so what you are saying that unless the wall is retaining then the rebar is not necessary?
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Old 02-01-2011, 08:33 PM   #13
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rebar in foundation


OK, assuming you are in the US, given a frost line of 12 inches, you must be down south. You should check with your local building inspector, they may require rebar, but if not you might want to consider it anyway if you live on expansive soils, or in a seismic area. Unreinforced block foundations perform very poorly in earthquakes, when subjected to lateral load from retained soil, or if the ground settles or rises (expansive soils). Even if reinforced, they are not very good compared with a poured concrete foundation, but the reinforcing does improve performance somewhat.
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Old 02-02-2011, 10:33 AM   #14
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rebar in foundation


having built ' down south ', we always filled block walls w/grout giving special attn to proper waterproofing before backfilling,,, yes, we lost jobs due to cost but so what ? #4 bar lateral reinforcement was every other course,,, #5 vertical bar 4' o/c tied into the foundation,,, the foundation is no time to skimp on $ im-n-s-h-fo every inspection resulted in ' wow - that's more than code requires !

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