Building a Concrete Wall

My husband and I want to build a concrete wall (and finish it with stucco) on the windy side of a concrete slab which we intend to make a patio. The wall will be 20' in length by ~5 ft tall. Have a number of questions to which we could not find answers on the web or in literature: - do we need rebar in a 5 ft high wall? - how do we attach the wall to the house? - can we just start laying block on the slab or do we need to put some kind of footing in? - the cement slab has a crack in it cause by a tree root nearby (we think), will this cause the wall to shift or crack, could we span the crack by say laying every other block on the bottom row? - we live in central WA where the temp ranges from -20 to 106 (last week), do we need to use special mortar or do anything special because of the temp fluctuations? - any other advice? Thanks in advance.
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Whoa, what are you doing here? You say a concrete wall, then you say you are laying block. One or the other. Is it poured concrete (that does need rebar) or is it concrete block? Big difference in construction.
In any case, you need a footer. Depth of footer is dependent on climate and soil conditions and can range fro 12" to 60". Call your local building official to be sure.

You are asking for trouble. Find the problem, fix it, then start over, even if it means taking up the slab.

I think you are in over your head already.
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It sounds like you mean a cement block wall. An existing patio slab is inadequate to carry the load of a cement block wall.
It will need a footing down to your local frost depth. It will probably need to be quite wide or stabilized with piers. There is a tremendous amount of wind force against a 5' x 20' wall that is not supported at the ends or top. I see so many subdivision decorative privacy walls leaning or cracking due to inadequate footings. Most will have substantial pilasters every 10'. It should not be fastened to your house in my opinion unless your house is cement block which I doubt.
The wall will need rebar reinforcement both vertically and horizontally with appropriate grout fill.. ______________________________ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net

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Most walls 3 foot or more above grade require an engineer's stamp to be legal. They also must be inspected and certified as built to plan. You best check your local codes before you start..
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Colbyt
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OK, now you guys have me worried. It is a cement block wall that we had intended to build - and it sounded simple. I am especially worried about the wind part - we live in a very windy area - in fact today have a high wind advisory. So what do you suggest for a way to block the patio from the wind and provide a heat sink - just a wooden fence?
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snipped-for-privacy@yahoo.com wrote:

Concrete, not cement.
- and it sounded simple.
Anything that can kill a person if it falls isn't simple. My 96-year-old grandmother was killed when a concrete block wall collapsed on her, although she shouldn't have been climbing it. I think most locales require concrete or block walls over 3' tall to include steel reinforcement rod, or at least they should, and even strong wind can make an inadequately reinforced concrete wall topple. Wooden fences are inherently very strong.
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Don't get discouraged just yet! A 5' wall of CMU is very do-able. Follow the advice of others and make sure you have an adequate footing under there. A few points. Check with your local inspection/permit office for what's needed for a wall this size. This will tell you a lot in terms of the complexity you're under. I just built an 80' or so long by 5'6" high adobe wall here in NM (very different beast altogether) and didn't need to pull a permit at all so local rules will govern what you need to do. For such a short length, I wouldn't hesitate to overbuild the footer a bit just for a bit of safety margin. Laying block can be frustrating no matter what you do only for the fact that getting the morter on the block can be a real art (at least it is for me....I can never seem to get the mortar to either stick or go where I want it to!). When you dig out the footer, and I suspect you'll have to go down a fair bit given your climate, you'll be able to tell pretty quickly what's causing the crack that you describe. If it is in fact a tree root and it crosses where the footer will go, you will have to remove it. Once the footer is in place, you will need to build up the wall with rebar vertically and possibly horizontally as well (may be able to just use ladders). Again, your inspector should be able to help with the details. You will find as well that most places require the vertical cavities in the block to be filled with concrete every so many feet and that is quite easy to do. So at the risk of continuing to ramble here, I would highly recommend taking a trip to your local building office and start talking with them. They're really going to know what you need to do in your situation. Everyone's is different and you don't want to underbuild it and over building it too much costs more $$. It really isn't difficult, just a bit of hard work and getting the knowledge of what's needed, locally. Sorry for the ramble.... Cheers, cc
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On 30 Jul 2006 07:46:13 -0700, " snipped-for-privacy@yahoo.com"

A flat wall has very little stability, if you have some lateral elements it gets a lot more stable. (f you turn a row of block at a 90 in the run of the wall, making an 8" buttress it gets a lot stronger and then make a corner at each end. For a wind code wall in Florida you need 2 #5 rebar (5/8") in the footer which get tied to "dowel hooks" of #5 that protrude up into the cores of the block 36-40" on 4' centers. You then drop a hook down from the top tied to the up rod, put rebar on the top 2 courses and pour the dowelled cells and the top 2 courses of block solid with concrete. That gets you up into the 120+mph range. You end up with a matrix of concrete and steel, solid from the footer to the bond beam on top. The block in the middle are not really load bearing.
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You say you live in eastern or central Washington. Whether down by the Columbia or up in Okanogan country, or in the middle is not clear.
Whether at my sister's palce in Kennewick, or at sme friends' place just west of the dalles, I always see lots f old farm areas with the houses shelded by vegation. Poplars, especially. I'd be looking at vegetation, not concrete block or a wood fence.
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Jim McLaughlin

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1/4 inch away and this will alow for movement

is at least 1/2 the total height of the wall above grade adjustments my be necessary for your frost line.

Remove or cut this tree root if it infact goes under the slab. We have replaiced I dont know how many slabs (mostly driveways) that have roots from a large tree doing the same thing. In most cases the root is cut and removed or cut and left and it is advised that each year you run a trenching shovel in this area to cut off any new growth.

can add automotive antifreeze to the mixture to keep it from freezing.
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