Help with A concrete block wall?
Question:I am building a wall of concrete blocks which will be 5ft high. What sort of foundation will I need for this.
Answers:
You need to know the soil's bearing capacity [how much can a square foot of the soil carry without yielding] Different soils have different values. Rock, gravel and clays are best, with muck, peat, sand, top soils being not suitable. Samples can be taken and tested when in doubt.
Then you need to know how much of a load you are going to have [this includes dead load, live load, wind load, seismic, etc] per sq foot. from there you simple do the math to size how wide the footing should be.
As a general rule for one and two story home construction, you need to be below the local frost level [36" here], the concrete footing should be about 8" thick and 2" to 4" bigger than the block inside and outside. [In your case you may go narrower] I normally use 3.5 sack concrete, with at least two continuous #4 rebars.
As an option, on a wall like yours I'd dig a trench 12" or 16" wide down to the frost level and fill with concrete to a level where the first block was just below the surface. While the cost in concrete is greater, you'll save some back on the block and a lot of labor below grade.
The base should be one-half the height of the wall, and made with rebar.
u have to put a footer out of concrete below yor frost line so when th eground freezes the wall does not heave up. any where from 24" to 48" deep
My local building inspector - I live in the UK - suggests foundations should be 1 metre deep and 450mm wide. Sounds like overkill to me, but he is supposed to be an expert.
I'm a bricklayer by trade and do this on a daily business. Go below the frost level( usually 4-5 ft) pour your footings around 6 inches thick the footings should be 11/2 times wider than the foundation for this wall you are building. This will be sufficient enough for a 5 ft wall.If this is going to be a load bearing wall (which doesn't sound like it) .You might consider running re-bar through it and fill it with cement
drill hole in center of blocks and put re bar through it to stable it
before you start digging the founds, hire yourself a live cable locator.or double check that there is no cables or services. these are usually laid in a 3 foot trench, well within the depth of your foundations.
you dont have to be an engineer to figure this out...rule of thumb is the footer should be below frost line...twice as wide as the unit you are laying and as thick as the unit you are laying...so if youre laying an 8 in. wall pour it 16 in. wide and 8 in. deep and i dont know where you live but here we go 3 ft. deep.
you need to go down a minimum of 600mm ..and if you are still finding top soil or made up ground at that depth then you will need to go deeper .if the wall is a single block ..100mm..then you will need to make it 450mm wide ..with a double width pillar at either end ..and a built in pillar every 1800mm..or it will fall over !..if its two skins thick then the footing will need to be 600mm wide ..
the depth for freeze protection is different areas. in upstate ny, it just went to 42 inches, lord knows why. it was 3 ft back when we had WINTERS. anyhow, make it app. a ft wide and about 6 in. thick. for a 5 ft wall, it should be fine.
if your ground is solid and virgin then 12" x12" will be OK
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