by ron holcomb

(yucaipa ca usa)

**Question:**

Hi Ron,

Detail 8 is for monolithic pour meaning if you pour the slab and footing simultaneously. The way you describe your project, you should use detail 9 which gives you the option of pouring the slab later or use gravel, sand, or asphalt for floor.

Detail 9 will need two forms for either faces of the wall. You don't have to go with the full 1'-6" that is shown, 10 or 12 inches deep might work too.

Here is how you calculate how much concrete that you need.

Total length of footing: 12+12+9+9 = 42 feet long

Volume of concrete: LxWxH = 42x0.5x1.5 = 31.5 cubic feet of concrete. The 94 lbs Portland cement will make 4.5 cubic feet of concrete. Take 31.5/4.5 = 7 bag. You will need 7 bags Portland cement.

If you want to order cement from concrete ready mix company, take 31.5/27 = 1.2 cubic yard or 1 and quarter yard of concrete. There are companies that specialize in small loads, something you might want to consider.

If you want a 12 inches deep footing here is the calculation: 42x0.5x1 = 21 divide by 4.5 yields 4.7 or 5 bags Portland cement.

The concrete for your slab works like this:

11'x9' = 99 square feet multiply by 4 inches for slab thickness: 99x0.33 = 33 cubic feet divide by 4.5 = 7.33 or 8 bags for your slab.

If you want to do monolithic pour, you are looking at 2.5 cubic yards of concrete to do the whole pour in one shot.

You will also need 6 #4x20 ft long rebars and about 20 anchor bolts.

Hope this helps

Tonga

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