Number of Blocks required to build wall

[305Gurl]

I am looking for a nice estimating book to help me with construction problems, or some sample problems that's available with problems which involves estimating # of blocks or bricks required to build a wall, given its length, width and thickness.

Could someone explain if this method is correct.

If asked how many blocks to build a wall: given the length, width and thickness of this wall, if a regular block is 8" x 8" x 16".

In order to solve this problem, would it be the L X W of the wall (total wall area) divided by the area of one block?

The wall thickness of the wall is irrelevant, unless the wall is thicker that one concrete block (or > 8").

Another way to look at this is: If the wall required to be built is 16" thick (2 block thickness), then the amount of block required would, in essence double?

B) what if an area of a footing is also give and the # of block required. Would calculation still be similiar to abouve?

Thanks you.

 

[blybrook PE]

First, good luck on the test. I do not have an estimating book that I can recommend, but there's probably a few other members that can suggest a good reference manual for you.

Now, to the questions at hand.

A) You also need to know the height of the wall being constructed instead of the width (that's the same as the thickness). Say you have a single 8" wall that is 12' long by 14' tall; this is a wall surface area of 168 ft2. Each standard CMU block has a surface area of ~.889 ft2, so you will need a minimum of 189 blocks for this wall (a direct number found by taking wall area & dividing by block area, but always give a few % overage for breakage).

If the wall is to be thicker; use the appropriate sized block, or you can figure out how many layers of block you will need and multiply the total number of blocks for one thickness to account for the total wall.

B ) I'm not quite sure what you are asking here. I think further clarification is needed, is what I have below what you are asking?

Givens: Footing area of "x" (is this the top of the footing, the side, the end?) Are any other information on the footing, or are you to assume a length & width? And you are given the total number of block.

Find: The final length or height of the wall that can be built.

 

[MA_PE]

Don't you need to add 3/8 to 1/2 in for mortar joints between blocks?

 

[blybrook PE]

Not if you're using a dimension of 8" x 8" x 16". That will already account for a 3/8" standard grout joint. Otherwise, you are doing the calculations with a block that is 7-5/8" x 7-5/8" x 15-5/8".

 

[305Gurl]

Now, to the questions at hand.

A) You also need to know the height of the wall being constructed instead of the width (that's the same as the thickness). Say you have a single 8" wall that is 12' long by 14' tall; this is a wall surface area of 168 ft2. Each standard CMU block has a surface area of ~.889 ft2, so you will need a minimum of 189 blocks for this wall (a direct number found by taking wall area & dividing by block area, but always give a few % overage for breakage).

If the wall is to be thicker; use the appropriate sized block, or you can figure out how many layers of block you will need and multiply the total number of blocks for one thickness to account for the total wall.

Thanks for your response to my question.

So if I now assume that this was was not 8" thick wall, but 16" thick. Would the number of blocks required be (189 blocks x 2) 378 blocks.

B ) I'm not quite sure what you are asking here. I think further clarification is needed, is what I have below what you are asking?

Givens: Footing area of "x" (is this the top of the footing, the side, the end?) Are any other information on the footing, or are you to assume a length & width? And you are given the total number of block.

What I meant was: Say given a footing of 2 feet by 2' by 2'; the # of blocks required for the footing, (assume 8" thick wall) would be 32sf/0.889 = about 36 blocks? This is 8sf (perimeter of one side of footing) * 4 equal side of the footing = 32sf, which is then divided by 0.889 (one block)= ans. above 32blocks?

 

[IlPadrino]

Not if you're using a dimension of 8" x 8" x 16".

Yeah... the difference between nominal and actual dimensions of CMU is 3/8".

And don't forget that at the corners, 8" of the perimeter is covered by the short end of the block. When estimating, I figure out how many blocks I need for the first course all the way around and then just multiply by the number of courses needed. This is important, especially when you have to account for lintel block when bond beams are needed.

 

[blybrook PE]

A) You also need to know the height of the wall being constructed instead of the width (that's the same as the thickness). Say you have a single 8" wall that is 12' long by 14' tall; this is a wall surface area of 168 ft2. Each standard CMU block has a surface area of ~.889 ft2, so you will need a minimum of 189 blocks for this wall (a direct number found by taking wall area & dividing by block area, but always give a few % overage for breakage).

If the wall is to be thicker; use the appropriate sized block, or you can figure out how many layers of block you will need and multiply the total number of blocks for one thickness to account for the total wall.

Thanks for your response to my question.

So if I now assume that this was was not 8" thick wall, but 16" thick. Would the number of blocks required be (189 blocks x 2) 378 blocks.

Correct, you would take the number of blocks figured for the first wall at the block thickness and multiply it by (total wall width / block thickness). Hence a 24" thick wall with 8" blocks from the above information would be a minimum of 567 blocks (189 x (24/8)).

B ) I'm not quite sure what you are asking here. I think further clarification is needed, is what I have below what you are asking?

Givens: Footing area of "x" (is this the top of the footing, the side, the end?) Are any other information on the footing, or are you to assume a length & width? And you are given the total number of block.

What I meant was: Say given a footing of 2 feet by 2' by 2'; the # of blocks required for the footing, (assume 8" thick wall) would be 32sf/0.889 = about 36 blocks? This is 8sf (perimeter of one side of footing) * 4 equal side of the footing = 32sf, which is then divided by 0.889 (one block)= ans. above 32blocks?

I don't know why you would use CMU for the footing itself, as it doesn't have the compressive strength of regular concrete. I'm not saying it hasn't been done, just non-typical.

Should you utilize CMU for a footing that is 2' x 2' x 2', you have three courses high, three courses thick (2' / 8"), and 1.5 courses wide (2' / 16"). This is 3 x 3 x 1.5 or 13.5 blocks minimum. It is easier to calculate by turning this problem into a thickened wall problem.

The way you have calculated the perimeter is incorrect as it would be 8 ft, not 8 sf (each wall has a surface area of 4 sf). This gives you a total wall surface area of 16 sf and a volume of 8cf. The volume of one 8" x 8" x 16" block is ~0.593cf. This results in a minimum number of blocks of (8/.593)=13.5 blocks.

And IIPadrino is correct about the corners. That is why I say this is the minimum number of blocks required. Due to corners and breakage, you will always use a more (I've seen 5-10% for new contractors, 2-3% for seasoned ones).

 

[MA_PE]

Not if you're using a dimension of 8" x 8" x 16". That will already account for a 3/8" standard grout joint. Otherwise, you are doing the calculations with a block that is 7-5/8" x 7-5/8" x 15-5/8".

thanks. I couldn't remember and was too lazy to look it up.

 

[blybrook PE]

Yer welcome. The sizes have been engrained into my mind over the years.