Let’s use the attached simple gatehouse design with one 900mm x 2100mm door, a 1200mm x1200mm window and a 600mm x 600mm toilet window plus a 750mm x 2100mm toilet door. (I have done the elevation to ensure all possible elements are visible on the elevation).

OK – This is it.

Our 1st task would be to find the linear length of the entire building line i.e. how long is the block if we put them in a single line; we would achieve this easily by taking one grid-line after the other.

Grid 1 = The linear length of blocks on grid-1 is 4500mm (its that simple), now lets take for others.

Grid 2 = 4500mm also (now you’ll notice i omitted the windows and door opening on grid-2, we would come back to deduct those.

Grid A = 3000mm

Grid B = 3000mm

Grid C = 3000mm

Now, lets add to get the total linear length of building = (4500×2) + (3000×3) = 18,000mm [its important to group similar dimension especially when dealing with larger drawings to safe time].

Now that we have the linear length remember the block works are divided into 2. The Foundation Blocks (Sub-Structure) and The Building Blocks (Super-Structure)

NOTE: The length of a standard block (in Nigeria) is 450mm and the height is 225mm for both 6″ and 9″ blocks….

A. BLOCKS NEEDED FOR FOUNDATION

Question: How many courses of blocks are you planning for your foundation? I would use 4 courses for this calculation.

Number of Blocks needed per course of block = [TOTAL LINEAR LENGTH / LENGTH OF BLOCK] = [18,000 / 450] = 40 blocks per course but remember I’m using 4 courses hence; TOTAL BLOCKS NEEDED TO COMPLETE THE FOUNDATION = 40 blocks x 4 courses = 160 blocks (whether 6″ or 9″￼

Note: We didn’t need to deduct for openings, obviously in the foundation – we have none. (If your design has a foundation drawing, then use the foundation drawings to calculate the nos of blocks needed for in the foundation and the ground floor plan for the super-structure quantities)

B. BLOCKS NEEDED TO ROOF LEVEL

Question: What is the height of the structure I’m building? In this design I have used a building height of 2700mm; this means that the number of courses I’ll have would be = [HEIGHT OF STRUCTURE / HEIGHT OF 1 BLOCK] = [2700 / 225] = 12 courses of blocks.

Number of Blocks needed per course of block = [TOTAL LINEAR LENGTH / LENGTH OF BLOCK] = [18,000 / 450] = 40 blocks per course but here we have 12 courses of blocks to go. (If you plan to tie your lintel all round the structure because its a small one, then minus 1 course taken by the lintel and use 11 courses BUT I don’t advice that, so I’ll use 12 courses and use my lintels only over opening), so;

TOTAL BLOCKS NEEDED TO COMPLETE THE WALLS = 40 blocks x 12 courses = 480 blocks(whether 6″ or 9″￼ BUT, there are opening where blocks wont be needed so we MUSTdeduct those out.

B(ii). DEDUCT OPENINGS IN B ABOVE

Opening in drawing:

a. 750mm x 2100mm

b. 900mm x 2100mm

c. 600mm x 600mm

d. 1200mm x 1200mm

There are no half blocks, so every numbers would be rounded to the nearest whole number.

a. 750×2100 {where 2100 is the height of door; see elevation}

Nos of blocks needed per course = 750 / 450 = 1.6667 = 2 blocks

Nos of courses in door = 2100 / 225 = 9.3333 = 10 courses

Number of blocks in 750x2100mm door = 2 x 10 = 20 blocks.

b. 900×2100.

Nos of block needed by course = 900 / 450 = 2 blocks

Nos of courses = 2100 / 225 = 9.3333 = 10 courses

Number of blocks in 900×2100 door = 2 x 10 = 20 blocks

c. 600×600 {where 600mm is the height of window}

Nos of blocks needed per course = 600 / 450 = 1.333 = 2 blocks

Nos of courses in door = 600 / 225 = 2.6667 = 3 courses

Number of blocks in 600x600mm window = 2 x 3 = 6 blocks.

d. 1200×1200 {where 1200mm is the height of window}

Nos of blocks needed per course = 1200 / 450 = 2.6667 = 3 blocks

Nos of courses in door = 1200 / 225 = 5.333 = 6 courses

Number of blocks in 1200x1200mm window = 3 x 6 = 18 blocks.

TOTAL BLOCKS CALCULATED INTO OPENINGS (in this design) = 20+20+6+18 = 64 blocks

Now lets deduct B(ii) from B = 480 blocks – 64 blocks = 416 BLOCKS NEEDED

TOTAL BLOCKS NEEDED TO BUILD THE STRUCTURE (Foundation + Main building) = 160 + 416 = 576 Blocks.

But we should consider waste and broken blocks right? – lets add 10% for waste and broken blocks = 576 + 58 = 634 blocks.

IMPORTANCE OF THIS CALCULATION:

You could use this calculation to:

i) Calculate how much you would spend on blocks by multiplying quantities above by the price of 1 block.

ii) You could also use it to estimate approximately, how many bags of cement would complete the block-works

iii) You could use it to negotiate and have an idea of how much to pay the bricklayer

iv) Plan your budget.

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