Sunday, 2 November 2014

Updated: How To Calculate For The Number Of Blocks For Your Building

As a builder, it i have come to understand that one of the most commonly asked questions from a would-be house owner is no other than "How many blocks do you think would be just complete the building"?

It is because of the regularity of this question that i have decided to write this post on how to calculate the number of blocks required to complete your buidling project. The calculation of course would be done based on the Architectural plan issued to you by your Architect.


Now How can you calculate the number of blocks that would enable you complete your 2-Bedroom apartment?



I am going to use the floor plan of a 2 bedroom nungalow shown above as a case study, so i would like you to pay more than usual attention as i gradually unfold this for your understanding...

Before i begin the calculation of the number of blocks needed to complete a 2-bedroom apartment, i would like you to have these points at the back of your mind as i know you'll find it hard to understand this tutorial if you don't know them

Point A: There are 3 different types of block in Nigeria, these are 

i. 5" Sancrete Block or 125mm block
ii. 6" Sandcrete Block or 150mm Block
iii. 9" Sandcrete Blocks or 225mm Block

Of all these, 5" and 6" are the most common because they are usually cheap and commonly used for small projects

Point B: The length of a sandcrete block is 18 inches or 450mm or 0.45m

Point C: Depending on the nature of thr site,  the blocks laid from the foundation level to the DPC (The level at which you Damp Proove or apply Over-site concrete) is usually 4 coaches or levels unless its a swampy site where the you may get to 5-7 coaches before the DPC

Also, from DPC to the base of the window, you're required to have 4 coaches, from the base of the wondow up to the top of the window, you have another 5 coaches. Now from the top of the window to the base of the roof is another 3 coaches. We are going to neglect the lintel or concrete on top of the window

Having Known these points, lets now answer the question "How to Calculate the number of blocks needed for a 2-bedroom bungalow"

Remember we are going to be using the 6 inches block or 150mm sandcrete blocks all through the building.

Now the first thing to do is to add up all the external and internal dimensions from the architectural plan above.

we have successfully marked the plan into 4 different sides: A, B, C, D

So from the sides, we Calculate the Building girth

How to Calculate the External girths of a building

Add up all the external dimensions

A 9500mm +
B 9600mm +
C 9400mm +
D 9600mm = 3800mm
==========================
The total = 38000mm or 38m
==========================

How to Calculate the internal Girths Of A Building

Having Added the externals, lets also add the internal dimensions (The dimensions other than those outside the building)

We are going to follow the gridlines as they would help us to achieve this

(From Grid 7, We have The Following)
150mm +
3600mm +
150mm +
150mm +
3600mm +
150mm= 7800mm or 7.8m
===================

(From Grid 6, we have the following)

1350mm +
150mm +
2250mm +
150mm +
825mm +
675mm +
150mm = 5550mm or 5.55m
=====================

(From Grid 1b, we Have The Following) 

800mm +
2400mm +
1300mm +
900mm +
100mm = 5500mm or 5.5m
====================

(From Grid 2, we have the following)

2600mm +
900mm +
100mm +
150mm +
100mm +
900mm +
500mm +
150mm = 5400mm or 5.4m
====================

(From Grid 3, We have The following)

1800mm +
150mm +
650mm +
900mm +
250mm +
900mm +
1450mm = 6100mm or 6.1m
====================

(From Grid 3b-Kitchen, we have) 

900mm +
50mm +
1200mm +
50mm +
150mm = 2350 or 2.35m
==================

And lastly
(From Grid 7b-toilet, we have) 

1800mm or 1.8m
==============================
Total Internal Girth = 34500mm or 34.5m
==============================

Remember total External Girth = 38500mm or 38m

Therefore, the total Girth (External + Internal) = 38000 + 34500 = 72500mm or 72.5m
=================================================

Now, lets estimate the number of Blocks that would be able to enable us get to the DPC Level (Here, we will not remove doors since the digging covers everywhere including doors and windows)...

Since the length of one block =450mm, we are going to divide the total Girth which is 78500mm by 450mm

78500/450 = 161 block/coach (This means for every coach, we would need 161 blocks).

To get the total for all 4 coaches, we multiply by 4

So 161 x 4 = 644 blocks (Would be required to reach the DPC Level)

Now Lets Determine the total number of blocks needed for the entire 2-bedroom bungalow

To do this, we need to know the number of block for each segment of the building

From Foundation to DPC = 4 Coaches
From DPC to window level = 4 Coaches
from Bottom of window to top of window = 5 Coaches
from Lintel to the base of the roof or Gable = 3 coaches.

We have a total of 16 Coaches In all

So We Multiply 161 x 16 = 2576 - 644 (used to dpc level above) = 1932 Blocks

We will now Deduct for Voids

What Are Voids In A Building?

Voids are open spaces like doors and windows

They are not usually covered with blocks thus the name.

Now lets Subtract windows and doors from 1932 blocks

Now for every 1200mm window, we understand from experience that a total of 14 blocks would be needed to fill the space so we remove this 14 blocks for all 1200mm window

How to Know the number of Blocks to remove for every 1200mm Winow

1200/230 = 5.2
also, 1200/450 = 2.7

(5.2 x 2.7) = 14

How many 1200 windows do we have in the building?

Counting, we have exactly 12 windows with the 1200mm dimension

so the number of blocks to be subtracted for windows = 12 x 14 = 168 blocks

Now we would also calculate to know the number of blocks to be deducted for doors

What is the Dimension for doors in a building?

The standard door for a bungalow is usually 900mm or 3 feet

How many Blocks do i deduct for a 900mm door?

You deduct a total of 18 blocks for every doo

How do i calculate the number of blocks deductable from a door?

Its simple

The height of a door is usually 2100mm
divide this by 225 (2100/225 = 9) + width of the door divided by 450 (900/450 = 2) now 9 x 2 = 18 blocks for every 900mm door...

Now How many doors are there in a 2-bedroom bungalow?

we have a total of 8 doors, so we say 18 blocks  x 8 doors = 144blocks

Now sum the number of blocks deductable for doors and windows + 168 + 144 = 312 Blocks

Now remove 312 Blocks from 1932

1932 - 312 = 1620 blocks

Therefore, a total of 1620 + 644 = 2264 Blocks would be required for the job

I hope you found this useful in your practice as a site engineer, Architect or an estimator.

Now i hope i have been able to answer the question "How do i know the number of blocks required to build a 2 Bedroom Bungalow" and i hope you will find this useful.



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