Today we will look at the basic 5 things to know before you can accurately estimate the total number of blocks from a building plan.
1. Know the block Types
Commonly used sandcrete blocks in Nigeria for masonry are :
- 9 inches hollow blocks: Suitable for almost all building works especially where there is enough space.
- 6 inches hollow blocks: Used in most bungalows and duplexes especially where there is limited space.
- 5 inches solid: which is mostly used in fencing work
- 6 inches solid: Not so popular because of its weight and cost of production. It is produced under special recommendation.
- 4 inches solid blocks are no longer in use.
Other types of blocks also exist for use in different construction works.
2. Know the dimension of blocks
This is very necessary because blocks used in masonry are not of the same dimension. Most sandcrete blocks used in Nigeria, are of the same height and length. The only difference is the thickness or width. The area of all standard blocks are the same. For example, the area of a 9 inches block is 225mm x 450mm, same goes with that of a 6 inches block and a 5 inches block. The unlike tge area, the volume of each block types are not the same.
The volume of 9 inches block is 225mm x 450mm x 225mm.
The volume of a 6 inches block is 225mm x 450mm x 150mm
The volume of a 5 inches block is 225mm x 450mm x 125mm
3. Pay attention to what the specification says
While the may not be needed to calculate the number of blocks specified in the drawing. It is necessary to calculate the cost of the blocks because the cost of single 9 inches block is higher than a single 6 or 5 inches block.
4. Know the ratio of the total block wall area to a unit block area
The ratio of the total wall area to a unit block area gives us the number of blocks. For example, a wall of 3600mm x 3600 mm will produce x blocks
X = (3600 * 3600)/(225*450) =128 blocks
5. Deduct the area of openings and other structural members
To get a fairly accurate result, you will need to deduct the area of openings like windows (like 4 feet window which is 1200mm x 1200mm), doors and other members like lintels, columns and other beams.
Note that it is not necessary to deduct the spaces occupied by the block bonds or “chucking” because the are negligible and can serve as safety factor for wastage during wall construction process.