Estimating Construction Costs
The approximate material cost for using 9 parts Earth : 1 part Cement.
For this exercise here, the costs calculated are based on standard unit pricing with cement costing $8-50 per (20kg bag) and brickies sand/loam mixed with course/washed river sand at $60-00 per cubic metre. The cost of these materials can vary depending on the supplier. Costs can be much less than that used in this exercise, if the price of materials are negotiated in a bulk buy and can be as low as $30-00 per cubic metre.
$4.25 per block (representing the cement component only and using suitable on-site earth material, that is freely available)
$7-60 per block, (for cement and earth material purchased from a supplier)
One Square Metre of wall is equivalent to 5.5 'Formblock' blocks.
The equivalent wall comparison is a standard double brick wall which requires 100 bricks per square metre plus mortar.
A reference guide for bricklayer rates can be found on the National Federation of Bricklayers & Masonry Employers Association website http://www.nfbme.com.au/sitebuildercontent/sitebuilderfiles/bricklayersdompricelist2010.pdf
Material cost per Square Metre of Formblock wall
Free earth plus cement, equals approximately $23-50 per sqm (One lineal metre of 2.4m high wall = $57-00)
Purchased earth and cement, equals approximately $ 42-00 per sqm (One lineal metre of 2.4m high wall = $100-00)
To calculate how many blocks you will need to produce a wall, follow these steps;
1. Find the overall area of the wall to be constructed by multiplying the length by the height. (i.e. 2.4m high x 10m length = 24 sqm)
2. Subtract the area of any door and window openings from the overall area. (standard single door 2.1 x 0.9 = 1.9 sqm,)
3. Multiply the remaining sqm area by 5-5 to find the number of blocks required. (i.e. a solid 24 sqm wall = 132 blocks. The same wall with one standard door and three windows at 1.8m x 1.8m openings = 13 sqm of wall / 72 blocks)
4. To calculate the amount of earth needed, divide the number blocks in the wall by 18. (One cubic metre of earth equals approximately 18 blocks. The volume of one full block equals .054m³). A 24 sqm wall will require approximately 8 cubic metres of earth material
5. To estimate the number of cement bags (20kg) (at one part cement, to nine parts earth), divide the number of blocks to be made by 2. (i.e. 24 sqm wall would require 66 (20kg) bags)
Estimating hired labour costs
To hired a labourer, ( at daily cost of based on approximately rate of $200). A fit and experienced labourer can generally achieve setting up formwork and pouring between 10 - 15 blocks per day. A team of three can average around 40 blocks (7sqm of wall) per day. Cost estimate for hired help range between $75 - $110 per sqm.
Combined with purchased earth material, costs estimates range between $120 - $160 per sqm of wall.
A 10 metre long wall, 2-4m high (without door and window openings), 24 sqm wall = 132 blocks.
a. Free Earth, Cement and no hired labour = approx. $600 (with hired labour = approx $3500 - $4500)
b. Purchased Earth plus Cement and no hired labour = approx $1000 (with hired labour = approx $4000 - $5000)
The same 10 metre wall, 2-4m high (with one standard door and three 1.8m x 1.8m windows), 13 sqm of wall = 72 blocks
a. Free Earth, Cement and no hired labour = approx. $310 (with hired labour = approx $3200 - $4200)
b. Purchased Earth plus Cement and no hired labour = approx $550 (with hired labour = approx $3500 - $4500)
Our estimating guide only gives an estimate of the cost of walls only. It is only suitable for use before any detailed plans are made. For accurate construction costs you will require detailed design plans and the services of a quantity surveyor or licensed builder.
* Figures quoted are based on average Australian retail prices as at 2010 and are subject to variation and change.
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