Construction works involve a lot of measurement. The materials used in construction are sold in the market based on unit quantities and these unit quantities have unit prices. Accurate estimation of construction cost involves accurate measurement of construction quantities. In this post I would show how to accurately estimate unit quantity of five common construction materials. With these unit quantities one can get total quantity required, append unit price and get the total overall project sum. This post would be of assistance to beginners in quantity surveying and civil engineering as well as practicing engineers. It is not to replace their task. It would only show unit quantities. How to get the overall quantity, determine and append unit price cannot be done without expertise in this field.
The quantities to be estimated are:
- Mortar for block laying and plastering
- Concrete work
Determination of block quantity
In Nigeria, there are about six (6) classes of block made from usually (1:6) mix ratio of cement: sand. The usual block sizes are as shown blow in the order of Length x Width x Breadth. These blocks can be hollow or solid depending on demand.
- 450 mm (18 inches) x 225 mm (9 inches) x 225 mm (9 inches)
- 450 x 200 x 225
- 450 x 150 x 225
- 450 x 125 x 225
- 450 x 100 x 225
- 450 x 75 x 225
Among these lists, 450 x 225 x 225 and 450 x 150 x 225 whether hollow or solid are commonest in building construction in Nigeria. Blocks are jointed together by mortar which usually have a thickness of 25 mm (1 inch) but this thickness can vary and the variation should be considered in determining mortar volume for work. In determining the area of block within an area of wall, the mortar thickness is necessarily considered.
Ideally, the area of a 450 x 225 mm block embedded in 25 mm mortar joints on all sides should be:
(25/2 + 450 + 25/2 ) x (25/2 + 225 + 25/2) = (12.5 + 450 + 12.5) x (12.5 + 225 + 12.5) = 475 x 250 = 118750 mm2 (0.11875 m2) instead of 450 x 225 (101250 mm2 or 0.101250 m2).
To determine number of blocks in 1 m2 of wall, then = 8.42 blocks
Adding 10% as waste, we have 8.42 + 0.842 = 9.262, say 10 blocks. Thus, we have 10 blocks in 1 m2 of wall
Determination of mortar for laying and bedding blocks
The mortar for laying and bedding block is measured in m3/m2. The volume of mortar required for solid block is different from the volume required for hollow block.
Generally, volume of mortar required for solid block = volume of block (including mortar) – volume of block only
Gross volume of block (including mortar) = 475 x 225 x 250 = 26718750 mm3 = 0.02672 m3
Volume of block only = 450 x 225 x 225 = 22781250 mm3 = 0.02278 m3
Volume of mortar for solid block = 0.02672 – 0.02278 = 0.00394 m3
For hollow block, the hollow of the block should be subtracted from the volume of mortar for solid block to get volume of mortar for hollow block.
Table below presents the block sizes, type, joint thickness and mortar volume
Table 1; Block sizes and corresponding mortar required per block/per square meter of wall
Assuming the block size specified above and the joint thickness are applicable to ones work, one can read off the mortar volume required per block from Table 1 and multiply by the total number of blocks to get the total volume of mortar required for the block work.
Mortar usually comprise of cement, fine aggregate (sand) and coarse aggregate (stone). Having determined the mortar volume required to lay bricks or blocks, the quantity of each of these materials can be determined from Table 2 based on some nominal mix ratio for 1 m3 of mortar to enable appending of prices to them.
Table 2; Nominal mortar mix ratio and required constituent materials
The same rule applicable to mortar for laying and bedding blocks applies to mortar for plastering. In the later case, one need to determine the volume of mortar (m3) required. Once the volume of mortar required is known, Table 2 can be used to get the quantity of each of the materials required within the volume. Remember when calculating these quantities to include allowance for wastes. In a follow-up article titled pre-contract allowances for wastes in Nigerian construction industry, I have shown allowances for wastes that should be made for some materials in estimation. In a later article, I would also show the allowance to be made for shrinkage because some construction materials like cement, sand, aggregate undergo shrinkage when they react with water and this shrinkage affects the volume of the plastic mass: mortar or concrete.
Civil Engineering Standards Method of Measurement (CESMM)
Concrete is one of the key construction materials. Concrete consists of mixture of cement, fine aggregate and coarse aggregate and it is usually measured in cubic metres (m3). To determine the quantity of concrete required for an item of work, compute the volume of that item of work by finding the product of its length, width and depth (or height). This volume is the minimum volume. Put allowance for shrinkage and waste to get the true and most probable volume of the concrete. The constituent materials can be determined by design (design mix) or if nominal mix would be used, Table 3 below shows the different constants one can use to determine the quantity of cement, sand and stone. Let me give a demonstration of how these constants are obtained using a particular mix ratio.
Assuming we want to determine the quantity of materials required to obtain 1m3 of concrete using nominal mix ratio of 1:2:4
Sum the ratio as 1+2+4 = 7 of total quantity of materials
Cement quantity = (1/7)x 1 m3 = 0.142857142 m3
Allow 10% for waste and 35% for shrinkage, thus 0.142857142 x 1.1 x 1.35 = 0.212142857
Assuming density of cement = 1440 kg
Mass of cement = density x volume = 0.212142857 x 1440 = 305.4857143 kg
Number of 50 kg bags required = 305.4857143/50 = 6.109714286 bags, say 6.1 bags
Sand quantity = (2/7)x 1 m3 = 0.285714285 m3
Allow 10% for waste and 35% for shrinkage, thus 0.285714285 x 1.1 x 1.35 = 0.424285714 m3, say 0.424 m3
Stone quantity = (4/7) x 1 m3 = 0.571428571 m3
Allow 10% for waste and 35% for shrinkage, thus 0.571428571 x 1.1 x 1.35 = 0.848571428 m3, say 0.849 m3
Consult Table 2 below for other nominal mix ration constants. The constants below are provided for 1 m3 of concrete. Thus when you get the volume of concrete required, multiply by the values below to get an equivalent for the particular volume of concrete concerned.
Table 3; Nominal concrete mix ratio and required constituents
Reinforcement is an important quantity in reinforced concrete. It is usually measured in lengths (m) or weight (kg and ton). It is the duty of the structural Engineer to provide the quantity in length of structural steel required in the building. The quantity estimator need to be in contact with the structural engineer in this aspect to get the bar bending schedule (BBS) that species this. When the total length is cumulated, allowance is also made for waste, usually 5% when the bars are cut, bent and fixed at site, otherwise allow 1% if the bars are delivered to site cut and bent. The Table 4 below provides the classes of bar available in Nigeria together with their weight per metre length and number of such lengths in 1000 kg (1 ton) of rod.
Table 4; Sizes of rods, weight per metre and quantity
Reinforcement bars are tied in position using tying wires often called binding wire. The Table 5 below provides the tying wire requirement (in kg) per 1000 kg of each class of rod. In Nigeria, one roll (bundle) of binding wire weighs 20 kg.
Table 5; Tying wire requirement per 1000 kg of rod
In some light construction works such as drainage or ground floor slabs that does not bear much suspended or lateral loads, British Reinforcement Company (BRC) wire mesh or welded steel wire mesh are used to provide some tensile restraint. The Table 6 below provides the fabric reinforcement to BS 4483.
Table 6; Fabric reinforcement sizes
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How to estimate painting and decoration work for buildings
To calculate the quantities of materials, you need to multiply the total centre line length with breadth and depth of the construction. The centre line length will be reduced by half of breadth of every junction where the main wall is joined with the cross walls, partitions or verandah.What are the factors responsible for high cost of building materials in Nigeria? ›
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Procedure To Calculate Cement Bags In 1 Cubic Meter:
Weight of 1 bag cement = 50 kg. =0.0347 cum. = 6.25 bags.
Thus, the quantity of cement required for 1 cubic meter of concrete = 0.98/0.1345 = 7.29 bags of cement. The quantities of materials for 1 m3 of concrete production can be calculated as follows: The weight of cement required = 7.29 x 50 = 364.5 kg. Weight of fine aggregate (sand) = 1.5 x 364.5 = 546.75 kg.What are the 3 most expensive components of a building? ›
- The Lot. The land that your home will be built on will make up a substantial portion of the cost of the home. ...
- The Foundation. ...
- Framing. ...
- Plumbing & HVAC Systems. ...
- Windows and Doors.
The price index for steel is the highest contributor to the overall cost of construction materials, itself rising 112.7 percent in the last 12 months. The price index for plastic rose 35 percent and architectural coatings rose 24.3 percent. Lumber and plywood rose 21.1 percent.
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The unit price can be found using a simple formula if the quantity and total cost is known. Simply divide the total price by the quantity to find the unit price. Thus, the unit price is equal to the total price divided by the quantity.What is the formula to calculate price per unit? ›
Cost per unit formula
The cost per unit formula involves the sum of fixed and variable costs, which is then divided by the total number of units manufactured during a period of time. Here is how to find the cost per unit: Cost per unit = (Total fixed costs + Total variable costs) / Total units produced.
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Now question is how many Brick in 1 CFT ?, there will be simple answer, there are 14 nos bricks in 1 CFT brick work.What are the 7 types of construction? ›
- Residential Building Project.
- Private Project.
- Commercial Project.
- Industrial Project.
- State Construction Project.
- Infrastructure and Heavy Construction Project.
- Federal Construction Project.
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It commonly includes wood, concrete, steel, cement, aggregates, bricks, clay, metal, and so much more. In the olden times, people have been using pure bricks, or wood, or straw. But in this modern age, engineers have learned to mix and match the right materials to come up with higher quality structures.
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The Most Popular Construction Method for New Homes
According to the National Association of Home Builders (NAHB) Research Center, stick-built homes account for more than 90 percent of all new homes built in the nation each year.
- Transparent Wood.
- Carbon Fiber.
- Self-healing concrete.
- Liquid granite.
- Bending, flexible concrete.
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- Metals. ...
- Wood. ...
- Paper. ...
- Natural Textiles. ...
- Synthetic Textiles. ...
- Leather. ...
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Being one of the cheapest building materials out there, concrete is the go-to building material of today's homes. It is a marvellous material — water & fireproof, has acoustic properties and can withstand disasters like flooring and earthquake.
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Volume of Cement in Kg. =
The density of cement is 1440 kg per m. There are 0.08 cement bag is required for the plastering work of one square metre.
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volume=(50 kg1440 kg/m2)=0.0345m3. Q. A cement bag contains 0.035 cubic meters of cement by volume. How many bags will one tonnes (1000 kg) of cement comprise?
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* 108 x 20kg bags of Boral Cement Concrete Mix will fill 1 cubic metre (m3).How many bags of cement do I need for 1 m3 of M25 concrete? ›
So, approximately 11 bags cement are used in M25 grade of 1m3 concrete.Which building material is most profitable? ›
- Prefabricated panels. One of the most profitable materials in the construction market is prefabricated panels. ...
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- Industrial steel and iron. ...
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- Foundation. The foundation is the most critical structural component of any structure and many failures are probably due to faulty foundations rather than any other cause. ...
- Plinth. ...
- Wall. ...
- Shear Wall. ...
- Column. ...
- Floor. ...
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according to the seasonally adjusted figures. This followed a 1.0% decrease in March 2022, compared to March 2021. The month-on-month change shows a 1.7% decrease in April 2022. This followed a 1.8% decrease in March 2022, on the same basis.Why are building materials so expensive 2022? ›
2022 Notice: Material Prices Are Surging
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The cheapest way to build a home is to design a simple box. Sticking to a square or rectangular floor plan makes the building and design simple. Generally speaking, building up is cheaper than building a sprawling one-story home, so you may want to consider planning for a multiple-story home if you need more space.
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- Area of Square Cross-section = L2.
- Area of Square (A) = Perimeter x Height of Square = 4L x H.
- Volume of Square (V) = Area of Square (A) x Height of Square.
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- 4 ÷ 12 = .33.
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- Gross Square Feet (GSF) = Net Usable Square Feet + Structural Square Feet. ...
- Net Usable Square Feet (NUSF) = Assignable Square Feet + Nonassignable Square Feet. ...
- Net Assignable Square Feet (NASF) = Sum of the 10 Major Space Use Categories of Assignable Space.
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- Amount of Aggregate Required. = Builtup area × 0.608. = 1000 × 0.608. = 608.00 Ton. ...
- Flooring. = Builtup area × 1.3. = 1000 × 1.3. = 1300.00 Sq.
Volume of Cement in Kg. =
The density of cement is 1440 kg per m. There are 0.08 cement bag is required for the plastering work of one square metre.
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After you know the capacity of individual circuits and of the home's full electrical service, you can then compare this with the load, which you can calculate simply by adding up the wattage ratings of all the various fixtures and appliances that will be drawing power at the same time.