Comprehensive Guide to Quantity Surveying and Cost Estimation Methods in Building Technology

Estimate

Approximation, projection or prediction of a quantity of work; a statement of the approximate or projected cost of work to be done, such a building or any other project that entails material, labor and services costs; a general calculation of size, value, magnitude, extent of work to be done including materials, labor and other parameters that require quantification.

Quantity Survey

A term describing the detailed calculation of all components necessary to construct a building generated by quantity of materials, labor and other parameters; a detailed analysis and listing of all items of materials and equipment necessary to construct and complete a project.

Detailed Estimate of Construction Cost

A forecast of construction cost prepared on the basis of a detailed analysis of materials and labor for all items of work, as contrasted with an estimate based on current area, volume, or similar unit costs.

Bill of Materials

A term used to describe the materials, sub-components needed to manufacture a finished product.

User-unit Method

This estimating method involves the determination of user or occupants to quantify space and to establish cost, e.g. number of students, patient beds, inmates, etc.

Area Method

Estimating by area method involves costing and quantification using area and multiplier or factor. This method is commonly used to provide a rough estimate of project cost by multiplying area by cost per unit area (usually square meter) based on prevailing rate.

Volume Method

This method involves a three-dimensional aspect of the project. Such method is an extension of the area method but involves the height of the building project as height affects cost of the project.

Parametric Method

Parametric method involves the identification of several major factors in estimating such as architectural, structural, electrical, plumbing/ sanitary, mechanical, etc. components of the project each with a corresponding percentage cost.

Modular Cost Method

Modular cost estimates applies to repetitive work or work made of similar components or project composition such as apartment, housing units or hospital room units where cost can be calculated based on the cost per unit.

Detailed Estimate by Quantity Take-off (Quantity Survey) Method

This method is considered as the most precise of the different types of estimating method. Materials are quantified base on specifications - type, composition, application, commercial sizes and other parameters.

Combination Method

This method may be used although not that accurate if the project and the scope of work is incomplete or some areas of the project are not clearly defined, hence, a combination of different methods becomes practicable.

Earthwork

Calculate total volume of earth for filling.

Excavation

Earth volume (m3) = excavation dimensions (lwd) x 1.25.

Filling/Backfilling

Total earth volume (filling/backfilling) = volume of earthfill (measured volume) x 1.25.

Excavation Calculation Example

Calculate total excavation volume: Vexcavation = 1.0 m x 1.0 m x 2.5 m x 12 = 30 m3.

Footing and Column Volume Calculation

Vftg/col. = (1.0 m x 1.0 m x 0.3 m x 12) + (0.2 m x 0.3 m x 2.2 m x 12) = 5.184 m3.

Backfilling Calculation

Subtract total footing and column volume from total excavation volume: 30 m3 - 5.184 m3 = 24.816 m3.

Volume of Earth for Filling Example

A lot measures 20 m x 30 m, with the shorter side abutting a street (frontage). The lot is sloping from the front to the back with a depression at the farthest end of 1.5 m.

Backfill Volume

Vearthfill/backfill = 24.816 m3 (1.25) = 31.02 m3

Class AA Concrete Mix

Mixture: 1:1 ½: 3; Cement: 12 bags/m3; Sand: 0.50 m3/m3; Gravel: 1.0 m3/m3

Class A Concrete Mix

Mixture: 1: 2: 4; Cement: 9 bags/m3; Sand: 0.50 m3/m3; Gravel: 1.0 m3/m3

Class B Concrete Mix

Mixture: 1: 2 ½: 5; Cement: 7.5 bags/m3; Sand: 0.50 m3/m3; Gravel: 1.0 m3/m3

Class C Concrete Mix

Mixture: 1: 3: 6; Cement: 6 bags/m3; Sand: 0.50 m3/m3; Gravel: 1.0 m3/m3

Class D Concrete Mix

Mixture: 1: 3 ½: 7; Cement: 5 bags/m3; Sand: 0.50 m3/m3; Gravel: 1.0 m3/m3

Special Concrete Mix

Mixture: 1:2:3; Cement: 9.47 bags/m3; Sand: 0.51 m3/m3; Gravel: 0.77 m3/m3

Mortar Mix 1:2

Cement: 17.40 bags/m3; Sand: 0.93 m3/m3

Mortar Mix 1:3

Cement: 12.98 bags/m3; Sand: 1.05 m3/m3

Weight of Portland Cement

A bag of Portland cement weighs 40 kgs

Weight of Dry Sand

A cubic meter of sand (dry) weighs 1,600 kgs

Weight of Loose Sand

A cubic meter of sand (loose) weighs 1,442 kgs

Weight of Loose Dry Gravel

A cubic meter of gravel (loose, dry) weighs 1,520 kgs

Plaster Volume per Block (1 face)

4x 8x 16: 0.0015 m3; 6x 8x 16: 0.0015 m3; 8x 8x 16: 0.0015 m3

Plaster Volume per Block (2 faces)

4x 8x 16: 0.003 m3; 6x 8x 16: 0.003 m3; 8x 8x 16: 0.003 m3

Class B CHB Mix

Cement: 0.19 bags/m2; Sand: 0.014 m3/m2 for 4" x 8" x 16" CHB

Class C CHB Mix

Cement: 0.29 bags/m2; Sand: 0.024 m3/m2 for 6" x 8" x 16" CHB

Class D CHB Mix

Cement: 0.34 bags/m2; Sand: 0.028 m3/m2 for 8" x 8" x 16" CHB

Compressive Strength of CHB

Non-load bearing block: 350 psi; Load-bearing block: 750 psi

Face Area per Block

Face area per block = 0.20 m x 0.40 m = 0.08 m2 per block

Number of CHB per m2

12.5 blocks per m2

Volume of Mortar for 491 blocks

V = 491 blocks x 0.0008 m3/block = 0.3928 m3

Volume of Filler for 491 blocks

V = 491 blocks x 0.0045 m3/block = 2.2095 m3

Volume of Plaster for 491 blocks (2 faces)

V = 491 blocks x 0.003 m3/block = 1.473 m3

Total Volume for Mortar, Filler, and Plaster

Vtotal = Vmortar + Vfiller + Vplaster(2 faces) = 4.0753 m3

Recommended Slumps for Reinforced Foundation

Max: 125 mm; Min: 50 mm

Water Cement Ratio for 2500 psi

Non-air-entrained concrete: 7 ¼ gals per bag; Air-entrained concrete: 6 ¼ gals per bag