Quantity Surveying Principles and Measurement

Quantity surveying is a vital discipline in the construction industry, focusing on managing project costs and budgets from inception to completion. This comprehensive guide delves into the fundamental Quantity Surveying Principles and Measurement techniques essential for students and professionals. Understanding these principles is crucial for accurate cost estimation, tender preparation, and efficient project management in civil engineering and building construction.

Understanding Quantity Surveying: Core Principles and Roles

Quantity surveyors are construction professionals specializing in cost and contract management. They play a pivotal role throughout a project's lifecycle, acting as cost estimators, expense managers, negotiators, project coordinators, and advisors. Their expertise ensures financial control and helps resolve disputes between various parties involved in a construction project.

Key Duties of a Quantity Surveyor

The duties of a quantity surveyor span several stages of a construction project:

• Pre-contract Stage (Design & Tendering):

• Liaising with clients to define needs and specifications.

• Studying plans and preparing project cost estimates and feasibility reports.

• Offering cost-saving advice and practical solutions to stay within budget.

• Preparing detailed estimates and Bills of Quantities (BoQ).

• Advising on tendering and contractual arrangements.

• Evaluating tenders and assisting clients in selecting contractors.

• Providing guidance on insurance, responsibilities, warranties, and bonds.

• Performing technical auditing and drawing up contracts.

• Construction Stage:

• Determining the value of work completed for interim payment certificates.

• Implementing cost-saving measures to minimize variation costs.

• Providing cash flow data to clients for financial planning.

• Assessing cost impacts of variations that could delay the project.

• Providing project reports to banks when necessary.

• Resolving disputes among project stakeholders.

• Post-construction Stage:

• Preparing the final account within 60 calendar days of practical completion.

• Issuing the final payment certificate.

• Providing copies of all necessary project documents.

Importance of Site Visitation

Site visitation is crucial for a quantity surveyor, both before starting work on the BoQ and throughout the project:

• Prior to BoQ:

• Ensuring technical and financial viability of the project.

• Assessing risks and determining necessary conditions.

• Gathering specific data on regulatory factors (zoning, building codes, environmental regulations, insurance).

• During Project Phases:

• Identifying any overlooked costings.

• Noting on-site changes.

• Meeting with other stakeholders.

• Evaluating contractor's work for payments.

• Checking project progress.

Essential Measurement Techniques in Quantity Surveying

Accurate measurement is the cornerstone of quantity surveying, transforming drawn information into descriptions and quantities for costing and project management. The process involves precise booking of dimensions and detailed descriptions.

The Standard System of Measuring Building Work (SSM)

The Standard System of Measuring Building Work is a guiding document with uniform rules for preparing Bills of Quantities. Issued by the Association of South African Quantity Surveyors (ASAQS), it serves as a crucial reference for quantity surveyors and students alike. It ensures consistency and clarity in documentation, reducing disputes and promoting competitive tendering. Its primary function is to standardize the bill of quantities.

Dimension Paper and Forms of Dimensioning

Measurements are recorded on specially ruled dimension paper. Understanding the forms of dimensioning is key:

• Cubic: For volume (e.g., concrete, excavations).
• Square/Superficial (Super): For areas (e.g., walls, plaster, screed).
• Linear: For lengths (e.g., skirting, pipes).
• Enumerated: For countable items (e.g., doors, windows, hinges).
• Itemized: For items without a specific unit of measurement, marked simply as 'item'.

Recording Dimensions and Descriptions

When booking dimensions, several techniques ensure clarity and accuracy:

• Order of Dimensioning: Horizontal (right angle to line of sight), Horizontal (parallel to line of sight), then Vertical.
• Bracketing of Descriptions: Used to link dimensions to their common descriptions, especially when multiple dimensions relate to one item.
• Timesing: Multiplying identical dimensions for items occurring multiple times (e.g., 2 | 13,56 2,45 for two plastered wall areas).
• Dotting On: A system for grouping similar numbered items across different locations.
• Deductions (Omissions) and Additions: Deductions (e.g., for openings) are prefixed with 'Ddt'. The first addition item after a deduction is prefixed with 'Add'.
• Alterations to Dimensions: Incorrect dimensions are neatly crossed out, and 'NIL' is entered in the squaring column; dimensions are never erased.
• Sign-posting (Referencing): Clear references (e.g., room names, drawing numbers) indicate the source and location of measured items.
• Side Casts: Reference calculations written in the description column, indicating how measurements were derived. These are given in millimeters and to three decimal places.

Detailed Measurement: Roof Structure, Doors, and Foundation

Measurement in quantity surveying is broken down into substructure, superstructure, and specific elements like roofs and openings. Each requires adherence to specific guidelines and specifications.

Measuring Roof Structures

Measuring a roof is subdivided into three main parts: construction, covering, and rainwater goods. Specifications dictate timber sizes, spacing, overhangs, pitch, and materials.

• Construction: Involves measuring elements like wall plates, trusses (38x114mm pre-treated SA Pine, 750 c/c spacing), and the true lengths of truss members (common rafters, tie beam, king post, struts, queen post).
• Covering: Includes fibre cement sheets, fibre cement ridge (15 x 200mm), and purlins (52x76mm sawn purlins, 76x76 WSAP purlins).
• Rainwater Goods: Covers items like gutters, down pipes, swan necks, shoes, and stormwater channels.
• Gable Wall: Consists of triangular and rectangular sections, with its area being the sum of these two shapes.
• Beam Filling: A half-brick wall built from under the wall plate up to under the roof covering.
• Hipped Ends: Note that hip rafters and jack rafters are typically not dealt with at the N4 level but can be determined trigonometrically or graphically.

Measuring Door Openings

Doors are categorized into internal and external, each with potentially different specifications and finishes. However, the adjustments for openings are similar.

• Specifications: Often include framed, ledged, braced, and batten doors, meranti door frames (70x100mm), external face brick with soldier course lintels, internal plaster, standard precast lintels (75x100mm), granolithic thresholds and steps, meranti skirting (76x19mm), and paint coats.
• Take-off List for Doors: Door, door finish, frame (built-in), paint. Adjustments include deducting wall, external wall finish, and internal wall finish.
• Arches and Lintels: Supports over openings to prevent wall collapse. Lintels can be standard precast concrete.

Measuring Foundation (Substructure)

The substructure is the lower part of the building, typically below ground level, comprising foundations (footings and walls) and sometimes basements. Measurement involves:

• Site Clearance: Clearing and removing all obstructions, vegetation, and debris (e.g., 1.5m beyond building line).
• Excavation: Moving soil, rock, and other materials (e.g., depth of trench 730mm).
• Concrete in Foundation: Classified by grade or mix (e.g., 15 MPa mass concrete). Length and width usually match trenches, with specified thickness (e.g., footing width 600mm, height 200mm).
• Brickwork: Foundation walls are measured by thickness (e.g., 330mm foundation wall in English bond, 1:4 cement mortar). Specifications indicate brick types (e.g., ordinary brickwork, face brick up to two courses below ground level).
• Waterproofing: Damp-proof sheeting (e.g., between hard-core filling and concrete surface bed).
• Beam Filling: As mentioned for roofs, also relevant to substructure context.

Measuring Superstructure

The superstructure is the part of the building above the substructure, including walls, floors, and roofing up to under the wall plate.

• Specifications: Typical specifications include brickwork (stretcher bond, 1:4 cement mortar), external face brick, internal fair-faced walls, granolithic floor finishes (19mm) and skirting (75mm), rhino board ceiling (6mm) on brandering (38x38mm), H-section cover strips, cove cornice (75mm), and paint coats (e.g., two coats PVA on ceiling).
• Take-off List: Damp-proof course, surface bed, brick wall, external finishes, facings, internal finishes, fair facing, floor, skirting, ceiling, cornice, painting.

Office Procedures and Bill of Quantities Production

The production of a Bill of Quantities (BoQ) follows a structured office procedure, ensuring accuracy and comprehensive documentation.

Key Office Procedures

• Receipt of Drawings: All drawings are date-stamped and entered into a register upon receipt, often arriving in phases over weeks.
• Preparation of Drawings: Before measuring, the quantity surveyor must peruse drawings to understand the building's nature, construction type, and finishes. Dimensions are checked, and missing overall dimensions are filled in. Drawings are also checked for errors.
• Query List: A list of uncertain items compiled by the quantity surveyor, which must be clarified by the architect. Solutions are formally recorded.
• Measuring List (Take-off List): A preliminary list of all items to be measured, serving as a reminder and guide.
• Collection: Preparatory side casts (calculations) done before the main take-off, identified by clear headings.
• Checking Collections: All calculations in collections are checked thoroughly to avoid carrying mistakes forward.
• Colouring in Plans: Measured items are colored on drawings (e.g., red for brickwork, brown for timber, dark grey for reinforced concrete) to monitor progress and prevent over-measurement. Plain openings, doors, and windows are not colored.

The Bill of Quantities (BoQ)

A BoQ is a document used in the tendering process to itemize materials, labor, and services, detailing contract terms and conditions. It allows sub-contractors to price work accurately.

• Advantages of BoQ:

• Promotes financial control and reduces risks.

• Ensures competitive tenders based on uniform information.

• Provides a mechanism for adjustments, reducing disputes.

• Includes contingency money for unforeseen events.

• Serves as a database for future estimating.

• Facilitates interim valuations and final accounting.

• Disadvantages of BoQ:

• Time-consuming to compile, potentially delaying project start.

• Reliability issues if items are measured as provisional amounts and require adjustment.

• Errors can significantly impact budget and duration.

• Increases documentation period costs.

• Absence can lead to variability, increased risk, and more disputes.

The Procedure of Preparation (Chronological Order)

1. Study Drawings & Specifications and Taking Off: The process of identifying and measuring construction elements.
2. Squaring: Calculating volumes, areas, or lengths from the dimension column and entering results in the squaring column.
3. Abstracting Items and Checking the Abstract: Sorting and grouping similar items, then transferring dimensions to 'abstract paper' to consolidate quantities for billing.
4. Work Up the Abstract, Billing, and Checking the Bill: Writing out the abstracted items fully on 'bill paper', including descriptions and total quantities.
5. Type and Read Over the Bill of Quantities: Finalizing and proofreading the document.

Important Quantity Surveying Terminologies

• Circular Work: Work constructed in an arch or circular form, measured separately.
• Measured Net: Measurement excluding extras, waste, or laps.
• Variation Order: Written instruction authorizing a change that alters the contract amount.
• Interim Money/Payment: Part payment to the contractor for work done up to a certain stage.
• Retention Fund: A percentage of money withheld from interim payments as security against faulty work, paid at the end of the defect liability period.
• Casting Up: The totalling process on dimension paper after squaring dimensions.
• Reducing: Adding or subtracting details ignored during initial measurement.
• Drawings: Graphical documents showing scope of work (side, top, sectional views).
• Interim Valuations: Monthly estimations of satisfactorily completed work.
• Contingencies: A lump sum in the BoQ to cover unforeseen costs or conditions (e.g., adverse weather, technical problems).

FAQ: Quantity Surveying for Students

What are the key stages of Bill of Quantities preparation?

The key stages involve studying drawings and specifications, taking off quantities, squaring dimensions, abstracting similar items, working up the abstract, billing, and finally typing and reviewing the complete Bill of Quantities. Each step ensures accurate and standardized documentation for tendering and project management.

How does a Quantity Surveyor ensure accuracy in measurements?

Quantity Surveyors ensure accuracy through systematic methods such as using the Standard System of Measuring Building Work, meticulously booking dimensions on dimension paper with clear descriptions, using bracketing, timesing, and dotting-on techniques, and meticulously checking all calculations. Site visits and clarifying queries with architects also contribute significantly to accuracy.

What is the difference between substructure and superstructure in quantity surveying?

The substructure refers to the lower part of a building, typically below ground level, including foundations, footings, and basement walls. The superstructure is the part of the building constructed above the substructure, encompassing everything from walls and floors to the roof structure, up to the underside of the wall plate.

Why is a 'query list' important in quantity surveying?

A query list is crucial because it allows the quantity surveyor to document all uncertain items, details, or specifications identified during the perusal of drawings. These queries are then addressed by the architect, ensuring that all information is clear and unambiguous before measurements begin, thereby preventing errors and disputes later in the project. The responses to these queries are carefully recorded as evidence.