Introduction to Taking off Quantities | Take off Sheet

Taking off quantities is major role of the quantity surveyor, In this article we will discuss about tds sheet quantity surveying, taking off sheet (construction takeoff sheet) and taking off quantities in construction.

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Read more: Procedure of Contractual Claims in Construction Contract...

Measurement is used by various stakeholders and construction professionals throughout the development process to calculate the quantity of work to be done. For example,

> A project manager may require the gross floor area of a proposed office block to establish a building budget at the initial stages of a contract.

> A quantity surveyor may calculate the approximate quantities of work during the design development stage to produce a cost plan to check the adequacy of the building budget.

> A quantity surveyor may take off quantities from detail drawings to produce a bill of quantities for tendering purposes.

> On smaller projects an estimator may need to measure the quantities from the tender drawings and specifications as pan of a tender submission.

> A contractor will present measured variations as part of a final account settlement.

The purpose of measuring any building work is to establish the correct amount of work to be done. This involves producing accurate quantities in a way which is comprehensive, technically accurate and clear in its approach and presentation.

Measurements must be carefully made regardless of whether the measurer is sitting comfortably at an office desk or is on site up a scaffold in the rain, other people's money depends on it and so does the measurer's reputation. They are spending employer's money every time a dimension is entered. It is assumed they are conscious of the responsibility and are worthy of it.

Measurement has two basic essential activities; description and quantification.

Description usually involves 'translating' information contained on drawings, specifications and technical reports and communicating that information accurately and concisely so that another person will completely understand the writer's intentions.

The measurer must be able to describe concisely what the designer has drawn or the builder has built. In practical terms this means that the description must be clear enough to enable an estimator or valuer to visualise the detail without having to refer to the drawing. The description will only be adequate if the estimator is capable of fully pricing the original detail. Designers and quantity surveyors must be aware that others will rely on their descriptions when pricing building works. Descriptions must therefore be accurate, clear, concise and unambiguous.

Quantification on the other hand is reasonably straightforward. Accuracy, again, is the objective, however the level of accuracy which is to be expected depends on the degree to which the design has been developed and the purpose for which the measurements have been taken. The accuracy required usually increases in tandem with the detail of the design. It would not be intended that an undimensioned 1:1000 block layout produced during the initial phase of the design process would be used to measure lengths of walls to the millimetre. It may be perfectly acceptable to measure outline drawing to a lesser degree of accuracy to generate approximate quantities as part of a preliminary budget cost estimate.

Quantity surveying practices now produce bills of quantities using various software packages, each of which has its own techniques for entering dimensions and composing descriptions. However, it is often uneconomic and unnecessary, particularly for other construction professionals, to purchase these packages and other approaches must therefore be considered. The traditional method of teaching building measurement through hand written worked examples is considered by this author to be an effective approach to developing a sound understanding of, and ability in measurement procedure and the potential problems which may be encountered. The author believes that the pen-and-paper approach to measurement has served the profession well, and should remain the necessary and pragmatic first steps in mastering the basic principles on which digital measurement is founded.

Read more; Building Estimating Software in Construction Sector

Introduction to Taking Off Quantities

The quantification process involves recording dimensions and is referred to as taking off because it involves reading or scaling (taking off) dimensions from a drawing and entering this information in a standard manner on purpose ruled paper called dimension paper or take off paper.

Dimension Paper | take off sheet

An example of traditional dimension paper is illustrated at below picture. These sheets are normally printed in A4 portrait format.

traditional dimension paper - take off sheet

The traditional dimension sheet (take off sheet) is divided vertically into two identical halves each comprising a set of four columns. In effect, the rulings on the right half of the sheet may be considered to be a continuation of those on the left side of the sheet.

traditional dimension sheet - taking off sheet

traditional dimension sheet | take off sheet

Columns A - are he timesing columns; these columns are used to enter multipliers when there is more than one of the particular item being measured.

Columns B - are he dimension columns; where the dimensions of the item being measured are recorded.

Columns C - are the squaring columns; these columns are used to calculate the quantities which are produced by multiplying the timesing factor in column A by the dimensions in column B. The results are then totalled to derive the final quantity of work.

Columns D - are the description columns; these wider columns are used for descriptive content such as location references and explanatory notes called annotations. Preliminary calculations, called waste calculations may also be carried out in these columns. In the UK these columns contain the written description, often abbreviated, of the item being measured.

The double lined column on the extreme left of the sheet is a binding margin and it is not used in the taking off process. The division of the dimension paper into two halves permits a number of items to be measured on a single sheet. This author, however, recommends that plenty of space be left between items on the dimension sheet. Cramped work is often difficult to follow and there may be instances where work is missed if it appears to be a continuation of the previous item being measured; both will result in the loss of marks in examinations and project work.

Entering Dimensions

The four principal units of measurement encountered on introductory measurement courses are number, length, area, and volume. Occasionally standard methods of measurement require the insertion of an 'item'. This is an item of work without a measured quantity, for example disposing of surface water in excavation work, labours on brickwork, testing the drainage system, and so on. try to understand the process for entering dimensions for various following work items in taking off quantities.

taking off quantities example

A particular focus of this paper is to explain how measurements are prepared for inclusion in bills of quantities compiled in accordance with standard methods of measurement.

These stipulate that "Work shall be measured as net as fixed in position and each measurement shall be taken to the nearest l0mm (i.e. 5mm and over shall be regarded as l0mm, and less than 5mm shall be disregarded)." (ARM4 Rule A5) This rule requires measurements to be entered in the dimension column in metres to two places of decimals with the decimal point between the metres and fractions. For example, where the length of a skirting is 5994mm it would be entered as 5.99m. If, however the length is 5995mm it would be entered as 6.00m.

Note that dimensions are always entered to two places of decimals even where it may not appear to be entirely necessary. For example if the length of the first pipe in below figure, above was 7000mm precisely, it would still be entered as 7.00m. rather than just 7! Figured dimensions should always be used in preference to scaled dimensions, which should only be used as a last resort.

Number/ Enumeration of Take of Sheet

Many items in building work are counted, for example precast concrete lintels and sills, prefabricated roof trusses, joinery items such as doors, and windows, electrical and mechanical fittings such as lights, radiators and pumps, sanitary fittings such as baths and so on. Where items are counted they are entered as whole numbers in the dimension column with a line drawn horizontally across the dimension column below each entry. For example in above figure, six flush doors have been counted in one particular location and another three are located elsewhere. The whole numbers 6 and 3 have been entered in the dimension column with a horizontal line across the column below each entry. Note that the actual dimensions of enumerated items are stated in millimeters in the description. This identifies the door's width, height and thickness.

Lengths

Linear measurements (lengths) are taken for items such damp proof courses, details such as bands and cappings on brickwork, carcassing and first fix timbers, runs of pipe, etc. Linear measurements usually state the cross section size of the item in the description.

above figures enters the measurements for three drain pipes in metres to two places of decimals in the dimension column; these are: 7.20, 11.90 and 3.45 metres long respectively. A line is drawn across the dimension column under each length to indicate that it is a linear measurement.

Areas

Items such as walls, roof coverings, floor boarding, and most finishes are measured by area. These are sometimes referred to as superficial measurements. The description usually states the thickness of the item of the work. The measurements comprise two dimensions; a length and width when the item is on plan, or a length and a height where it is vertical. Dimensions are arranged in pairs in the dimension column with the horizontal line appearing under the second dimension. Above figure shows the measurements of two block walls. The dimensions read as 5.16 m long by 2.40 m high and 4.00m long by 1.23m high respectively.

Volumes

Excavation, earthwork and concrete work are typically measured by volume. These items contain three dimensions which ideally are arranged in the order of length by width by depth. Again, the sets of three dimensions are identified by the horizontal line under the third dimension of the set. The concrete foundations in above figure identify two separate trenches where the longer trench is 900mm wide and the shorter trench is 1200mm wide.

The convention of underlining indicates which unit of measurement is being used and removes the need to stipulate whether the measurements are lengths, areas, volumes or numbers. Where each dimension is underlined the unit of billing is the metre, where the second dimension in a pair is underlined the unit is square metres, and where the third dimension in a set is underlined the unit is cubic metres.

Timesing of Take of Sheet

Quantity surveyors use the term 'timesing' rather than 'multiplication' to refer to the number of times a particular item occurs in the course of measurement in taking off quantities. The timesing factor is entered in the timesing column and is registered by a backslash mark across the border between the timesing and dimension columns.

Below figure shows various timesing techniques which can be used to speed up the measurement process by avoiding the needless repetition of identical dimensions.

The second entry in the door measurement indicates that them are three separate groups of three doors.

The measurement of the drain pipes show that there arc two runs of 7.20m and I I.90m pipe and three 3.45m lengths of pipe.

The measurement of the block walls demonstrates that timesing can be repeated where similar designs are located in different pans of the project. Example 4 shows that there are two instances of the first type of wall in two separate parts of the project. This entry reads twice times twice times 5.16m long by 2.40m high walls - i.c. there are four walls with these dimensions. Likewise the second entry shows that there are six (three times twice) walls that are 4.00m long by 1.23m high. This technique is particularly useful when measuring work of a repetitive nature such as housing schemes and hotels or multistorey buildings with repetitive floor layouts.

The measurement of the concrete foundations demonstrates a technique called dating on. This technique is not encountered frequently in practice. but there may be occasions where a further item or items have been discovered after similar work has already been measured. The process is signified by inserting a conspicuous large 'dot' behind and above the timesing factor while entering the number of the additional items. In the concrete work in Figure 4 the multiplier for the first set of dimensions reads (three plus one) times. i.e 4 times. Likewise the second entry reads twice times three times (two plus one) i.e six times the dimensions.

use of the timesing column of take of sheet

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Sunday, November 3, 2019