1 UNESCO-NIGERIA TECHNICAL &
VOCATIONAL EDUCATION REVITALISATION PROJECT-PHASE II
YEAR 2- SE
MESTER 2
THEORY
Version 1: December 2008
NATIONAL DIPLOMA IN
QUANTITY SURVEYING
TENDERING AND ESTIMATING II
TABLE OF CONTENTS
WEEK 1:
1.0 PRICING OF PRELIMINARIES I 1.1 What are Preliminary Items?
1.2 Estimating for Typical Preliminary Items
WEEK 2:
2.0 PRICING OF PRELIMINARIES II
WEEK 3:
3.0 PRELIMINARIES ANALYSIS WORKSHOP 3.1 Preliminary Bill 3.2 Class Workshop WEEK 4: 4.0 PREPARATION OF TENDER 4.1 Decision to Tender 4.2 Collection of Information 4.3 Enquiries and Quotations 4.4 Visit to Site
4.5 Visit to Consultants Offices 4.6 Receipt of quotations
4.7 Planning and Mid Tender Review 4.8 Preparation Of The Estimate 4.9 Final Review
4.10 Action after Submitting a Tender 4.10.1 Action with a successful tender 4.10.2 Action with an Unsuccessful Tender
4.11 Factors in Pricing General and Special Attendance on Subcontractors
WEEK 5:
5.0 MAJOR FACTORS AFFECTING TENDER PRICE 5.1 Factors Affecting Tender Price
3 WEEK 6:
6.0 PRICIPLES OF ANALYTICAL ESTIMATING 6.1 Elements of a Unit Rate
6.2 Calculation of Unit Rates 6.2.1 Materials
6.2.2 Plant 6.2.3 Overheads 6.2.4 Profit
WEEK 7:
7.0 BUILD-UP HOURLY RATE FOR PLANT & EQUIPMENT 7.1 Calculation of Unit Rates
7.2 Groundworks 7.2.1 Hand Excavation
7.3 Excavation using Mechanical Plant 7.4 Banksmen
7.5 Disposal of Excavated Material 7.6 Earthwork Support
WEEK 8:
8.0 BUILD-UP UNIT RATE FOR SURFACE EXCAVATION 8.1 Surface Excavation
8.2 Removal of Excavated Materials
WEEK 9:
9.0 BUILD-UP UNIT RATE FOR CONCRETE WORK I 9.1 Concrete Work
9.2 Reinforcement
9.3 Guide to Using this Student Learning Pack 9.4 Concrete Works
9.4.1 Site Mixed Concrete 9.4.2 Ready Mixed Concrete 9.5 Concrete Reinforcement
10.0 BUILD-UP UNIT RATE FOR CONCRETE WORK II 9.6 Concrete Work
9.6.1 Site Mixed Concrete 9.6.2 Ready-Mixed Concrete 9.8 Concrete Work
9.7 Reinforcement
WEEK 11:
11.0 BUILD UP UNIT RATES FOR REINFORCEMENT 11.1 Bar Reinforcement
WEEK 12:
12.0 BUILD-UP UNIT RATE FOR FORMWORK 12.1 Formwork
WEEK 13:
13.0 BUILD-UP UNIT RATE FOR ROOFING 13.1 Roofing
WEEK 14:
14.0 BUILD UP UNIT RATE FOR MASONRY 14.1 Guide to Using this Student Learning Pack 14.2 Masonry works
14.3 Fact and Figures
WEEK 15:
15.0 PRACTICE QUESTIONS FOR TUTORIAL CLASS 15.1 Questions
5
Course: Tendering and Estimating II
Course Code: QUS 210
Contact Hours: 2hrs
Course Specification: Theoretical Content
General Objective for Week 1: Appreciate the Build-up for Preliminary
Items
WEEK 1: PRICING OF PRELIMINARIES I (1.0)
1.1 What are Preliminary Items?
Preliminary items are items of cost which do not relate to any particular work section and usually listed in the first bill of quantities. Many estimators prefers to inserts a lump sum for all the preliminaries usually worked out as a percentage of the total of the measured works. It is good practice however to put a price to each of the item. The price quoted should read at after careful consideration of each item as it applies to the particular job at hand e.g water for the works. It will be pipe bone water readily available on site or water has to be transported to site on trucks.
1.2 Estimating for Typical Preliminary Items
(1) Site Supervision: These include the salaries and allowances paid to the site agent or engineer and the administrative staff on the site such as cashiers, clerks, time keepers, material checkers, store controllers etc. when this staff are sent aways from the area in which they normally work and this necessitate them having to leave away from their usual place of residence for a period of time a subsistence allowance may have to be added to cover the additional expenses they will incure e.g
site agent salary / month = 10,000 Housing allowance = 8,000 Transport allowance = 2,500 20,500 = 20,500 Cashier Salary / month = 5,000 Housing allowance = 4,000 Transport = 2,000 11,000 = 11,000
Clerk Salary / month = 3,500 Housing = 1,600 Transport = 1,500 6,600 6,600 Store controller Salary / month = 3,500 Housing = 1,600 Transport = 1,500 6,600 = 6,600 Messenger Salary / month Salary / month = 1,000 Housing = 800 Transport = 500 2300 = 2,300 47,000/month Contract duration 12 month
Add 1 month before project and
Add 3 months for defect liability period
Total month 16
16 months x 47,000 = 752,000 Add 10% for insurance and I.T.F = 75,200
827,200 Add 25% for profit and overhead = 206,800
1,034,000 (2) Site Accommodation
The contractor is usually expected to provide and maintain temporary site accommodation for
(i) Supervising consultant on site (ii) Site agent and site staff (iii) Hut for workmen
(iv) Storage, shed for materials, tools etc.
7 (a) Initial construction of accommodation
(b) Removal on completion and making good ground disturbed (c) Maintenance of accommodation throughout duration of the project (d) Furniture including ventilation and air conditioning
(e) Overhead and profit from these estimator must remove the resale value of items are still useable at the end of the projects e.g
Site office
Initial construction cost
Architect office 7.5m2 Engineer office 7.5m2 Quantity Surveying 7.5m2 Site agent 7.5m2 General office 10m2 Contractor’s room 12m2 Rest room 2.5m2 54.5m2 55m2 Circulation space 10% 5.5m2 60.5m2 61m2 61m2 at 9,000 = 549,000
Less resale value of items (about 27%) 149,000
N400,000
Demolish and cart away from site including making good @ 500/m2 x 61m2
= 30,500
(3) Mechanical Plant
This include all mechanical plant not allocated to unit rate such as cranes, lift, dumpers, hoist, tractor, generating set, drills, forklift etc. the contractor is expected to allow for this items whether they are purchased specifically for the project or they are already owned by the firm or they are to be hired for the period they are required on the project. The usual thing is to allow for
(a) cost of transporting plant to site (b) Hire rate for the period plant is on site (c) Cost of maintenance on site
(3) Tools
This include items such as shovels, portable drills, wheel barrows, batch boxes, guage etc. smaller tools such as hammer, trowel, plumb level, plumb lines, paint brushes etc. that are associated with a particular trade are not aloe for, here. They are usually taken care of in the tool allowance included in the all in-labour rate for such fields. If the project is large enough to used up small tools such as paint brushes, sand papers etc. then the cost of such are included in the unit rate for the items that required their use in pricing consideration is given to the cost of purchasing of the tools less their resale value.
(4) Scaffolding
The total height and the type of construction determined the amount and type of scaffolding required for a project, the contractor may purchase scaffolding for use in the work. Whatever they may be, in pricing consideration is usually given to the following.
(a) Hire rate for the duration of the project (b) Labour cost for erecting scaffolding on site
(c) Labour cost for adopting scaffolding for special uses
(d) Labour cost for dismantling scaffolding at the end of the project
(e) Transportation cost for bringing to site and removing from site all scaffolding (f) Profit and overhead
9
WEEK 2: PRICING OF PRELIMINARIES II
(6) Water For The Work
Water required for the project is provided in either of the two ways supply by water tankers if the site is far from a source or pipe bone water. In pricing consideration is given the following:
If the site is far from the source: Cost of water supply by water tanker. It may be necessary to write out an approximate estimate of the quantity of water required for the project from previous project, certain allowance can be made for concrete work 480 liters/m3
For Block work 350 liters/m2 Rendering 30 liters/m2 Workman hut 2000/day Site accommodation 20,000/day
Based on these allowances total quantity of water can be estimated for the whole project and priced at prevailing water tanker rate for that areas.
Cost of Temporary Storage: This include
(a) Cost of labour and materials in constructing surface tank, overhead tank, pipe work and its pumps.
(b) Cost of cleaning and maintaining tanks, water pipes and water pumps.
(c) Cost of removal of water storage and temporary pipe work and making good ground disturbed
(d) Overheads and profits
(a) Pipe Bone Water: Pricing will include
(i) Cost of water connection by water board (ii) Cost of labour and material for laying pipes (iii)Cost of temporary storage
(iv) Water rate are usually charged as flat rate per plot. Therefore no need to estimate approximately
(v) Cost of disconnection, removal of pipe and making good defect (vi) Overhead and profit
(7) Lighting and Power for Work
As in the case of water, provision of power is effected in either of two ways (a) Power generating set: If site is far from existing mains, pricing will include (i) cost of hiring generating set for the duration of the project.
(ii) Cost of cables, wiring and light fittings
(iii) Cost of running and maintaining generating set for duration of project (iv) Cost of labour and materials for constructing temporary sheds for generators (v) Cost of dismantling shed, removal and making good
(vi) Cost of transporting generating set to site and removal on completion of project. (vii) Overhead and profit
(b) Electrical supply from electrical authority mains, pricing will include (i) Cost of connection to the electrical authority
(ii) Cost of cables, wiring and light fittings (iii) Cost of electricity bills
(iv) Cost of disconnection on completion of project
(v) Cost of hiring a standby generator in case of electricity failure (vi) Overhead and profit
(8) Temporary Road
In certain building and civil engineering construction, temporary road have to be constructed from the existing road to the site in order to get access to and make possible the distribution of materials to various part of the site. Temporary road may also be required is first worked and priced with the following considerations
(a) Cost of labour during clearing the road
(b) Cost of excavation either by hand or by mechanical plant (c) Cost of labour and materials in laying laterite, blinding, gravel (d) Cost of maintaining the road for the duration of the project
(e) Cost of removal of temporary road if not required at completion of all works on site and making good ground disturbed
(f) Overhead and profits (9) Temporary Telephone
If the project requires the telephone, the constructor must arrange for telephone communication to be installed on site for easy communication for the duration of the contract, pricing will include
(a) Cost of telephone installation by telephone organization in this case NITEL (b) Cost of telephone bills
11 (c) Cost of maintenance
(d) Cost of disconnection\ (e) Overhead and profit
(10) Control of Traffic and the Additional Cost
Reconstruction and repairing of existing road, lying sewers, water mains etc. in existing roads and construction works in congested areas may create the necessity for closing part of some road temporarily to traffic. In such cases the provision of one way traffic control, diversions and access to adjoining houses, shops etc. may become necessary. The following should be given consideration
(a) control of traffic which involves (i) Cost of speed breakers (ii) Cost of constructing barriers (iii) Cost of red flags
(iv) Cost of labour flagging traffic (v) Cost of providing diversion
(vi) Cost of removal of sign board to adjoining house, shops, garage etc. (b) The provision of access road to adjoining houses, shops, garages etc
(i) Cost of labour and materials to provide pedestrian and vehicular access to shops, houses, cars and park etc.
(c) Additional cost of work on existing road where traffic is involved (i) Cost of delays to progress of work due to traffic and congestion (ii) The presence of existing water mains, cable sewers, culverts etc. (iii) Watching and lighting the work
(iv) Overhead and profit
(11) Welfare and Safety of Work People This will comprise the cost of (a) First aid box
(b) Drugs, antiseptics, bandages etc. (c) Providing a nurse or medical attendant (d) Maintaining first aid box
(e) Removal
(f) Protective clothing such as overall, element, nose mask, face mask, ear plug, boot eye shield (industrial goggle)
(g) Safety equipment such as hose, fire fighting equipment (h) Overhead and profit
(12) Temporary Fencing, Hoardings, Screeds, Fans Gantries and Similar Items. Each will comprise the cost of
(a) Labour and materials (b) Maintenance
(c) Removal and making good (d) Overhead and profit
(13) SITE SECURITY: This will comprise
(a) Cost of labour and materials to construct temporary security shed post (b) Labour and materials to installed security lighting, intruder alarms (c) Furniture, stationeries, tags, I.D card etc.
(d) Wages for workmen (e) Hiring of watch dogs
(f) Removal of sheds and lightening on completion of project and making good ground disturbed
(g) Overhead and profit
(14) Removing Rubbish and Site Clearance on Completion of Project. This involves the cost of
(a) Labour and materials clearing off such rubbish.
(b) Plant, lorry and labour loading such lorry transporting the rubbish from site (c) Labour and materials cleaning up door, windows etc.
(d) Overhead and profit
(15) Site Meeting: this will Comprise the Cost of: (a) Provision of stationeries at each meeting (b) Provision of refreshment at each meeting (c) Wages of attendant
(d) Overhead and profit
(16) Setting out of the Work: this will comprise the cost of (a) Pegs, templates and ropes or line
(b) Hiring of theodolite, precise level and other survey equipment
13 (d) Fees for engineer and the assign team
WEEK 3: PRELIMINARIES ANALYSIS WORKSHOP (3.0)
3.1 Preliminary Bill
The preliminaries bill gives the contractors the opportunity to price overheads which is described in the Code of Estimating Practice as “the cost of administering a project and providing general plant, site staff, facilities and site based services and other items not included in bill rates.
Preliminaries costs vary from contract to contract depending on complexity of work, size of contract, specialist plant and equipment required, conditions imposed by the employer etc. On relatively simple contracts preliminary costs may be in the order of 10 – 15% of the contract sum whereas on complex contracts this figure could be much higher.
A contractor must calculate the cost of the preliminary items separately for each contract, no two contracts are the same.
SMM7 recommends that fixed and time-related charges should be identified separately in a bill of quantities.
A fixed charge is defined as “the cost of work which can be considered as being independent of duration”
A time-related charge is defined as “the cost of work which is to be considered as dependant on duration”.
3.2 Class Workshop
The appendix below is a summary of the bill for the case study project. Students will be expected to appreciate and be able to work out how preliminary items in the bill are priced and distributed between time or cost related and fixed charges for the purpose of monthly valuations.
Procedures:
The work book will be made available to students at the beginning of the lecture. Time will be allowed for students to read and comprehend the notes. Students will then be asked to sit in groups of between 3 and 4 to discuss their understanding and set up query list on the project.
After about 30 minutes, each group will be required to use the preliminaries breakdown form to identify percentage allocation of each preliminary item across the table and to provide justification for the allocation on each item.
15 Appendix 1 attached shows the tender submission details and actual progress achieved on site for monthly valuation purposes on a typical construction project.
(a) Allocate the preliminaries to ‘time related” and “lump sums” sections (Use form
Appendix 2).
APPENDIX 1 TENDER SUBMISSION DETAILS
Bill No. Preliminaries
A Supervision £ 14,000.00 B Plant 1,200.00 C Scaffolding 1,200.00 D Welfare Facilities 2,100.00 E Site Huts 1,000.00 F Site Telephones 400.00
G Temporary Lighting & Power 400.00
H Programme 200.00
J Watching 1,250.00
K Site Hoarding 1,800.00
L Temporary Roads 950.00
M Setting Out 400.00
N Drying the Works 500.00
O Cleaning Away Rubbish 500.00
P Water for the Works 727.00
Q Insurance Against Injury to Person and Property 3,401.00
Total Bill No. 1 £30,028.00
Bill No. 3 External Works
A Soiling and Seeding £ 4,082.16
B Paths and Pavings 6,111.27
C Retaining and Screen Walls 2,017.33
D Drainage 9,127.16
Total Bill No. 3 £ 23,150.11
Bill No. 2 Measured Work
A Demolition £ 1,200.00
B Excavation and Earthwork 11,526.16
C Concrete Work 29,526.41
D Brickwork and Blockwork 31,416.12
E Roofing 14,112.16
F Woodwork 35,516.44
G Plumbing and Mechanical Installations 18,642.12
H Electrical Installations 9,216.14
J Floor, Wall and Ceiling Finishings 17,316.18
K Glazing 4,127.13
L Painting and Decorating 12,011.14
£184,610.00
Bill No. 4 Prime Cost Sums Nominated Sub-Contractor
A Piling £ 8,500.00
B Profit 5% 425.00
C General Attendance Item 170.00
D Specialist Landscaping 27,000.00
E Profit 5% 1,350.00
F General attendance Item 600.00
Nominated Suppliers G Kitchen Equipment 18,000.00 H Profit 5% 900.00 J Sanitary Fittings 12,000.00 K Profit 5% 600.00
17
L Ironmongery 5,000.00
M Profit 5% 250.00
Statutory Undertakings
N Water Main Connection 1,200.00
O Profit 5% 60.00
P Gas Main Connection 500.00
Q Profit 5% 25.00
R Electrical Main Connection 5% 500.00
S Profit 5% 25.00
T Sewer Connection 1,400.00
U Profit 5% 70.00
Total Bill No. 4 £78,575.00
Tender Summary
Bill No. 1 Preliminaries 30,028.00
Bill No. 2 Measured Work 184,610.00
Bill No. 3 External Work 23,150.11
Bill No. 4 Prime Cost and Provisional Sums 78,575.00
Bill No. 5 Daywork 9,050.00
TOTAL TENDER SUM £325,413.11
Bill No. 2 Item A complete Item B complete Item C complete Item D complete Item E complete
Item F 50% complete Item G 40% complete Item H 40% complete Item J 20% complete Item L 10% complete Bill No. 3 Item A 20% complete Item B 20% complete Item C 40% complete Item D 40% complete Bill No. 4 Item A complete Item D £8,600 Item G £8,000 Item J £6,000 Item L £2,000 Item N complete Item P complete Item R complete Bill No. 5 Variations £9,000.00 agreed. Materials on Site £6,237 agreed.
The following AI’s were received from the Architect in respect of the following Prime Cost and Provisional Sums:
1. Accept a quotation of £10122.50 from Keane & Bonney Piling Ltd.
It was observed that the Piling nominated sub-contractor had erroneously left out the main contractor’s discount in their quotation for the works.
19 2. Accept a quotation of £27500.00 from Landson Landscape plc.
3. Accept a quoation of £19012.00 from Kitchen & Sons for the supply of kitchen fittings. 4. Accept a quoation of £13176.00 from Loo Ltd for the supply of sanitary fittings.
APPENDIX 2
JCT 80
Breakdown of Preliminary Items
Cost Related
Time Related
Lump Sums Total
Start Finish Supervisor Plant Welfare Site Huts Telephones Temporary Lighting and power Programme Watching Site Hoarding Temp Roads Setting Out
Drying the works
Cleaning Rubbish
Water
Insurance
21 Questions:
(1) Define prelimiaries and give three examples of a “prelimiary item” (2) How do contractors price these items?
(3) Define fixed costs and provide five examples of an item you think would be priced as a fixed cost item
(4) Define time related costs and give five examples of preliminary items you think a contractor would price as a time-related cost.
GENERAL OBJECTIVE FOR WEEK 4: Know the tendering procedures.
WEEK 4: PREPARATION OF TENDER (4.0)
Reference: CIOB (1997) Code of Estimating Practice, 6th Edition. Ascot: CIOB The preparation of a tender can be divided into six stages.
4.1 Decision to Tender
The tender documents arrive and the estimator records all relevant information such as: • The time allowed for preparing the tender
• Drawings available
• The approximate value and extent of the project • The client, Architect, Q.S and other consultant • Value of main contractors own work
• Project Details eg phased work, conditions of contract, access to site, working conditions. • Firm price or fluctuating price tender required
• Current workload and timetable for project
After reviewing the above information, management must decide whether to tender for the project or decline the invitation. If it is decided not to submit a price, the tender documents should be returned immediately to the architect/supervising officer. If it is decided that a tender should be submitted, the contractor move to the next stage.
4.2 Collection of Information
The time allowed for preparing a tender is always limited; the estimator must plan the programme very carefully. The work which has to be undertaken in a typical 4 week tender period comprises:
• Despatching enquires • Visit consultants offices • Visit the site
• Receipt of quotations and examinations
• The ‘mechanical’ process of pricing the tender documentation
• Meetings with plant manager, contracts manager etc to determine a preliminary programme, construction methods and likely plant requirements.
23 Suppliers
Enquires should state:
• The specification of the material • The quantity required
• The anticipated delivery dates
• The terms upon which the price is required • The date by which the quotation is required • The address of the site and access details
• Period for which the quotation is open for acceptance
Sub-contractors
Photocopies of the relevant parts of the bill of quantities, specifications and if possible copies of drawings, should be sent out to perspective sub-contractors. Enquires should state clearly: • The items to be priced
• The terms of the main contract
• The period for which the quotation is open for acceptance
• The plant, materials, attendance etc to be provided by the main contractor • Anticipated commencement and completion dates
• The form of contract and details from the appendix • The terms of payment
• Date by which the quotation is to be submitted • Address and details of the site
4.4 Visit to Site
The visit to site can be made after all enquires have been despatched and before prices begin to come back. The visit to the site will enable the estimator to produce a report giving the following information:
• The position of the site in relation to roads etc • Names of local and statutory authorities
• Details of site/ground conditions, spot items etc • Site access, egress and possible site layouts
• Facilities for disposal of surplus excavated materials etc
4.5 Visit to Consultants Offices
It may be that only drawings showing plans and elevations will be sent out with the tender documents and that further details and working drawings can be examined at the consultants’ offices e.g. the estimator may require further details of manufactured joinery, steelwork joinery fittings etc, before these sections can be priced accurately.
4.6 Receipt of quotations
Prices received from sub-contractors and suppliers are examined for sufficiency, terms etc
4.7 Planning and Mid Tender Review
The project is discussed with other managers to determine a preliminary programme, construction methods, sequence of work, site layouts and what other plant, services, labour and site staff are required.
It must be decided whether:
• All labour can be obtained locally or will it be necessary to recruit for the project. • Sufficient plant is already owned or is it necessary to purchase/hire additional items. • It would be desirable to sub-let any further work.
The preliminary programme should also be prepared containing the following information: • Contract starting and completion dates
• Any work to be done in stages
• Work to be sub-let by main contractor
• Work to be done by nominated sub-contactors (if JCT 98 form)
4.8 Preparation Of The Estimate It can be divided into 4 stages:
1. The establishment of all-in rates for key items i.e. labour, gang costs, plant costs etc. 2. The selection of domestic sub-contractors and suppliers
3. The use of these ‘all-in’ rates together with costs per unit for materials to calculate unit rates for each item in the bill
4. The pricing of the preliminaries and project overheads
25 The consideration of the estimate to produce a tender is the responsibility of management. The estimator and other senior staff will prepare reports for consideration by management who will consider the following items before determining the tender figure;
• Project reports
• Conditions of contract
• Contractual and construction risks
• Terms of the quotations from sub-contractors • Capital required for the project
• Technical and management staff required • Current workload
• Market Conditions • Competition
• Reputations of client, consultants and area.
Following evaluation of the alternatives, risk and scope for profitability the ‘mark up’ is determined and the actual tender figures calculated. The decision being made within the framework of company policy.
A record of all tenders should be kept together will the results (if known) for future reference.
4.10 Action after Submitting a Tender 4.10.1 Action with a successful tender Check contract documents to ensure that:
• The dates, penalties etc are the same as those contained in the tender documents • The bills have been copied correctly from the original
• The drawings are those which were circulated with the tender documents
Disseminate information
Information should be made available to those responsible for purchasing, construction planning and plant.
Feedback information
Feedback from site on labour and plant outputs etc, to be kept for future pricing
Cost/Value Reconciliation
At regular intervals during the construction period, the costs at that time should be compared with a meaningful valuation of work done in order to check that the job is ‘on target’
4.10.2 Action with an Unsuccessful Tender
It the tender has been unsuccessful the contractor must assess why this is the case. Records of tenders submitted must be kept and estimators must evaluate their performance. Suppliers and sub-contractors should be notified of results as soon as possible.
Factors in Pricing General and Special Attendance on Subcontractors
Each site has its own peculiar characteristics which can have considerable influence on the total cost of development. Some of the more important factors are:
(1) Location of site: - Due to higher wastages, materials and other cost, it is expensive to erect a similar building in an urban area than in a provincial setting. Some parts of the areas are subject to higher rainfall than others and this can lead to a greater loss of working time even within the same region, the cost of operating on different sites can vary widely. A project on a remote country site may involve long length of temporary access road and temporary power cable for electricity supplies and increase cost of transporting operatives and materials and components, protection of adjoining buildings and the public and restrictions on the use of mechanical plant. Taking these problems will incure additional cost. Furthermore, a very expose site may make working conditions more difficult and costly. Some locations may be more vulnerable to vandalism and theft and so require more costly protective measures.
(2) Demolition site clearance: A site may contain buildings which requires demolition, paved areas which requires breaking up and trees which requires felling, grubbing up and disposal of their roots, another site may be cleaned of all obstruction.
(3) Contours: Few sites are entirely level. The most steeply slopping, the more greater will be the cost of foundation and earthwork, the steeping of strip foundation increase their cost. Most buildings requires constant floor levels and this will involve considerable excavation and fill on its slopping site.
(4) Ground conditions: Where the strata is low load bearing capacity. It may be necessary to introduce pile or other more expensive types of foundation. Raft foundations on made up ground or in areas liable to mining subsidence may be three trust as expensive as normal strip foundations where as pile foundation used to convey loads to a deeper load bearing strata could be as much as five times as expensive. The cost of excavation in rock could be five to eight times as expensive as working in normal ground, the provably length of haul in the disposal of surplus soil also needs consideration. Where ground water is close to the surface of the site, costly pumping operations may be needed. A wet site may also involve raising temporary sheds and offices on brick bases and more costly temporary
27 roads. The types of strata will also influence the form and extent of timbering or other means of supporting that will be needed to the sides of excavations.
GENERAL OBJECTIVE FOR WEEK 5: Know factors affecting tender figures.
WEEK 5: MAJOR FACTORS AFFECTING TENDER PRICE (5.0)
“Construction cost” is a broad phrase or term and can be interpreted to mean cost of any sort to anyone associated with construction work. It depends on the point of view let us say you are a contractor, your costs are your expenditure on labour, materials and plant. The client’s cost of land, consultant fees and so on.
The base cost of construction therefore comprises of expenditure on materials, labour and plant, the quantities of materials, labour and plant required for a job are determined & attaching prices to these defines the basic construction cost, but to these are also a variety of factors that affect this basic cost: -
5.1 Factors Affecting Tender Price (1) Market Condition:
The volume of work in progress in the area at a given point in time affect construction cost. When the market is burying with many project, tender price list are generally high. Most consultants are busy and competition is not keen. However during ausle times when there are few projects, contractors are anxious to out bid themselves so as to stay in business, so construction cost tends to be lower.
(2) Availability of Materials:
When required materials are readily available in an area where a project is to be executed, materials will be cheaper than where they are not so available. Generally, materials are cheaper where they are produced e.g if you can buy cement directly from Ashaka, the price will be a lot cheaper than in Kaduna because of transportation and profit margins of middlemen and so on. Imported materials for similar reasons are more expensive than locally produced materials.
(3) Availability Of Labour:
Where a certain type of labour is not readily available in the area where a project is to be constructed, it may be necessary to import from an area where such labour is available. Some inducement may have to be offered before such labour will move from its base such as transportation, accommodation, inconveniences allowances etc. these add to the cost of construction.
29 (4) Transportation:
The farther a site is from town, the more expensive will be the construction cost e.g the same building to be constructed in Barnawa and also near Kaduna Airport will cost differently, the additional cost of transporting materials, labour and plants to the airport site will increase the cost of construction.
(5) Location:
The standard of living in an area affects the cost of construction. People are willing to pay higher prices for construction in places like Lagos and Abuja than are to pay in other places like Benin, Kaduna or Enugu.
(6) Location of Site: -
The particular location of the site can have significant effect on cost. Remote site may require additional cost for the provision or access roads and temporary services or the provision of additional security measures. Also, a site in a congested or restricted area also gives rise to major problems such as delivery & storage of materials and components, protection of adjoining buildings and the public, restriction on the use of mechanical plants and so on, all these will increase the cost of construction.
(7) Time Consideration: -
For certain reasons, a project may need to be completed in a very short time, this tends to push up construction cost. Labourers may be required to work overtime and overtime rates are usually higher than normal rates. Incentives scheme may have to be introduced to increase labour productivity. Closure supervision is necessary as mistake must be avoided, there may be time to apply remedial action.
(8) Site Condition:
May affect the construction cost of a particular building. The nature of ground may necessitate more complex form of foundation. The ground water level when close to surface will involve costly water pumping operation. A wet site may involve rising temporary sheds and offices above ground level and they involve more costly temporary roads. Steeply sloping site may involve major cost in cutting and filling requirements, existence of buried pipes and cables may involve major cost to re-root such.
(9) Total Height of Building:
The higher a building is, the longer it takes and more difficult it is to get the point of execution of works. It is also more difficult to work at such height. Labour charges for
working at great height are higher than abnormal height, there is also the cost of providing additional safety measures and insurance. Also, the need for special scaffolding, hoist, tower crane, elevators etc. will tend to increase the cost of very tall building over the cost of building requiring the same quantities at ground level.
(10) Legislation:
Has a way of affecting construction cost in dramatics manner as we have seen in Nigeria over the years e.g minimum wage, import restrictions and duties, labour policies, fiscal policies such as exchange rates, interest rates etc. in for costing construction cost, an estimator need to keep an eye on legislation, to decide which are likely to affect construction cost and how.
(11) Class of Contractors:
There are various types of contractors in the market. These gives rise to different classification.
- Small contractors comprises of one man board of directors. They usually carry little general overhead and keep very few permanent staff
- Medium contractors usually have a board of at least two but not more than five directors they employ a few more permanent staff, have a reasonable office and possess some equipment and official cars.
- Large contractors have a lot of times publicly owned with many share holders having at least six members on their board of directors, fleet of cars and equipments, large office space and a lot of staffs of various discipline. Generally, the larger the firm, the higher their cost. Also, the level of profit expected by the share holder of larger firms is a lot more than that required by the smaller contractors. The rates for the small contractors therefore tends to be much lower than for large contractors (e.g AG Ferrero and small firms)
(12) Type of Client:
the type of client or developer can affect the cost of construction.
Some clients are willing to and are capable of paying more for construction than others. Also, some clients have methods to be taken into consideration while estimating construction cost (e.g U.N.T.L will pay on time than N.N.P.C when a contract is carried out)
31 - Architect: - Some architects are very difficult to work with, their initial designs are
not detailed and they rely a lot on instructions on site. Many variations occur and delays are frequent. These will add to the cost of construction. The same applies to Engineers and other designers. Contractors are therefore known to increase their prices by a certain percentage when it is known that they would be working with particular consultant.
(14) Types of Tendering:
Open tendering generally brings lower prices than selective tendering, and this in turn result in lower price than negotiated tendering which brings the highest price of fall.
GENERAL OBJECTIVE FOR WEEK 6:
WEEK 6: PRICIPLES OF ANALYTICAL ESTIMATING (6.0)
6.1 Elements of a Unit Rate
To analyse something is to break it down into its constituent parts and study each part in detail. Therefore analytical estimating involves the analysis and costing of construction resources to produce an estimate.
The production of an estimate normally involves the calculation of unit rates i.e. the cost of an individual measured item for example a square metre of brickwork, a cubic metre of concrete or a metre of skirting. As found in a Bill of Quantities.
Analytical estimating is therefore the most accurate form of estimating as each resource and unit rate is analysed and costed individually. This form of estimating is used for pricing contracts with bills of quantities, specifications and drawings or where the contractor has measured and prepared their own quantities of work.
6.2 Calculation of Unit Rates
Unit Rates maybe calculated in one of two ways: • Net Rate – (Excludes Overheads and Profit) • Gross Rate – (Includes Overheads and Profit)
Unit Rate Materials
Labour Plant
33 In our industry most estimators will calculate costs based on net rates these will then be enhanced later to include overheads and profit. Gross rates are sometimes referred to as
all-in rates.
The Resources which compromise a unit rate are labour, materials and plant. In the construction industry labour is often employed in two main ways, these are: 1. Direct –
Often referred to as ‘cards in’, the employer pays all the costs of employment including for example national insurance and sick pay amongst others.
2. In-Direct –
These workers are self employed or referred to in industry as ‘on the lump’ these are often labour only sub-contractors without the normal costs of employment along with the other legal protections such as redundancy, sick pay and minimum notice periods.
Labour may be paid for on an hourly, daily, weekly or piecework basis. Directly employed operatives are usually paid in accordance with a working rule agreement which will specify the rates and allowances to be paid. However, some contractors are trying to move away from the national wage bargaining and introduce local wage rates. Ultimately the actual rates paid for labour will depend on market forces.
6.2.1 Materials
Several factors affect the cost contractors pay for materials.
In the box below highlight the factors you think impact on the price a contractor pays.
In the material element of a unit rate, in addition to the actual cost of the material the estimator must also consider:
• Transportation costs
• Unloading and Stacking costs • Materials movement on site • Extra Materials to compensate for:
o Wastage
o Allowance for materials being measured net in B o Q o Loss in consolidation, shrinkage etc
Note: Where prices of materials are described by suppliers as ‘ex works’ this means the price
at the factory and delivery costs will have to be added.
Plant may be divided into two main categories, the costs of which can be allocated to contracts in differing ways.
Non-Mechanical Plant
Basic items of plant including – barrows, hosepipes, spades, trestles, scaffolding, small powered hand tools etc
With the exception of scaffolding and one or two other items it is virtually impossible to allocate the cost of non-mechanical plant items to a contract, let alone to a specific unit rate e.g. a wheelbarrow may be used on several contracts in its lifetime.
The cost may be included in overhead charges as a percentage, as a lump sum in the preliminaries bill or, more accurately, on longer contracts a list of non-mechanical plant items is prepared, costed and included in the contract sum.
Mechanical Plant
Mechanical plant such as excavators, lorries, dumpers, mixers etc require a more complex approach. Mechanical plant can be very expensive. Contractors may buy, hire or lease plant. The purchase of plant must be viewed as an investment on which a return is required. Only detailed analysis will show whether it is in the contractor’s interest to buy, hire or lease mechanical plant.
6.2.3 Overheads
Overheads may be defined as the cost of maintaining (running) the contractors organisation. There are two types of overheads:
(1) Head Office
Annual cost of staff salaries, expenses, rents, rates, gas, water, electricity, telephones, office equipment, postage, insurance, maintenance of buildings and equipment etc. The cost of these items is expressed as a percentage of a company’s turnover and included in the tender.
(2) Project or Site
Project site costs including non – productive (manual) site staff, site office costs, storage facilities and other preliminary / site organisation costs. Items are priced as individual items and may be fixed or time related costs or a mix of fixed and time related costs. The costs of these items are included in the tender.
35 6.2.4 Profit
The amount of profit that a contractor can make is determined by a number of factors largely outside the remit of an estimator. However, in larger companies the senior or managing estimator may be a member of the management team and in smaller companies / firms the estimator may be a director or the managing director. In both cases they may be party to, or may have to make commercial decisions regarding profit margins.
Factors affecting profit levels are: • Market forces of supply and demand • Amount of competition
• Who the competitor are • Size / Value of contract • Risk involved in contract • Interest rates.
Student Questions
1. Define analytical estimating
2. Explain the difference between net and gross unit rates 3. List the elements of a unit rate
4. Identify the organisations, which produce working rule agreements 5. Define non-productive time and holiday credits.
WEEK 7: BUILD-UP HOURLY RATE FOR PLANT & EQUIPMENT (7.0)
7.1 Calculation of Unit Rates
The following sections cover the calculation of unit rates. The process of calculating unit rates could be described as “mechanical” because you must consider each of the unit rate elements in turn. Some rates may include all elements, others only one, but you must think carefully about each element and calculation before commencing.
You may use the Wessex Price Book, or other similar price book, for information on the output/productivity of labour and plant. Materials and plant prices can be obtained from builders' merchants and plant hire firms.
In practice estimators must always use productivity outputs analysed from site feedback and the current cost o f other resourcs.
In the following unit rate calculations the hourly labour rates used are £9.50 for craft operatives and £7.00 for labour operatives.
7.2 Groundworks SAQ 2
Explain how the following factors may affect unit rates for groundworks? • Type of excavation e.g. trenches, pits, basements
• Ground conditions e.g. clay, sand, soil, rock • Depth of excavation
• Ground water
• Time of year when excavating • Mechanical or hand excavation • Distance and availability of tips • Estimated bulking of materials 7.2.1 Hand Excavation
Excavation work is usually measured in cubic metres (m3) Typical labour outputs for excavating in firm earth ;
Reduce levels maximum depth 0.25m 3.15 hours/m3 Trenches max. depth 1.00m 3.25 hours/m3 Basements max. depth 2.00m 3.94 hours/m3
37
ADD the following factors for other ground conditions ;
Dry or wet clay 20%
Compact gravel 50%
Rock not requiring a compressor 75%
Running silt or sand 100%
Example
Excavate trench maximum depth 1.00m in firm earth, unit of measurement m3. Labour;
£ - p 3.25 hours for a labourer @ 7.00/hour 22 - 75 ---
Net Rate per m3 22 - 75
If you want a Gross Rate add for
overheads and profit, say 10% 2 - 28
---
Gross Unit Rate per m3 25 - 03
======
TQs 1 - 3
Calculate net unit rates for the following ;
1. Excavate to reduce levels max. depth 0.25m in firm earth,
unit of measure m3
2. Ditto basements max. depth 2.00m in dry clay
unit of measure m3
3. Ditto to reduce levels depth 0.25m in compact gravel
unit of measure m2 (square metres)
Rates for different types of mechanical plant vary enormously between contractors depending on the method used to calculate the costs.
When calculating “all-in” hourly rates for mechanical plant the following items should be considered ;
• Capital cost • Depreciation • Interest on capital • Expected life of plant
• Number of hours worked per annum • Maintenance • Insurance • Road licence • Operators wage • Fuel • Lubricants
Think about how the above factors will affect the hourly cost of mechanical plant.
Example
The following is one method of calculating the all-in hourly cost of a mechanical excavator. This method is neither the simplest nor most complex method which can be used but it does produce realistic costs.
Capital cost (purchase price) £37,000 Residual Value (resale/scrap value) £6,000
Interest on capital 6% compound
Expected Life 5 years
Hours worked per annum 1600
Maintenance costs 10% of capital cost per annum
Insurance included in company overheads
Road Licence £200 per annum
39
Fuel 5 litres/ hour @ 40p/litre
Lubricants allow 10% of fuel costs
Standing Charge £ p
Capital Cost 37,000-00
Less Residual value 6,000-00
---
Depreciation 31,000-00
Interest 6% compound on £37,000 over 5 years 12,506-00 Maintenance 10% of capital cost per annum 18,500-00 Road licence £200 per annum for 5 years 1,000-00
---
Total for 5 years 63,006-00
---
Therefore cost per hour is;
Total cost for 5 years divided by total hours worked in five years
£63006 / (1600 hours x 5 years) £7-88
Running Charge
Drivers wages 1856 hours @ £7.50 13,920-00
Fuel 1600 hours x 5 litres/hour x 40p/litre 3,200-00
Lubricants 10% of fuel costs 320-00
---
Total for 1600 hours 17,440-00
---
Therefore cost per hour is £17440 / 1600hours £10-90 Therefore total cost per hour is:
Standing Charge £ 7-88
Running Charge £10-90
---
======
TQ 4
Using the following information calculate the "all- in" hourly cost for a 16 ton tipper lorry ;
Capital cost £68,000
Residual Value £5,000
Interest on capital 6% compound
Expected Life 10 years
Hours worked per annum 2160
Maintenance costs 10% of capital cost per annum
Insurance £3000 per annum
Road Licence £1,200 per annum
Operatives rate £7-50 per hour
Fuel 10 litres per hour@ 80p/litre
Lubricants allow 10% of fuel costs
7.3 Excavation using Mechanical Plant
Excavate trenches maximum depth 2.00m in clay.
Calculate the net rate per m3 using an excavator with an output of 5m3/hour for excavating and loading into lorries.
Hourly cost of excavator / output in m3 per hour
£18-78 / 5m3 per hour £3 - 76
SAQ 3
The output of the excavator may also be expressed in hours per m3 , what is the output in hours per m3 ?
Recalculate the rate using your output in hours per m3.
7.4 Banksmen
Banksmen are usually employed to supervise excavator/s. They check the excavation for obstacles i.e. underground services, make sure the excavator operator is working to the correct line and level and trim the sides and bottoms of excavations when necessary.
41
TQ 5
Recalculate the last rate and include for one banksman supervising two excavators, banksman’s rate £7.00 per hour.
7.5 Disposal of Excavated Material SAQ 4
Explain how the following factors may affect the cost of disposing of excavated material • Bulking of material
• Availability of tips/landfill sites • Distance to tip
• Average speed of lorry • Loading time
• Tipping time
• Tipping charges/costs • Consider alternatives
TQ6
Using the excavator and lorry from the previous example and the following information, calculate the cost per m3 for disposing of excavated material off site
Note ; The following items are all variables (will vary on every contract) therefore a new rate must be calculated for each contract
Assume ;
16 ton lorry will carry approx. 6.5m3 of bulked clay Output of excavator 5m3 per hour
Distance to tip 5 miles round trip Average speed 20 miles per hour Tipping time 15 minutes
Tipping charge £20 per load
7.6 Earthwork Support
Defined in the Standard Method of Measurement as ;
“Whatever is necessary to support the faces of excavations other than steel sheet piles”. It is measured to the faces of all excavations over 250mm deep.
The contractor has to decide what is necessary and cost it accordingly. This is referred to as a contractor’s risk item
The following factors affect the cost of earthwork support ; • Ground conditions
• Depth of excavation
• Distance between opposing faces of excavation • Method of support used
Contractors should also consider alternative methods of construction, which may be less expensive e.g. over excavate and backfill.
Timber used for earthwork support (EWS) can be re-used up to say 6 times therefore the cost of providing the timber should be divided by the number of uses to obtain a “cost per use”.
Operatives fixing EWS are usually paid an additional allowance for skill and responsibility.
Materials 100 x 100 costs £1-92/m 150 x 100 costs £2-88/m 150 x 150 costs £4-32/m 200 x 50 costs £1-92/m Labour
Fixing EWS in moderately firm earth to faces of excavation up to 2.00m apart and up to 2.00m deep (see sketch) - 0.77 hours per m2
Ditto in loose ground or running sand (as sketch) - 1.65 hours / m2
43
WEEK 8: BUILD-UP UNIT RATE FOR SURFACE EXCAVATION (8.0)
8.1 Surface Excavation
In building up rate for excavation, the following should be considered. (a) Types of excavation i.e surface or trench excavation
(b) Means of excavation i.e manual or mechanical (c) Nature of excavation
(d) Volume of excavation (bulking) (e) Distance of tipping (haulage)
Bulking Sand 12.5% Gravel 10% Clay 133 1/3% Rock 50% Multiplier
Medium labour constant multiplier
Sand and gravel 0.75
Natural soil 1.00
Stiff clay 1.50
Soft rock 3.00
Hard rock 8.00
OUTPUT
Excavation 2.5m3 / labour /day Spreading and leveling 4.5m3 / labour / day Wheeling / haulage 8.0m3 / labour / day Placing of concrete 4m3 / labour / day
Task I:
Surface excavation n.e 300mm deep and average 150mm, considered a gang of 12 labour and the supervisor. Calculate the cost/m3 given that the supervisor is N1500/day and the labourer N700/day
Solution
Labour cost
1 supervisor @ 1500/day N1500
12 labourer @ 700/day N8,400
Add 5% for tools N495
N10,395 Output of gangs / day = 2.5m3 x 12 = 30m3
Labour cost/m3 = 10,395 x 1/30 = 346.50 Add profit and overhead 20% 69.30
Cost/m3 = 415.80 Task II
Cost of spreading and leveling excavated materials n.e 50m from excavation. Consider a gang of 12 labourers and 1 supervisor
Solution
1 Supervisor @ 1500 = N1500
12 labouers @ 700 = N8,400
5% Tools = 495__
10,395 Output gang / day = 4.5 x 12 = 54m3
Loabour cost / m3 = 10,395/54 = 192.50 Add overhead and profit 20% = 38.50 97.33
8.2 Removal of Excavated Materials
Use wheel barrows when the distinction is less than or equal to 50m .Used lories/tipper. When the distance is greater than 50m.
Task III
Removal of excavated materials using the same distance of cart away is less than or equal to 50m using the same information used for excavation of surface
Solution
1 Supervisor, 12 labourers and 5% for tools = 10,395 Out out of gang/day 8.0 x 12 = 96m3
45 Add 20% profit and overhead = 21.66
225.94 355.88
When lories / tipper are used the following should be considered (b) Cost of hire or cost of owning
(c) The capacity of the lorry (d) Total distance to and fro the hill (e) Speed of lorry
(f) Tipping time
(g) Labour loading the lorry (h) Bulking of materials
TASK IV
(a) For the cost of hiring plant is 600/hr (b) Capacity of lorry 6m3
(c) Total distance to and fro is 3km (d) Speed of lorry 30km/hr
(e) Tipping time 9 minutes
(f) Output of labourer loading the lorry is 2hrs / labour /m3 (g) Bulking of materials 133 ⅓%
SOLUTION
Volume of excavated material = 6/133 ⅓ x 100 = 4.5m3 (assume 4 labour) loading time = 4.5m3 x 2hrs = 2.25hrs
4
Traveling time = 3km x 60m = 6mins 30km/hr
Total time for loading + traveling + tipping 2.25 + 6m + 9
2.25 = 2.15hr + 6m + 9m Cost of hiring lorry/hr
= 2.5hrs x N600/hr = N1500/hr
Therefore, cost/m3 = N1500 = 333.33/m3
Labour loading
Cost for 1 labour /m3 = 150/8 x 2.5hr x 4 labour = 187.50
Add 5% for tools = 9.38
196.88
333.33/m3
530.21
Add 20% overhead and profit 106.04
47
WEEK 9: BUILD-UP UNIT RATE FOR CONCRETE WORK I (9.0)
9.1 Concrete Work
Explain how the following factors may affect unit rates for concrete work ; • Whether ready mixed or site mixed concrete is used
• Whether concrete is reinforced • Surcharges for part loads • Location of mixing plant on site • Type and size of mixing plant
• Method of transporting, hoisting, placing and compacting mixed concrete • Cost of protecting and curing unset concrete
Operatives working with concrete receive additional payments for skill and responsibility. Items of plant should be priced separately.
Concrete is usually measured in m3 Site Mixed Concrete
TQ 7
Calculate the cost of mixing a m3 of Grade 15 concrete on site using the following information ;
To produce 1m3 of mixed Grade 15 concrete requires ; 250Kg of cement at £80 per tonne
600Kg of sand at £10 per tonne 1200Kg of aggregate at £9 per tonne Waste say 5%
Concrete mixer all-in rate £2-50 per hour, output 2m3 per hour Labour rate £7.20 per hour
Labour out put 0.5m3 per hour Ready-Mixed Concrete
TQ 8
Calculate the cost per m3 for laying plain concrete 20N/mm2 in foundations over 300mm thick laid against faces of excavation.
Waste say 5%
Labour output 1.00 hours/m3 Labour rate £7.20 per hour
SAQ 4
What will happen to the labour output if the concrete is laid in foundations 150mm thick? Reinforcement is measured separately in bills of quantities. Would you expect the unit rate for laying reinforced concrete (excluding the cost of reinforcement) to differ from the unit rate for plain (unreinforced) concrete for similar items of work and if so why?
9.2 Reinforcement
Reinforcement may be bar type or mesh/fabric
Waste
Bars are usually delivered to site already cut and bent, if this is the case then allow 1% for loss and damage.
If straight bars are to be cut and bent on site allow 5% for waste.
On complex reinforced concrete work steel fixers are usually paid a craft operatives rate. When laying straight bars or mesh an enhanced labourers rate is usually paid.
Mesh reinforcement is sheet material therefore allowances have to made for general waste say 2.5% plus an additional allowance for laps. The percentage to allow for laps will depend on the lap specified e.g. 150mm side and end laps.
TQs 9-10
Sheets of mesh are approximately 4.80m x 2.40m if they are to be laid with 150mm side and end laps what % must be allowed for loss in cover due to the laps ?
Mesh reinforcement Ref. A193 in beds laid with 200mm side and end laps. Calculate the rate per m2.
Mesh costs £14-00 per sheet
Labour 0.05 hours / m2 at £7.20 / hour
Allow say 20p / m2 for spacers and tying wire
9.3 Guide to Using this Student Learning Pack
Throughout this and the series of learning packs you will find, extensive notes on the various aspects of work you will be measuring followed by a series of three tasks, These tasks are
49 designed to increasingly develop your skills in the aspect of measurement covered by the learning pack, and will include, one basic task, which requires you to copy down a worked example, using the correct measurement layouts. The second task and third tasks form the second section of the class, where the class develops into a tutorial based
9.4 Concrete Works
As with groundwork, before looking at the calculation of unit rates we must understand that our final unit rate will be influenced by several variables.
Task One
In the box below, describe how you think the following factors would impact on cost.
When considering concrete there are two main methods of producing concrete: 1. Site mixed concrete
2. Ready mixed concrete
In addition to the method of concrete production when costing concrete work we must also consider concrete accessories including:
1. Formwork 2. Reinforcement
3. Operatives working with concrete usually receive additional payments for skill and responsibility
4. Items of plant concerned with concrete mixing and placing are usually measured separately.
9.4.1 Site Mixed Concrete
1. Ready mixed or site mixed concrete
2. Whether the concrete is reinforced or un-reinforced 3. Surcharges for part-loads
4. Location of site in reference to mixing plant 5. Type and size of mixing plant
6. Method of transportation, hoisting, placing and compacting mixed concrete
Calculate the cost of mixing one m3 of grade 15 concrete on site using the following information:
The production of 1m3 of grade 15 concrete requires: • 250kg of cement at £92.70 / tonne
• 600Kg of sand at £17.25 / tonne • 1200kg of aggregate at £18.02 / Tonne • Waste allowance say 7.5%
In addition allow for:
• concrete mixer @ all – in rate of £3.00 / hr • Labour rate @ £8.68 / hr
9.4.2 Ready Mixed Concrete
Calculate the cost per m3 for laying plain concrete 20N/mm2 in foundations over 300mm thick laid on or against earth or unbinded hardcore.
• Ready mixed concrete say £80.59 / m3 • Waste say 5%
• Labour output = 1.00hrs / m3 • Labour rate £8.68 / hr
Questions:
1. How would the labour output be affected if the concrete is laid in foundations 150mm thick?
2. What would be the financial impact? (If any)
9.5 Concrete Reinforcement
Reinforcement is measured separately in bill of quantities. Would you expect the unit rate for laying reinforced concrete (excluding the cost of reinforcement) to differ from the unit rate for plain (unreinforced) concrete for similar items of work, if so why
Reinforcement maybe either bar reinforcement or mesh / fabric reinforcement. Waste
Bars are usually delivered to site already cut and bent, if this is the case then allow 1% for loss and damage.
If straight bars are to be cut and bent on site allow 5% waste
On complex reinforced concrete work steel fixers are usually paid a craft operatives rate. When laying straight bars or mesh an enhanced rate is usually paid.
51 Mesh reinforcement is sheet material therefore allowances have to be made for general waste, say 2.5% plus an additional allowance for laps. The percentage to allow for laps will depend on the lap specified e.g. 150mm side and end laps.
Qu 1.
Sheets of mesh are approximately 4.80m x 2.40m if they are to be laid with 150mm side and end laps what percentage must be allowed for loss in cover due to the laps?
Qu 2
Calculate the rate per m2 for laying mesh reinforcement Ref A193 in beds, laid with 200mm side and end laps.
Additional information
• Mesh costs £15.08 per sheet
• Labour 0.05hrs / m2 @ £8.68 / hour
• Allow say 20p / m2 for spacers and tying wire • Waste on mesh 5%
WEEK 10: BUILD-UP UNIT RATE FOR CONCRETE WORK II
9.6 Concrete Work
Explain how the following factors may affect unit rates for concrete work; • Whether ready mixed or site mixed concrete is used
• Whether concrete is reinforced • Surcharges for part loads • Location of mixing plant on site • Type and size of mixing plant
• Method of transporting, hoisting, placing and compacting mixed concrete • Cost of protecting and curing unset concrete
Operatives working with concrete receive additional payments for skill and responsibility. Items of plant should be priced separately.
Concrete is usually measured in m3
9.6.1 Site Mixed Concrete TQ 7
Calculate the cost of mixing a m3 of Grade 15 concrete on site using the following information ;
To produce 1m3 of mixed Grade 15 concrete requires ; 250Kg of cement at £80 per tonne
600Kg of sand at £10 per tonne 1200Kg of aggregate at £9 per tonne Waste say 5%
Concrete mixer all-in rate £2-50 per hour, output 2m3 per hour Labour rate £7.20 per hour
9.6.2 Ready-Mixed Concrete
TQ 8
Calculate the cost per m3 for laying plain concrete 20N/mm2 in foundations over 300mm thick laid against faces of excavation.
53 Ready mixed concrete costs £49.00/m3
Waste say 5%
Labour output 1.00 hours/m3 Labour rate £7.20 per hour SAQ 4
What will happen to the labour output if the concrete is laid in foundations 150mm thick? Reinforcement is measured separately in bills of quantities. Would you expect the unit rate for laying reinforced concrete (excluding the cost of reinforcement) to differ from the unit rate for plain (unreinforced) concrete for similar items of work and if so why?
9.7 Reinforcement
Reinforcement may be bar type or mesh/fabric
Waste
Bars are usually delivered to site already cut and bent, if this is the case then allow 1% for loss and damage.
If straight bars are to be cut and bent on site allow 5% for waste.
On complex reinforced concrete work steel fixers are usually paid a craft operatives rate. When laying straight bars or mesh an enhanced labourers rate is usually paid.
Mesh reinforcement is sheet material therefore allowances have to made for general waste say 2.5% plus an additional allowance for laps. The percentage to allow for laps will depend on the lap specified e.g. 150mm side and end laps.
TQs 9-10
Sheets of mesh are approximately 4.80m x 2.40m if they are to be laid with 150mm side and end laps what % must be allowed for loss in cover due to the laps ?
Mesh reinforcement Ref. A193 in beds laid with 200mm side and end laps. Calculate the rate per m2.
Mesh costs £14-00 per sheet
Labour 0.05 hours / m2 at £7.20 / hour
Allow say 20p / m2 for spacers and tying wire
9.8 Concrete Work Concrete
Material - cement
- sand - aggregate
plant – concrete mixer, poker, vibrator 1m3 of ………….. weight 1440
TASK
Example a tonne of cement cost N14,000, sand cost 560/m3,coarse aggregate cost 900/m3 for a mix of 1:2:4. Calculate the cost/m3
Solution
1m3 cet will cost 1.44 @ 14,000 = 20,160 2m3 of sand will cost 2 x 560/m3 = 11,120 4m3 of aggregate will cost 4 x 900/m3 = 3,600
24,880 7m3 = 24,880
1m3 will cost 24,880 = N3,554.29 7
Add 50% of void and compaction 1,777.14 5,331.44 Add 20% overhead and profit 1066.29
6,397.73
Mix shrinkage broken stone
cement sand agg cement sand agg tonnes m3 m3 tonnes m3 m3 1:1:2 0.524 0.36 0.72 0.552 0.38 0.76 1:2:4 0.304 0.42 0.84 0.32 0.44 0.88 1:3:6 0.440 0.44 0.88 0.23 0.46 0.92 (void and compaction here have been taken care of)
Plant
Cost of mixer/hr
The cost of owning and operating a 10/7 concrete mixer. Assume initial cost of N150,000, a scrap value of N10,000
Life span of 6yrs @ 2000 hrs/year Compute the cost/hr
