INTRODUCTION TO ESTIMATING

Introduction To Estimating-Free PDF

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2 CHAPTER One,The design build and construction manager general. contractor CM GC project delivery systems are gaining in 6. popularity In the design build delivery system the contrac. tor acts as both the designer and the general contractor In 55. UVKOCVG EEWTCE, the CM GC delivery system the contractor and some of the. key subcontractors are involved in the design process pro 1. viding expertise in construction methods and costs as well. as managing the construction process Integrated project 2 4 64. delivery IPD a relatively new delivery system involves 537 4. the owners designers contractor and some of the key sub 116. contractors in the design process IPD differs from the CM 241 6. GC delivery system in that the owners designers contractor 1 2 4 510. and key subcontractors share governance risk contingency. and the profit on the project All of these delivery systems 6KOG VQ QORNGVG. require the contractor to provide cost estimates for the pro FIGURE 1 1 Estimating Time versus Accuracy. posed project throughout the design process, At the conceptual stage of the project the contrac. tor prepares a cost estimate based on the project s concept Each piece of work that is to be performed by the contractor. This is known as a conceptual estimate When performing a has a distinct labor requirement that must be estimated The. conceptual estimate typically drawings are not available or items that are to be installed by others need to be defined and. they are very limited What exists is often verbal or written priced Caution needs to be exercised to ensure that there is. description of the project scope which may be accompanied agreement between the contractor and the subcontractor as. by a few sketches When preparing this type of estimate the to what they are to do and whether they are only to install or. contractor makes assumptions about virtually every aspect both supply and install the items In addition there needs to. of the project The conceptual estimate is used early in the be an agreement about who is providing support items such. design process to check to see if the owners wants are in as cranes and scaffolding The contractor is responsible for. line with their budget and is often used as a starting point to making sure that the scope of work is divided among the. begin contract negotiations contractor and subcontractors so that there are no overlaps in. During the design process the contractor prepares and the individual scope of works and that everything has been. maintains a cost estimate based on the current but incom included in someone s scope of work. plete design In addition the contractor may prepare es The detailed estimate must establish the estimated. timates that are used to select between building materials quantities and costs of the materials the time required for. and to determine whether the cost to upgrade the materials and costs of labor the equipment required and its cost the. is justified What all these estimates have in common is that items required for overhead and the cost of each item and. the design is incomplete Once the design is complete the the percentage of profit desired considering the investment. contractor can prepare a detailed estimate for the project the time to complete and the complexity of the project The. principles used to prepare the detailed estimates are covered. in Chapters 4 and 6 through 21,1 2 ESTIMATING METHODS. The required level of accuracy coupled with the amount of Assembly Estimating. information about the project that is available will dictate. the type of estimate that can be prepared These estimating In assembly estimating rather than bidding each of the in. methods require different amounts of time to complete and dividual components of the project the estimator bids the. produce different levels of accuracy for the estimate The re components in groups known as assemblies The com. lationship between the time to complete the estimate and the ponents of an assembly may be limited to a single trade. accuracy of the estimate is shown in Figure 1 1 The differ or may be installed by many different trades An example. ent estimating methods are discussed below of a simple assembly would be a residential light switch. which includes a single gang box a single pole switch. cover plate two wire nuts and an allowance of 20 feet of. Detailed Estimate NM B 12 gage wire The entire assembly would be installed. The detailed estimate includes determination of the quan by an electrician A residential electrical estimate could be. tities and costs of everything that is required to complete prepared using assemblies for the switches outlets lights. the project This includes materials labor equipment in power panels and so forth rather than determining the in. surance bonds and overhead as well as an estimate of the dividual components An example of a complex assembly. profit To perform this type of estimate the contractor must would be a metal stud gypsum board partition wall which. have a complete set of contract documents Each item of the would include bottom track metal studs top track drywall. project should be broken down into its parts and estimated screws tape joint compound insulation primer paint and. M01 PETE1165 09 SE C01 indd 2 7 20 17 4 06 PM,Introduction to Estimating 3.
other miscellaneous items needed to construct the wall This uses broad assemblies care must be exercised while prepar. assembly would be installed by multiple trades ing a square foot estimate to ensure that the projects used. Many high end estimating computer programs such as to determine the cost per square foot are similar to the pro. WinEst and Timberline allow the user to prepare detailed posed project Companies such as RSMeans publish annual. estimates by taking off assemblies For the switch assembly guides such as Square Foot Costs that contain a range of. the estimator would take off the number of switch assem unit costs for a wide variety of building types These guides. blies needed for the project and the software would add one provide a number of adjustments to compensate for varying. single gang box one single pole one cover plate two wire building components including the city where the project is. nuts and 20 feet of NM B 12 gage wire to the detailed esti located Square foot estimating is discussed in Chapter 22. mate for each switch assembly This simplifies the estimat. ing process and increases the productivity of the estimator Parametric Estimates. Assembly estimating is also useful for conceptual and. preliminary estimates By using broad assemblies an estimate Parametric estimates use equations that express the statistical. can be prepared quickly for an entire building For example relationship between building parameters and the cost of the. an estimate for a warehouse can be prepared by using assem building The building parameters used in the equation may. bles for the spot footings the continuous footings the founda include the gross square footage number of floors length of. tion wall the floor slab slab reinforcement granular base perimeter percentage of the building that is common space. vapor barrier and fine grading the exterior wall personnel and so forth For an equation to be usable the parameters. doors overhead doors joist and deck roof structure including used in the equation must be parameters that can be deter. supports roof insulation roofing wall cap skylights bath mined early in the design process otherwise the equation is. rooms fire sprinklers heating lighting and power distribu useless Parametric estimates are similar to square foot esti. tion This type of estimate can be prepared in hours instead mates however the equations used in parametric estimates. of spending days preparing a detail estimate The trade off is are more complex and may use log functions ratios of pa. that this type of estimate has many broad assumptions and is rameters and multiplication of parameters Parametric esti. less accurate This type of assembly estimating is good for mating is useful for preparing conceptual estimates based on. estimates prepared with limited drawings to compare design assumptions of key building parameters or estimates based. approaches and as a check of a detailed estimate If the as upon early designs As with square foot estimates and as. sembly price comes from previously completed projects it is sembly estimates that use broad assemblies care must be. assumed that this project is identical to the completed proj taken to ensure that the proposed project is similar to the. ects This assumption is clearly not valid in the construction projects from which the equation has been derived. of buildings Weather conditions building materials and sys. tems as well as design and construction team members change Model Estimating. from project to project all adding to the uniqueness of every Model estimating uses computer models to prepare an esti. project Skill and judgment must be used while preparing mate based on a number of questions answered by the esti. this type of assembly estimate to ensure that proper adjust mator Model estimating is similar to assembly estimating. ments are made by taking into account the varying conditions but it requires less input from the estimator For example an. of each project Companies such as RSMeans publish annual estimate may be prepared for a warehouse by answering the. guides such as Square Foot Costs that contain pricing for following questions. assemblies Assembly estimating is discussed in Chapter 22. dd What is the length of the building, How many bays are along the length of the building. Square Foot Estimates dd,dd What is the width of the building. Square foot estimates are prepared by multiplying the dd How many bays are along the width of the building. square footage of a building by a cost per square foot and. dd What is the wall height above the grade, then adjusting the price to compensate for differences in. the building heights length of the building perimeters and dd What is the depth from the grade to the top of the. other building components In some cases a unit other than footing. square footage is used to measure the size of the building dd What is the floor thickness. For example the size of a parking garage may be measured dd Do you want wire mesh in the slab. by the number of parking stalls in the garage The informa dd How many roof hatches do you want. tion required to produce a square foot estimate is much less dd How many personnel doors do you want. than is needed to prepare a detailed estimate For example. dd How many and what size of overhead doors do you want. a schematic set of design drawings a single line floor plan. and key elevations would have the dimensions that are nec dd How many and what size of skylights do you want. essary to prepare a square foot estimate Square foot esti dd Do you want fire sprinklers. mates are helpful to check whether the project as designed dd What bathroom facilities do you want separate male. is within the owner s budget Like an assembly estimate that and female unisex or none. M01 PETE1165 09 SE C01 indd 3 7 20 17 4 06 PM,4 CHAPTER One. On the basis of the answers to these questions the order the materials required to build the framing for a home. model prepares a preliminary estimate for the project Logic this knowledge is needed to do the best job possible at the. is built into the model such that the model selects the neces most competitive cost Others involved include the project. sary components for the estimate based upon the answers designer drafters engineers contractors subcontractors. to the questions For example the size of the spot footings material suppliers and material representatives In the fol. in the center of the building that support the roof and their lowing sections a few of the estimating opportunities are. costs are selected based on the area of the roof the footings described. support which is equal to the width of a bay multiplied by. the length of a bay The length and width of the bays are Architectural Offices The architectural office will re. calculated from the first four questions A simple model es quire estimates at three design stages preliminary rough. timate Warehouse xls for a warehouse is provided on the square foot or project comparison costs cost evaluation. companion website This model makes many assumptions during drawing preparation usually more accurate square. as to the design of the warehouse such as assuming the ex foot or assembly costs and a final estimate usually based. terior wall is constructed of concrete masonry units CMU on material and installation costs to be as accurate as pos. The model ignores the site and excavation cost which needs sible For projects built using the design build or CM GC. to be added to the estimate from the model to get a complete delivery systems the preliminary estimate is often used dur. estimate ing negotiation with the general contractor Once the general. Estimating models may be complex and may prepare a contractor is hired the general contractor s estimator will. detailed estimate for the entire project or the models may be prepare the remaining estimates. simple and prepare a preliminary estimate for part of a proj In large offices the estimating may be done by an es. ect As with square foot estimates assembly estimates that timator hired primarily to do all the required estimating. use broad assemblies and parametric estimates care must In many offices the esti. competitive cost estimate for the project The competition in construction bidding is intense with multiple firms vying for a single project To stay in business a contractor must be the lowest qualified bidder on a certain number of projects while maintaining an acceptable profit margin This profit margin must provide the general contractor an acceptable rate of return and compensation

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