Estimation and Specifications PDF

Estimation and specifications Fourth lecture By Dr. Taghreed Khaleefa EXAMPLE 2 Prepare a Rough-cost Estimate of a residential building project with a total plinth area of all building of 1500 sq.m. given that: plinth Area Rate = 14915/ sq. ft. Extra for special architectural treatment = 1.5...

Estimation and specifications Fourth lecture By Dr. Taghreed Khaleefa EXAMPLE 2 Prepare a Rough-cost Estimate of a residential building project with a total plinth area of all building of 1500 sq.m. given that: plinth Area Rate = 14915/ sq. ft. Extra for special architectural treatment = 1.5 % of the building cost. Extra for water supply and sanitary installations = 5 % of the building cost. Extra for internal installations = 14 % of the building cost Extra for Electric & gas services = 16 % of building cost Contingencies 3 % overall Supervision charges = 8 % overall Design charges = 2 % overall DETAILED ESTIMATE Detailed estimates are prepared by carefully and separately calculating in detail the costs of various items of the work that constitute the whole project from the detailed working drawings after the design has been finalized. The mistakes, if any, in the rough cost estimate are eliminated in the detailed estimate. Detailed estimates are submitted to the competent authorities for obtaining technical sanction. The whole project is sub-divided into different items of work or activities. The quantity for each item is then calculated separately from the drawings as accurately as possible. The procedure is known as "taking out of quantities". The quantities for each item may be estimated and shown in the pattern which is called "Bill of quantities." The unit, in which each item of the wok is to be calculated, should be according to the prevailing practice as followed in various departments of the country. Each item of the work is then multiplied by its estimated current rate calculated by a fixed procedure to find out cost of the item. At the end, a total of all items of the work are made to get the total estimated cost.  The rates are usually as per the Schedule of Rates for the locality plus a premium to allow for rising labor and material rates over and above the schedule of rates. A percentage, usually 5% is also provided on the total estimated cost for the work to allow for the possible contingencies due to unforeseen items or expenditure or other causes, besides 2% establishment charges. -Besides drawings and details of measurements and calculation of quantities (Bill of Quantities), the following documents are also usually submitted with the detailed estimate for obtaining Technical Sanction: 1. A report explaining history, necessity, scope and main features of the project, its design, and estimate, etc. 2. Specifications lying down the nature and class of work and material to be used in various parts of the work. 3. The abstract of cost (priced Bill of Quantities) showing the total quantities under each sub-head, rate per unit of measurement, and cost. 4. Calculation sheets show calculations for important parts of the structure. In fact, estimating the art and skill lies only in the computation of details without any omissions, of all parts of the building or work. CLASSIFICATION DEPENDING UPON PURPOSE OF DETAILED ESTIMATE 1- CONTRACTOR ESTIMATE It is made by the contractor for determining the price or prices to be bid. It is usually a carefully prepared detailed estimate. 2- ENGINEER’S ESTIMATE This type of estimate is made by the Engineer (Consultant) usually for the purposes of financing the work and for checking bids and running bills submitted by contractors. 3- PROGRESS ESTIMATES These are made by the Engineer at regular intervals for the completed parts of the project during the progress of the work for determining the amounts of partial payments to be made to the contractor. On large contracts, such estimates are commonly made each month and, hence, are frequently called monthly estimates. METHODS OF DETAILED ESTIMATE The dimensions, length, breadth and height or depth are to be taken out from the working drawings (plan, elevation and section). Junctions of walls, corners and the meeting points of walls require special attention. For symmetrical footings, which is the usual case, earthwork in excavation in foundations, foundation concrete, brickwork in foundation and plinth, and brickwork in superstructure may be estimated by either of the two methods: (1) SEPARATE OR INDIVIDUAL WALL METHOD (2) CENTER LINE METHOD SEPARATE OR INDIVIDUAL WALLS METHOD The walls running in one direction are termed as "long walls” and the walls running in the transverse direction, as “short walls", without keeping in mind which wall is lesser in length and which wall is greater in length. Lengths of long walls are measured or found "Out-to out" and those of short walls as "In-to-in". Different quantities are calculated by multiplying the length by the breadth and the height of the wall. The same rule applies to the excavation in foundation, to concrete bed in foundation, D.P.C., masonry in foundation and super structure etc. SEPARATE OR INDIVIDUAL WALLS METHOD For symmetrical footing on either side, the center line remains same for super structure, foundation and plinth. So, the simple method is to find out the center-to-center lengths of long walls and short walls from the plan. Long wall length out-to-out = Center to center length + half breadth on one Side + half breadth on other side. = Center to center length + one breadth Short wall length in-to-in = Center to Center length - one breadth. This method can also be worked out in a quicker way., as follows: For long walls First of all, find the length of the foundation trench of the long wall “out-to-out” in the same manner as explained. The length of the foundation concrete is the same. For the length of the first footing or first step of the brick wall, subtract two offsets in foundation concrete from the length of the trench or concrete. For the second footing subtract from the length of the 1st footing two offsets, for 3rd footing subtract from the length of the 2nd footing 2 offsets and in this way deal with the long walls up to the super-structure. For short walls Follow the same method but instead of subtracting add two offsets to get the corresponding lengths in-to-in.