Building cost index and an approach of proposal for constructing a computer aided concrete framed housing cost index

The aim of this study is; to introduce the indexes which are the cost estimating and research elements in building construction projects, to explain the use of them, to evaluate the different kinds of indexes and their methods at home and abroad, and in the result of this, to construct a concrete fra med housing cost index for our country. For constructing a building cost index, the methods of calculating and estimating costs must be known. They are; The unit method of approximate estimating seeks to allo cate a cost to each accommodition unit of the particular building, be it persons, seats, beds, car spaces or whatever. The total estimated cost of proposed building is then deter mined multiplying the total number of unit accommodated in the building by the unit rate. In the floor area or cube method, the unit ma or m3 costs -VII-are multuplied by the floor area or the cubic content of the building. Building cost are calculated as multiplying the building functional elements quantity by the unit price of the building functional elements. Also, building costs are calculated as multiplying the construction works quantity by the unit price of the construction works. 2) Main Conceptions : Indexes measure the changes in prices, quantities and values according to the time and location. The qualifications of indexes are : 1) An index is actually a percent 2) Each index has a base period. The base number of all indexes equals to 100. 3) If the base is 100, the percent change from the base period to current month or year can be easily determined. There are a different kinds of indexes and they can be constructed by different methots. The different kinds of indexes are : -VIII-2.1) Simple Indices : Bilding cost indices are calculated according to one variable. Different kinds of simple indices are price relatives, quantity relatives and value relatives. 2.2.) Compile Indices : Compile indices are calculated according to more than one variable. The different kinds of compile indices are : - Simple Aggregate Method - Average of relatives Method - Weighted Aggregate Method - Index With A Fixed Base - Chain Index - Special Purpose Index (Location index; consumer price index) There are problems when the indexes are construe ted. They are average and weighting problems. It is diffucult to decide which average must be used in the index calculations. It is also diffucult to decide which weightings must be used in the index calculations, base year weightings or current year weightings. Calculation of the index numbers is easy when base year weightings are used. This method is called Laspeyres -IX-index and it is used more. Calculation of the index numbers with current year weightings is called Paasche index and the calculation of the index numbers with this method is more difficult. Another problems when indexes are calculated are base year problems and problems of selection of items. Main problem is; if the base year will change. The selection of items is a problem of compile indexes. Because it is diffucult to decide which items can be put into the index calculation. Calculation of indexes wiht more items is better but the num ber of yhe items must be determined. 3) Building Cost Indexes : Construction sector is one of the most important sector in our development. To examine the changes in the prices of production and materials is useful. It can be made by indexes. Indexes are organized once a year, sometimes they are orga nized four times a year. Indexed are used to indicate the changes in the building cost ipdating the cost plans of buildings which were const ructed, in private researches, in extropolation of existing trends, in calculation of price fluctuations, in identification of changes in cost relationships, in assessment of market conditions. The building cost indexes are constructed by pricing the same building, pricing the measurable quatities of consruction -X-works and changes in the input prices of constructions. The different kinds of building construction cost indexes are : - Input price indexes - Construction work, work category, functional element indexes - Building cost indexes - Tender price indexes I PRODUCTIVITY - CONSTRUCTION WORK INDEX - WORK CATEGORY INDEX - FUNCTIONAL ELEMENT INDEX BUILDING COST INDEX PROFIT MARGIN TENDER PRICE INDEX -XI-4) The Studies On The Building Cost Indexed At Home And Abroad The studies on the building cost indexes are made by Istanbul Chamber of Commerce. State Institue of Statistical Prime Ministry Republic of Turkey, Turkish Scientific And Tecnical Research Council, inşaat magazine and our universty in our country. The studies on building cost indexes in Sweden, Canada, Finland, England and United Nations are examined and in the result if this, for constructing a concrete framed housing cost index, a method is proposed. 5) An Approach of Proposal For Constructing A Computer Aided Concrete Framed Housing Cost Index For constructing this index, 27 bills of quantities of concrete framed housing projects which have different number of storeys are obtained. Every bills of work item quantities are priced with 1981 unit prices of Ministry of Public Works And Housing which is the base year. As state Institute Of Statistical Prime Ministry Republic of Turkey uses 1981 as a base year, 1981 is also selected for this study. After pricing the bills of work item quantities fo project the values converted to a percentage of the total. These are the weights of construction works. -XII-Construction works are allocated into work categories according to groups of unit price of Ministry of Public Works And Housing and weights are organized according to work groups. Weights are averaged for each type of work category to obtain a weight of work category. Then work category indices are calculated for each year. Work category index numbers are multiplied by the weight of each work category and for each year an average cost index value is obtained. With this study, concrete framed housing cost increases are determined and with trend analyse the future costs of concrete framed housing can be approximately calculated. Cost indices are used for estimating the future costs. This is the most use of them.