THE COST ESTIMATOR
The cost estimator can be seen as a complement to the quantity surveyor. The cost estimator relates prices and costs to resources and items measured by the quantity surveyor. Generally, quantity surveyors focus more on the formal market and less so on the domestic market. The quantity surveyor deals more with ‘items’ as opposed to ‘resources’, for example:
- a quantity surveyor measures a given structure in square metres of brickwork
- a cost estimator measures a given structure at resource level (bricks, sand, cement, etc) and prices them.
Reports generated by cost estimators can be likened to Bills of Quantities or Bill of Material, although they go one step further by applying an estimated price or cost to that specific item. The independent cost estimator has, in recent years, become an acceptable means to establishing costs of domestic and commercial projects.
Like the quantity surveyor, the cost estimator requires a set of working drawings to measure off, and for a single wall will quote numbers of bricks, cement, sand, stone and other related resources and price them. This method of pricing a structure can be considered as one of the more accurate, and with the assistance of computer technology, can produce information quickly, consistently and accurately.
A badly designed building will generally cost more money than initially envisaged. If design elements are not thought through carefully during the design process, the building will almost certainly be faced with unforeseen problems. These problems cost money. Square metre building rates are the biggest myth in the building industry. No two structures can possibly be identical; it is therefore obvious that a general square metre building rate cannot be assumed. There are examples of homes equivalent in size that vary in cost by two hundred percent. There are four major areas in construction that one must take into account when considering building costs. These are listed below.
Various site conditions may affect the cost of building. The first consideration is always the slope or gradient of the site. Visually, a site always seems more level than it actually is. A variance of only one metre across a two hundred square metre house (assuming a length of 20 metres) would increase the brick quantity by approximately ten thousand bricks. If one considers the price of the bricks, mortar and labour, this could amount to nearly R7,000-00. In terms of building regulations, the height of the foundation brickwork may also require that the thickness of the wall be increased; amounting to more cost. Sites with very steep gradients usually require retaining walls, which are extremely expensive, particularly when structural reinforced concrete is required. Retaining walls also require vertical damp-proofing and agricultural drains.
Natural obstructions such as trees and rocks cost money in terms of removal or incorporating them into the design. The roots of a large tree may require excavation of up to three cubic metres. Rocks are usually a lot bigger than they seem on the surface.
The perception about building a house on a rock does not usually work in practice. If a structure is bridged across any rock, an engineer will be required to design specific foundations.
Unexpected obstructions can also cost money if not identified during design. These obstructions would include electrical poles, fire hydrants, storm water drains and trees planted on the pavement. An electrical pole blocking a proposed driveway could be a costly exercise to remedy.
As mentioned above, the gradient of a building site will affect the cost of the foundations. There are however, other factors that may influence costs. Poor soil conditions may require engineered foundations. A 250 square metre home built in Gauteng in 1997 incurred an additional cost of R70,000-00 due to soil conditions and the necessity to use concrete piling. It is good practice to have the to have the soil conditions tested by a geotechnical engineer before design and, if possible, before even buying the stand. Complicated structures with split-levels or columns will always increase the foundation cost, even if built on a level site.
These elements are contained in the structure between the foundation and roof, the major element being the walls. There are many elements that will influence the cost of the superstructure. Unlike the foundations there are doors, windows and types of materials utilised that present numerous variables when considering costs. Presented below are a number of costing models to demonstrate how costs vary depending on the elements used in construction.
SINGLE STOREY VS DOUBLE STOREY
Costing models show the difference in cost for a single storey dwelling and a double storey dwelling. Basic models show that a double storey structure costs 4% more than a single storey structure. In practice, very few double storey dwellings are built with equal floor area on the ground and first floor. The average is closer to 60% ground floor area and 40% first floor area. In this case, a double storey dwelling would cost less than 4% more. When the excluded common elements are included, the percentage difference drops even more. It is therefore safe to assume that the difference in cost between a double storey and single storey is negligible.
TYPES OF WALLS AND RELATED COSTS
Depending on slopes and other issues thicker walls may have to be built. The thicker the wall the more it will cost.
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