Using BIM quantification tools
This approach associates with the use of specialised Quantity TakeOff (QTO) software, e.g. Autodesk QTO, Vico Office, and Exactal CostX, that transfer the BIM models and their embedded information from BIM design tools into their system. Similar to the previous approach, these tools can support both the automated extraction and manual take-off features. They can generate visual take off diagrams while providing visualisation of models whereby the quantity surveyor can mark off the building components using colours enabling to cross check the take-off lists and to see which components have or have not been included in the estimate (Eastman et al., 2011).
The items and assemblies are inter-linked and the quantity surveyors are able to insert additional annotations to the model to clarify the conditions whenever necessary during the quantification process. The approach provides an advantage for the quantity surveyors to work using familiar QTO software without having to possess an indepth understanding of BIM design platforms. According to our study, this is also the most likely approach that will be adopted by QS in UK.
Furthermore, BIM is argued to be adding new complications to the cost estimating processes for QS; including
3D model management, navigation and model export, identification and linking building components to estimating data, rapid responses to changes and design alternatives along design development stages.
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Automatic quantification and understanding of costing software
The role of the quantity surveyor will adapt within the BIM environment. The largest difference will be the volume of detailed measurement by hand that is no longer required and will be replaced by automatic quantity take off. There are a number of software solutions that can be used for this; however, in this project it was considered shrewd to opt for software that not only had automatic take off, but also the ability to produce and link to costing documents within the same application.
The chosen costing software groups quantities by the object’s name and type. For example, if two doors or two lengths of wall are named exactly the same then the quantities or dimensions of those objects will be grouped in the same ‘dimension group’. This is why it is so important for robust naming protocols to be agreed, so that each object should be in its correct dimension group. Furthermore, the required parameters of each object should be included within that object, as agreed within the execution plan, so that, for example, each wall will have the wall area identifiable and not just the length of wall. This is also a key point for the quality assurance check: a quick review of the dimensions will show up any obvious errors.
Another important factor is to be able to create a costing document within the software and import the quantities from the model and the rates from a database. In order to do this a library of cost items was created along with associated rates so that a priced document could be built. This links in with the cost detail and LODs agreed on in the execution plan. The costing software has provision to further interrogate (‘drill down’) levels of a cost plan, revealing increasing detail. What this creates is an elemental breakdown of items with detailed measurement, rates and costs in a level beneath that breakdown. This also allows extra detail to be included that was not included within NRM formal cost plan 2, but was modelled for detailed requirements.
Once the cost plans have been established they allow for a quick update to the project costs, subject to a thorough quality assurance check. Quantities from the model and rates from the rate library are ‘live linked’ to the costing document; as such, whenever the drawings are revised, so long as the naming protocol has been followed, the cost will automatically update. However, it should be noted that, as this was a tender document, and was issued with all zero rate values, actual tender figures are added back once they have been received as part of the return.