Exchange Cost Model - Preconstruction Estimate

Project Stage

Stage	Name	Valid
0	Portfolio requirements
1	Conception of need
2	Outline feasibility
3	Substantive feasibility
4	Outline conceptual design
5	Full conceptual design
6	Coordinated design and procurement
7	Production information
8	Construction
9	Operation and maintenance
10	Disposal

Overview

Please ensure that you have read the process mapping document 'pm_cost_modelling' before proceeding with this exchange requirement.

The scope of this exchange requirement is cost modelling stage 4 - Detailed Estimate.
That is, the cost model is based on the elements that are expected to be incorporated within the construction of the building and ancillary services associated with that construction. The unit cost basis of each type of element will be defined by a set of rules that are typically provided in a standard method of measurement whose use has been agreed for the project.

This exchange requirement assumes that a full conceptual building model has been defined and that relevant information can be obtained from shape representations that it contains. The full conceptual model provides sufficient detail to enable the extraction of information to enable the pre-construction estimate to be derived. For instance, in defining a system group for a heating system, the group should contain all of the heat emitters within the system as the unit price may be per heat emitter.

Note that the general principles of defining a pre-construction estimate are similar to those for defining an approximate estimate. The difference between the exchange requirements is that the cost value information associated within a pre-construction estimate is expected to be better defined than for an approximate estimate so that it can be used as an indicator of expected construction cost.

During this stage the information available is limited to the following requirements:

• a building is defined in terms of its shape and the number of building storeys that it contains (or is expected to contain)
• the spatial layout and configuration of elements that define the construction will be conceptually established
• the services and structure of the building will be conceptually established
• it should be located in a particular place and on a particular site
• there are factors that may be applied to affect the 'approximate estimate' cost; these may include (but are not limited to)
  • factor for height working
  • factor for working in hazardous conditions or in hazardous places
  • general risk or predictability factors
• cost information from sources of information that suit the circumstances of the building are available (where such cost information may be defined from similar projects or by reference to preliminary cost information provided by suppliers/manufacturers)

Particular information that is required to determine a 'pre-construction estimate' cost includes:

• the name of the project (for identification purposes) and the units generally used throughout the project;
• the current stage of the project; whilst this is generally optional, it should be mandatory for this exchange requirement
• the location and expected area of a site on which a building is to be located
• the building or buildings for which the cost is required (at least one building must be specified)
• the building storeys within the building together with their area
• the conceptual configuration of building elements
• the conceptual configuration of structural elements
• the conceptual configuration of distribution systems elements and their separation into distinct systems
• values for factors that may affect the cost
• classification of objects for collection into groups and assemblies for costing purposes

Note that specific pre-construction estimates may be required for particular element groupings either as sections of a whole estimate or as separate estimates. For example, the distribution elements forming the building services system may be within a different pre-construction estimate to the building and structural elements.

Information Requirements

Context	Information Needed	MAN	REC	OPT	Actor Supplying	Functional Part
Precursor	The provisions of the exchange requirement er_exchange_building_model (full_concept) must be satisfied				Building Design	er_exchange_building_model (full_concept)
Cost Groups (Grouping)	Elements that are to be costed as count group elements need to be collected together as groups.				Building Design OR Cost Modelling	fp_assigns_to_group
Cost Groups (Quantities)	For each cost group that is identified, the total value of the reference quantity that is to be used for costing within the cost item (see below) needs to be determined.				Cost Modelling	fp_define_quantity
Cost Groups (Cost)	Unit cost information should be assigned to the cost groups to enable total cost to be determined.				Cost Modelling	fp_associate_cost
Cost Impact Factors	Various factors may be provided for the element groups to identify their expected impact on the approximate estimate cost in comparison with reference costs.				Building Design OR Cost Modelling	fp_define_quantity (count)
Cost Item (Measured)	A cost item should be defined for each element group. The cost item brings together the quantity of the group, the unit cost for the group and all the relevant cost factors and provides a result that is an overall cost value.				Cost Modelling	fp_model_cost_item
Cost Item (Ancillary)	Cost items that deal with specifically assigned costs such as preliminaries, external works, contingencies etc. should be individually identified and assigned to the 'head' object in the model to be used for costing. Typically, this is expected to be the project.				Cost Modelling	fp_model_cost_item
Cost Schedule	Costs and quantities may be collected together into cost items and ultimately into a cost schedule for further work.				Cost Modelling	fp_model_cost_schedule

Results

Result type (FP/ ER/ Document/ PSet/ Specification etc.)	Information Provided	MAN	REC	OPT	Actor Receiving	Result Identifier
Model	Model of proposed building with elements collected together into groups so that they can have a total unit measurement or so that typical items can be counted.				Building Design Client
Schedule	A schedule of costs with cost items broken down into line items, cost groups and cost parts.				Building Design Client