BIM Based Quantity Take-off, Estimating
and Scheduling
This white paper describes the basic concepts and the process of BIM based
quantity take-off, estimating and scheduling.Each software vendor have their
own terminology, but our principles should be generic. The paper also describes Tocoman’s solution for BIM based estimating and scheduling.
Basic Concepts
Building information model (BIM)
contains information about the design of a building. Such a model
consists of object types (e.g. spaces) and their properties (e.g. name,
number and area). The BIMs may
be created either by designers or
by the construction company from
the 2D drawings produced by the
designers. The latter option is typically seen as a temporary solution
while designers are adopting BIM.
Construction recipes describe a
building from the construction point
of view – as building elements and
components (or activities) required
making them (see figure 1).
Figure 1 – Construction recipe.
Building elements and components
are typically classified by system
and trade. This enables to query
the information in a flexible way,
e.g. concrete works (trade) in the
foundations (system).
Process
The properties of BIM objects cannot be used directly for cost estimating or scheduling in most cases. Foundations objects, which are
different from the design point of
view, might be grouped together
because they will be built using the
same production method. Single
space, on the other hand, could
produce quantity information for
multiple cost estimating items, like
surface materials, equipment and
furniture. Thus construction quantities need to be calculated from the
design quantities in BIM.
The quantity take-off is done by
linking the design quantities with
recipes. The result is component
quantities, which can be used e.g.
for cost estimating and scheduling
(see figure 2).
Figure 2 – Process for BIM based
cost estimating and scheduling.
The cost estimating and scheduling
happens by applying unit cost and
production rate information into the
BIM based quantities (see figure 2).
F 12 EW- 1 Wall, concrete, 300mm M2
F 12 1100 Finishing M2
F 12 2200 Concrete M3
F 12 2510 Reinforcement KG
Building
Element
Components
Construction Quantities
(component quantities)
Design Quantities
(object quantities)
Estimate
Schedule
Production
Rates
Unit
Costs
Construction
Recipes
Design
BIM
Copyright © 2010 TocoSoft Oy. All rights reserved.
Tocoman’s Solution
Tocoman has developed a suite of
applications bridging the gap between current BIM applications and
existing cost estimating and scheduling applications. The Tocoman
solution contains two applications
(see figure 3).
Figure 2 – Tocoman BIM solution.
Tocoman iLink for calculating
the quantities from various BIMs
and linking them with recipes.
Tocoman Express for integration with various estimating and
scheduling applications. The application enables to read the recipes from a cost estimating application and write BIM quantities
back into the estimate of various
scheduling applications.
Tocoman’s solution is implemented
in a way, which decouples end user’s choice of BIM application from
the choice of the cost estimating
and/or scheduling application. Any
supported BIM application can provide quantities for any estimating
and/or scheduling application.
Tocoman also uses intelligent linking technology, which minimizes
the requirements for the building
model’s content. The solution does
not require using certain BIM object
properties e.g. for identifiying wall
types.Instead the user can select,
which property he wants to use.
Tocoman’s requirements for building models, which are used for BIM
based quantity take-off, are generic
by nature.
Must be consistent
All building model contents must
be modeled as agreed between
the project team.
Must be identifiable
It must be possible to identify all
objects from the viewpoint of
quantity take-off. The exact BIM
object and property is not relevant, if it is consistently used.
Must be measurable
All building model content must
be modeled using objects, which
offer the required information for
quantity take-off. Modeling walls
e.g. using a generic mass object
is not recommended, if the BIM
application has a native wall tool.
