Transcript Document

Introduction to
Construction Estimating
The use of computers on estimating and bidding
Introduction to Construction Estimating
Marcos Bastian
In the business of design and construction,
profitability is based on accurate and complete
cost estimation
“Cost estimating is employed as one of the main tools of
successful cost management. Once an initial budget has
been established, it is important to test its assumptions by
employing a series of increasingly precise cost estimating
techniques that coincide with further development of
design and construction details.”
National Institute of Building Sciences. (http://www.wbdg.org)
Introduction to Construction Estimating
Marcos Bastian
Estimating requires a talent to
predict or avoid the
unexpected.
A good estimator understands
construction materials,
methods and systems, as well
as the labor and equipment
required to complete all tasks
in their correct sequence, on
time and on budget.
Introduction to Construction Estimating
Marcos Bastian
The structure of an estimate
Estimates are typically organized in a work-breakdown structure (WBS).
A work breakdown structure (WBS) is a hierarchical system used to define and
group discrete tasks or elements, covering the work scope of the project.
100% Rule:
A WBS must include 100% of the work defined by the project scope and
capture all deliverables – internal, external and interim.
The rule applies at all levels within the hierarchy: the sum of the work at the
“child” level must equal 100% of the work represented by the “parent” and the
WBS cannot include more than 100% of the project’s scope.
The Construction Specification Institute’s (CSI) has created the "de facto"
standard for the Construction Industry (known as MasterFormat).
The CIS has also created the UniFormat, a new design-based structure
focusing on early stages of a project planning.
Introduction to Construction Estimating
Marcos Bastian
MasterFormat
(also referred as the CSI Format)
- Created by the Construction Specification Institute CSI, 1961
- Used by nearly every business, in specifications and pricing
- Focus on materials and methods (construction approach)
- Contains 49 divisions (as of 2008)
- Better suited for pricing & construction
Example:
DIVISION 05 – METALS
05 00 00
METALS
05 01 00
Maintenance of Metals
05 10 00
STRUCTURAL METAL FRAMING
05 12 00
Structural Steel Framing
For more information
http://www.csinet.org/s_csi/sec.asp?CID=1377&DID=11339
Introduction to Construction Estimating
Marcos Bastian
Uniformat
- First introduced in 1998, Guiding Principles established in 2007
- Functional elements of a project (design approach)
- Organized in nine categories
- Better for conceptual understanding of a building
- Provides a way to compare major components of different projects
A
B
C
D
E
F
Substructure
Shell
Interiors
Services
Equipment & Furnishings
Special Construction
& Demolition
G Building Sitework
Z General
Introduction to Construction Estimating
Marcos Bastian
Uniformat
(cont.)
UniFormat is an arrangement of construction information based on physical parts of a facility called
systems and assemblies. These systems and assemblies are characterized by their function without
identifying the products that compose them. Systems and assemblies render a view of a constructed
facility different from the view rendered by a breakdown of building materials, products, and activities
such as MasterFormat. UniFormat is intended to complement MasterFormat.
CSI – (www.csinet.org)
The purpose of UniFormat is to:
- achieve consistency in economic evaluation of projects
- enhance reporting of design program information; and
- promote consistency in filing information for facilities management, drawing
details and construction market data.
For more information:
http://www.csinet.org/s_csi/sec.asp?TRACKID=&CID=1379&DID=11342
Introduction to Construction Estimating
Marcos Bastian
Types of estimates
ROM (Rough Order of Magnitude) Estimates
- Used in strategic or preliminary planning, proforma analyses
- Used to assist go/no-go decisions
- Low level of accuracy, general in scope
Detailed Costs Estimates
- Increased accuracy
- Used to define tasks and schedules
- Based on assemblies & systems
National Institute of Building Sciences Classification
- Preliminary estimates
- Intermediate estimates
- Final estimates
Introduction to Construction Estimating
Marcos Bastian
Preliminary estimates (20% - 25% margin of error)
- Early planning stages
- Systems-based WBS (eg. Uniformat)
- May also be based on other metrics
cost/parking space, cost/hospital bed
may be referred to as “guesstimates" of “ballpark numbers”
- Feasibility focus
- Large contingency values (low confidence)
Intermediate estimates (10% - 15% margin of error)
-
SDs & DDs
Focus on systems, alternatives & comparisons
Begin migration from ‘systems' to ‘materials & labor‘
Frequent updates, refinement with design
Gradual reduction of contingency
Final estimates (2% - 3% margin of error)
-
For bidding, construction & control
Multiple bidders, comparisons by major tasks/systems
Very detailed take-offs and specifications
Contingency reduced or eliminated
Once construction is completed, data can be used for future projects
Introduction to Construction Estimating
Marcos Bastian
Time and Accuracy Relationship in Estimates
Data based on John D. Bledsoe’s - Concept to Bid…Successful Estimating Methods
Introduction to Construction Estimating
Marcos Bastian
Major elements of an estimate
-Direct costs (may be grouped in systems or assemblies)
Materials
Labor
Equipment
- Indirect costs
Taxes
Insurance
Bonds
Operating costs
- Overhead, profit, other markups
- Contingency
- Time & escalation
- Phasing & mobilization costs
- Geographic index
Introduction to Construction Estimating
Marcos Bastian
The use of computers
“Years ago we created estimates using a calculator and a yellow tablet.You sat down, counted the parts
and pieces, added them up and that was the cost for a job.”
Mac Crawford, Crawford Construction. Lexington KY
- The practice of cost estimating precedes the use of computers
- Because of this legacy, many of its original methods persisted even after
computers were introduced
- Computers are today an intrinsic part of the business, used not only in actual
calculations, but also in the storage, organization, retrieval and reporting of
data, as well as a collaboration tool between different disciplines
- As a result, estimates are now much more accurate and detailed, and the
industry’s requirements have also increased accordingly
- There are thousands of software packages on the market, ranging from
simple “excel-like” spreadsheet programs to complete corporate solutions.
Pricing also varies widely with the complexity of the software
- One of the greatest challenges is to migrate ‘field knowledge’ to the
computer. Experienced field professionals often rely on others to operate
estimating software.
Introduction to Construction Estimating
Marcos Bastian
Common estimating options
- Spreadsheets and manual takeoffs
“Excel is still the king”
- CAD and digital takeoff systems
- Online databases and services
BNI
R.S. Means
- Corporate software (modular systems)
- Building Information Modeling (BIM)
Introduction to Construction Estimating
Marcos Bastian
Estimating Software -
Desirable Features
- Must be able to handle multiple projects (!)
- Hierarchical/WBS organization
- Detailed view per item
- Take-off system (screen-based or digitizing devices)
- Handling of complex systems and assemblies
- Items linked to cost of products & resources
(labor, materials, subcontractors, etc)
- Automated calculations
- Indirect costs, markup & overhead
Introduction to Construction Estimating
Marcos Bastian
Estimating Software -
Desirable Features (cont.)
- Purchasing & contracting
- Cost comparisons (between different systems &/or providers)
- Closeout capabilities, (Manual overrides & customization)
- Reporting (links to scheduling)
- Import/export capability
- Database storage vs. flat-file structure
- Online updates and subscription
(cost data, specs.)
- Archival, backup & historic data
- * GOOD SUPPORT & DOCUMENTATION
Introduction to Construction Estimating
Marcos Bastian
To Be or not to Be(IM)
BIM Advantages
- Better coordination
- Problems identified earlier
- Hidden conflicts are discovered more easily (Structural vs MEP)
- Reduction of RFIs
- 2D Drawings are an output of model
- Produce takeoffs (debateable)
-BIM Challenges:
- Heavy requirements (processing power, storage, net traffic)
- Adoption of same technology across
different disciplines
- Existing legacy of 2D CAD
- No standards to date
- Does not replace knowledge of materials & systems
- Misconception that BIM will do the work for you
For more information: http://bim.arch.gatech.edu/?id=402
Introduction to Construction Estimating
Marcos Bastian
Conclusion
How have computers changed estimating?
- Level of detail (depth of work)
- Accuracy (takeoffs, calculations)
- Better WBS structure
- Ease of navigation (from general view to individual tasks)
- Automated recalculations (less chance for error)
- Cascading updates
- Online pricing and specification databases
- Systems integration (design, documentation specifications, estimates,
construction)
- * Field experience vs. computer literacy
Introduction to Construction Estimating
Marcos Bastian
Questions
Introduction to Construction Estimating
Marcos Bastian
Thank You!
Introduction to Construction Estimating
Marcos Bastian
Introduction to Construction Estimating
Marcos Bastian