AECbytes Tips and Tricks Issue #51 (May 27, 2010)
A Quick Primer to Using Autodesk QTO for Model-Based Takeoff
Christopher Alexander
Technical Consultant, CAD Technology Center, Inc.
In the cost estimating world, the majority of us are still doing our take-offs by hand or by using a program such as On Center’s OST (On-Screen Takeoff) or Timberline. This seems counterproductive as we witness the rise of building information modeling (BIM) and BIM applications such as Autodesk Revit. It is highly possible that the drawings from which a take-off is being done may have actually been generated from a Revit model. The migration towards Revit is underway for many of the large commercial firms as well as for the smaller commercial firms and home builders. One of the primary reasons for this is the intelligence contained in the BIM model and how peripheral programs are capable of using this rich data for a multitude of applications—including preventing issues in the construction field that come back to haunt us as designers.
A relatively new player in the cost estimating world is Autodesk Quantity Take-off (QTO). Autodesk QTO is currently the only cost estimating program that can be fully integrated with a Revit model for creating take-offs and estimates. Other programs do have some integration with Revit, but not to the level of Autodesk QTO.
Why Autodesk QTO?
With all the cost estimating programs available, not to mention custom built spreadsheets, what sets Autodesk QTO apart from the rest? The main differentiator is full integration with DWF files. The capability to remember past element assignments and automatically reassign similar items in future Autodesk QTO projects is also a huge benefit. QTO can quantify items not typically modeled, such as concrete formwork, or tar paper and insulation via assemblies. Exact accuracy of sizing is calculated on the basis of what was exported from the Revit model.
How It Works
The appeal of Autodesk QTO is its simplicity. You are empowered with an easy to use take-off program capable of creating estimates on the level of Timberline but with the simplicity of OST. The initial model take-off is done by going to the Takeoff drop down and selecting Model. This reads all elements exported from Revit to the 3D DWF, as shown below, and incorporates parameters associated with these elements for use in the Autodesk QTO reports. Items can then be assigned from the takeoff to the catalog elements that have all cost and assembly information associated with them.
Both cost estimates and quantity estimates are created by utilizing the Takeoffpalette, shown below. This palette is created and stored in a catalog file that has all cost information, assemblies and element assignments. Cost and assembly information is used in the creation of reports. This catalog file can be continuously reused on the same project as revisions occur, or in new projects to speed up the process of creating cost estimates when standardized naming allows assignments to be re-used.
The items in the Takeoff palette are created by simply right clicking on a group and choosing Add Item. You can then begin creating assembly or cost information by double clicking on the newly created item. After item creation is complete, you can create assignments to this item from the Revit model takeoff by right clicking an item and choosing Assign to Item. This assignment is stored for later reuse by Autodesk QTO, speeding up future takeoffs.
The layout of the catalog itself is currently not controlled and can be altered according to company preferences. Many companies prefer to use the CSI-16 or CSI-48 standard layouts. There are examples of both of these layouts that come with the basic installation of QTO and they can be built upon and customized for your use.
All of this information for cost and assemblies is then used to generate reports. These reports are your final quantity/cost estimate for the project. Reports can be generated to show a summary of all groups in a project, individual items, or items and their assembly information, as shown below. Object properties that were exported from Revit can be used as well. This provides a wealth of information that can be scheduled and used for purchasing.
Junk in, Junk out
This is a phrase we hear often but don’t think much about. This does have a lot of meaning when a model begins its life cycle outside of Revit. Some serious model considerations must be made when using Autodesk QTO. True wall heights will only be displayed by the Unconnected Heightparameter found in Revit. This does not take any top offsets into consideration in or out of Revit. Most house designers will build a wall height up to the top level of their building and will attach gable ends to a roof at this point. This leads to an incorrect wall height reading in Autodesk QTO. To remedy this, the wall should be brought up to the bottom of the roof peak and then attached to the roof to finish the cleanup, as shown below.
There are many additional examples on how to generate better Revit models for use in peripheral BIM products such as Autodesk QTO. If you are working on a residential house, for example, have the floor system cut through the core of a wall to the outside substrate layer, as opposed to the common practice of cutting to the inside of the core—this would be an important factor for creating correct takeoffs of floor framing and sheathing. The best thing to keep in mind when building a model for use with Autodesk QTO is to create the model exactly how the final building would be constructed.
Conclusions
When it comes to creating exact and accurate quantity and cost estimates from Revit projects, Autodesk QTO is the way to go. A new level of accuracy can be gained with the ability to use exact property information from the Revit elements and assemblies to create takeoffs and reports. New levels of automation can be enabled with the use of element assignments, eliminating the need to spend more time refining the final cost and quantity numbers.
About the Author
Christopher Alexander works as a Technical Consultant for CAD Technology Center, Inc. (CTC), an Autodesk Gold Partner. He has over 10 years experience in construction as a designer, cost estimator, and CAD/BIM Manager. His experience ranges from small residential design to heavy industrial design for the agricultural industry.
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