The information contained in this document is time-sensitive as the technology and system requirements continually evolve.
The AUTODESK REVIT family of products (Architecture, MEP and Structure) presents new opportunities and challenges to designers. Revit concentrates all information in one central model database rather than several drawing files. Because every designer uses and shares the same central Revit file, problems created by one user will often affect all users. Revit models also contain far more information than just geometry; hence the term Building Information Modeling. Revit, of course, is not simply an AutoCAD upgrade and we are learning how different it is every day. These are some of the lessons we’ve learned supporting designers using Revit.
1. Never leave inserted AutoCAD DWGs in a Revit model. Although you can insert a block or draw into Revit it can cause severe performance and stability issues. DWG files bloat the model by using far more memory than pure Revit entities. Also, AutoCAD DWG files can corrupt the file, causing internal errors, excessive warnings, and language barriers, which slow down the performance of the model. We recommend that you recreate your favourite blocks as Revit Families. If you must insert a DWG file for tracing or reference, purge it as soon as possible. Regularly check the model for blocks and DWG files to make sure it stays lean. Never explode DWG files that have been imported into Revit as this makes the problem worse and more difficult to resolve. It also can make the issue a permanent one as some elements, once exploded, can never be removed. If the AutoCAD file is necessary as a background, linking the file in rather than importing it can prevent and reduce some of these issues.
2. Don’t let unresolved Revit warnings languish. Large numbers of unresolved warnings can seriously degrade model performance and stability. Resolve warnings as they occur to keep them from building up in the model. Periodically check the “Warnings” tool on the “Modify” ribbon to see what warnings (if any) have built up in the model.
3. Don’t use Revit Families from Manufacturers without checking them first. Building Product Manufacturers are responding to your requests for Revit content by having families of their products created in Revit. These families may look great when viewed, but if they contain too much detail they can quickly bloat your model. One unnecessarily detailed door family could add dozens of megabytes to your Revit model and slow you down. Additionally, we have found some manufacturer-provided families include imported DWG files (see number 2 above).
4. Don’t over-model. One of the most common mistakes among new users of Revit is to put too much detail in the model. Determine how much detail is really necessary to convey your design intent, and then monitor your team to prevent over-modelling.
5. Don’t use in-place families too often. While it is inevitable that you will have to use in-place families in a typical project, be selective in their use. If you create an in-place family and later decide that it should be a component family, there is absolutely no way to convert it. If you must use an in-place family, do not duplicate it. For example, if you have to use in-place families to create light coves in several rooms, create them all in one in-place family; don’t create a different in-place family for each room.
6. Don’t over-constrain model geometry in a project file. Dimension and alignment constraints add overhead to the file and increase the potential for the dreaded “constraints not satisfied” error message. If you’re not absolutely sure that you should constrain something, then you probably shouldn't.
7. Don’t lose control of your views. Exercise good view management. Don’t create unnecessary views and don’t leave views unnamed. During the course of a project, the project browser can become populated with a large number of views. Bad naming practices or unnecessary views can make the view list even more unwieldy. Also, utilize the browser organization tools to your advantage to sort views in ways that make them easy to navigate.
8. Don’t over-use Groups and Design Options. An inordinate number of groups in a project can impact performance and bloat the model. Make sure to purge unused groups from the model regularly and turn off the “Group and Associate” option when using the Array tool. Likewise, be careful not to get carried away with Design Options which are meant to allow for multiple possibilities for minor changes in the model. Improper use of Design Options can duplicate many entities and increase model size significantly.
9. Don’t use Worksets to control visibility. The workset of an object can change at any time and since there are no rules that say a tree can’t be on a “Roof” workset, for example, it can cause unexpected issues with object visibility and printing down the road. Grouping can also affect the workset assignment of objects, causing further problems with this method of visibility control.
10. Don’t create a “Demolition” phase. Demolition is an action and not a phase. While phasing will still work if you create a “Demolition” phase, it adds one more phase that you have to manage and is completely unnecessary and redundant.
In conclusion, these 10 nuggets should prove very helpful in your transition into the world of BIM through Revit. In addition, though, we offer one thing you should do: read the Revit Platform Model PerformanceTechnical Note posted to the Autodesk website. Simply navigate to www.autodesk.com, and enter “Revit Platform Model Performance Technical Note” in the search window.
Originally published at www.dccadd.com and revised on December 17, 2009.
