ashrae_bim_intro_150What’s the correct definition of 4D BIM? Stay tuned…

As you’ve most likely already heard, ASHRAE has released their “An Introduction to Building Information Modeling (BIM)” guide. This document intends to provide information on how to adopt BIM tools for use in business practices. While I’ve seen links to this document posted on dozens (millions, perhaps 😉 ) of sites dealing with BIM, I have yet to read a constructive review or any feedback on the quality of this document. So, I gave it a once over.
Now, mind you, I haven’t gone through it with a fine tooth comb yet. While it’s obviously intended as an ‘Introduction’, thus, fairly elementary, it does appear to present a nice overview. That being said, I’ve already noticed an inconsistency in the definitions included in this guide that I feel is necessary to clear up.

On page 5 of the guide, 4D and 5D are defined as follows:

I believe most BIM proponents will agree with me that these definitions are actually flip-flopped.

The industry accepted definitions are:

4D is 3D + schedule (time)
5D is 4D + cost

To back this up, please refer to the following sources: In the BIM Handbook by Chuck Eastman (commonly viewed as the definitive authority on the current state of BIM), 4D is used throughout to refer to schedule.

The National Institute of Building Sciences (NIBS) defines 4D states:

The acronym “BIM,” is historically linked in the minds of many to 3-dimensional and now 4D (time) and 5D (cost) virtual modeling of buildings. BIM, however, has the capability and even the responsibility to be much more.


The GSA’s BIM Guide, another heavy hitter in the BIM world defines 4D as “3D + Time”.

If you do research on 4D simulations, you will see that it  refers to animation of the sequencing and schedule of a project. While many contractors are using 4D extensively, it is taking some longer to embrace 5D with BIM and rely on the information in these models for cost estimating purposes.

I believe it is very important to avoid confusion in this regard as we work together to promote efficient BIM workflows.

If you’ve noticed anything else you’d like to point out about the ASHRAE Introduction to BIM document, or would like to weigh in on the definition of 4D vs 5D, leave a comment!