BIM Cost Estimating for Subcontractors

One topic that I think is important is how to estimate BIM costs.  Here are some thoughts on the best way to estimate and track BIM costs if you are a part of the subcontractor community.  

BIM is a planning tool - you're planning and defining how work is to be installed - and the best way of estimating those costs as a subcontractor is to align the input (hours by a 3D modeler) with the output (hours required to install the work).  If you consistently define a ratio of these two numbers, you can estimate the expected amount of time it takes for BIM on your projects.  Based on your understanding of future projects, you can also handicap and adjust your numbers to cover potential liabilities.  

Here's an example:

Let's say you're an electrical subcontractor.

  1. Define your "input" as the cost of 3D modeling, which includes initial modeling, clash detection, and coordination.  It's up to you whether you include the detailing (creation of shop drawings, layout drawings, Trimble survey files, etc) in your "input".  I would often be inclined to include it, except if your organization were big enough to have this be a completely secondary process to 3D modeling and coordination.  
  2. Define your "output" as some type of field labor hour. The best number to use is the total number (or total expected number) of field labor hours.  If you're estimating work, remember to account labor hours for allowances carried as unknowns at bid time.  For some organizations, it may work better to sum the total number of foreman hours, rather than total labor hours.
  3. The ratio of these two numbers is then your trackable and forecastable metric.

Why is this a good method?  If it's hard to install, it's hard to model and coordinate.  Your field labor estimate will pick up the difficulty of the project and your BIM time is directly related to that complexity.  

(Some firms try and estimate based on square footage.  But square footage doesn't directly account for project difficulty.  This is just a fundamentally bad idea.)

What does this enable you to do on your projects?  

  1. At bid time, you can handicap your BIM costs based on what you think will happen on the project.  Let's say there's an unusual Level of Development (LOD) or there's a fast coordination time frame.  You can baseline your number then say to yourself, "This project will be 1.5x harder than typical" and estimate accordingly.  
  2. Your project ROI's come into clarity. Let's say you have a foreman who says that BIM allows his team to be 10% more effective in the field.  Using your standard ratios of BIM time to field labor time, you can quickly back into a direct ROI.
  3. You can track your BIM costs through different categories of project.  BIM costs vary based on individual personnel, general contractor, project type.  Over time, your estimates will only get better.
  4. If you're really forward thinking and persuasive, you can pre-determine BIM charge-back rates for design changes with your clients.   Why couldn't you write into a contract, "BIM costs for change orders will be one hour of modeling time for ever X number of field hours"?  If you have historical data, this would be a great way of managing an element of change order complexity.   

I hope this method has been useful and insightful.  Of course, there are lots of ways to estimate work.  (Dartboard anyone?)  

If you don't actually work for a subcontractor, I hope this helped you think about how you can find an alignment between inputs and outputs on your BIM costs.  (This thinking makes for a great question during subcontractor interviews.)  If you actually work for a subcontractor and don't do this, I suggest you start.  There are few things more frustrating than a blown BIM budget...

Tags: BIM Construction

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