FinallyItsOver wrote:

“After 35 years working as a Mechanical Engineer, I am retiring. I want to build a very large ICF workshop/man cave on our retirement property. I am a stickler for details and want to do as much work as possible myself. At the same time, I want to engage professionals in areas where my limited experience might be a detriment. In your opinion, where are the critical design and construction areas that will maximize the probability of project success?”

Answer:

Oh, it’s just beginning!

As you know from your former career, planning, planning and more planning will reduce problems in the field. Here are a few thoughts:

I would encourage you to engage a structural engineer if:
a. If your design includes retaining walls (basement or partial basement). This is one of the most common structural failure threats. The lateral pressure exerted by soil is often underestimated.
b. If your design includes long spans for the roof. You might choose pre-engineered trusses and delegate the design to a truss fabrication company. With the proper help, your roof can be erected in short order.
c. If you are in a heavy snow (10 psf +) area of the country. Let’s keep that roof up!
d. If you are in a high wind region. Let’s keep that roof down!
I haven’t designed with ICF’s (insulated concrete forms) but I imagine the suppliers of the forms have scads of proprietary details that you can use. It is important that the interface between the concrete and the supported structure is constructed properly.
Plumb, square and level are tough to do, especially with larger structures… but if you spend enough time when laying out the site and setting up the foundations, you’ll save yourself headaches during the framing phase. If you aren’t comfortable laying it out, you might hire a local surveyor to provide you with corner pins.
Concrete flatwork (slabs) are a bit of an art and require experience and equipment if you want to “burn it in” properly. I always hire a concrete subcontractor to install flatwork.
Electrical depends on your level of comfortability. I do my own (design and install) as long as it is typical residential and not 3-phase. I don’t think an electrical engineer will be required… just engage a good, licensed electrician if this is not in your bailiwick (I just had to look “bailiwick” up to see the origin. HERE is a link, if you’re interested).
Plumbing… yuck. I can sweat pipes or use compression fittings for flexible pipes but I just assume have someone else do that part. Again, no licensed professional is likely needed unless you have an unusual circumstance. Get a good, licensed plumber to at least make a tap for supply and sewer and run main lines… maybe you can do the rest.
Architects… only if you are looking for an exterior aesthetic that is extraordinary. Seems like a shop/man cave would not require a deeper mind with regard to space utilization.

Hope that helps a bit.