Debate: Should a drafter correct a structural engineer's obvious mistake?

I was working on a foundation plan for a project outside Nashville and the engineer called for a 6 inch slab on grade over 2 feet of compacted fill. I flagged it because the local code requires 4 inches max over fill unless you add reinforcement. He got defensive and said just draft what I tell you. But I argued my stamp is on the permit set too. So what would you do, keep your mouth shut or push back on a licensed engineer?

4 comments

4 Comments

kim_mason553mo ago

Your engineer buddy needs to remember that YOUR stamp carries weight too, especially on the permit set. What does he think happens when the inspector shows up and sees 6 inches of concrete over 2 feet of fill with no rebar? They're going to red tag the whole pour and then it's YOUR name on the line for approving the plans. Honestly, that sounds like a lazy engineer who doesn't want to rework his own design. Have you actually shown him the specific code section that says 4 inches max over fill? Maybe he just needs a visual reminder of the liability he's putting on both of you.

luna2613mo ago

Wait, is it really 4 inches max over fill or does that depend on the soil conditions?

taylor.brooke2mo ago

4 inches is a pretty standard rule of thumb but soil conditions absolutely matter. Clay soils that expand and contract a lot or really loose fill that hasn't settled yet will crack the concrete way faster than stable soils will. I've seen plenty of slabs do fine with 6 inches over well compacted fill, just depends on what you're working with.

webb.hannah3mo ago

Yeah I actually read a pretty good article in Concrete Construction magazine about this exact issue. It said fill settling under thick concrete without reinforcement creates voids that crack the slab over time. @kim_mason55 is right that the inspector will catch this. Maybe pull that article and show it to your engineer buddy along with the code section. Sometimes seeing it from a third party source makes people listen better.