Drafted a whole basement wrong because I misread the floor elevation marker

Last spring I was working on a basement remodel in a house built in the 70s. I was going off the original floor plan and the elevation marker on the old foundation wall. Turns out that marker was for the original concrete slab before they poured a new floor over it later. I drafted all the walls, joists, and ductwork sitting 4 inches too high. Didn't catch it until the GC called me saying nothing lined up with the actual slab. Spent a full Saturday redoing the whole set and had to buy the GC lunch to keep him happy. My question is, how do you guys verify old elevation marks on remodels without just trusting the first one you see? I'm thinking I should always cross check with the actual slab height now.

2 comments

2 Comments

joseph_green138d agoMost Upvoted

Nailing three spots with a laser before drafting sounds smart, but what about checking the foundation edge along the whole perimeter? I've seen slabs that dip or settle unevenly over decades, so a single high spot could throw you off just as bad as a bad marker. Did the guy on that other forum mention if he also double checks against things like door jambs or window sills for a sanity check? Seems like you'd want at least one hard reference point that hasn't moved since the house was framed.

nancyramirez8d ago

Yeah I actually just read a thread on another forum where a guy was saying the same thing happened to him on a 60s house. He said the old foundation markers from back then are basically useless because they used to fill and re-pour slabs all the time without updating the marks. So now he takes a laser level and shoots the actual floor at like three different spots before he even starts drafting. Why would you ever trust a random mark on a wall that nobody's checked in 30 years right? I mean the original builder probably just scribbled that in with a grease pencil and called it good. Seems like a lesson a lot of us learn the hard way. That lunch for the GC was a cheap fix for a mistake that could have cost way more later.