mark676•19d agoMost Upvoted

Found a sneaky way to save $4k on our foundation pour

We were pricing out a slab for a 2,400 sq ft house in Columbus and every quote came back around $18k. I called around to 6 different concrete guys and they all gave the same story about fiber mesh and rebar spacing. Finally one old timer at the supply yard told me to ask specifically about a "voided slab" design instead of the standard 4 inch thick pour. Turns out you can run rows of cheap cardboard tubes in the middle of the pour to create air gaps and use less concrete. The engineer signed off on it because it actually handles frost heave better. We ended up paying $14,200 and the slab passed inspection with no issues. Has anyone else tried this method or is my engineer just weirdly chill about alternative designs?

2 comments

2 Comments

kim_nelson19d ago

Voided slabs have been around for years, mostly in commercial work where they need long spans. The cardboard tubes do save material but you need to make sure your rebar is positioned above and below them, not sitting right on the cardboard. You saved a solid chunk of change and the frost heave advantage is real, just keep an eye on your concrete coverage over the tubes during the pour.

the_miles19d ago

Honestly the frost heave thing is a bigger deal than people give it credit for. One thing I don't see anyone mention is how much easier it is to run utilities through a voided slab later on. If you ever need to add a drain line or electrical conduit, you can just punch through the thin concrete covering the tube instead of core drilling a solid 6 inch slab. That saved me a huge headache on a garage slab where I had to add floor drains a year after the pour.