Using Piers and Grade Beams to Support a Garage Slab

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This big hole in the ground with 4 walls is going to be the 3 car garage for our new house.
Let me show you how we’re going to build the floor so it’s strong enough to hold the weight of cars and will never settle.
We poured two piers centered from front to back in the garage, these piers will support columns with grade beams above them.
A grade beam is basically a ditch in the slab where the concrete is extra thick.
They will be a foot thick verses the slab that’s only four inches thick.
The grade beams are supported by the piers in the middle and by the foundation walls at the edges.
They will ensure that the garage floor doesn’t settle.
You can see here I’m doweling in ½” rebar into the footing with some epoxy.
Some people use sonotubes for these piers, but I like to dry stack 8” concrete block to make my piers.
I stack two together and then turn directions and stack two more on top, alternating as I go.
This makes a 16” square column.
The cores of these blocks will get filled with cement when we pour the slab.
Here’s a chart showing the grade beam layout.
There’s one beam that runs from side-to-side and two more that run from front to back- all of them crossing over the cinder block piers for support.
We also put pockets in the foundation wall to help support these beams, here you can see what one looks like.
Here’s how it will look when it’s all done- there’s two piers made out of dry-stacked cinder blocks.
We’re gonna fill most of this area with crushed concrete and then a layer of crushed stone on top.
The four-inch slab will be extra thick over the piers- that will be our grade beam.
The slab will have a one-foot rebar grid running both ways and there will also be rebar connecting down through the piers into the footings.
I’m using crushed concrete to fill in this garage rather than crushed stone because it is about half the price.
I will put a layer of stone at the very top because it’s easier to rake and form up the grade beams.
In theory this slab is completely suspended and once the concrete is poured you could actually go in and dig the gravel back out without it affecting the structure.
Funny story, I once had an engineer tell me “you can fill the thing up with Dr. Pepper cans for all I care- it’s just to hold the concrete up until it cures”.
I started out by filling everything I could reach from the edges with the skid steer, and then I made a ramp so I could drive the skid steer into the garage to fill the rest.
Going over a ramp like this with a track machine always feels a little sketchy- especially when you’re backing up.
My advice is to just go slow and work with the balance of the machine so you’re not being slammed around.
I think I put about 12 loads of crushed concrete in this garage. That’s about 200 tons, and it’s still going to take a couple of loads of crushed stone for the top.
We’re showing step-by-step how to build a house from start to finish, so if you’re net yet following our channel make sure to like and subscribe. @hausplans

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