I'm having a pole barn built and would like to add a concrete floor. The building will have a 2x8 skirt board around the base. I need atleast 4" of concrete and will install pex tube for heat, I need some insulation as well. My question is how much stone do i need beneath the insulation?
Thanks, Ron C

 

I would put no less than 8 inches of gravel and be sure it can drain.

 

So, I wold have to dig out about 6" after the building is up?

 

This site will give you about everything you need to know. Good luck with your project.

How to Build High Quality Slabs on Grade - The Concrete Network

 

It is your building and you can do whatever you want. A proper slab has gravel under it to allow ground water to flow under the slab without causing pressure to build up and force the water into the slab. Yes plastic sheating is placed before the concrete is poured to help with this but the plastic gets walked on while pouring the slab. Also the weight of the concrete presses it down and some holes will be made in the plastic. The gravel is to keep the water as far away as possible from the slab.
You want 4 inches of concrete and 3/4 inch or 1 inch foam for insulation above your plastic and gravel. You said a 2x8 skirt board went around the building. That gives you 7 1/2 inches.
I am assuming the skirt board top is at the level the bottom of the doors will be.
If you did not dig to install these skirt boards then they are setting level with the ground at their bottom. If it rains the water will run across the ground toward your building and pass into the gravel. If water puddles on the ground it is also puddling in the gravel under your slab.
If you can insure that 2 inches of gravel will drain this water away from the slab to a lower spot then all you need is 2 inches of gravel.
Naturally if the building is atop a hill then you will never get any water under the slab unless it floods.
The gravel below the slab needs to be deep enough to keep the water away from the slab.
Contractors normally put 8 inches to ensure the water never comes up to the level of the slab.
I know it took me a lot of words to say you can do what you wish. I just wanted you to understand why the gravel is used beside the fact it is a stable base.