5" foundation = 3in gravel + concrete?

[skinnydoc]

Hello...
am planning out a Casa 2g 90 build, will be laying my first foundation.

When the install guide says 5 1/2 slab, then goes on to say 3" gravel to start with plastic on top, does that mean excavate 8 1/2" do the 3" gravel, then do a full 5 1/2 slab? or is the 3" included in the 5 1/2"? I'm guessing its total 8 1/2" slab, but not clear and I dont know better, and I dont want to mess this part up!

other questions:
-how to estimate how much concrete is needed?
-looking at the corner install plan they have in the manual, how much bigger does the foundation need to be?

thanks

Ben

[Neil2]

"does that mean excavate 8 1/2" do the 3" gravel, then do a full 5 1/2 slab?"

Yes.

Measure your slab in cubic feet. For example a 6 ft by 6ft by 5 1/2 inch slab = 16.5 cubic feet, or about .6 cubic yards.

If you are going the pre-mix bag route, there is 0.6 cubic feet in one 80 pound bag. Therefore the slab will require 16.5/.6 = 28 bags. Get more than you need , you can always return un-opened bags.

[skinnydoc]

thanks for that info... I started my excavation today, assuming that I needed 3" gravel then 5 1/2 in slab.


More questions to follow, I'm sure!

Ben