Rigid foam boards stacked near recently excavated foundations: what's it for?

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Flyover

Trying not to screw things up worse
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On my daily walks with the kids through the new development one neighborhood over, we pass houses in all various stages of construction. Next to the ones that are only a freshly dug hole in the ground, there is usually a bundle of rebar, a pile of gravel, and a stack of 8x4 rigid foam boards. The stack is never more than maybe 6 or 8 boards thick.

I try to give educated guesses to my son about what they're going to do with all the materials I can see, but I'm genuinely puzzled about what that foam is for. Can anyone tell me?
 
Could be many different things.
It can be used under a slab for insulation.
On the outside of the foundation.
Insulate the rim joist.
Used as sheathing.
 
Given these are fairly large houses I figured there wasn't enough board to insulate the whole foundation or even just the slab. Maybe not even just the rim joist. Maybe an 8x4 goes a lot further than I realize?
 
Maybe that's it, but then why so few of them?

I wish I could just hang out at a site all day and see for myself. Unfortunately I have to work for a living! :(
 
Work? What is this 4 letter word?
 
i see those as well and I believe they’re used for void filling under the foundation vs, say, thermal insulation.. i hane seen the foam around municipal roadway construction as well as smaller home builds. what do you think?

https://tinyurl.com/4vcfkmb
 
Laying on top of Septic pipe? The guy that did my concrete shop pad said to put the foam down over my septic pipe that runs from the shop to my tank, across what will be a future driveway on the side of the shop.

He said to do that, put dirt down, grass if I want, whatever works, roll with it for years if I decide to, etc. etc, and call him if I want a concrete driveway in the future because he has never seen a busted sewer pipe in said situation with trucks driving on top of Schedule 40 pipe.

You have to get your own answer from a concrete pro before proceeding with said operation, but he's been in business for 30 plus years, never seen a problem.
 
Are there any doors coming out of the basement? If so then the footing needs insulation to keep the frost out as a fill will not be deep enough.

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I don't think any of these houses I'm seeing have walk-out basements, but they do all have windows in the basement.
 
Maybe that's it, but then why so few of them?

I wish I could just hang out at a site all day and see for myself. Unfortunately I have to work for a living! :(
Well you get (6) 8” strips out of a sheet and it takes 2 strips to form 8’ of footer. So one sheet will do 24’ and 8 sheets will do 192’ of footer. If the house was square that would be 48’x48’ house. That’s a good size house or if it was 24’x 72’ that would be a good size ranch. Next time count the rebar and see how many feet of that there are? :coffee:
 
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