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rubble trench foundation

bill1952

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Aug 12, 2021
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748
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Clayton NY
Finally submitted permit application for a modest detached accessory building. Dropped off in person and verbal approval in 20 minutes. I show a base foundation detail with footer and cmu stem wall as well as an alternate foundation detail using a rubble trench.

I wondered if officials here had ever approved a rubble trench foundation, and in general your thoughts on it. Near same materials cost but huge time savings. (Entirely solo diy build except excavation.)
 

mtlogcabin

Sawhorse
Joined
Oct 17, 2009
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8,695
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Big Sky Country
Not here in my seismic zone "D"

Crushed stone footings shall be limited to Seismic Design Categories A, B and C.

R404.1.2.1 Masonry foundation walls.
Rubble stone masonry walls shall not be used in Seismic Design Categories D0, D1 and D2.
 

bill1952

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Aug 12, 2021
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748
Location
Clayton NY
I think a "rubble stone masonry wall" is not the same thing as a "rubble trench foundation". There is no unbalanced backfill.
 

bill1952

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Aug 12, 2021
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748
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Clayton NY
28' x 32' and a grade beam sits on rubble (no. 2 clear), beam 16" or more below grade. I see little different than if building where frost line is only 16", stone instead of undisturbed soil under footing. Just eliminates a lot of concrete.
 

ICE

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Jun 23, 2011
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10,403
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Ca. concrete jungle
I had a tilt-up footing where the engineer called for a foot of rock at the bottom of the trench. The footing was large and deep. I'm not sure why the engineer called for the rock but there is a premise that with expansive soil the voids between the rocks give relief. Well when I showed up for the inspection, the bottom steel was sitting on the rock. There was no 3" clearance so the inspection failed. That happened twice. The third time the steel cage was sitting on dobies with the clearance....while I was there a train rolled by. The tracks were about forty feet away and I watched the dobies vibrate into the rock. The solution was a fleet of backhoes and chain suspending the cage for the pour.

There's a pool engineer that recommends clean gravel under pool decks for the relief feature. Of course it is just a recommendation so I did not require it.
 

bill1952

Sawhorse
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Aug 12, 2021
Messages
748
Location
Clayton NY
So the grade beam is the foundation/ footing and you are using the rubble to get down to frost depth? Sort of?
Yes. Trench 4 or more inches below frost depth, non-woven geotextile "lining", 4" (at least for this size building) perforated drain pipe, clear (or clean) crushed stone, up to a footing or grade beam depth, wrap geotextile over stone, place grade beam or footing on gravel. Soil on exterior sloped to help drainage. Either slab on ground or short crawl space walls and typical floor construction. SOG and grade beam is a little below grade. In the crawl space, bring rubble to grade and build on top.

It doesn't seem different than building on any approved fill with not frost depth problem. Obviously not to or buildings with basements.

Quicker and much less concrete (for those who believe in the human induced climate change and would like to reduce the carbon footprint f to om concrete.) Does not save much money in materials; should save in labor.
 

bill1952

Sawhorse
Joined
Aug 12, 2021
Messages
748
Location
Clayton NY
Completed rubble trench foundation today. Learned a lot so next one, if ever, will be a lot smarter with less work and cost.
 

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