Stopped in at a new build today and the contractor has dug down at least 7 feet and placed 3/4" stone down and is packing it down and laying the footings on that as opposed to footings directly on the native soil. The foundation will be and ICF.
R403.1 General. All exterior walls shall be supported on continuous solid or fully grouted masonry or concrete footings, crushed stone footings, wood foundations, or other approved structural systems which shall be of sufficient design to accommodate all loads according to Section R301 and to transmit the resulting loads to the soil within the limitations as determined from the character of the soil. Footings shall be supported on undisturbed natural soils or engineered fill. Concrete footing shall be designed and constructed in accordance with the provisions of Section R403 or in accordance with ACI 332.
That is the standard around here on commercial work. Stone is used to achieve a level grade under footings and provides a great bed for the concrete.
Stone is pretty much self compacting, but the vibrator plate kind of settles the bed of marbles all in place.
Timothy, I know of no code that prohibits that practice, but I never do it. I don’t see the point. The gravel can wash out or settle leaving a gap (weak spot) under the footer (my word for footing). Gravel is used to provide a level grade under the footer, but who cares if the bottom of the footer is level? I only care that the top is level. Concrete can only be strengthened (and not weakened) by being thicker in some areas. Besides, concrete isn’t that much more expensive than gravel and placement is easier.
Standard practice Nick to use 3/4" stone to level the subgrade under footings to compensate for the out of level surface.
National average for concrete is $75 depending on the mix and local prices.
Stone is about $12 a yard and if things are done right, will be on site for use as perimeter drainage material etc…
Compaction under the footings should also be done with a plate vibrator to settle the stone and disturbed original grounds.
And Footings is the proper word for the base of a foundation wall. ;)
made of concrete and used under chimneys and columns as well as under foundation walls to distribute the weight of the structure over a greater area and thus prevent settling. Footings are placed below the frostline to prevent movement during freezing.