Footers

Crushed Stone Footer vs. Traditional Poured Concrete Footer

Why not use a traditional concrete footer?  Superior Walls are placed on a crushed stone footer for a few reasons:

Footer-Crushed-StoneIt is Dry: A crushed stone footer allows for extra moisture under the foundation to flow freely into the drainage system.  With a crushed stone footer, there is no place for the water to “dam up” and find its way inside the home.

It is Strong: Crushed stone transfers the load of the house structure better than concrete to the virgin soil below. (see chart below)  All houses are ultimately supported by the virgin soil, not the footer.  Wider Bearing Width = Stronger Foundation

It is Double Footing: The Superior Walls system is actually two footers: One is a 10.25” steel-reinforced concrete footer that is cast with the wall itself. The second footer is compacted ½” crushed stone laser leveled. “You don’t use a footer?” No, actually we use two!footer-train1

It is Level: In order to achieve a level foundation, a compacted crushed stone footer must be used.  The Superior Walls Certified Installation Crew, on site just prior to installing the wall panels, laser-levels the stone footer. Level Footer = Level Foundation = Level Home

It is Proven: Since 1981, Superior Walls foundations have been installed on the same material: crushed stone. Before then Frank Lloyd Wright used crushed stone footers under his architectural works of art. Before then road beds and train tracks used crushed stone footers, and still do. Before that the great pyramids of Egypt were built on crushed stone footers. Crushed stone footers are actually more traditional than poured concrete footers!

It is Stable: The crushed stone footer under a Superior Walls foundation cannot “wash away” because the stone is kept in place by backfill and the concrete floor slab.  The wider effective bearing width also acts as a stabilizing force for the foundation and the entire structure.

It is Economical: The bottom line is that crushed stone can be used under just about any structure.  Stone is also less expensive than traditional concrete footers, and will continue to be used as a resourceful and efficient footer.


The Physics of the Crushed Stone Footing:

  1. The purpose of any wall footing is to distribute the wall’s load over a sufficiently
    large area of soil so that the weight-bearing capacity of the soil is not exceeded.
  2. The load of the building is carried by the Superior Walls panel and is transferred to the 1/2” clean crushed stone.
  3. The load distribution path through the crushed stone is at an angle approximately 60 degrees from the horizontal.
  4. As the depth of the crushed stone layer increases, the effective bearing width on the underlying soil also increases. (see chart below)
Crushed Stone Footing / Effective Load Bearing Width Chart
Crushed Stone Footing Depth (inches) Effective Bearing Width (inches)
4 14-7/8
5 16
6 17-3/16
7 18-5/16
8 19-1/2
9 20-5/8
10 21-13/16
11 22-15/16
12 24-1/8
13 25-1/4
14 26-7/16
15 27-9/16
16 28-3/4
17 29-7/8
18 31-1/16
19 32-3/16
20 33-3/8

 

Code Reference: 2012 IRC Section: R403.4 Footings for precast concrete foundations. Footings for precast concrete foundations shall comply with Section R403.4. (See Section R403.4.1 Crushed stone footings.)