Hello:
We're doing a 2nd story addition on an existing 1 story slab on grade house and in the past have made the exterior footings larger by underpinning them to a new width of 15" and a depth of 18". From reading the 2010 CRC (California's version of the 2009 IRC but basically the same); Per TABLE R403.1 it appears that if we can show the load-bearing value of the soil to be 2,000 psf or more then we can keep the width of the footing at 12".
Also, per R403.1.4 "R403.1.4 Minimum depth. All exterior footings shall be
placed at least 12 inches (305 mm) below the undisturbed
ground surface. Where applicable, the depth of footings shall
also conform to Sections R403.1.4.1 through R403.1.4.2."
So from these two pieces of data it appears that if we do a soils test and it comes back at the soil bearing value to be at least 2,000 psf then we can forego having to upsize and underpin the existing slab on grade footing.
Any feedback and opinions would be appreciated,
Rio
We're doing a 2nd story addition on an existing 1 story slab on grade house and in the past have made the exterior footings larger by underpinning them to a new width of 15" and a depth of 18". From reading the 2010 CRC (California's version of the 2009 IRC but basically the same); Per TABLE R403.1 it appears that if we can show the load-bearing value of the soil to be 2,000 psf or more then we can keep the width of the footing at 12".
Also, per R403.1.4 "R403.1.4 Minimum depth. All exterior footings shall be
placed at least 12 inches (305 mm) below the undisturbed
ground surface. Where applicable, the depth of footings shall
also conform to Sections R403.1.4.1 through R403.1.4.2."
So from these two pieces of data it appears that if we do a soils test and it comes back at the soil bearing value to be at least 2,000 psf then we can forego having to upsize and underpin the existing slab on grade footing.
Any feedback and opinions would be appreciated,
Rio