How deep must a grade beam (on helical piles) extend below grade?
I’ve reached a stumpling point in my research, and was hoping for an answer. Im building an addition to my home in a zone 7A climate. It will have a conditioned crawlspace, built from ICF blocks (including grade beam) installed on helical piles (with a void form between piles).
The grade inside the crawlspace will roughly be the same grade as outside. Im wondering though how deep below grade must the bottom of the grade beam be installed? Obviously a more shallow depth is less work, with since I won’t be putting the beam down anywhere near the frost line (because of the piles and void), will it even matter if the bottom of the grade beam is only 6 inches into the ground versus a foot or more?
How do you figure this part of the equation out?
-Dave
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Replies
DJ,
Unfortunately, the answers in both cases can only be determined by an engineer. Helical columns are driven into the ground until they reach a specified resistance - you should get a readout from the installer for each pier - so each one may be a different depth. Any beams in contact with the surrounding grade need to be protected from frost heave. Apart from that consideration the depth doesn't really matter.
Be sure to consider thermal bridging from the ground into the center of your ICFs. And what code says.