It depends on the framing method and the foundation type. There is not just one way to build a house.

Pretty standard around here in TX.

Provides extra fastening for exterior wall sheathing, sidings, flashings/weep screeds for stucco, etc.

Provides extra fastening for interior wall board, wider base boards, toe kick installs,etc.

Considered structural especially in seismic areas where in strategic areas, foundation bolts are required to be 8"o.c. depleting the bottom sill plate of integrity because of the many bolt holes. The upper bottom plate provides that along w/ the extra fastening advantage.

Generally only used on slab foundations as m.a. stated.

It is not necessary to space anchor bolts 8" apart in any jurisdiction that I am aware of unless required by an engineer for a special condition. In any event it is still necessary to pick a framing method before making generalizations about plates.

Hi Mighty, 8"o.c 5/8" foundation bolts were/are required in some areas of southern ca. along w/ simpson foundation ties that are an integral part of the footing. Mostly seen in commercial applications, it has been required on residential builds in some areas and imo, does more harm than good because it completely renders the bottom sill plate useless w/ so many bolt holes as well as if the double bottom plate system is used, very dependent on the concrete crew ahead of you for proper height placement of the bolts. You still have to bore out the upper bottom, but if done right by the creters, not all the way through, so in that case, it helps, but still dpeletes the load and nailing value of the plate(s), again only in my opinion as im not an engineer but have seen many improper place foundation bolts in the framing days w/o consideration for stud layout and openings. I think things are better theses days.

Doubled bottoms are also common on garage stem walls as well.

Ca. is changing over to the i.b.c. effective by '09. The 8" o.c placement could very well be an engineered requirenment but still coinciding w/ codes. It's nice to see that ca. is finally getting on the same page w/ the rest or most of the country. They are coming up w/ more stringent energy codes under article 24.

When the IRC requires 8" o.c. bolts you can opt for using ACI 332 which is far more reasonable.

If I were in earthquake territory I would be asking an engineer to design the foundation.

Out here they are as well as the structural elements including shear, ties, strapping, hold downs,etc from foundation to the roof framing. All by a licensed engineered coinciding w/ current codes and im sure that will be the continued m.o even w/ the change of '09

The Ontario Building Code [at 9.23.6.1. (2)] requires anchor bolts at a maximum spacing of 2400 mm o.c., (a little less than 15 ins.).

Correction: a little less than 15 ins. 94.488 in.

We are in Maine and we have a triple sill plate, bolted down. Double seems to be the standard that DH always does when he frames, and they did the additional one for some reason I can't remember.

OP is in Lousiana if I remember correctly. Most likely slab foundation.

Anchoring 1st 2x4 to the floor and floating the wall above creating double bottom plate (hanging the wall from upper joists) allows the floor to move without buckling the studs within the wall, eliminating cracks and damaging drywall. Drywall is then left 1/2-1” to be covered by base. Allowing expansion and contraction with climate and humidity.

You must be talking about interior walls.