Hello, I was looking for this info on AMVIC side but can't find it. How is the corner piece of the vinyl siding attached on the ICF wall? I ask this because I see the ICF plastic insert in the corner piece at just 11.25" from the actual corner edge (https://www.amvicsystem.com/wp-content/uploads/2017/03/6in-standard-corner-short.pdf), but the vinyl corner has the flanges at around 6". So how is itinstalled? Will required entire siding to be installed on strips of lumber attached on the wall first? Thank you.

According to the photo on this page, https://www.amvicsystem.com/insulated-concrete-forms there is a plastic flat corner piece in the foam. On my Buildblock corners, which are similar, I cut the foam out and laid in a strip of OSB. I nailed 1 x 4 trims piece on the corner to the OSB as well as the ends of my Hardiplank siding. Look for the plastic corner piece and see if you can fasten the corner piece to it directly. If not then embed an OSB strip wide enough to fasten your siding to it.

I would never install osb outside untreated or protected. It will delaminate and turn black. Normally you install treated during strips on the blocks, screwed into the webs. That creates an air gap / drain screen to promote drying of the siding. Regardless wither it is Hardie, smart side or wood, best practice is to keep them dry. Once the strips are installed you can fasten as per factory recommended spacings. Most blocks have corner webs to install too. The ones that don’t, need treated installed with 6” tapcons countersunk.

It'll deteriorate if it's exposed, yes. But the strips as I put them in are under the siding, not exposed at all.

Thing is, you'll still get condensation behind the siding, even if you NEVER get other forms of water behind there.

While OSB won't just fall apart at the first exposure to water.  Over time, it'll break down from repeat exposures.

Bent sheet metal on both inside and outside corners to the second web, secure with screws to web, you know have something to fast the corners to

Amvic corner blocks have horizontal plastic insert all the way to the edge which u can nail siding to

.. u were referring to a vertical insert that could be 11inches away

Yes, galvanized steel sheet metal on outside corners is what we do as well. BuildBlock also has a 1” diameter or so vertical channel about 2” from corner edge that you can insert PVC pipe to further improve corner exterior siding/trim fastening. We like to initially leave a section of this PVC pipe exposed above the top of ICF to enable fastening strings used to ensure the walls are straight prior to and during the pour. After the pour, the PVC pipe is then driven flush to the top of the ICF.

I also wouldn't recommend using OSB anywhere near an ICF wall. Moisture in the concrete core will easily pass through the EPS into the OSB. Only PT lumber should be used near an ICF wall IMHO.