If you need to stack posts end to end to reach the full height of the wall cut 1 4 inch from the bottom of the top post and position it so that it overlaps the lower post by 1 inch or so so it will shed water.
Installing vinyl siding corner posts.
Start by cutting off a few inches of the j channel portion on the post.
Expansionwhen the temperature changes vinyl siding expands and contracts.
After checking with a level for plumb nail them every 12 inches.
Installing inside corner posts.
Position corner posts at exterior and interior corners and suspend them by two nails driven into the uppermost slot.
Below the bottom of the starter strip.
Hammer the first nail into the nailing slot.
The way to allow for this expansion is to install the corner post down from the soffit or top of the corner.
Mice bees and all sorts of other critters love making their home inside vinyl corner posts.
Inside corner posts are installed at the existing corners running from 3 4 in.
Fold back the remaining flaps and gently tap a crease into them with your hammer.
Each corner should be hung straight so drop a plumb line for each corner post.
This video shows how to install certainteed outside corner posts for vinyl siding.
If vinyl soffit is to be installed allow proper distance below the underside of eaves for soffit installation accessories which vary according to the accessory used.