Any time I used T-1-11, which was not often and a very long time ago, I used it as a siding material that was applied over the sheathing.

@ Mark Bischak, Architect, did you lay down a weather barrier sheet over the sheathing then lay the T1-11 on top or did you put down stripping's to keep an air gap to prevent it lying on top and not have it rot from potential moisture behind?

My 1968 house was T111 applied as siding over another sheathing

Not all T1-11 is rated for structural use. If you use it as shatahing or a combined sheathing and exterior cladding make sure it's got the stamp for structural use.

Most likely a building wrap was applied over the structural sheathing before applying the siding. Sheathing used as siding provides little to no protection to the sheathing.

See: diychatroom.com

I lived in a house with T1-11 directly over studs (with felt paper if I remember correctly). This was in a drier climate and it worked, kinda. It had started it's life as masonite board over studs, but that started to fall apart after 20 years.

Your questions are confusing and may contain some wrong assumptions.

Exterior plywood structural sheathing is usually 15/32" CDX that needs to be covered with siding.

T1-11 is considered a combination of siding and sheathing and is usually 19/32" because of the cuts. Both are more than strong enough for lateral bracing.

T1-11 gives a reverse board & batten appearance and has lapped long edges. Corner boards will be needed at the house corners. Horizontal joints will need metal z flashing.

IMO the drawback to T1-11 on studs is the window and door detailing. The exposed T1-11 will need to be stained (paint doesn't work well on softwood). Exposed and butted edges will be a liability. Watch a Youtube video.

Backup and tell us your goals and limitations so we can offer useful advice.

I built a house in 96 with t 1. Still looks good. For what it is. House has been through a 7.2 earthquake with no problems. Use a good paint sprayed on and back rolled. Plan was to reside one day but now we have sold it. But the t 1 did its job well and looks good.

As others have said, T1-11 is used for siding, not sheathing. Sheathing is done with either standard plywood or OSB, depending on lateral and wind requirements.

As others have said, T1-11 is used as siding. Sheathing (beneath the siding) is typically done using plywood or OSB, depending on lateral and wind requirements.