caulking exterior plywood siding

[TMB]

Hoping some knowledgeable individuals can chime in on a particular issue:

I have a house in coastal Southern California.  It was built in the late 1970'S.  Split level design so 2ish stories over about 24 feet in total.  Exterior is plywood sheets with 1x over all the seams (believe this is called batten board style).

During various works I've had a chance to remove some of the 1x.  I haven't seen any evidence of flashing used beyond over one of the doorways.

Issue:  I am looking to paint the whole house.  As part of that process I was thinking it would be best to caulk much of the trim work.  My plan was to caulk vertical the upside of horizontal trim work but leave the bottom edge of horizontal trim work to allow the water drainage/vapor.

However, the limited research I could find online was inconclusive on whether this the proper approach.  It appears that the concerns are creating a situation where moisture can't escape.  There is also some concern regarding movement of wood.  Given that the plywood itself is likely very stable given its nature, I'm unsure whether this concern is applicable to my situation (versus solid wood siding).

My goal is to minimize water damage and minimize options for termite intrusion.  Given my location, the termite issue is the higher concern.  We don't get much rain, but the house already has had significant termite damage. 

So, safe to caulk as I outlined above or am I encouraging trapping moisture, which would likely make termite issues worse on the long term?

[nereo]

Is there a drainage planer behind the plywood? (What;s behind the plywood siding?)

[TMB]

Behind the plywood is tar paper.  Perhaps it is something special but in my limited experience, it appears to be standard roofing tar paper.

[ChpBstrd]

I would caulk all the seams. I'd caulk between the plywood pieces that will be beneath the trim and then I'd caulk all the edges of the trim.

My attitude toward exterior wood is that the caulk and paint's job is to keep the moisture from soaking into the wood or getting past the wood into the wall. Especially in a semi-arid environment, I would not expect there to be a moisture issue from having too good of a vapor seal. 

[Dicey]

I would caulk all the seams. I'd caulk between the plywood pieces that will be beneath the trim and then I'd caulk all the edges of the trim.

My attitude toward exterior wood is that the caulk and paint's job is to keep the moisture from soaking into the wood or getting past the wood into the wall. Especially in a semi-arid environment, I would not expect there to be a moisture issue from having too good of a vapor seal.

^This^. Use the proper caulk and it will flex with the wood. There's no such thing as too much prep before painting, lol.

[lthenderson]

I'm with the others above. I would caulk all seams using a highly flexible exterior caulking like Big Stretch or something similar. The egress for any moisture should be at the bottom of plywood around the sill plate.

[sonofsven]

I would not caulk the batts to the plywood. It's not necessary from a water/moisture intrusion standpoint and can definitely cause trapped moisture issues that can damage the plywood.
It's most likely that any termite intrusion is coming from the bottom edge of the plywood where it covers the transition from foundation to sill which is not really "caulkable".
What is the nature of the existing termite damage-framing, or siding? Did you find any of the tubes they use on the side of the foundation?

[TMB]

Thank you for the responses all.  Always appreciate views from others with more experience.

I would not caulk the batts to the plywood. It's not necessary from a water/moisture intrusion standpoint and can definitely cause trapped moisture issues that can damage the plywood.
It's most likely that any termite intrusion is coming from the bottom edge of the plywood where it covers the transition from foundation to sill which is not really "caulkable".
What is the nature of the existing termite damage-framing, or siding? Did you find any of the tubes they use on the side of the foundation?

Regarding the termite damage, the worst I've found was higher on the walls near the roof.  Though, this may be because in that particular bedroom I had removed the drywall to install a sound reduction system.  There is definitely other termite damage, and we have had subterranean termites in the past, but I haven't seen any reintroduction of them since the property was treated in 2014 or 2105.

[sonofsven]

Thank you for the responses all.  Always appreciate views from others with more experience.

I would not caulk the batts to the plywood. It's not necessary from a water/moisture intrusion standpoint and can definitely cause trapped moisture issues that can damage the plywood.
It's most likely that any termite intrusion is coming from the bottom edge of the plywood where it covers the transition from foundation to sill which is not really "caulkable".
What is the nature of the existing termite damage-framing, or siding? Did you find any of the tubes they use on the side of the foundation?

Regarding the termite damage, the worst I've found was higher on the walls near the roof.  Though, this may be because in that particular bedroom I had removed the drywall to install a sound reduction system.  There is definitely other termite damage, and we have had subterranean termites in the past, but I haven't seen any reintroduction of them since the property was treated in 2014 or 2105.

I think treatment is the key then, not caulking.