How to seal exterior corners of octagon tower?

[jimthewingman]

Greetings, Does anyone have any suggestions for sealing the exterior corners of an octagon stairwell tower? Currently the corners need frequent caulking due to seasonal expansion of the butt-joint. The angle of each corner is 135 degrees (trim board ends are cut at 22.5 degrees). I made bent aluminum shields (as a test) and they kept the rain out but condensation would often develop under the aluminum on some mornings. Any ideas other than frequent caulking?

 

[user 4883]

change them out for lap joints.

 

[jimthewingman]

Thank you very much for your suggestion. I will seriously consider that option!

 

[Sparky617]

In addition to the lap joints, I'd consider using cellular PVC lumber (Azek is one brand) for the wood. I'd also have roofing felt or Tyvek behind the trim. I believe the Azek can be bonded together with a solvent adhesive that will turn it into essentially one piece.

 

[jimthewingman]

Thx Sparky617, I'll purchase a piece of PVC trim lumber and experiment a bit with your bonding idea.

 

[Steve123]

I have glued up PVC trim board many times.
I use PVC cement that I get in the plumbing department. "Clear" cement is a little less common, but still readily available.
When I tested the strength of the bonded joint, the PVC board broke at the parent board, not the joint.
Glue set-up time is very quick. If you are gluing long pieces, you will have to put some thought on how you are going to make a set up that you can quickly locate and clamp the two pieces.