I have a timberframe shop under construction and need to finalize exterior insulation.

I’m in Southeast Alaska—technically Zone 7—but realistically much more like a Marine 4C of Seattle, Washington, just a little colder and a fair bit wetter.  Moisture is my biggest concern in a design.  Siding will get wet, even with 3′ overhangs.

For aesthetic reasons, I (and my customer) really don’t want to infill, even if it’s just part way in to the timber plane.

I’ve struggled with the most efficient way to build fairly efficient walls to the exterior of the timber plane.  2Xs can run top to bottom from plate beam to floor beam.  With wraparound porches, a deck ledger also needs to be incorporated.

I assume there needs to be at least a single layer of plywood with WRB, but we’ve also played with the design of plywood on both sides of the wall.  OSB just doesn’t stand up in our very wet maritime climate.

Walls don’t need to be super-insulated…this is a shop that will be unheated most of the year, with a wood stove as the sole source of heat off and on in the later fall through spring.  I was hoping for at least 3″ to 4 1/2″ of rigid insulation.

Customer already has red cedar vertical board and batten siding on hand, which makes it all a bit more difficult for drainage planes, but siding will be firred out for ventilation.

The good news is that the area has plenty of wind, which dries wood quickly, even moisture behind siding.  My own house has old growth board and batten siding over 100 years old with tar paper directly behind, and it’s still in good shape.

Below is our best effort at a partial infill design…but again, aesthetics are sure hoping for a fully exterior solution.

Any thoughts or schematics are MUCH appreciated.

Thank you.

Zach