Is it a good or bad idea to spray foam directly on the interior of shiplap siding?

When you are insulating the exterior walls of a home to improve energy efficiency, you have to make sure walls can dry. Applying spray foam directly to the back siding of your cladding doesn’t sound like a good idea to me, but I’d need a few more details. And first check out this page to see how we install siding – 

How to install exterior siding so walls can dry

So a few questions – Where are you building? Building for your specific climate zone is important (find your building climate zone here). What is the current wall assembly? I don’t quite understand how you would get the insulation onto the siding unless this is a cottage with open stud walls so you see the back of the siding from inside the house. But the short story is – walls need to be able to dry, and I don’t see how they will if you spray foam the back of the wood. Exterior siding is meant as a weather shield, it protects the control layers of your wall (air barrier, vapor barrier, insulation, weather barrier), so you should have an air space separating your control layers and your siding to allow humid air to escape and moisture to drain.  If I’m missing something here please give me more details and we would be happy to help. 

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