[Ray88]

What does portland in the middle of the forest have to do with moisture destroying walls?
Like you said, portland USED to be a jungle. Not anymore.
You do know that humidity level during winter is extremely low, considering most of the water vapor in the air has crystallized.

I find it a bit ironic how based on one epiphany, you jump to conclusion. Have you ever broken down an old wall subjected to long terms of humidity? Perhaps not. Long exposure of water vapor to walls can cause bacteria to reproduce (mold). The preliminary symptom would be peeling paint, followed by mushy walls, to eventually the collapse of it; a reason why we have ventilation fans in bathrooms/washroom and kitchens.

<!-- m --><a class="postlink" href="http://lmgtfy.com/?q=mold+on+wall">http://lmgtfy.com/?q=mold+on+wall</a><!-- m -->
^that's what happens to walls if you live in tropical/high humidity/high-altitude regions without proper ventilation