I'm building a large outdoor living space in the pacific northwest (Vancouver, Canada) with rafters, purlins, beams, and posts all douglas fir. It will all be covered with transparent polycarbonate roofing (Suntuf). The roofing will block most UV light and all the rain except some occasional horizontal/windy rain.
I love the dark red color doug fir turns indoors when totally untreated. What will happen in 5-20 years if I leave my outdoor fir untreated (no paint/stain/oil/anything)? Is ambient humidity in a wet climate enough to rot the fir? Or make it go grey or black?
Thanks so much for your experience!