Untreated wood becoming wet can be the first problem.
Leaving siding untreated.
Wood siding that is too close to the ground or that does not have a rain screen or some other form of protection is particularly prone to these issues.
Wet conditions make for a nice breeding ground on untreated wood being used outdoors.
It does weather though changing color throughout time offering a much more rugged look than stained cedar siding offers.
By al rubin pages 24 26 journal of light construction april 1992.
This is going to cause the wood to decay rot and grow fungus over time.
Cedar has natural antibacterial and anti fungal properties allowing you to leave the wood untreated without worry of excess warping rotting and cracking.
It should always be performed on new.
Leaving cedar untreated and exposed to the elements causes its natural honey color to become weathered and gray.
Too much direct sun causes the siding to dry out warp and crack.
Wood planks and shingles too close to the ground are more likely to swell warp or rot leaving your home with uneven looking contours.
In siding as in much else the natural look is in vogue these days with many customers wanting to leave their cedar or redwood siding unpainted and unstained.
Keeping the natural look on wood siding.
Most typically when using untreated woods outdoors you are going to run into several potential issues.
In very dry climates the opposite can also occur.