Pete in Holland MI
Wood rots because it doesn't have a chance to dry. The wrong joint design on outside wood projects collects moisture and extends drying time.
Your choices are:
1) Better design to not hold water, especially if end grain is trapped and becomes a straw.
2) Rot proof materials (plastics).
3) Shielding from the water (roof).
4) Wood preservatives that will repel water, and upkeep of that coating.
Paints & hard sealers do a good job of shielding the wood from water, but wood is dynamic, and eventually, this "shell" will start to break down, and now water that gets inside, can't dry, and wood rots from within.
Me? My 25 year old deck, in the sun, and living thru winters in SW Michigan, is now 27 years old. Made from pressure treated wood. It gets pressure washed every spring, and a coat of oil based deck stain/preservative/water repellent with a tint of color every 3 years. Railing tops get sanded prior to staining. Still in great shape.