Whether you have a log cabin or just exterior trim in various areas of your home that is unpainted it is of vital importance to keep this wood in the best shape possible so you don't have to spend tens of thousands of dollars replacing it. The best way to keep your wood protected properly is to stain once every three to five years using a high quality oil based stain, we recommend using Sikkens stain. The time in between staining will vary depending upon amount of exposure to the elements a piece of wood will receive. For example something on the west side of your home will get much more sun damage than something on the south side, and thus will need to be stained much sooner. If you don't want color on your wood they do sell many clear oil based coatings that you can apply for protection but will retain the woods natural appearance. In contrast if you have painted wood on your exterior it should be primed and painted at least once every 10 to 15 years. Keeping wood well maintained will save you a lot of money in the future on things like replacements and will help to retain your homes value. Of course while this maintenance will keep your wood in good condition there are always possibilities that some caulking was missed allowing water to enter and damage the wood beyond repair. Even applying material in improper weather conditions can cause the curing process to fail which means the material will fail significantly sooner than necessary. This is why it is of vital importance to hire a professional when possible to keep the integrity of your home intact, and to keep the things you love on the inside of your home from getting damaged from leaks.