When siding begins to look dull and lifeless, oxidation is the culprit. Running a finger along the siding will come away with a powdery film that needs scrubbed away. Siding gives the home individual personality and provides the interior protection from the elements. Metal, wood, vinyl, cement fiber and composite siding are all subject to dirt and oxidation problems. Annual cleaning is the best defense. Keeping the surface clear of oxidation improves the looks and extends the life of all types of siding.