Only an experienced pressure-washer should use this technique. Cleaning can also be done with a broom, garden hose, and chemical cleaner of the type used on decks. Water-repellent preservatives vary in composition and effectiveness. Some treatments contain copper naphthenate, an effective preservative that offers protection for up to five years. Zinc naphthenate can also provide long-term protection.
Some preservatives contain paraffin or wax to help the wood shed water.
If the cost of cleaning and preservative treatment is prorated over the five years or so between treatments, it will seem less daunting. We recently moved into a house that has metal heating ducts running through the basement. Some of the ducts are round, some rectangular. These ducts make lots of banging and clunking noises, especially after the heater shuts off. A Metal air ducts expand and contract when the temperature of the air moving through them changes.