Step 1: Creation of a replacement granary tree or alternate habitat
Woodpeckers need a place to drill holes and store their acorns. Dead oak trees (snags) and other appropriate wooden poles will give the woodpeckers a much better option for drilling and storing foodstuffs. The birds prefer trees and snags and will choose these replacement granary sites over the buildings if given the opportunity.
A commercial product called "Scary Spiders" has been proven to be highly effective in discouraging acorn woodpeckers from drilling into the sides of buildings. These are battery operated spiders that automatically descend and ascend while making noises to scare away woodpeckers. These "spiders" need to be installed at proper intervals and monitered for battery life, but can be extremely effective deterrents.
More info at http://www.attackspider.com/
Temporarily hanging netting or plastic sheeting from the eaves and suspending it several inches from the woodpecker-attacked walls will deter them. Making the preferred area difficult to access will encourage the birds to find easier places to drill their holes. Providing granary trees while implementing netting on a temporary basis will ensure that drilling does not continue.
Strips of Foil
Hanging strips of aluminum foil, scare tape or cloth that flutters in the wind from the eaves can serve to frighten the woodpeckers away. Mylar balloons have also been used successfully to discourage woodpeckers. Big, scary things that flap in the wind will discourage these birds. This solution can be implemented on a temporary basis until the birds have established a new granary site.
Replacement of Imitation Stucco
A longer-term solution synthetic stucco material on the walls to a harder substance that is more difficult for the woodpeckers to drill into. This can and will discourage future drilling.