In this part of California there are a lot of small spiders that create cobwebs on the exterior.  Power washing does not do a great job getting the off. they really need to be mechanically removed.  Putting a corner broom head on a long pole / telescoping pole is an easy way to do that.  Telescoping poles for this are sold by painting companies but they are very expensive. 

This  pole was made using: 

EMT Tubing  - 1/2" x 10'  -- $7

EMT Tubing - 3/4" x 5'  - $7

Modified Acme pole adapter - $6

Telescoping Coupling  - $4