Exterior Stain: It is recommended to gently wash your house every year, preferably towards the end of summer to remove the dust accumulation. Stains do not cover as a solid skin, instead the penetrate into the wood. Dust and dirt build up on the surface can act as a sponge, holding moisture against the surface of the stain reducing its life.
Check once a year for mildew growth, if mildew is noticed it can be killed with a fungicide sprayed, once applied rinse of the spray. Follow manufacturer directions.
Exterior Paint: To ensure long life of your paint keep dirt from being up against the siding and avoid sprinkler systems being sprayed on siding. This constant moister on the siding can jeopardize the paint and siding. Washing every few years will help prevent mildew growth and staining.