White and green can be very attractive when coordinated properly - if your socks match. Mold and mildew love a big night out, but daylight just doesn't go with their lifestyle. Mold and sunlight don't get along because mold requires a cool, moist environment. Your south-facing roof is like the Sahara Desert to a mold spore. But since dew doesn't evaporate readily on the shady side of your house, mildew prospers.Streaks from siding and oxidizing minerals can also proliferate in moist areas. The minerals show up as rust, depending on the iron content, and older siding isn't solid color core and will lose its color coating to streaking. Power washing, as you wrote, isn't the answer, but with a mixture of clorine bleach, a powerful jet of water is probably the best way I've found to remove the mold. If your shingles are lighter weight, they may be thin and brittle from age. Power washing can split them if the water pressure is too strong. Shingles need to be washed from above the roof level, with the jet of water pointing downward so that it isn't forced up underneath them, which can lift and tear them. This is essentially what you see happening during the news footage of a hurricane. Water from below will also penetrate the roofing membrane and rot the plywood or other wood substrate below, creating a secluded colony of mold that will literally eat you out of house and home.You may want to try a brush with clorine bleach and Pine-Sol or Lysol, to name two detergents that are toxic to mold. Rubbing your shingles with a brush can be just as harmful, and I, um, bristle at the thought of you scrubbing off the small layer of granules that protects your shingles. Water pressure, believe it or not, when directed downward, is less damaging, provided that the pressure isn't extreme. Regular readers know that I often recommend leaving certain jobs, like this one, to the pros, because such a seemingly simple job can sometimes lead to long-term disastrous results. I don't mind do-it-yourself projects being done with full knowledge of the ramifications of one's own actions, but most people don't study the science of building forensics, which often illustrates the damaging effects of doing simple things incorrectly. So consider hiring a professional if you aren't sure about balancing on a ladder or lack the tools to get above the shingles at the correct angle. It helps the economy, keeps you safe and secure on the ground, and leads to years of enjoyment of your home. Once the roof is clean, periodically spray the areas with a little diluted bleach to keep the mold and mildew from returning, and the only green you'll have to worry about is those matching socks. Good luck.Readers are encouraged to send questions to: HERALD Homes, 379 Central Avenue, P.O. Box 220, Lawrence, N.Y. 11559-0220Attn: Monte Leeper, architect.
