If you have a damp, usually shaded environment, you will get mildew and algae. All good housepaints have chemical mildecides in them. There are, however, additional mildecides sold to add to paint. Usually about $5 for enough for a gallon. I don't know how effective they are in addition to that which is already in the paint.

If you have a power washer, mildew is not that hard to get rid of by injecting bleach into the water stream. Buy a "high pressure nozzle" from the equipment supply house or online. These will allow you to shoot a stream 15 or 20 feet upward. They also merely replace the normal nozzle, so you don't have to wait for 50 feet of hose to clear, nor does it go through the pressure pump, potentially damaging it. Such a tip costs about $40.

I buy Ivory dish washing liquid and ut as much in the bleach bottle as will fit. I then put the siphon hose directly in the bottle and hold the bottle in my hand, along with the power washer wand. The Ivor is a gentle soap which will not hurt anything TSP can etch glass!). The important thing about Ivory is that it sudes up like crazy. I know that where ever I see the suds, the bleach got there too. Keep the wall wet for about 5 minutes with the bleach and then rinse it down. the mildew will just vanish.

If you are not re-painting, be careful to first wet the siding down and then spray the bleach water from the bottom up. You do not want dirty bleach water running down dry siding, as permanent streaks can result. It is the same reason inside walls are always washed from the bottom up, when done merely for cleaning, and not repainting - streaks!

Also, wet all foundation plants down thoroughly before bleaching, and then right afterwards. What goes into the ground does not seem to affect the plants, but leaving bleach on the leaves will!

Yes you can stop mildew, add additional UV protection since most paints are polymers, add carpenter bee retardants etc. These are reasons to buy from a paint store, rather than a big box. When a tree fell on our house, the new gallon matched exactly with the 12 year old paint. This is why you should ask if the paint is the best you can buy from them. The labor saved in upkeep is off the chain.

trickyputt,

Whether your paint matched after 12 years is more a matter of its color, rather than the paint. My guess is that your color did not have any yellow in the formula, a color that is notorious for fading. Earth tone colorants, such as raw umber and lamp black, are far more resistant to color change than the primary colors, especially yellow.

I can tell you that EVERY Behr product has a mildecide in it. Mildecide is the first thing to go when a paint manufacturer is trying to get to a minimal price. Even Behr's base grade Premium Plus exterior house paint is 100% acrylic based and uses only premium titanium dioxide as its white pigment, rather than cheap filler pigments. Behr products consistantly rank at or above the other nationally marketed paints, often WAY above those carrying outrageous prices.

Behr's new premium Marquee line features a new low fade yellow and an additional UV blocker, and still comes in at the mid $40's. Those who are paying $70 for a gallon of paint are being delusional in thinking price always equates to quality!

Its green. Sort of a darker foresty green because we are surrond by trees. But you know how oxidation makes a paint lose its luster? This paint is still slick. It has now outlasted the roof. Its some polyurethane acrylic blend I think we get from Pittsburg Paints but frankly I would have to go look at the can.