I suppose it depends where you live and what your weather is like.

We do nothing to the siding on our house and neither does anyone in town so far as I know and no one seems to have a problem with mold or mildew. Then we live in an area that has very little humid weather and half a year of winter.

Look at a product called Wet and Forget.

And I'm not a spammer, just someone who hates mildew and read about this product in the Costco Connection.

Here is a link that might be useful: Wet & Forget

patrice:

I don't know what hadiboard is, but before you go with vinyl you might want to look at cementboard. We chose it for looks and durability over vinyl siding. It has the same look as wood without the need to paint and has a terrific guarantee. Like the above poster said, I think humidity (mildew) and color would play a part in how often it needs washing. We have white and have had it on about a year and a half and don't need to wash yet. HTH

Cement board is hardy board.

Pretty much the only time it really gets cleaned is before we restain it - which is about every 8-10 years. We have cedar siding that's about 37 years old.

I have a BIL who has hardi plank siding and thinks it's the greatest thing every invented. I've never heard him mention that he has to wash it every month. Maybe he does but he talks more about how low maintenance it is.

Yes, actually you're supposed to. At least that's what my house painter said when we had the whole house repainted after a remodel 4 years ago. He recommended hosing or using a power washer on soft setting once a year to get all of the accumulated dust and dirt off the painted siding. We live in the Pacific NW so with all of the wet winter storms and wind the outside does get battered months on end.

I think what we fail to see on top of the paint or vinyl is the same dirt that's on your windows. We all clean our windows periodically, you can imagine that stuff building up over 10 years on the outside of the house!

Not often enough. I am taking a break from that right now. I have been around with a long brush to get all the spider webs and am about to go back out and do the windows. But I have rough cedar board-and-batten -- how does one clean that?