While I’ve seen Rainhandler at work and they can get the water bit further away from the building IN A GOOD RAIN. However they don’t address the problem of too much water too close to the foundation. Unless that is addressed with drainage or grading (or both) their use can lead to large water flows toward and down the foundation and in the north inducing frost driven push forces on the foundation.

It’s normal.

Dust and dirt act as a food source. Muggy humid summertime temps provide moisture.

I suppose it could be algae as well. The walls themselves are actually fine, it’s the underside of the soffits where I see this happening. Currently my home has wood soffits. They are three foot overhangs with quite a bit of venting. At some point in the future, I’m looking to move to a non-maintenance product (metal, vinyl, Masonite). Biggest issue on that is figuring out something aesthetically pleasing – 3 foot overhangs are no the norm, so I don’t know how many options I’ll have.

The stone stays clean because of the protection from the overhangs. There are a few spots (kickout knee wall, mailbox) that are exposed to the elements where the stone grows things (moss, lichens, algae, etc).

I’m in northern Illinois, so we get it all.

The comment on shading and cooling is very true. I believe my home was designed with that in mind as it is a sprawling ranch. It’s got a large southern exposure that brings in lots of natural light and in the winter, heat from the lower sun. During the summer those big overhangs keep things much cooler. The home is also built around a large thermal mass (double stone fireplace) – so we do see some help from that in the milder weather. Works against us in the extremes I think, but I’m no expert.

To explain,
They can keep rain off the walls.
Yes, having a larger overhang can contribute to moving the water away from the walls. They will have varying degrees of success due to rain and wind direction. Overhangs are not a replacement for an excellently detailed and installed drainage plane.

They can contribute to ice dams in ways that are not obvious (I’m leaving off all discussion of classic Ice Dams in this. They happen, they are bad, and they are not the only way Ice Dams form.)
This is a tough concept that normally gets a lot of negative comments, people saying I’m wrong, etc… Large overhangs and ventilated eaves/roofs can actually increase Ice Dams. Here’s the physics. Anytime you have snow piled on the roof, especially the eave, it is extremely sensitive to 32Fdeg (or 0Cdeg). As soon as the snow layer reaches freezing and above, it’ll melt. With a Ventilated Roof, on a ‘warm’ winter day, you can actually be introducing above freezing air to the bottom of the roof sheathing; instant snow melt and freeze when the snow melts. Large(r) Overhangs can enhance this on the Sun Side of the home, because they can trap the warm air that naturally rises off the Sunlit wall and can direct it into the roof/attic through the same soffit vents put there to ventilate the roof; same result, instant snow melt and freeze when the temp drops. To a lesser degree we can have some seriously awful temperature changes here in Minnesota that can also have it ‘Snow’ or ‘Rain’ in an attic, but I’ll try to elaborate on those in a different thread.

They can contribute to mold and mildew growth.
As noted above in the comment about the stone house, Overhangs can facilitate Mold and Mildew growth. This is usually noticeable where the wall is basically totally shaded and also somewhat blocked from airflow. Moist stagnant air can collect below the eave, usually wetting the siding surface, which encourages a build up of both spores, and ‘dirt’. Organics + water+ food + temps = Mold/Mildew; simple biology.

They can be terrible to detail and get right.
Today’s design still is Gables, Gables and More Gables. All of that geometry has to connect somewhere and the overhangs, both Rakes and Eaves, have to work together. Kickout Flashings, Valleys, Gutters, etc all have to work in larger fashions as the sizes of the overhangs increase. The gables also mean greater concentrations of water as noted above in the very telling images of the 1930’s – 40’s Cape. Imagine 3 or 4 or more all concentrating water.

Sometimes you just need to give up and cut them off.
There have been homes where we trimmed rakes back to minimal to meet a ‘style’, and also to minimize some ot the issues above. It looked good (to our eye, and the customer), but we needed to really watch the detailing to make sure everything was ‘shingled’ and was ‘pushed out’ at every layer.

To sum up, I’m not against overhangs. I’m for them because of where we live, but like every part of Building Science, making one choice will always lead to needing to make several more.

“You’ve got to think about big things while you’re doing small things, so that all the small things go in the right direction.” Futurist Alvin Toffler

John M6: I don’t think it’s the overhangs that increase the risk of fire. It’s soffit vents that pull embers from nearby fires (wild or otherwise) into the attic. Because the problem has been increasing, there are now fire-resistant vents available.

David: Thanks for bringing up the shading aspect. I meant to mention that in the article.