Aloha Bonzgirl, It probably depends on the age of the asphalt roof. If you have just installed it, then let it get washed off by a couple heavy rains first. After that, it shouldn't be any problem IMO. Actually, the grit that comes down off the asphalt shingles may help the chickens digest grain? You could get some sort of a water filter if it worries you, although that seems like an un-necessary step, but I'm not an expert on this stuff. Almost all of the roofs around here are tin so we don't have a lot of experience with asphalt roofing. A hui hou, Cathy

Maybe this Ultra-Urban Filter would be useful. It says it removes 90% of oil & grease (which I believe is what hydrocarbons are), and they say it's low-cost. Didn't see a price. http://www.abtechindustries.com/uuf.asp Sue

With a metal roof you are supposed to have strips that prevent sliding. We have them on the pool room part but not the garage. If you live in an area with heavy snow you should also be using a snow rake on the roof to prevent heavy accumulation if you have a lower pitch roof to prevent ice damming during freeze, thaw cycles. At my last house we had asphalt shingles on the roof and still would have snow that would slide from the roof because it was a really high pitch on the roof that we couldn't reach even with a snow rake. Luckily we didn't get as much snow there as we do here. As you can see in the attached photo. There is hardly any snow on the roof at the time of the picture and hardly any on the ground where it would slide off. The huge hill is due to drifting snow. Another pro to metal roofing for me is in the collection of rain water. With asphalt roofing you always get more debris, often times pieces of the asphalt. Just for fun, here's another shot of the kind of winter we had here in 2013/2014. That was the longest and worst winter ever. The snow blower wasn't working and thankfully our neighbor would plough our driveway every once in a while with his tractor. That huge pile was as tall as the roof. It was a combination of drifts and piled snow as we shoveled the walkway. That was also the year the water froze down at the barn and we had to carry buckets of water every day. Both hubby and I threw our backs out that year.

Ichabod, we're in the desert southwest, but I probably should have expanded on that comment! Our annual average rainfall here is under 10". Snow does happen but is not common. Ice dams are not a problem here, for example, so local code does not require ice and water shield at the eaves, either. We recently had a wet 6" snow but that is fairly remarkable for us, down here in the southern part of New Mexico. Also to you and tlbean2004, thanks for your thoughts on the metal flashing. We may request metal valley flashings, with ice and water underneath. Metal flashings got the roof through 17 years with no problems, so I'm not sure why to abandon them now...unless the technology of modern underlayments has rendered metal valley flashings obsolete. I thought that was what the roofer was implying, and we weren't sure if that was correct. I'll admit I am also a bit more worried about this roof than I would be if it was not such a low pitch. So you folks are a big help. klem1, thanks for your explanation. Nope, no interest here in removing the 2x2 trim to try to treat the rafter tail end grain (DH would leave me if I suggested that) so it looks like the consensus is to keep a very wide metal flashing. I guess it will be less distracting when painted to match the wood. Our house was built in 1965 and I sure don't want to make uninformed decisions that lead to damage...all for the sake of looks. (As much as I dislike the look of the big drip edge.) I guess a smaller drip edge and rotted wood would not be very pretty, either. I need to figure out which ice and water shield product will work in our hot temperatures, if we want it under the metal valley flashing. One bid specifies GAF Weatherwatch (but the contractor isn't local.) I don't know how heat resistant that product is. I know Grace Ice and Water has the best reputation, but I was surprised to see the Grace website says that only their most expensive product, Grace Ultra, should be used in the desert southwest: Grace IWS Contractor's Guide So if the esteemed Grace Ice & Water Shield (regular product) will not stand up to desert southwest heat, I wonder how any of the (much less expensive) GAF ice and shield products would work. There are a few scary stories in some roofing forums about "bitumen bleed" when ice and shield products are used in higher temps than recommended. (Roofing is not for sissies, have you noticed?)