Mildew on rafter tails and purlins

Jim Hardee
5/10/2004
I built a new vacation home on the water in Florida three years ago. I have a Galvalume roof with exposed rafter tails and purlins. About 6 months after construction, the rafter tails and purlins became black with mildew. I thought that it was the fault of the paint job. Six months ago, I had the house repainted by a very good paiinting coontractor. He pressure washed it thoroughly and applied a very high quality paint with extra mildewside. The rafter tails and purlins have already started to mildew badly. Please let me know if you have ever encountered this problem and if there is a remedy. Thanks for your help.
Allan Reid
Dura-Loc Roofing Systems, Inc.
5/10/2004
I assume the rafter tails and purlins are wood. Unlike Galvanized metal, Galvalume does not leach off zinc at the same rate which makes the Galvalume last longer however it does nothing to kill mildew. Galvalume does not support mildew, mold etc and providing you have a positive slow, flushes everything off with each rain. I suspect that somehow the rainwater is getting on your framing mambers. Metal on lower slopes tends to sipho water back up under the leading edge with the smooth surface. Quite possibly your builder did not install a drip edge which stops the problem. Have a look and if you have any further questions, please contact me directly with a photo.
Guest User
5/10/2004
I have a 70 year old house with Asbestos shingles on the roof. It has been a great roof all these years, but it starting to break-up in places now. my question is can I have a verticle metal roof installed over top of it? thanks Charlie
Jim Hardee
5/11/2004
Thanks for your reply. The rafters and purlins are wood. I'll send you photos. The painter thinks that condensation is building up between the metal and the tails and purllins and causing the mildew. Please let me know if this is common and if there is a method of preventing it. Also, is it standard practice to prime and put a finish coat on the tops of the tails and purlins prior to installing the roof. Jim
Todd Miller
Classic Products, Inc.
5/11/2004
There have certainly been instances of successful installations over asbestos shingles. This is usually done either with one of the shingle, shake or tile metal products or with a vertical seam product, in which case the vertical seam product would have to be installed over battens. I suggest working with the manufacturers of products you like to determine how appropriate this type of installation for your situation. If you go to my company's website (www.classicroof.com) and click on For the Architect, you can go to our list of Technical Bulletins and download our bulletin on Roofing over Asbestos.
Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.