Aluminum VS. Galvinized Steel/Coastal S.FL/Radiant barriers

L Kelly
3/23/2005
I am interested in a standing seam metal roof, but am kind of overwhelmed by all the options and differences in the metal itself, the paint, and the insulation(radiant barriers). I was informed by a roofer that a new product called "Prodex" (basically a double sided foil back very thin bubble layer). I am told that Prodex can be installed between the Titanium underlayment and the metal panel. I have read through several of the posts on this board and it sounds like it does not make sense to sandwich a radiant barrier between the underlayment and the metal panel, instead it needs an open airspace on one side. Is this true with this Prodex product or similar products? I am totally lost on whether using a radiant barrier is actually worth it when it is sandwiched. Would it actually send heat into the house? Also if there is no barrier but the sheathing, underlayment, and metal panel, does the metal actually heat up the house as well? I have no attic insulation and currently have damaged asphalt shingles. I like the idea of the high reflectivity of metal, but if it actually heats the house up...does that make sense? On another separate issue...I live close to the intracoastal and have gotten conflicting information on aluminum and steel standing seam products. Does aluminum rust or corrode? Also does steel rust or corrode? Is the paint coat the primary protection against the salty elements...and in this "harsh" salty climate will a prepainted finish most likely deteoriate rapidly? How can you repaint it? Would it require a special paint? Sorry I have so many questions... I am totally confused at this point! Thank you for any and all information. I greatly appreciated it! P Kelly
Todd Miller
Isaiah Industries, Inc.
3/24/2005
Great questions! First of all, the purpose of laminating radiant barrier on foam like that, I think, is to create the required airspace. Still, I do not know how well it works. I would ask them for substantiated third party test results in a standing seam roof system to verify their claims. I might also look for either a light color standing seam or for a colored standing seam which has a paint system with reflective pigment. Either of those will be better than the radiant barrier, I believe. Regarding coastal applications ... most steel roofing manufacturers have some requirements against coastal applications. I am not aware of any aluminum products carrying that requirement. Steel roofing, especially quality galvalume (minimum painted AZ50) or galvanized (minimum G90) has built-in corrosion resistance. Over time, though, the cut edges may get some corrosion, and you may also get corrosion on scratches or from the back side of the roofing. Make sure that steel panels are not saw-cut on the job. They should be cut with shears or a guillotine. Saw cuts leave a nasty raw, rust-prone edge. All aluminum roofing will be painted. Paint or other coatings also enhance the corrosion resistance of galvanized and galvalume steel. Aluminum, if bare and exposed in a wide area, will corrode. Aluminum, however, from just a raw edge or a scratch exposed to solt air, will develop a small protective patina that will not be damaging over time. That is why all aluminum roofing will be painted. I hope this helps.
Guest User
3/24/2005
Hi Todd, Thanks for all the information. I still have a few more questions. Because I have no insulation in my attic and the only ventilation is my soffits and two turbines... will a metal roof either aluminum or steel prepainted white, actually heat up my attic (because of emissivity) and result in a higher electric bill? The primary reason I like the metal roofing is the reflectivity factor, however, if my attic is actually hotter with a metal roof then my electric bill may end up higher than it already is. If you walk on an aluminum roof is it more likely to dent or puncture as compared to a steel roof? Does a pre-painted aluminum need to be repainted after it ages? Is it something a homeowner could paint themselves? All help is greatly appreciated!! Thanks so much! Pat Kelly
Todd Miller
Isaiah Industries, Inc.
3/25/2005
The only situation I have heard of a home getting hotter with metal was when the previous roof was wood shake on lathe -- those tend to breathe a lot. I have some energy test data I can send to you if you email me with your email address. My email is [email protected] The ability of metal to be punctured is determined by the metal chemistry, thickness, and, to some degree, configuration. I cannot make a direct "generic" comparison of aluminum to steel. All of these roofs have been engineered and tested for durability though. Many metal roofs today use Kynar / Hylar paint finishes which are warranted for fade and chalk. Should they need to be freshened up for appearance in 40, 50 or more years, yes, they can be re-painted by a spray process.
Guest User
10/29/2008
Bonsoir Todd, We are building our home. We have decided to put a metal roof. We do now realise that it is expansive. We want the standing seam. If you did have the choice in between a metal roof and aluminum roof for the same price, what would be your choice? The aluminum company Interlock tells us they will give us a lifetime warranty and metal is 30 years.The fact that the aluminum feels so thin scares me but not my husband. We need to make a decision in the next week and we do not find much research about that. Thank you!
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