Where can I take an aluminum trim coil (like aluminum siding sheet) i.e. larger than 20 and 24 inches?
Answers: You can buy a 48" by 12' by 1/16" gummy piece from McMaster-Carr. You may not want to though, it is rather pricey:
http://www.mcmaster.com/param/asp/psearc...
You should be capable of buy 28" mill finished aluminum in 50' rolls at a roofing supply shop. Mill finish system the coil will not be painted - you will need to verbs off the grease, prime with an aluminum primer and consequently paint. This is more of a roofing item than a siding item, thus the need to find a roofing supplier.
I don't believe this will look good long residence. Wide pieces of aluminum tend to "oil can". Aluminum expands and contracts slightly a bit with heat and cooling. It can't move when fastened, so it distorts a bit resulting in noticeable defects. Creases and joint in the metal lend a hand. You will have a easier said than done time finding anything wider than 24" because it is not commonly used. Even the 24" wide is usually any cut or bent. If this were my project, I would use at lowest three pieces to make the 28" to minimize the distortion next to lap seam.
For what it is worth, you can buy painted steel in 40" or 44" yawning pieces from companies that make 3' all-embracing metal roofing panels. These game the width of the unprepared stock before it is ribbed. It will grease can as well, but not as fruitless because the metal is thicker. Also would come painted, although in a fixed number of colors. If you need white, you should be within good shape.
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