Metal
Metal roofs are available in 3 basic types: screw down metal panels, standing seam and metal shingles.
Screw down metal panels are the most economical and most common type of residential metal roofing. This roofing material comes in panels either 2� or 3� wide, which run the full length of the roof rafter.
There are a wide variety of colors to choose from, including mill finish and galvalume, and also a number of different patterns or profiles. Typically the profiles consist of wide, flat pans varying 6� to 12� in width interrupted by raised sections, known as ribs. The ribs may be peaked or flat on top and may raise from the surface of the pan as little as 1/2� to as much as 2�.
These panels are screwed directly to the roof deck with long screws whose heads are set into a rubber grommet. This rubber grommet is designed to make a water tight seal between the screw head and the metal roof.
This brings us upon a major controversy in the roofing industry that divides roofers into almost 2 equal camps. The first of these believes in following the manufacturing recommendation in placing the screws in the pan. They believe this is the correct procedure because: 1-the manufacture recommends it. 2- It�s much easier. 3- You can depend upon the grommet to keep water from leaking into the screw head. 4- If you put the screws in the ribs you can over tighten the screw causing the panel to spread making it more difficult to keep the roof panels aligned. The second camp, of which I am a proud member of, believes the screws should be put in the rib. We basically have only one reason for doing so, that being that the water runs in the pans and not in the ribs. And only an idiot would put thousands of holes in his roof that would be submerged by water every time it rained. We accept the fact that it�s harder to do and more time consuming and that we have to be careful not to spread the panel but worth the extra time and effort because we do not put total faith in the rubber grommet, even initially, and we are positive that the combination of the grommet�s failing and a screws backing out will eventually lead to water leaks if the screws are in the pan.
The second type of metal roofing is standing seam metal panels. These consist of panels fabricated to run the length of the rafter and distinguish themselves from the screw down metal panel by having no exposed metal fasteners. The panels are attached by clips recessed under the panel. By eliminating the thousands of screws and the holes that they make in the metal this roof system removes much of the potential for developing a leak.
These roofs are labor intensive and cost about twice as much as the screw down metal panel and are therefore most often found on commercial properties such as banks and schools. Like prepainted metal panels standing seam metal roofs are usually made of steel coated with either a galvalume process or a baked on paint finish.
The third common type of metal roofing is metal shingles. Just like the name implies these are small pieces of metal overlapped and/or interlocked in the same way that shingles or tile are installed. These come in a wide variety of styles, colors and materials. Usually stamped out of copper, steel or aluminum they may resemble wood shakes or slate, or bear symbolic designs such as a fleur-de-lis.