Metal roofs have one characteristic not typical of asphalt shingled roofs: snow often slides easily over the smooth surface, and proper design must either locate building entrances so as not to be in the path of sliding snow or provide bars to prevent snow slide. However, for all roofs, rapid melting of snow cover and formation of ice dams and big icicle formations nearly always is due to interior heat getting to the underside of the roof deck. That results from improper air sealing at the attic floor, or, in the case of a cathedral ceiling, improper sealing at the lower boundary of the ceiling cavity where it sits on the walls. The other cause of ice formation is lack of sufficient insulation, notably where the roof plane meets the walls.
In the case of the Rite-Aid store in Meredith (yes, a shameful result for a brand new building), the problem could have been the architect's fault for failing to design and isolate the roof from interior heat leakage, or it could have been the GC's fault for shoddy implementation of what could well have been proper design. There is simply no excuse for a building showing what this one does, when roofs all around it in the area still retain their snow cover. Diagonally across the street is the bank building, and soon after a new snow storm it seems there always is an impressive display of icicles hanging from the roof edge all across the front facing the street. Now, that is an older building, but still one crying out desperately for a thorough energy audit and meaningful remediation. In the bank's case, a fairly straightforward solution would be removal of the roof surface, applying about four inches of polyiso insulation board, covering that with a nailing deck and WRB, and finally new roofing.
There is a wealth of information on how to do roofs properly and to fix ones with ice problems. Two good sites for searching are
www.buildingscience.com and
www.greenbuildingadvisor.com. In particular, this blog on the latter covers the science fairly well:
http://www.greenbuildingadvisor.com/...and-insulation