These installations can be complicated due to the length of roof pan versus seam length, cleat design and spacing, and the physical expansion characteristics of copper sheets. This expansion must be accommodated by fixing the pan at one end (which accumulates the expansion at the loose end) or by fixing the center of the pan (which accumulates half of the expansion at both free ends). In addition to panels, copper roof tiles can add uniqueness to a roofing system. They can be used on any roof shape and in all types of climates. While most modern construction materials are fairly resistant to moisture penetration, many joints between masonry units, panels, and architectural features are not. The effects of natural movement due to settlement, expansion, and contraction may eventually lead to leaks. Copper is an excellent material for flashing because of its malleability, strength, solderability, workability, high resistance to the caustic effects of mortars and hostile environments, and long service life. This enables a roof to be built without weak points. Since flashing is expensive to replace if it fails, copper's long life is a major cost advantage. Cold rolled hard temper copper is recommended for most flashing applications. This material offers more resistance than soft copper to the stresses of expansion and contraction. Soft copper can be specified where extreme forming is required, such as in complicated roof shapes. Thermal movement in flashings is prevented or is permitted only at predetermined locations. Flashing installed incorrectly can promote line corrosion and shorten the life of valley flashing, especially in acidic environments. The risk is most prevalent at the leading edge of shingles where the shingle edges rest on the copper flashing. Through-wall flashing diverts moisture that has entered the wall before it can cause damage. Counterflashing diverts water to the base flashing, which, in turn, diverts it to other materials. Various types of copper flashings and copings exist. Diagramatic explanations are available. Leaking gutters and downspouts can cause serious damage to a building's interior and exterior. Copper is a good choice for gutters and downspouts because it makes strong leak-proof joints. Gutters and downspouts made with copper are expected to outlast other metal materials and plastics. Even in corrosion-prone seacoast environments or in areas with acid rain or smog, copper gutters and downspouts can provide 50 years or more of service. Downspouts can be plain or corrugated, round or rectangular. cold rolled copper is typically used.