When choosing what size of downspout to install, it is important to consider all of the different options. Every option available has its own unique set of advantages and disadvantage to consider. What follows should help you understand the differences between different materials and sizes of downspouts.
Aluminum is relatively inexpensive, but makes quite a good material to make a downspout out of for two reasons. First, aluminum will not rust, unlike certain other metals. Second, aluminum is very easy to maintain. However, it has a few down sides. Aluminum will expand more than other materials. It is also relatively weak and prone to denting and other types of damage.
Copper is a relatively expensive downspout material. It is especially expensive after factoring in the installation costs, as it is relatively difficult to work with and requires skilled workers to deal with it. However, once installed, copper makes an excellent downspout material. Copper does not rust. Additionally, it tends to last for a long time due to its strength and durability. It does not even require paint, which is definitely an advantage.
Galvanized steel works perfectly well as a downspout material. It is quite strong. Also, it does not expand or contract very much, making it an excellent choice of downspout material in areas that have very cold winters with snow and ice.
However, these advantages come at a cost. Galvanized steel will rust if exposed to the elements directly. Normally, galvanized steel is painted, making this not a problem, but paint on galvanized steel is prone to damage, particularly when painted on the spot where they cannot be cleaned and prepared properly.
Plastic works quite differently than metal as a downspout material, and comes with many unique advantages and disadvantages because of this. Plastic comes in a wide variety of colors, which can be very useful if you are considering aesthetics — particularly if you have a color on your home that is difficult to match. Additionally, plastic downspouts do not rust and require no paint, so they are quite simple to maintain. Installing plastic downspouts is simple, as they come in kits that can be snapped together by anyone willing to do a little bit of work. They are also surprisingly durable, and not vulnerable to snapping or breaking due to their flexible nature.
However, plastic downspouts have some disadvantages as well. Plastic bends instead of breaking, which is good. However, over long periods of time, this tends to mean that plastic downspouts will permanently bend and twist out of their original shape, reducing their functionality and sometimes even rendering them useless.
Different homes in different locations will require different sized downspouts based on two conditions. Proper downspout size depends on the maximum amount of rain your gutters will have to drain in a short period, and also your roof's watershed area. Watershed area is determined by square footage and incline. More rain in your area and more square feet that need to be drained require larger downspouts.