Downspout Theory and Capacity

A Rain Gutter is only as effective as the size, and number of Downspouts associated with it.  Standard sized Downspouts (2 inch Round or 1 3/4 inch X 2 3/4 inch Rectangular) are connected to a 2 inch (diameter) round Drop Outlet (metal sleeve) that is inserted and sealed into the Gutter.  The area of a standard 2 inch round hole is 3.14 square inches.  Considering the average rainfall in Northern California, the general industry rule of thumb for Standard Downspouts is one for every 35-40 linear feet of Rain Gutter, on an average sized roof, with little associated leaf debris.  If there is a larger than average roof area, or a significant ammount of leaf debris, there should be more Standard Downspouts installed on the Rain Gutter then the general rule of thumb would suggest.  In high leaf debris areas, having an effective Leaf Protection Product installed on the Rain Gutters will dramatically reduce the number, and size Downspouts necessary to effectivley drain the roof water.  With Standard Rectangular Downspouts, the Standard 2 inch Round Drop Outlets can be upgraded to Rectangular Outlets (1 1/2 inch X 2 1/2 inch), which have an area of 3.75 square inches, and produde a 19% increse in water flow.

Oversized Downspouts (3 inch Round or 2 inch X 3 inch Rectangular) are suggested in conditions where there is a large surface area of roof, a heavy ammount of leaf debris, or if fewer Standard Downspouts are desired.  2 inch X 3 inch Rectangular Downspouts come with an oversized Rectangular Drop Outlet (1 3/4 inches X 2 3/4 inches), that has an area of 4.81 square inches, which results in a 53% increse in water flow.  The 3 inch Round Downspouts come with an oversized 3 inch Round Drop Outlet, that has an area of 7.07 square inches, which results in 125% more water flow than the Standard 2 inch Round Drop Outlets.  3 inch Round Downspouts are standard with the 6 inch Half Round Gutter, and can also be used with the 5 inch Ogee Gutter at full capacity.  3 inch Round Downspouts can also be used with the 5 1/2 inch Fascia Gutter, however the bottom of this Gutter is only 2 1/2 inches wide.  In this application, the 3 inch Round Outlets have to be ovaled to fit in the narrower Gutter base, which slightly reduces the water flow capacity, but is still a significant increse over the Standard Downspouts.  

Un-painted Galvanized Rectangular Downspouts

Un-painted Galvanized Rectangular Downspouts come in the Standard and Oversized sizes.  They and are the Highest Quality Steel Rectangular Downspouts that can be installed.  The Oversized Rectangular Downspouts (2 inch X 3 inch) ONLY come Un-painted Galvanized.  Un-painted Galvanized Downspouts are the Highest Quality because they are made out of a thicker gauge metal, and can be soldered together.  They are extremely durable, essentially welded Downspouts.  Being able to solder allows us to do make very custom Downspouts that we are not be able to do otherwise.  Because of the metal thickness, these Downspouts tend to be much quieter than than the Standard Pre-painted Downspouts when water runs through them, and are much less likely to make the dreaded dripping noise.  Many of our competitors do not offer these type of Downspouts because soldering is a skill that not all installers posses.  All of our installers are highly trained sheet metal Craftsman, and are capable of fabricating and installing the most complicated custom Downspouts.  Much of our work is Seamless Gutter Systems on brand new homes.  Every new home we do gets Un-painted Galvanized Downspouts because most all builders recognize their un-matched Quality.  There is nothing nicer than a smooth soldered Downspout that gets painted the same exact color as the the siding.  The Downspouts disappear more and blend into the house better when they are painted this way.  Un-painted Galvanized Downspouts do not need to be painted.  They could be left Un-painted forever, but most folks prefer them to blend and disappear.  

Pre-painted Galvanized Rectangular Downspouts

Pre-painted Galvanized Downspouts only come in the Standard Rectangular size (1 3/4 inch X 2 3/4 inch).  They are availablein all of the CustomBilt Metal Pre-painted Steel colors.  We cannot solder a pre-painted metal, so these Downspouts have to be riveted and sealed with a clear sealant at every miter (turn).  As one could imagine, rivets and sealant are not nearly as strong and nice looking as a solder that has been painted.  We are limited to how custom we can make these Downspouts, because they cannot be soldered.  Pre-painted Standard Rectangular Downspouts perform and cost exactly the same as the Un-painted do.  However, they are a thinner gauge metal, so they are not nearly as durable and quiet.  We often get complaints from our customers that they can hear the water run through these Downspouts more than they did with their old soldered galvanized ones.  We end up installing a lot of Pre-painted Downspouts because many folks do not want to do any painting along with their Gutter System replacement, but we always inform our customers of the pros and cons.  

Round Downspouts

Round Downspouts come in 2 sizes.  2 inch and 3 inch (diameter).  Round Downspouts only come Un-painted Galvanized.  Pre-fabricated Elbows are used for all the turns.  The elbows create nice smooth turns which is why these Downspouts are usually the quietest, and leaf debris tends to flowthrough easier without getting backed up.  2 inch Round Downspouts can handle the least ammount of water, while the 3 inch offers the most water flow capacity.  In some peoples opinion, Round Downspouts do not look good on every style home.  However, there is no match to the amount of water and leaf debris that can flow through a 3 inch Round Downspout.