What Size Are Gutter Downspouts?

This article was written and published by Rain Gutter Solutions.


A guttering system must have the right measurements on all ends to work properly. This includes downspouts that match the gutter’s preferred size. Likewise, if you are building new gutters to match the size of existing downspouts, a mistake could affect your entire drainage system, letting water pool all around your property. Aluminum Gutters and Downspout Installers take all factors into account to prevent problems down the line, including the right size of gutter downspouts.

Choosing the Size of Your Gutters and Downspouts

Gutters and downspouts work together at all times, and that’s why it’s so important to consider the guttering system as a whole unit, even if you’re just installing/replacing a portion of your gutters.

The measurements of gutters and downspouts are marked by a series of factors. For example, the amount of rain that’s expected to fall around the area and the frequency of storms throughout the year. Some gutter profiles may look great around a home, but they aren’t wide enough to hold large amounts of rainwater without eventually being affected by the weight. This is fine in a mostly arid climate, but in areas with a long rainy season, a gutter may not last long unless it runs at around 6 inches of width.

The size of the roof also plays a huge part in the final decision. Before choosing a gutter or downspout size, you need to know the area of your roof and calculate its pitch factor. A steeper pitch is likely to collect more water, needing a larger gutter with reliable water-holding capacities.

What Size Are Gutter Downspouts?

A general rule, both for commercial and residential properties, is to have a downspout after every 30-40 feet. Just like you have multiple gutter designs to choose from, you can also pick a boxy or a round shape for your downspout, always prioritizing its capacity in relation to the expected runoff.

The most common downspout styles are: square, rectangular, and round, usually built to match k-style gutters and half-round gutters respectively.

Standard downspouts can run at 2×3 inches or 3×4 inches, which is what fits most residential gutter profiles. A downspout can also be as wide as 6×6 inches, but downspout sizes larger than 4×4 inches in diameter are only paired with gutters and buildings that also exceed the average in terms of size.

In relation to gutter styles, both k-style and rectangular downspouts are available in a 2×3-inch and 3×4-inch format, with the latter also allowing a 4×5-inch run. Round downspouts have a diameter of either 3, 4, 5, or 6 inches.

Whatever you choose, the size must stay consistent along the whole downspout run and it shouldn’t exceed the bottom width of the gutter.

Additional Downspout Tips and Facts

Downspouts are usually installed at the side of a building to avoid blocking the entrance area. Many homeowners also find downspouts harder to conceal, while the gutter run can be seen as part of the roof when it’s custom-made. To keep the downspouts from affecting the home’s esthetic value, some homeowners strategically place vines, bushes, or other plants around the downspout. If you plan on doing this, make sure the greenery doesn’t end up blocking the downspout outlet.

Downspouts lead the water flowing from the gutter to a disposal area that’s at least 10 feet away from your property. To do this, the downspout needs to have a sloped discharge area that will redirect the water without any of it slipping out on the way.

When it comes to preventing corrosion, contractors recommend having the downspout made with the same material you’ve chosen for your rain gutters. If you have dissimilar metals, the water running inside the guttering system will act as a conductor and trigger corrosion around the seams connecting the downspout and the gutter run. Keeping the same metals and colors between your gutter and downspout will also bring a more attractive appearance.

It’s easy for details like these to escape your notice when conducting a DIY installation job. The expertise of an installation company is an asset that takes all the heavy work off your back. A professional contractor has the foresight to remember all the important factors and the knowledge to work through all the necessary measurements. This way, you won’t risk finding an unpleasant surprise days/weeks down the line, once it starts raining.

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