A decent gutter with the right cross-section and slope, should smoothly carry away all but the heaviest deluge of rain. However, if it overflows it can spill moisture on more than your head. That’s why choosing the right gutter size for your roof does matter.

Many clients approach us for a recommendation, because their eavestrough systems are overflowing. Some believe a seamless aluminum system is all they need ‘because the water will flow smoothly’. However, they may also need gutters with a larger cross-section, which would cost more than the standard-size version.

How the Roof Dictates the Solution

The size of the roof determines the amount of water arriving in the gutters. But the speed with which it flows down affects what happens next. A steeper roof puts a greater load on the system, and the type of roofing material also comes into play. That’s why we always recommend 6″ gutters for anything other than asphalt shingles.

How to Determine the Right Gutter Size

Let’s assume for a moment you have gutters on all four sides of your house that flow together, and you wish to know the gutter size you need:

• Establish the dimensions of each area of your roof.
• Avoid going on the roof, ESTIMATE them from below.
• Multiply each set of dimensions for the square footage.
• Add these together to calculate the total roof area.

Next, obtain two twelve-inch rulers and a ladder. Hold one ruler level at a convenient point, with the upper end touching the roof. Use the other ruler to measure the distance from the lower end down to the roof. This determines the pitch over twelve inches.

You now need to adapt the total roof area by a factor according to the degree of the pitch. But perhaps that’s best left to a roofing expert, because the roof type affects the flow, and there may be other factors in play. Although as a general rule the steeper the pitch, the more voluminous the flow.

What Difference Does a 6” Gutter Make?

A six-inch gutter carries 40% more water than a five-inch one. But remember, gutter size is not everything. You also need to right-size the down pipes to receive the flow. Speak to Valiant Exteriors if you are in Calgary and are considering an eavestrough installation or modification. We won’t charge to stop by and estimate.

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Why You Need a Decent Eavestrough System (Martin Cathrae BY CC 2.0)