The third decision a person buying a gutter system makes is the size of gutter. Gutter size is the measurement from the back to the front of the opening to the gutter channel. The larger the gutter, the more expensive the gutter system will cost. But it’s important to get the gutter size right – too small, the gutters won’t be able to handle the amount of rainwater flowing through the system; too large, they can become expensive overkill.
Determining the Required Gutter Size
While the total square footage of the roof is the main determining factor, there are other things to consider when selecting the correct gutter size that will protect your home. These other factors include:
- calculating the square footage of the drainage area
- establishing the annual rainfall for the past seven to 10 years
- determining the number of inches falling per hour in extreme rainfall conditions
- establishing the gutter system’s handling capacity based on profile (shape), including the number of downspouts
If you plan to install the gutters yourself, there are a number of gutter size calculating tools available on the internet.
The most common residential gutter sizes capable of handling the typical amount of rain that falls in the Vancouver area are 5-inch K-style and 5-inch half-round gutters.
For larger homes or homes with a multi-level roofing system, standard 6-inch K-style or 6-inch half round gutters would be used.
Depending on climatic and microclimate conditions, a six-inch gutter system can channel up to 45% more water than 5-inch gutters.
An integral part of the gutter system is the downspout. A determining factor for how many downpipes your gutter system might need is one downspout for each 30-foot section of gutter.
A rectangular 2 x 3 inches downspout or a round 3-inch downspout is typically paired with 5-inch gutters.
Standard 6-inch gutters are commonly matched with a rectangular 3 x 4 inches downpipe or a round 4-inch downpipe.
When added gutter size, for example, a 7-inch gutter system, would spoil the aesthetics of a home’s exterior, often 5-inch gutters are used with a larger downspout size to help an increased volume of water exit the gutter system.