How to make sure your gutters are installed correctly
The main variables in sizing a gutter system are:
- gutter size
- 100 year rainfall levels for a storm event
- roof surface area
- roof slope
- gutter slope
- number of downspouts
In a storm event rain does not fall straight down but is blown. With blown rain the steepness of the roof impacts the amount of water that needs to be drained. The steeper the roof, the more water to be drained. Knowing the surface area of the roof, the steepness and the maximum rain level as specified by the Internation Plumbing Code (for example Everett gutter systems need to handle 2.1 inches of rain per hour) your gutter installer can determine how many gallons per hour the gutter system must carry.
Each manufactured gutter system including half round, box, and k-style gutters are specified for capacity. Capacity is also affected by the slope of the gutter. The higher the slope, the more capacity. Moving from a 1/16 inch slope to a 1/2 inch slope increases capacity by more than 2.5x Alternatively, more downspouts can be added to the system. Surface area drained decreases with each additional downspout.
While it is possible to make all the trade-offs yourself, you might want to consider allowing a professional gutter installer plan out your system for you.