Gutter and Downspout Water Capacity
So what’s the trick to designing the perfect gutter system? How to make sure your gutter is large enough and you have enough downspouts? Use the helpful charts below and you’ll be a near expert in no time! These are “safe” numbers, meaning designed to work under the strongest rainfall not the average for your area. You may be able to undersize based on these charts and be fine 90%+ amount of the time, but if you never want to worry better to be safe than sorry.
Gutter Sizing Water Capacity
|Gutter||Roof Area (Square Feet)|
|Per linear Ft of gutter underneath|
|ROOF PITCH||Up to 6/12||7/12||8/12||9/12||10/12||11/12||12/12|
|5″ K Style||22||20.79||18.71||16.84||16.17||15.28||14.05|
|7″ K Style||48||45.36||40.82||36.74||35.27||33.33||30.67|
|Notes: Max Roof Pitch 6/12 for these numbers|
|No Obstructions into gutter|
|Recommended Slope No Greater than 1/16″ per ft|
Downspout Capacity Based On Size
|Down Spout Size||Max Area of Roof draining to one down|
|3″ Round||450||Sq Ft|
|4″ Round||700||Sq Ft|
|5″ Round||1200||Sq Ft|
|(Safe for maximum rainfall)|
|* Reduce by 10% per 90 degree turn|
|Assumes proper pitch and no obstructions or turns|
Problems with Gutter Sizing
Many factors can effect the proper size of gutter. Most of all is location and your average rainfall during a large downpour. For the vast majority of rains gutter and downspouts sizes considerably less than recommended will do the job.
Primary cause for water spillage is DEBRI IN THE GUTTER. It doesn’t take many sticks, leaves, or needles to impede the proper flow of water in the eavestrough. Make sure your gutters are clean at all times.
Secondary cause of gutters not working properly is improperly maintained or failing gutter protection systems. Screens and filters can eventually clog. Covers that rely on surface tension get dirty and need cleaning. You must maintain your gutter covers even more than the gutter itself many times.