What Causes Water To Spill Over Gutters?

Q:   I noticed this morning, during the moderately heavy rain we had, that the rain was falling over the gutter (north side of the house, over my porch/sidewalk) in sheets.

The ground below quickly became a little lake.
What would cause that? Are there more “design issues” on the front that need to be attended to? That might also require a larger gutter and downspout?
Might the downspout or gutter itself be clogged, so that the water is just overflowing?
Appreciate any ideas you’ve got!
A: There are several things that cause these problems.
  • One is that the gutter is not pitched so the area where the spillover was happening is actually a low point in the gutter.
  • The second thing that causes this is either insufficiently sized downspouts for the run or else a clogged downspout (often up near the top of the downspout but still in the gutter).   Aluminum downspouts come in either traditional widths of 2” x 3” and oversized, 3” x 4”.  At Energy Masters we install the larger ones to accommodate larger flows.  A word of caution here — some gutter installers will simply choose a cookie cutter approach of adding an additional downspout.  This often does not solve a problem and usually when we see this approach used, it is not an effective plan anyway because the entire gutter needs to be pitched in such a way as to split the volume of water going toward the two downspouts.
  • Finally, sometimes there are underground drain tiles (black corrugated tubing in most cases but sometimes white PVC) that has become clogged.  This creates a problem where water backs up and creates a funnel-effect — effectively making it so that water cannot get down the downspout fast enough so it backs up in the downspout and spills over the gutter.  There are two sizes of this drain tile, 3” and 4”.
Use caution when companies suggest a larger gutter.  In most cases a 6 inch gutter is overkill for residential applications.  While we offer 6 inch gutters, they just don’t quite look right on a house and in most cases the companies that are pushing the larger gutters are still using the same sized downspouts — which brings you back to the funnel-effect I referenced earlier.
However, it is worthwhile to assess the amount of roof that spills into the gutter and that the downspout must accommodate.
All of these issues should be done in concert with an assessment of the slope of the property and understanding of how the water can be managed to flow away from the foundation as quickly as reasonably possible.
That’s may be more than you wanted, but now you know more than 90% of the guys who install gutters for a living.
I hope this helps,
All my best,
Jim McGuigan
Owner, Energy Masters
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