Leaking Gutters
There are three ways to construct a miter on a gutter for a house. There is the hand tabbed method, where the miter is screwed together by tabbing the pieces together. This method looks clean but can pull apart with expansion and contraction and cause leaking gutters. Then there are pre-fab box miters. These are for the most inexperienced gutter installer. They require sealing the corner in three places. Because they are pre-fab, they do not always match the profile of the actual gutter, and this causes leaking gutters almost from the outset. The best method of doing miters is the strip miter. The strip miter is a narrow piece of aluminum, made to fit the corner as the two pieces of gutter come together. It allows for the actual expansion and contraction and looks very clean and works great. That is the method we use at St. Louis Gutter & Siding, Inc.
Another reason for overflowing or leaking gutters could be the age of the gutters. If the house has had gutters for 15-20 years, the house can shift ever so slightly, thus knocking out the drain possibility in the gutter. At that point then the water will overflow at the closest point where it cannot flow any more. This requires the replacement of guttering to give proper drain.
One last thought. If the gutters have not been cleaned recently, they may have debris in them causing the outlet tube to be clogged and not allowing water to flow into the downspouts. It can be as simple as a small stick and a leaf wedged in the outlet tube to cause them to overflow. Keeping them cleaned and free of debris is important to help avoid leaking gutters. If you have areas that are too high to reach safely for gutter cleaning, gutter protection should be considered.