One of the most common places for gutters to leak from is the corner sections, which are called miters. When two sections of gutter come together at an angle they are joined together with a miter, which covers the seams of the gutter sections and connects the two pieces. Whenever you have a gutter corner leaking it is often a sign that the gutter system is not functioning properly.
In this article we explain what a gutter corner leaking indicates about your gutter system, and how to prevent gutter corners from leaking in the future.
Miters (and all other gutter seams) are sealed using waterproof sealants such as caulk. The sealant prevents water from being able to leak through the seams. For this article we are referring to the natural sealant failure process that comes from age. Other contributing factors such as improper gutter slope, clogged gutters, gutter neglect, etc.. drastically speed up the process of sealant failure.
Over time most gutter sealants that see water traffic will breakdown and fail before the gutters need to be replaced. Since aluminum gutters are rated to last anywhere from 20-40 years, and the sealants are only rated to last 5-10 years, it’s almost guaranteed. However sealants that don’t see much water traffic typically last as long as the aluminum gutters without ever needing to be serviced.
Anytime a gutter seal fails, whether due to gutter slope issues, time, clogged gutters, etc.. it needs to be resealed. To do this properly the old sealant needs to be removed and the surface cleaned and dried before applying a new sealant. In addition to the surface needing to be clean and dry, the sealant also needs adequate time to cure before the next rain. Most sealants require anywhere from 4-24 hours to cure properly. Therefore be sure to check the weather before applying new gutter seals.
Keep in mind if the sealant failure was caused by another issue than old age, the issue will need to be rectified before applying new sealant. Otherwise the sealant will fail again.
Arguably the most common cause of a gutter corner leaking is when the gutters are not pitched properly. Gutter pitch, or otherwise known as gutter slope, is the angle at which the gutters are set so that they drain towards the downspouts. When the gutter corner is set too low, or one of the gutters of a multi gutter section is not pitched correctly, the water often becomes stuck in the corners. The bad news about water in the corners is it causes the seals to rapidly degrade and leak.
The more corners a gutter system has the trickier it is to configure the gutters so that everything flows properly. All it takes is one of the gutters to be sloped incorrectly for the water to get trapped in the corner section. Therefore more corners equals more potential leaking points.
We see gutters out of slope in combination with gutter corner leaks more often than not. To repair this problem properly the gutter will first need to be set at the correct slope, usually by using a level. Once the gutter slope is adjusted the next step is to dry out the miter well enough to be able to apply sealant. The problem with leaky corners is they are usually full of water. Unfortunately for the sealant to cure properly it needs to be applied to a dry surface. Therefore if the miter is holding water when you re-pitch the gutter, you may have better luck waiting a few hours to apply the seal.
When a miter leaks due to gutter slope issues, the gutter slope will need to be adjusted before sealing the miter. Otherwise the water that isn’t able to drain will destroy the new miter sealant in no time.
For more information on Gutter Pitch/Slope please visit our Gutter Repairs page.
A gutter corner leaking in close proximity to a downspout is often an indication that the downspout is clogged.
Piles of debris in the gutter can cause the gutter to fill up with water and leak. Especially when the debris is causing a blockage near the miter. This works the same as gutter pitch as the sitting water in the gutter destroys the sealants. If the water is not able to drain, it destroys the sealants.
The solution to clogged downspouts or gutters is to either remove the clog from the downspout yourself manually, or contact a local gutter service provider for a gutter cleaning service. We recommend to also observe the water flow from the allegedly clogged downspout to confirm if the downspout is clogged. If there is barely any water coming from the downspout then that confirms that a gutter cleaning is needed. In contrast if there was a lot of water flow that would indicate the downspout is not clogged. Therefore the issue is likely gutter repair related, and the gutter corner sealant has failed.
Excessive water flowing down roofing seams will also contribute to the sealant failing at a much faster pace. In the short video below you will see water overflowing a home at the inside gutter corner. The water rushes down the roof valley from the upper gutter section and goes directly to the corner . When excessive water is directed at the corners like this, it rapidly degrades and wears out the seals. Therefore these situations are prone to causing gutter corner leaking.
The solution to the above situation is to extend the upper downspout into the lower gutter so that the water isn’t directed at the corner. To achieve this we typically would install a downspout elbow at the bottom of the extension that points away from the corner.
Allowing debris to stay in the gutters for extended periods of time results in sludge in the gutters. Through the seasons all gutter debris decomposes and turns to a nutrient rich mulch like substance. When it rains this much turns to a slimy sludge and spreads through the gutter system. The bad news is when the sludge gets stuck in the corners, because it also rapidly degrades the sealants. Which leads to the gutter corner leaking. If left to collect
Staying on a proper gutter cleaning schedule is the best way to prevent debris from building up in the gutter system and accumulating over time. The amount of trees you have nearby and how close they are to the home will determine how frequent gutter cleanings will be needed.
Over time gutters may rust or corrode, especially at gutter corners that are prone to leaking. The first sign of this happening is water leaking through what appears to be a small pin hole. Eventually one pin hole leads to more and more.
Acid erosion from excessive pollen is the main cause of aluminum gutters to rust over time. Aluminum is rust proof but under extreme circumstances rust can form. Acid from pollen is the main cause of rust to form in gutters. The next most common cause is heavy metals that react with aluminum, such as copper, stainless steel, nickel, or lead. These metals are not supposed to be used with aluminum because the two metals react and corrode each other.
Pin holes on a gutter can sometimes be caulked or sealed for a short period of time, as a short term patch or band aid. However if the holes were caused by rust, there is no solution but to replace everything the rust has infiltrated. Wherever there is one rust hole, more are sure to follow. Signs of corrosion along the miter seams is also a direct indication that the miter will need to be replaced.
Homeowners can help prevent gutters from rusting over time by cleaning them out in the spring once the pollen falls. This is suggested for homes with nearby trees that drop excessive pollen in the spring.
Bad craftsmanship should be higher up this list because it is fairly common. There are mistakes that can be made when installing miters to gutter corners. The most common is to not apply the sealant properly. If a small pin hole is missed the water will find it’s way and leak through. Another common mistake is cutting the gutter incorrectly which can leave a gap between the miter and gutter. This will lead to attempting to patch with excessive sealant. Screws that are too low or are not caulked will also leak.
Once somebody has hacked up with the miter or the gutter it connects to, replacement is almost always necessary.
Once aluminum gutters reach about 30 years of age (or sooner with gutter neglect) the paints start to fade and the aluminum starts to degrade. Eventually gutter sealants will not form a proper bond with the aluminum, which results in leaking more and more frequently. For example you could seal a corner and it will last a year. Then the next time you seal it, it will only last 6 months. And then the next time it will last 3 months, and so on until the seals become ineffective.
When the gutters become old enough that the sealants no longer bond to the aluminum, the only solution is to replace the gutters with new gutters.
A gutter corner leaking is often a sign of other underlying issues within the gutter system. The issue more than likely needs to be addressed before attempting to reseal the corner. Otherwise the sealant will fail again. The key point to know about gutter sealants is that they need to dry out between rains so that the seals aren’t compromised. Therefore when sealants are allowed to remain submerged in water, they simply will not last.
Don’t just take our word for it! See what the other experts are also saying about gutter corners leaking.
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93 Monocacy Blvd. A-6
Frederick, MD 21701