There are several facts to know when installing a leaf gutter guard and how the system will interact with or impact the edge of your shingles.
Most shingle manufacturers recommend a 1/4 to 3/8 inch overhang over your eave, which is where your roof ends by your gutter. In many cases, and particularly as home ages and settles, the roof edge at the eave edge can wave in and out by more than this amount. If a drip edge has been installed, some of this irregularity can be addressed by the rigidity in the metal. It can cover some minor flaws caused by any waviness.
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Shingle manufacturers want roofers to stay within this range so it will reduce the likelihood that wind could catch the shingle edge and lift it, which can damage the shingle.
We've seen references in some professional publications that like to extend the shingles to compensate for wavy eaves, but they do not suggest more than 1 inch over the eave. That's not too much of a difference from the manufacturer's specifications.
Too often, leaf gutter guard installers see conditions where roof shingles extend even further - by an inch or two. Sometimes, in the South, you'll see shingles touch the bottom of the gutter.
When shingles extend this far, what can happen to systems that sit flat or vitually flat on your gutter? If the shingle isn't trimmed back as part of your installation, then you can lose more than half of the water receiving area of the product, rendering it much less effective that it could be or was designed to be. You may also wind up with water overshooting the system in a heavy downpour.
In many cases, the shingle will extend over the leaf gutter guard and not come in contact with the system. This can create another set of issues. Debris, especially small debris, can get trapped under the shingle, where wind cannot blow it away. When it rains, this debris gets wet and stays wet longer than it would if it was exposed on the front of the system. Water will want to wick from this debris into the bottom of the shingle, onto your fascia board or into anything else it's touching. If your roof underlay is roof felt, it can cause it to deteriorate and lead to dry rot.
These systems tend to be the type of leaf guard that sits on a large plastic or metal bracket. They don't go near the shingle edge at the eave. In most cases, there is no impact. They do have other issues, however. Several are installed with screws that go through the roof shingles, not a preferred installation methodology of the shingle manufacturers. They also still allow debris to get into your gutters through the gap under the curve, particularly when it rains. Lastly, they can mask issues if the shingle does drop too far into the gutter. As the gutter fills with debris and possibly clogs, the mulch like material and standing water can come in contact with the shingle. Once the shingle acts like a wick or straw, it can cause roof issues hidden under the leaf gutter guard
A gutter guard shouldn't add to water issues on your home, it should eliminate them from starting.
At MasterShield, we make a point of mirroring our leaf gutter guard to the pitch of your roof. Since we extend out and down over your gutter, we can accommodate slightly longer roof shingles, but not too much or the filter will be covered. (We include instructions in our installation guide that shingles can't extend more than 10% over our filter on straight runs and not at all where there is an inside corners.) There will be occasions where you'll have long shingles and our dealer will accommodate them by suggesting 6 inch gutters or discussing trimming them back to best practice specifications.
MasterShield's Shingle-Safe Back also acts as a built in drip edge. It helps water drop forward, over the trough of the gutter, not back towards the fascia. Pitching with the roof with our system means you won't get dramatic shingle lift off the sub roof, even as you drop towards the downspout.
When you get an estimate for a leaf guard, you should ask the estimator to assess your roof shingles so that you know how far they extend over your eave. With this information, you'll have a better sense of issues that can develop or how the product will perform. Knowing what to expect after you install a leaf gutter guard can lead you to making a better informed choice from the start.
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