Gutter mesh is a barrier placed over the rain gutter installed on a roof. A metal or plastic netting or mesh, it permits the easy passage of rainwater to be channeled from the roof to downspouts, but blocks leaves, twigs and other objects from being able to get into the gutter and downspout system, potentially clogging them. There are many types of gutter mesh commercially available for homeowners who prefer to do such jobs themselves, and for contractors.
When precipitation strikes a roof, the water travels by the most direct route possible, leaving the roof and falling down to the ground. After a single rainfall, a small rill will have been formed in the ground underneath the roof's edge; over time, that rill will deepen and widen. Some of the water will run off, and some will seep into the ground and collect underground, potentially threatening the structure's foundation.
Gutters and downspouts were developed to prevent the natural erosive effect of water falling off a roof's edge. Gutters are metal or plastic troughs that are attached to a roof's edge to collect water instead of allowing it to fall off the roof. They channel the water to vertical tubes, or downspouts, that direct the water to the ground. Most structures have systems that either divert the water away from the foundation, such as downspout splash blocks, or collect it in rain barrels or cisterns for later use.
When gutters are left open, leaves and twigs falling from trees will collect in them, leading to a few different consequences. Leaves may follow the flow of water and enter a downspout, and in most cases will become stuck and become an obstruction to water and other debris. In warm weather, the obstructions will slowly decompose, and in cold weather, water can collect in and around obstructions and freeze, sometimes bursting the downspout. Downspouts also provide convenient thoroughfares for squirrels and other vermin, who can sometimes become trapped by obstructions in downspouts.
Debris also collects in gutters and decomposes. When gutters aren't regularly cleaned out, this rotting vegetation gains weight, especially when wet, and can pull away from the roof, causing significant property damage. Even when the gutter remains secure, vegetation frequently will take root and grow in the accumulated compost of an uncleaned gutter.
Plastic gutter mesh is available in rolls, generally 48 inches (1.22 meters) long. Slightly wider than most gutters, it's simply pressed into place, forming a slight arch over the gutter, and held there by its own tension. Over time, usually a period of years, the plastic will lose its springiness and require replacement. Metal gutter mesh is usually available in rigid strips of about 18 to 24 inches (46 – 61 centimeters) long. These strips are attached to gutters by means of clips, which secure them to the edge of the gutter attached to the roof. These clips are usually hinged, facilitating the opening of the gutter mesh to gain access to the gutter for cleaning or other purposes. Metal gutter mesh strips have sharp edges and are themselves not always resistant to weather, and may require periodic replacement as well.
When gutter mesh is installed, whether plastic or metal, leaves falling on the roof will slide down the roof and either fall off the gutter mesh or remain there until a breeze blows them off. Most debris isn't able to enter downspouts, so that water generally flows through the gutter and downspout system unobstructed. However, small leaves, twigs, and other organic material will eventually breach most mesh and lie in the bottom of the gutter, decomposing, until after some time, a layer of organic mulch has developed on the gutter's bottom and must be cleaned out. This is still far preferable, from the perspective of most homeowners, to the semi-annual chore of having to clean out unprotected gutters and downspouts.