What Blocks Gutters?

Gutters block with leaves, silt, moss, twigs and nests, each in a different way. Leaves fill runs in autumn. Silt settles and compacts. Moss washes down from roofs. This guide explains each debris type, and what it means for cleaning.

Leaves and twigs

Leaves are the largest debris by volume, and the main autumn blockage cause. They fill runs quickly in leaf fall, then mat together when wet. Twigs bridge across outlets and trap further leaves behind them.

Leaf blockages clear relatively easily when fresh. Once leaves have rotted into a mat, clearing takes longer, because the mat must be lifted in sections. Timing a clean after leaf fall, before rotting sets in, makes the job easier.

Silt and grit

Silt is fine material washed off roofs: dust, grit, moss fragments and broken tile granules. It settles in the gutter bottom and compacts into a dense layer. Silt blocks outlets from below, even where the gutter looks clear from above.

Silt is the hardest debris to clear by volume, because it is heavy and compacted. Vacuum cleaning handles loose silt well. Compacted silt may need hands-on clearing. Silt depth is a useful neglect signal: deep silt means the gutter has not been cleaned for a long time.

Moss

Roof moss loosens in rain and washes into gutters, where it forms a dense mat. Moss mats trap leaves and silt behind them, accelerating blockage. A mossy roof can block a gutter within a season of a clean.

Moss in the gutter signals moss on the roof above. Clearing the gutter alone leaves the source in place, so the blockage returns. Roof moss removal, combined with gutter clearing, addresses both.

Nests and other debris

Birds' nests block gutters and downpipes, usually in spring. Nests are dense, bulky and difficult to clear. They are also protected in some circumstances, which affects when and how they can be removed. That position is explained in the nests guide.

Other debris includes tennis balls, toys and roofing material blown into gutters. Each is cleared as found, and any roof material found in a gutter is reported, because it may indicate roof damage above.

Frequently asked questions