Algae: A rooftop fungus that can leave dark stains on roofing. The algae feed on the crushed limestone that is used in asphalt shingles. Rain spreads the algae down the roof, causing black streaks.

Asphalt shingles: A proven roofing material that consists of a base material coated with asphalt and infused with granulated minerals. It is one of the most widely used roofing materials because it is relatively inexpensive and fairly simple to install.

Cedar shakes: A wood hand-cut shingle that may be either tapered or of an even thickness. Installation is over roofing felt and the shakes may be laid onto spaced or solid roof sheathing.

Cedar shingles: Flat, machine-cut wooden pieces between 16 to 24 inches long and originally tan in color; fading to gray. Since they are capable of catching fire, they must be treated with a fire retardant.

Ceiling spots: Discolored spots on your ceiling that are a sign of moisture coming from above; an indication that your roof may be leaking.

Clay and concrete tile: Clay tiles are made from naturally occurring clay deposits which are processed, shaped and fired in kilns. Concrete tiles are manufactured from cement, aggregate, and water.

Dry rot: A fungal disease that causes wood to become brittle and crumble into powder.

Flashing: Thin pieces of sheet metal installed on a roof to prevent water from passing into a structure from an angle or joint.

Granules: Graded particles of crushed rock, slate, slag, porcelain or tile, used as surfacing on asphalt roofing and shingles. The granules help asphalt-based roofing products last from 30 to 50 years.

Lichens: A fungus that grows symbiotically with algae, resulting in a composite organism that characteristically forms a crust-like growth on roofs, rocks or tree trunks.

Metal roofs: A roofing system made from metal pieces or tiles. Metal roofs provide energy savings, beauty, and protection for a home and can last a lifetime.

Mold: Any of various fungi that often cause disintegration of organic matter. Mold or mildew makes black ugly streaks on a roof. Not only is it unattractive, it can actually shorten the life of your shingles.

Moss: A type of small flowerless plant, found in damp places, that forms a soft green covering on roofs. It lacks true roots, growing in low carpets or rounded cushions in damp habitats and reproducing from spores.

Power washing: A mechanical sprayer that, depending on nozzle size, can be used as a low volume, high-pressure water cleaner; or a high volume, low-pressure water cleaner to remove mold and other fungi from roofs.

Re-roofing: A job that consists of applying new roofing material over the existing surface. This is less expensive and easier than tearing off the old roofing and having it hauled away.

Shingle roofs: A roof covering consisting of individual overlapping elements. These elements are typically flat, rectangular shapes laid in rows from the bottom edge of the roof up. Each successive higher row overlaps the joints in the row below. Slate roofs: A fine-grained gray, green, or bluish metamorphic rock easily split into smooth, flat plates.

Tile Roofs: A roof covering designed mainly to keep out rain and traditionally made from locally available materials such as clay or slate. Modern materials such as concrete and plastic are also used, and some clay tiles have a waterproof glaze.

Zinc sulfate: The active ingredient for some moss killers, zinc sulfate will not stain roofs or corrode aluminum and galvanized gutters. Zinc sulfate can be applied as a powder directly on moss, or mixed with water in a spray.

Zinc strips: Usually considered the long-term solution for controlling moss, zinc strips and galvanized flashing are relatively safe and inexpensive. They effectively kill or retard the growth of moss and fungi.