The primary job of most roofs is to keep out water. The large area of a roof repels a lot of water, which must be directed in some suitable way, so that it does not cause damage or inconvenience.

Flat roof of adobe dwellings generally have a very slight slope. In a Middle Eastern country, where the roof may be used for recreation, it is often walled, and drainage holes must be provided to stop water from pooling and seeping through the porous roofing material.

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In most countries a roof protects primarily against rain. Depending upon the nature of the building, the roof may also protect against heat, against sunlight, against cold and against wind. Other types of structure, for example, a garden conservatory, might use roofing that protects against cold, wind and rain but admits light. A verandah may be roofed with material that protects against sunlight but admits the other elements.

Make roof repairs on a warm day, when shingles are more flexible (and therefore less likely to crack) and roofing cement spreads more easily.

Composition shingles are made of organic felt manufactured from wood and paper fibers. Fiberglass-base shingles are made of manmade fiberglass mat. Both kinds are soaked in asphalt, but the fiberglass base shingles are more fire-resistant than the organic ones. Asphalt shingles have mineral granules embedded in them; when you find these granules washing away, it's a sign that you need to repair or replace your shingles

Do your roof right (tips)

Nearly four-fifths of American homes have asphalt shingle roofs--and for good reason. Asphalt shingles are economical and fairly easy to install and repair. The two basic types are composition and fiberglass-base shingles.