There are two kinds of roofs: low-slope and steep-slope. Low-slope roofs are usually found on commercial and industrial buildings, such as factories and warehouses. But many apartment buildings and townhouses have low-slope roofs, too. Steep-slope roofs are what you find on most houses. You'll notice that many churches and stores also have steep-slope roofs.

Now that you know what slope is, it is time to take a look at low-slope roofs in more detail. Sometimes they are called flat roofs, even though they are not exactly flat. Roofs on most commercial buildings usually have at least a small slope of 1/4 inch per foot. Flat-looking roofs are the most common low-slope roofs. But some roofs are installed in barrel or sawtooth designs (see picture). These roofs are not flat at all.

There is a good reason that roofs have some slope. They have slope for water run-off, which is also called drainage. Having slope will make sure water runs off a roof. Sometimes water stays on a roof. When it runs into low areas and stays there in large puddles, it is called puddles. Smaller puddles are called bird baths. When it rains, water has to go somewhere, and that is why drainage is so important. Water should not stay on a roof., It is usually directed to drains on low-slope roofs.

Drains on low-slope roofs are located at the low points of roofs, called valleys (see picture). A valley is where two slopes meet at a low point.

There are two types of drains: interior and exterior. Sometimes interior and exterior drains are used together An overflow scup-per is an example. A scupper is an exterior drain. It can handle water runoff if the interior drain gets clogged. Another drain that can handle overflow is called an overflow drain.

Low-slope roofs may have areas called crickets and saddles. Both of these are small areas that help direct water to the drains (see picture).