Kinds of Angles in Roof Trusses

Truss Angle Basics

• A pure triangular truss contains three angles, which always add up to 180 degrees. However, these angles can assume any combination of values, from 90-45-45 to 60-60-60, 40-60-80 and even something strange like 37-54-89. Trusses with curved or bowed parts contain different angles in numerous measures. Angles also exist within a truss. For instance, a truss may assume a pure triangular shape, but contain a square within it. The angles of the triangle add up to 180 degrees, while each angle within the square equals 90 degrees, for a total measure of 360 degrees. Every angle in a truss measures less than 180 degrees, because a 180 degree angle constitutes a straight line.

Needs and Shape

• Trusses come in numerous shapes and styles, despite all assuming a basically triangular form. The shape and style of truss you use ultimately depends upon your needs. If you need a truss to support a steep roof, your truss needs tall sides. If your roof runs across a wide area at a slight pitch, you need very long sides with little slope to them. A roof with curved elements may require a truss with curved elements. A truss supporting a very heavy roof requires a good deal of support within itself, meaning it contains a number of beams creating additional angles in the truss frame.

Shape and Angle

• The shape of a truss determines the angles within the unit. For instance, assume you place a truss under a steep roof. Each side of your truss measures 15 feet, and the base measures 15 feet across. A triangle with three equal sides also contains three equal angles of 60 degrees each. Trusses with long sides sloping at low angles contain small angles at the sides and one large angle in the center. Keep in mind that whenever a triangle contains two equal sides, it also contains two equal angles opposite those sides. A flat truss, which consists of numerous squares in a row, contains a number of 90-degree angles. If a crossbeam cuts a 90-degree angle in half, it creates two 45-degree angles.

Measuring Angles

• Angle measuring tools present the easiest way to measure the angle of a roof truss. If you want to know the measures of the angles in your truss, simply head out to a hardware store and purchase one of these tools. If you’d rather use math, numerous equations exist for measuring angles, though most of them require that you know at least one angle. Luckily, a number of trusses, such as Attic, Howe, Kingpost and Queenpost contain 90-degree angles. You can use math like the Pythagorean Theorem to figure out the other angles. Remember that if your truss contains two equal sides, it contains two equal angles. If you know one of these angles, multiply it by two and subtract the product from 180 to find the measure of the third angle.