by Don Vandervort, © HomeTips
Driving through nearly any neighborhood, you can see that roofs have many different shapes. Houses have gable, hipped, mansard, gambrel, flat, and shed roofs. And many homes combine different roof styles in one roof.
It’s quite common, for example to see a hipped roof with gable dormers. Roof shape is one of the key factors in setting the architectural style of a house.
Roof shape also dictates how difficult and costly a roof is to build and how it will serve. For example, flat, shed, and in some cases gable roofs tend to be relatively affordable to build. Gambrel and mansard roofs offer more head height for attic rooms. Shed roofs are usually the easiest type to connect to an existing roof when adding on.
Roof framing can be simple or complex, depending on the roof. Overhangs, hips, and dormers add greatly to the complexity of the framing. Here the major framing components are shown.
Stick & Truss Construction
Nearly all roofs are framed using one of two methods: standard stick framing or newer truss framing. Stick-framed roofs utilize individual rafters that span from the top of exterior walls to the ridge. Truss-framed roofs are built from triangular-shaped, pre-made truss units.
Gable and hip roofs may be built primarily of trusses; other roof shapes, particularly those with dormers or on houses with cathedral ceilings, attic rooms, or attic storage areas, are stick built. Stick framing creates a triangle between rafters and ceiling joists. Collar beams add strength at the middle.
Rafters and trusses are spaced every 16 or 24 inches on center. Most roofs utilize 16-inch spacings for strength. Rafters are positioned directly above wall studs. A truss is one contiguous double-rafter/ceiling-joist unit.
Truss construction is just as strong as stick framing but is lighter weight and uses smaller sizes of lumber. Because trusses are carefully engineered units that shouldn’t be cut, they are not a good choice for roofs that may be modified at a later date. And because they have several intermediate support members, they don’t allow use of the attic space.
The angle of a roof is measured and referred to by either slope or pitch. The slope of a roof is the number of inches a roof rises in 12 inches of horizontal run. For example, a roof with a 5-in-12 slope rises 5 inches for every 12 inches of horizontal run. Pitch expresses the same two measurements as a fraction. The same roof has a 5/12 pitch.
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