Roof Design
Frame Roof Construction
Home Page - build-home-building-house.com| Roof covering material is supported by roof framing. The framing must be strong and rigid. Roof framing consists of several distinct structural elements. The first and most basic of these elements is the rafter. Common rafters are perpendicular to the top of the wall plate. They extend from the plate or beyond to the ridge of the roof. Figure 1-1 shows a plan view of the roof framing for a simple structure. Note that several types of rafters other than common rafters are identified. Rafters are cut to the proper dimensions by locating the ridge cut, the seat cut, the plumb cuts, and the tail cut, Fig 1-2 |
 The precise layout pf these cuts is determined by the slope or Pith of the roof and the width or Span of the building. Terms, which must be understood before calculating rafter dimensions and roof pith, are: RISE, RUN, and SPAN. The rise of the roof is the vertical distance measured from the top of the wall plate to the intersection of the centerline of the rafters. The run of the roof is one-half of the spans. Span is the horizontal distance form the outside of one wall stud to the outside of the opposite stud wall. Figure 1-3 graphically illustrates these terms. Figure 1-4 represents
the ratio between the rise and run of the roof.  The roof slope shown as a fractional pitch denotes the relationship between rise and the span larger image Figure 1-5 |
Roof slope may be given on a drawing by showing a slope ratio diagram or fractional pitch indication. The slope diagram, Fig 1-4 represents the ratio between the rise and run of the roof. The fractional pitch is calculated using the following formula.
Roof slope may be also
be shown using an angular dimension. However, this method is seldom used because
it is difficult to measure as accurately as either of the other methods. A roof
with a 45 degree slope has a 12:12 or ½ pitch. There are several common
roof pitches used in residential home construction. When designing a roof for your
new home, try to use on of the standard roof pitches. |
