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Unit 46

Unit 46. Basic Roof Types and Roof Theory. Basic Roof Types • Roof Layout Principles • Structural Factors in Roof Design • Roof Sheathing. Shed, gable, and hip roofs are the basic types of pitched roofs.

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Unit 46

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  1. Unit 46 Basic Roof Types and Roof Theory Basic Roof Types • Roof Layout Principles • Structural Factors in Roof Design • Roof Sheathing

  2. Shed, gable, and hip roofs are the basic types of pitched roofs.

  3. Gambrel and mansard roofs are similar to gable and hip roofs except that they have double slopes on each side.

  4. Butterfly and monitor roofs are variations of the shed roof design. Continuous‑slope gable roofs are a variation of the gable roof design.

  5. An intersecting roof is formed when two roofs are combined. Among the many possible variations are the L‑shaped gable and L‑shaped hip intersecting roofs, and the T‑shaped hip‑and‑gable intersecting roof.

  6. The shape of a gable roof is based on two right triangles. A common roof rafter forms the third side (hypotenuse) of each triangle.

  7. The unit rise of a roof is the number of inches the rafter will rise vertically for every foot of run.

  8. The total rise of a roof is based on unit rise and total run.

  9. Purlins and braces help support spans of longer rafters.

  10. The allowable span is the distance from the ridge to the outside wall plates. Rafter spacing and roof slope determine the allowable span. For example, 2 × 4 rafters spaced 16″ OC have an allowable span of 8′‑0″ if the unit rise of the roof is less than 4″. The allowable span is 9′‑0″ if the unit rise is 4″ or more.

  11. A slope cut must be made on the ends of ceiling joists.

  12. As high-velocity wind passes over a pitched roof an uplift force is created, pulling on the roof surface.

  13. Rafter and truss anchors tie rafters and trusses to the building walls.

  14. Panel products such as plywood and OSB are typically used for roof sheathing. Panels are attached to roof rafters using 8d common nails or screws.

  15. Panel clips are placed at the unsupported edges of roof sheathing panels and eliminate the need for blocking between rafters. Panel clips are made of galvanized steel and accommodate all panel thicknesses used for roof sheathing.

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