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Roof Construction

Roof Construction. Traditional Frame Roof Construction. There are several features of traditional frame roof construction. It is important to understand these features and their impact on the roof before designing a roof. Structural Elements.

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Roof Construction

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  1. Roof Construction

  2. Traditional Frame Roof Construction • There are several features of traditional frame roof construction. • It is important to understand these features and their impact on the roof before designing a roof.

  3. Structural Elements • The roof framing is designed to support the roof covering materials. • Must be strong and rigid. • Roof framing consists of several distinct structural elements: • Rafters • Cornice • Sheathing • Shingles or steel • Flashing

  4. Rafters • Rafter is the most basic of these elements. • Common rafters are perpendicular to the top wall plate. • They extend from the ridge of the roof to the plate or beyond. • There are several types of rafters: • Common rafters • Hip jack rafter • Hip rafter • Cripple jack rafter • Valley jack rafter • Valley rafter

  5. Figure 19-4

  6. Rafters • The precise layout of the rafter is determined by the slope of the roof and the clear span of the building. • Terms to understand: • Rise: vertical distance measured form the top of the wall plate to the underside of the rafters. • Run: 1/2 the distance of the clear span. • Clear-span: horizontal distance form the inside of one exterior stud wall to the inside of the opposite exterior stud wall. • Slope: slant of the roof.

  7. Figure 19-6

  8. Figure 19-7

  9. Rafters • Size depends on the: • Distance to be spanned. • Spacing of the rafters. • Weight to be supported. Rafters for roofs with low slopes may also serve as a base for the finished ceiling.

  10. Cornice • The overhang of the roof at the eave line that forms a connection between the roof and side walls. • 3 types of cornice: • Open cornice • Box cornice • Closed cornice

  11. Open Cornice • May be exposed-beam construction, contemporary, or rustic designs. • Rafter ends are exposed and are usually tapered or curved to prevent a bulky appearance.

  12. Box Cornice • Has the space between the end of a projecting rafter and the wall enclosed with a soffit board. • There are 3 basic types of box cornices.

  13. Close Cornice • One in which the rafter does not project beyond the wall. • Roof is terminated by a frieze board and molding.

  14. Rake or Gable End • Extension of a gable roof beyond the end wall of the house. • The amount of overhang and treatment at the gable should be about the same as the cornice. • A close rake is less expensive to build.

  15. Roof Trusses • An assembly of members that form a rigid framework of triangular shapes. • Permits wide, unsupported spans with a minimum amount of material. • Information to purchase trusses: • Span • Roof pitch • Spacing of the trusses • Anticipated roof load Many times trusses are less expensive. Gussets are used to fastened the members of wood truss together.

  16. Fig. 19-17

  17. Fig 19-18

  18. Ventilation • Providing for adequate ventilation in the attic space is a necessity. • If not provided moisture will probably form on the underside of the roof sheathing and in time damage will result. • Ventilation types: • Louvered openings in the gable ends. • Ridge ventilators • Roof vents Total area of ventilator openings should be at least 1/300th of the ceiling area. exp.: ceiling area 1200 sqft. = minimum of 4 sqft.

  19. Flashing • Used to shed water away from areas of potential leakage. • Used where the roof comes in contact with a wood or masonry wall, chimney or roof valley. • Material: • Aluminum • Copper • Galvanized sheet steel Drip edge is a type of flashing.

  20. flashing

  21. Drip edge

  22. Roof Sheathing • Placed over the rafters to support the roofing material. • Materials: • Planks • Individual boards • Plywood • Oriented Strand Board (OSB) Plywood used to be a popular choice,but is now being replaced with OSB. Thickness varies with the spacing of rafters. Depending on roof weight 7/16” OSB is used for spacing of 16” OC - 20” OC Sheathing should be staggered.

  23. Asphalt Shingles • Felt paper is place over sheathing. • One square is 100 sqft. • 2 common types: • 3-tab • Architectural Advantages of architectural: resist winds better adds a raised 3-D appearance less waste Disadvantages: more expensive Heavier to handle Harder to cut

  24. Metal Roofing • Gaining wider acceptance for residential construction. • Compatible with most roof designs. • High resistance to wind: up to 230 mph • Advantages: • Broad range of styles and colors. • Has long life with little maintenance. • Disadvantages: • Cost more than asphalt shingles. • Installation demands more precision. • Fading

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