Competency: 205.00 Draw roof plans

1. Competency: 205.00Draw roof plans Objective: 205.02 Apply concepts of roof construction.

2. Traditional Framed Roof (stick built) • Rafter size depends upon • The distance to be spanned • The spacing of the rafters (typically 24” O.C.) • The loads exerted on the roof from dead loads and live loads

3. Traditional Framed Roof (stick built) • Common rafters rest on the double top plate and extend to the ridge • Hip, valley, and jack rafters • Hip rafters extend from the ridge to a wall corner in a hip roof. • Valley rafters occur where two sloping roofs intersect forming a valley. • Jack rafters extend from the double top plate to either a hip or valley rafter. • Lengths vary as they occur higher on the roof • Shorter than common rafters

4. Traditional Framed Roof (stick built) • Collar beams • Typically placed ever 2nd or 3rd set of rafters • May serve as a ceiling joist for finished attics • Knee walls • Vertical studs that extend from the ceiling joists to the rafters. • Reduces rafter span • Adds rigidity • May form wall in finished attic

5. Roof Slope • Rise • Vertical distance • Measured from top of wall plate to underside of rafter • Run • Horizontal distance equal to half the clear building span

6. Roof Slope • Span • Horizontal distance between load bearing walls • Roof pitch • Ratio of actual rise to actual span • Indicated by rise to run ratio • Run always expressed as 12

7. Cornice/Eave • Composed of all materials used to join roof to exterior sidewalls • Roof overhang • Protects walls and openings from weather • Controls natural light entering structure

8. Cornice/Eave Types • Open Cornice • Exposed beam construction • Rafter ends exposed • Sometimes tapered or curved for appearance • Box Cornice • Fascia • Forms eave line • Projects below soffit to form drip edge • Nailed to lookout

9. Cornice/Eave Types • Box Cornice (cont’d) • Soffit • Material that covers bottom side of rafter tail • Attached directly to bottom side of overhanging rafter • Bottom of rafter tail may be cut perpendicular to soffit • Nailing strip attached to sidewall serve as continuous nailing surface • Wide overhangs require lookout perpendicular to wall

10. Cornice/Eave Types • Gable end (Rake) • Formed by extension of gable roof beyond end walls • Overhangs constructed similar to other walls • Lookouts attached to last rafters is less than 12” • Fascia attached to lookout

11. Roof Trusses • Prefabricated units include all members necessary to roof structure • Less expensive than conventional framing • Span long distances without interior load bearing walls or beams • Allows for open plans • Installed before interior wall construction

12. Roof Truss Assembly • Top chord, bottom chord, and web members • Joined with plywood or sheet metal gussets for light construction • Available in many styles • Fink (W) • Howe (King post) • Scissors • Purlins (horizontal members) • Perpendicular to trusses provide stability & nailing surface

13. Roof Ventilation • Cools attic area during summer • Removes moisture from attic • Bathing, cooking, cleaning • Condensation during winter

14. Roof Ventilation • Prevents ice dams in winter conditions • Melting snow refreezes at colder edges of roof • Water behind ice dam soaks under shingles • Ventilation regulates attic temperature

15. Roof Ventilation • Methods • Gable end vents • Louvered • Various shapes • Cupola • Small structure built above main roof level • Louvered sides allow air movement

16. Roof Ventilation • Ridge vents • Projecting devices exhaust air from attic • Turbine vents have moving parts • Flat, non-mechanical vents allow airflow • Soffit vents • Allow air to enter attic • Continuous strips or individual units • Screen covers prevent insect and pest entrance