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 (contd)
• 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