Presentation 20: UNIT TRIANGLE AND RAFTER THEORY
Unit Triangle • Unit Triangle is found on the floor plans. • It may be in many shapes.
Unit Triangle vs. House • Doubling the Unit Triangle gives a shape that is similar to the building, but smaller.
Triangle Names • The sides of the triangles have names. Length Rise Run Length Rise Run Each side of the unit triangle has UNIT added to it.
Triangle Names • Thus the Unit Triangle Unit Length Unit Rise Unit Triangle Unit Run Building
12′- 0″ Unit/House Relationship • How many units of run will fit into the building triangle? This building has six unit triangles. It depends on the size of the building.
Unit/House Relationship • How many units of rise will fit into the building triangle? In this building, six unit triangles.
Unit/House Relationship • How many units of length will fit into the building triangle? Again, six unit triangles.
12′- 0″ Unit/House Relationship • There are equal numbers of unit triangles along the run, rise, and length. If this building is 12′ wide, then six unit triangles fit under the rafter.
Unit Triangle Theory • The base of the unit triangle is always 12″ for a common rafter. • The unit rise is given on the house plans. • If the unit rise is 6″, 13.42″ • Then the unit length is … 6″ Pythagorean Theorem 12″ = 1 foot = 1 unit of run or Rafter Tables
20′- 0″ Example • If building is 20′ wide and unit rise is 6″, what is the rafter Total Rise and Line Length? 6″
134 3/16″ 6″ 134 3/16″ 60″ 10′- 0″ = 10 units of run Rafter Calculation Answers • Total Rise = Unit Rise x RUN 6″ x 10 = 60″ • Line Length = Unit Length x RUN 13.42″ x 10 = 134.2″ = 134 3/16”
Conclusions 12″ • Unit run for a common rafter is ____. on the floor plans • The unit rise is found _____________. • Unit rise is converted to unit length by _______________________. using the Pythagorean Theorem Total Rise • Run x unit rise = _____________. Line Length • Run x unit length = _____________.