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## Presentation 20:

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**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 = _____________.