1. 1 Presentation 20: UNIT TRIANGLE AND RAFTER THEORY

2. 2 Unit Triangle Unit Triangle is found on the floor plans. It may be in many shapes.

3. 3 Unit Triangle vs. House Doubling the Unit Triangle gives a shape that is similar to the building, but smaller.

4. 4 Triangle Names The sides of the triangles have names. Run Rise Length Each side of the unit triangle has UNIT added to it.

5. 5 Triangle Names Thus the Unit Triangle Unit Run Unit Rise Unit Length Unit Triangle Building

6. 6 Unit/House Relationship How many units of run will fit into the building triangle? It depends on the size of the building. This building has six unit triangles. 12′- 0″

7. 7 Unit/House Relationship How many units of rise will fit into the building triangle? In this building, six unit triangles.

8. 8 Unit/House Relationship How many units of length will fit into the building triangle? Again, six unit triangles.

9. 9 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. 12′- 0″

10. 10 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″, Then the unit length is … 13.42″ 6″6″ Pythagorean Theorem 12″ = 1 foot = 1 unit of run or Rafter Tables

11. 11 Example If building is 20′ wide and unit rise is 6″, what is the rafter Total Rise and Line Length? 20′- 0″ 6″6″

12. 12 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″ 10′- 0″ = 10 units of run 6″6″ 134 3 / 16 ″ 60″ 134 3 / 16 ″ 20′ = a run of 10

13. 13 Unit run for a common rafter is ____. The unit rise is found _____________. Unit rise is converted to unit length by _______________________. Run x unit rise = _____________. Run x unit length = _____________. Conclusions 12″ on the floor plans using the Pythagorean Theorem Total Rise Line Length