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UNIT TRIANGLE AND RAFTER THEORY

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... is found on the floor plans. It may be in many shapes. ... The unit rise is given on the house plans. If the unit rise is 6'', Then the unit length is ... – PowerPoint PPT presentation

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Title: UNIT TRIANGLE AND RAFTER THEORY


1
Presentation 20
  • UNIT TRIANGLE AND RAFTER THEORY

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

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

4
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.
5
Triangle Names
  • Thus the Unit Triangle

Unit Length
Unit Rise
Unit Triangle
Unit Run
Building
6
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.
7
Unit/House Relationship
  • How many units of rise will fit into the building
    triangle?

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

Again, six unit triangles.
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.
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?,

13.42?
  • Then the unit length is

6?
Pythagorean Theorem
12? 1 foot 1 unit of run
or Rafter Tables
11
Example
  • If building is 20' wide and
  • unit rise is 6?,
  • what is the rafter Total Rise and Line Length?

6?
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? 134 3/16
13
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 _____________.
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