Post on 05-Jan-2016
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Presentation 20:
UNIT TRIANGLE AND RAFTER THEORY
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Unit Triangle
• Unit Triangle is found on the floor plans.• It may be in many shapes.
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Unit Triangle vs. House
• Doubling the Unit Triangle gives a shape that is similar to the building, but smaller.
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Triangle Names
• The sides of the triangles have names.
Run
Run
Rise
Rise
Length
Length
Each side of the unit triangle has UNIT added to it.
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Triangle Names
• Thus the Unit Triangle
Unit Run
Unit R
ise
Unit Length
Unit Triangle
Building
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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″
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Unit/House Relationship
• How many units of rise will fit into the building triangle?
In this building, six unit triangles.
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Unit/House Relationship
• How many units of length will fit into the building triangle?
Again, six unit triangles.
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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″
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Unit Triangle Theory
• The base of the unit triangle is always 12″ for a common rafter.
6″13.42″
Pythagorean Theorem 12″ = 1 foot = 1 unit of runor Rafter Tables
• The unit rise is given on the house plans.• If the unit rise is 6″, • Then the unit length is …
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Example
• If building is 20′ wide and
unit rise is 6″,
what is the rafter Total Rise and Line Length?
20′- 0″
6″
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Rafter Calculation Answers
• Total Rise = Unit Rise x RUN
10′- 0″ = 10 units of run
6″134 3/
16 ″
60″
134 3 / 16″
6″ x 10 = 60″• Line Length = Unit Length x RUN
13.42″ x 10 = 134.2″ = 134 3/16”
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• Unit rise is converted to unit length by _______________________.
• Unit run for a common rafter is ____.
Conclusions
12″
on the floor plans
using the Pythagorean Theorem
Total Rise
Line Length
• The unit rise is found _____________.
• Run x unit rise = _____________.
• Run x unit length = _____________.