ROOF GEOMETRY

GABLE ROOFSIMILAR TRIANGLES

PYTHAGOREAN THEOREM

ISOSCELES TRIANGLE2 sides equal

The Perpendicular Bisector divides the base into 2 parts.

Two Equal Triangles Equal Angles

THIS IS THE LINE DRAWING OF THE SIDE VIEW OF THE GABLE ROOF

AB = AC = Rafter line; BD = DC = Total Run; BC = Total Span; AD = Total Rise

𝐴2+𝐵2=𝐶2

C =

Video on Pythagoras' Theorem

http://learni.st/learnings/99012-pythagoras-theorem?board_id=13622

This is a D.A.L. calculator

• Direct Algebraic Logic

• You enter numbers and

symbols as you would write

themPYTHAGORAS’ THEOREM

Given: A = 4’, B = 3’

Find: C

Calc.: C =

On the Calculator:

Press: ( 4 x2 + 3 x2 ) =

Screen: (42 + 32) = 5

Roof Slope is denoted by the # of inches of rise over 12” of run.

i.e. vertical rise over the unit horizontal run of 12”

Slope(imp.) = = = , for example

Written as 6 in 12, 6:12, 6/12, or

In metric, as per the Building Code, 1 in 2 or 1:2

12

6

12

6

Pythagorean Theorem

6

12

Hypotenuse

Hypotenuse =

=

=

= 13.42”

This is called the unit length of the Common Rafter.