[TempestV]

For a simple gable (example 5/12" pitch, 20' outside of wall to outside of wall, 1 1/2" thick ridge)-

With a regular basic function calculator (should work with most basic cell phone calculators):
Span= (total roof width-ridge thickness)/2
Total rise= (rise/run)*Span (measures from bottom of birds mouth plumb cut to bottom of ridge plumb cut)
Diagonal measurement=Square root of (span^2+total rise^2)
Use inches for easy math
Example:
20ft*12= 240"
240"-1.5" =238.5"
238.5"/2=119.25"
5/12=.4167
119.25*.4167=49.69"
119.25"^2=14220.6
49.69"^2=2468.85
14220.6+2468.85=16689.4
square root (16689.4)=129.188"~ 129 3/16"

With a scientific calculator (calc set to degrees):
Convert roof pitch to degrees- Degree measurement= inverse tangent of (rise/run)
Span= (total roof width-ridge thickness)/2
Diagonal measurement = Span/cosine of roof pitch in degrees
Enter all lengths in inches for easy math
Example:
20ft*12= 240"
240"-1.5" =238.5"
238.5"/2=119.25"
5/12=.4167
inverse tangent of .4167= 22.62 degrees
Cosine of 22.62 degrees= .923
119.25"/.923=129.188"~ 129 3/16"

For construction master:
Enter total span in feet and inches
Subtract thickness of ridge in inches
Divide by 2
Set answer as "Run"
Enter pitch in degrees or inches, and press "pitch"
Press "Diag" for answer
Example:
20 "feet" - 1.5 "inch"/ 2= 9 feet 11 1/4 inch
"Run"
5 "inch" "pitch"
"Diag"
answer is 10 feet 9 3/16" = 129 3/16"

 

[TempestV]

Didn't know how to convert pitch to degree using inverse tan till I read your post- thanks!

To convert from degrees to slope,
12*tan(degrees)
Example- 30 degrees to slope
Tan(30)=.57735
12*.57735= 6.93
6 15/16" slope

 

[TempestV]

I use the construction master app and a multi line scientific calc called Panecal for all of my phone based calculating needs, and switch to my Ti-89 titanium if I need a better calculator.

You might also check out andygraph, it's a whole set of emulators for some of the more basic Texas Instruments graphing calculators.

 

[TempestV]

Ummm, perhaps you went off a tangent...:laughing:
Doesn't slope = rise/run
slope = 0.577 or 6.93/12

btw- enjoyed reading your math

Yes, but it's common to leave off the 12 when naming a slope. For example, when entering a slope into a construction master, all you list is the top number, it's assumed that it's over 12. As far as I'm concerned, either way is right.