I believe you normally measure pitch from the roofline (or the high point of the roof) to the bottom edge of the roof. Pitch is just a measure of how far you drop in a foot of distance. For example a 4 in 12 pitch means that in 12 feet the roof drops 4 feet. I live on a steep hillside, and the pitch is more like 5 or 6 in 12. For every 12 feet you move down the slope, you drop 5 or 6 feet in elevation.
Thank you KB Baldwin!
I honestly thought that you can calculate the surface by applying the Pythagoras's theorem. Meaning - I tried to calculate the surface area by measuring the height at the center of the roof, multiplied with the width, and then I wanted to multiply that result with the width of the area... and then I realized that I have no idea what am I doing.
So not my proudest DIY project, but I think I'll just call a professional. Also, I was searching through the ads for quotes, and here is an interesting price calculator that doesn't have slope as an option, so I guess it's more of a guesstimate than a quote but works for me :)
http://lpzplumbingservices.com.au/roof-repair-price-calculator/
This is in Australia however, but I hope that prices here are at least moderately similar.
Two sites that may be of use. The first will get you a little more immersed in the nomenclature of pitch; the second is worth a look also.
https://en.wikipedia.org/wiki/Roof_pitch
http://www.homeadvisor.com/cost/roofing/install-a-roof/#height
The pitch corresponds to the inclination of a
surface or line with respect to the horizontal. It can be measured
according to an angle in degrees, radians or grades or in percentage, that is
to say according to the ratio height by length multiplied by 100.
The calculation
formula for the side lengths of right-angled triangles is:
a 2 + b 2 = c 2 (Pythagorean theorem)
Using this formula, you can calculate the roof pitch by simply replacing a and b with
the measured edge lengths. The c gives the length of the measured section
in the roof. Since you calculated c 2 using the Pythagoras theorem , you now need the
square root of the found value (preferably with the calculator) - it gives the
measured length C.
The length
of the sections determines the position in the triangle - and thus the angles. In
order to be able to calculate the angle of the roof - just the roof pitch - A
must first be divided by C:
A / C = sin β
Now calculate the roof pitch by
converting the sine value to the angle.
Surprisingly, there is no
satisfactory algebraic method that allows you to convert the sine value to
angle. You can read the values in the sine curve, in the unit circle -
or have your calculator do the work.
This is the method we use at Wilco Plumbing for our installations.
I hope this help.Thank you.
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