how does one determine the pitch of a roof from measuring the inside of the structure or house?

Answer 1

I think you have gotten some "partially correct" answers here. If I understand your question, you want to know your roofs pitch by measuring from the inside of the structure. There is a couple of inherant problems here. This will only work if the inside of the structure is the true slope of the roof. Some trusses have different angles. The roof is one angle and the ceiling is another. If you know that the rafter, drywall, truss, etc. is the same angle as your roof you can get an accurate measurement. This is where you would take a level, let's say a 4' level since that is the most common. Place the level on the rafter, drywall etc. and then bring one end down until the level reads level. If you don't know how to read level the air bubble will be between the middlemost lines when the level is level. While someone is holding the level "dead on" so to speak, have someone measure the distance between where the top part of the level is level and the rafter, ceiling, etc. above the level. This has to be done at the far end of the level, (the end not touching the ceiling. Lets say you come up with 16". You would then divide 16" (your roof rise in 4 feet) by 4 (you are using a 4' level) to get the pitch per foot. 16/4=4. Your pitch would be 4/12. Your roof rises 4 inches for every 12 inches of run (width). Hope I said this easy enough to understand.

Answer 2

The easiest method I've found is to use a level. If using the a two foot level put one end on the rafter and measure up if in the attic or down if on the roof. Then divide that measurement by 2. If you use a 4' level divide by 4. For example if you get 16" on a 2 foot level your pitch is 8:12. Usually the pitch is a whole number, but not always. The pitch on my 60 year house is 7.5:12 or close. Now to be more accurate you can use a t-bevel and a level, transfer the angle to a scrap board and use a speed square or framing square to determine the exact slope. In other words work backward, but if just getting a good guess for planning a project the first method is close enough.

Answer 3

You need to climb up into the attic. Drop a plumb bob from the ridge rafter down to the top of the attic floor (or ceiling joists of the room below, if the attic has no floor). This can be a nut on a piece of string.

Measure this distance -- ridge to floor. Now measure from where it touched the floor to where the rafters come down to the edge of the attic. Imagine a right triangle with the floor and plumb bob as two sides, and the roof itself as the hypotenuse.

Now divide the horizontal floor measurement by the vertical one, and you have the pitch. If it's 8 feet from the ridge to floor, and then 16 feet from there to the edge of the roof, you get 2.0, so the pitch is one in two: one foot of vertical rise for every 2 feet of horizontal run.

And you thought all that crap about triangles in high-school geometry class would be useless! Ha!

Answer 4

You must measure the side of the house and the distance from the top of the gutter line to the ridge vertically. The pitch of a roof is expressed as 3" in 12", or 4" in 12"ect. The vertical distance is first and the horizontal distance is second. Simply Half the width of the house and the vertical dimension and reduce them down to an "in 12"' figure.

Answer 5

from the angle of the roof in the attic

Answer 6

Just make sure you didn't cut it so fine you slide off doing the shingling or whatever, okay?