3417
25

Hello all, I have a roof question , just started a house, the main span is

59'2", the front is on a 9/12, the back is on a 8/12, I haven't put a roof on

With the commons on different pitches on forever, what is the easiest way to calculate the rafter lengths.? The front is also 12" higher the the back wall. Thanks.

59'2", the front is on a 9/12, the back is on a 8/12, I haven't put a roof on

With the commons on different pitches on forever, what is the easiest way to calculate the rafter lengths.? The front is also 12" higher the the back wall. Thanks.

1 - 20 of 26 Posts

This is for equal Plate heights w/equal Haps.

You need to subtract the Run on the rear (lower plate) to equalize the plate heights, (or add to the front, taller plate), do your calcs, (derives reciprocal runs) and +/- the run offset use to get back to the original plate heights. Calculate Rafters lengths from Runs.

Remember, the initial results are for the opposing, or reciprocal, Runs.

Hello all, I have a roof question , just started a house, the main span is

59'2", the front is on a 9/12, the back is on a 8/12, I haven't put a roof on

With the commons on different pitches on forever, what is the easiest way to calculate the rafter lengths.? The front is also 12" higher the the back wall. Thanks.

Cl of ridge is 26' 5 3/16" from the front

Theoretical rise (not including HAP) is 21'- 9 7/8" off the lower plate line.

The theoretical rafter length for the 9p is 33' 1/2"

The theoretical rafter length for the 8p is 39'- 4 1/8"

I would at least use sketch up to find the ridge line and then you can figure the rafters many different ways after you know the runs.

59'2", the front is on a 9/12, the back is on a 8/12, I haven't put a roof on

With the commons on different pitches on forever, what is the easiest way to calculate the rafter lengths.? The front is also 12" higher the the back wall. Thanks.

Travisw601 said:Is there a way to figure it with just a cm 5 calculator? Thanks for the advice

kiteman said:Yeah, not likely. Not even close really. Look, one guy gave you the formula, and one virtually calculated it for you. One of them is 17 and knows more about figuring roofs than you do. All of this can bee done on the CM5 if you follow the steps given.

Nevertheless, he knew how to do this when he was 17.

jlsconstruction said:Come on, nicks 18 now

24" (Rise)/8 (Pitch w/lower height) = 3, Adjusted Span is 3' less from lower plate, 8 Pitch side.

59' 2" - 3' = 56' 2" (Span @ Equal Plate Height)

56' 2" - 1-1/2" (Ridge Thickness (?)) = 56' 0-1/2" (Effective Span)

56' 0-1/2" / 17 (Sum of Pitches) = 3' 3-9/16"

((3' 3-9/16" x 9) (= 29' 8") + 3') = 32' 8" (Effective Run, 8 Pitch side) Rafter Length = 39' 3-1/8"

(3' 3-9/16" x 8) = 26' 4-1/2" (Effective Run, 9 Pitch side) Rafter Length = 32' 11-5/8"

*Assuming Ridge is 1-1/2" thick and HAPs are equal. (Rafters are of equal width ?)

I believe that Nick's dimensions (posted above) taken from his SU drawing are correct and the Ridge Line is where he says it is. However it should not be referred to as a Center Line, it is just the Ridge Line as this is where the planes will meet, and it is not centered, and nothing is centered on it either, for instance, "the ridge thickness" is not divide by 2. It too, is divide by 17 (The sum of the Pitches) and multiplied by each pitch tell you how much each pitch occupies of that space. Removing it from the equation will automatically place the Ridge in its proper place w/o having to bevel the ridge to make it plane at its equally divided Center Line.

Is there a way to figure it with just a cm 5 calculator? Thanks for the advice

Sometimes we get touchy when someone just tries to get an easy answer on their first post without an intro.

Sometimes we get touchy when someone just tries to get an easy answer on their first post without an intro.

1 - 20 of 26 Posts

- This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Contractor Talk - Professional Construction and Remodeling Forum

A forum community dedicated to professional construction and remodeling contractors. Come join the discussion about the industry, trades, safety, projects, finishing, tools, machinery, styles, scales, reviews, accessories, classifieds, and more!

Full Forum Listing
Explore Our Forums

Recommended Communities

Join now to ask and comment!