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Calculating Rafter Length?

Uncle Bob

Uncle Bob

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Joined
Oct 17, 2009
Messages
1,409
Location
Texas
Ok, I'm old; and it has been a few decades; and I don't have a framing square handy; and forgot how to use it anyway. :(

How do you determine the rafter length?

New Building:

Building span = 16 feet.

Overhang = 2 feet.

Pitch = 4 in 12.

No hurry; as soon as you quit laughing and can compose yourselve will be fine. :oops:

Uncle Bob
 
Re: Calculating Rafter Length?

ConArb,

Since I'd need 12' rafters anyway; cost wise, it doesn't matter whether the pitch is 4/12 (10' 6") or 6/12 (11' 3"); same money?

Uncle Bob
 
Re: Calculating Rafter Length?

Uncle Bob said:
Ok, I'm old; and it has been a few decades; and I don't have a framing square handy; and forgot how to use it anyway. :( How do you determine the rafter length?

New Building:

Building span = 16 feet.

Overhang = 2 feet.

Pitch = 4 in 12.

No hurry; as soon as you quit laughing and can compose yourselve will be fine. :oops:

Uncle Bob
Click to expand...
:lol: :lol: :lol: :lol:

Method #1: Buy "Rafter Master" by Nix Jacobsen and look it up on Page A-9. (12.65" per foot of run or 12 5/8")

Method #2: Buy "Simplified Roof Framing" by Wilson and Werner and look it up in Chapter VII Table II Page 125. (1/6 pitch = 12 5/8" length in inches, common)

Method #3: Buy Construction Master Pro calculator...read manual...

Method #4: Mathematical method = hypotenuse of right triangle (a² + b² = c²):

1. span of roof ÷ 2 = total run (16' ÷ 2 = 8' or 96")

2. total rise for 4/12 pitch = total rise (96" x 4" = 384" ÷ 12" = 32")

3. run squared = 9216" rise squared = 1024" run + rise = 9216 + 1024 = 10240"

4. square root of 10240" = 101.19 or 101 3/16" or 8'-5 3/16" calculated length to birdsmouth without deducting for ridge

5. add 25 1/4" for overhang (12 5/8" x 2) = 10'-6 7/16" length from ridge cut (1/2 of ridge not deducted) to fascia cut

:p
 
Re: Calculating Rafter Length?

UB,

Depending on the rafter width, you take a ruler 1/4" scale, mark 16' spand on a piece of paper, find the center, mark it at 8', measure up 4' for pitch. draw line from top of pitch to the 16' mark (wow it's a triangle)with your 1/4" scale, count the little marks on the 1/4" scale, (which represent feet) then add you desired overhang. In short order 12' long material or use your friends on this board! :)
 
Re: Calculating Rafter Length?

Conarb,

Where were you with these internet calculators 20 years ago?
 
Re: Calculating Rafter Length?

I always liked to step 'em off with a square and cut the ends to fit this or that. A kind of laying on of hands.
 
Re: Calculating Rafter Length?

I'd like to know why a plumber has a framing square.
 
Re: Calculating Rafter Length?

Except for ConArb or Hurricane; all the carpenters are either dead or retired. I haven't seen a framing square on job site in over 20 years. It's a lost art.

Besides, a "professional" would spend more on designing the damn thing than I'm going to spend building it. :lol: :lol: :lol:

It's just been a few decades since I was a carpenter; and my alzheimers isn't full blown yet,

Uncle Bob
 
Re: Calculating Rafter Length?

A failure to plan is a plan to fail.

Short of that, make your own lay out square. It is 4&12 not rocket science. Plumb cut 4/12

level cut 12/4 step it off! That doesn't mean walk on the rafter! :lol:

There are a few wood beaters left! ;)
 
Re: Calculating Rafter Length?

Uncle Bob said:
Except for ConArb or Hurricane; all the carpenters are either dead or retired. I haven't seen a framing square on job site in over 20 years. It's a lost art.......It's just been a few decades since I was a carpenter; and my alzheimers isn't full blown yet,

Uncle Bob
Click to expand...
Mine isn't kicked in too bad..... what was I talking about....

I'm still kicking but not swinging a hammer anymore except for the repair here and there.

A lost art is right I had a guy come in to do a few things that I could not (ok would not) do a few years ago. He could not cut baseboard and make it fit right the fifth or sixth time much less the first.
 
Re: Calculating Rafter Length?

Uncle Bob said:
......... I haven't seen a framing square on job site in over 20 years. It's a lost art.......
Click to expand...
I still have my same 2.

1 old rusty/crusty one for framing & general work.

1 newer aluminum one for stringers and rafters with my clip locks.

Don't see how you can build a house without one.
 
Re: Calculating Rafter Length?

Oh, Jeff..

Just use pre-manufactured components..

Hire framers..not carpenters..
 
Re: Calculating Rafter Length?

Y conoces tus derechos, Pack?

Pythagoras must be turning in his tomb.

Incidentally, I read that he was so shy he only lectured from behind a curtain. Those he knew and trusted were allowed to sit and listen behind the veil with him, thus the derivation of the term, "esoteric", which means "inside the cloth".
 
Re: Calculating Rafter Length?

WHEN, just when.. did any of us see a real carpenter on a job site?

It's a lost art..
 
Re: Calculating Rafter Length?

I've always (and still do...) had a "Reichers Rafter Manual" in my bags...where are all you '70's framers?????? Doesn't anybody remember the little blue book that fits in your bag or is it a Calif, thing....?
 
Re: Calculating Rafter Length?

Beach,

I was there So. Bay Cailf. 70's framer fun in the sun and paid.

No one up here cuts rafters they use trusses.

When I tell the framers up here we cut all the roof rafters on the ground they look at me funny.

The glory days!

Rick
 
Re: Calculating Rafter Length?

Glory days is right!!! I miss those days......Gratifying physical work, year 'round tan and you got paid for the work you actually did (if you pieced out) ;)

When I tell the framers up here we cut all the roof rafters on the ground they look at me funny.
Click to expand...
They look at you funny because they can't understand a word you say! :mrgreen:
 
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