Rafter Math Question

in-too-deep · May 17, 2015

I'm getting my paws on some roof steel. It's from a building that is 32 ft wide with a 5/12 pitch. If I used the steel on 4/12 rafters instead, how wide would my building be?Thanks!

Eric in IL · May 17, 2015

32.8876876659434 feet wide IF I still can do trig. correctly. I think that translates to 32 foot 10 and five eights inches roughly.

Spudm · May 17, 2015

For every 12 inches of run, you have a 4 inch rise.
Shouldn't be that hard to figure out from the 5/12. Good luck.

Ultradog MN · May 17, 2015

32.86'
I had to think about that one and then have my lovely wife who was a math major help me.

550Doug · May 17, 2015

(quoted from post at 16:52:41 05/17/15) I'm getting my paws on some roof steel. It's from a building that is 32 ft wide with a 5/12 pitch. If I used the steel on 4/12 rafters instead, how wide would my building be?Thanks!

Use Pythagorean theorem.
A 5/12 roof gives a hypotenuse of 13, so for a 32 wide building the right triangle will measure 16 by 6.666 since each side is expanded by factor 4/3. This means that the hypotenuse of 13 will also be expanded by factor of 4/3 giving 17.333 as the length of steel you have. Making this 17.333 as the hypotenuse of a 4/12 triangle will give sides of 16.44 and 5.45 thus making the new 4/12 rafter 32.88, so you only gain about 10.6 inches.
Of course the overhang on both buildings would be identical using these numbers.
That's my take on it.

Goose · May 17, 2015

What do you get when you divide the circumference of the moon by its diameter?

Pi in the sky.

Sorry, I couldn't resist it.

MSD · May 17, 2015

If the building is a gable type meaning the 32 ft. wide has each half of the roof being 16 ft then with a 5/12 pitch your tin should be 17' 4" not calculating any overhangs. With a 4/12 pitch you can go 16' 5 1/4 ". Now if it is a sloped one sided roof that is 32' then your tin is 34' 8" long. With a 4/12 pitch you could go 32' 10 1/2" wide.

dmbinva · May 17, 2015

Build it 32 foot let the overhang take care of the 5 and change inches on each side. all of your materials will work better at 32 ft, otherwise you will have a lot of waste. One of the best things dad did was to teach me how to read a framing square
Boss

Goose · May 17, 2015

An Indian chief had three daughters.

The first got married and in due time had a baby boy. The chief gave her an elk hide.

The second got married and in due time had a baby girl. The chief gave her a deer hide.

The third got married and in due time had twins, a boy and a girl. The chief gave her a hippopotamus hide.

It just goes to prove the squaw of the hippopotamus is equal to the sum of the squaws of the two other hides.

(Couldn't resist that, either).

in-too-deep · May 17, 2015

Good point.

ss55 · May 17, 2015

Check if the roofing sheets are one piece length or if two sheets are overlapped.

john in la · May 17, 2015

Goose;
Thanks for the laugh

Bob Harvey · May 17, 2015

Man, you are OLD ! Haven't heard that one since...............fill in your own blank. ;^)

Ian Beale · May 18, 2015

Eric,

With that many decimals you'd likely be a shoe-in for a job on the global warming gravy train!

Geo-TH,In · May 18, 2015

550Doug,
You stayed awake in geometry class. The older I get the more I find math/geometry a
useful tool.

Russ from MN · May 18, 2015

A squared + B squared = C squared! Glad I stayed awake during 9 grade Math class!

ed will · May 18, 2015

Hi, if your not into pythagorus just measure it out with
a tape and markers on your lawn. Ed will

ed will · May 19, 2015

Hi, if your not into pythagorus just measure it out with
a tape and markers on your lawn. Ed will

Rafter Math Question

in-too-deep

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Eric in IL

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Spudm

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Ultradog MN

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550Doug

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Goose

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MSD

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dmbinva

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Goose

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in-too-deep

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ss55

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john in la

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Bob Harvey

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Ian Beale

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Geo-TH,In

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Russ from MN

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ed will

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ed will

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