How To Calculate Length of Common Roof Rafter - Carpentry And Construction Math 

This is the best roof rafter math that I viewed. Particularly find the modulus of "5 in and 13 in" (right this case) first then to get rise and rafter length. Smart!

Legit teachings!! Thanks for sharing 🙏🏾

The conversions between feet and inches and between fractions and decimals make a good argument for us switching over to the metric system.

A seasoned carpenter built our home ,3800 sq ft, 7 on 12 slope , hip roof with a 4 on 12 bell around entire roof. he cut everything on a pair of saw horses with only a pencil and framing square (No calculators) , did a little math but nothing this extreme. I don't think that framers could do all of this math and get anything done without a lot of mistakes, But you know your stuff and thanks for a great video.

This is excellent, thanks for posting!!

Really informative, the best example I have ever seen, thanks

Thanks, this help me a lot, you makes it’s easy to understand.

Love framing roofs.

Good stuff, what size were thickness and width were the rafters 2x6 or 2x7? How did you work that out, Cheers

Muy buen video Como puedo hacer para ver tus videos subtitulados al espanol amigo Me seria de mucha ayuda

You are a real good teacher thank you

Thank you so much, excellent.

Good work I appreciate your time thx

Loved It!

I am coincidentally building a roof right now. I'm finding that there is FAR too much variability in pretty much every measurement to rely on any math like that, though. So I settled on a much simpler method. I have a jig that is pre-cut to my 4:12 pitch and it has a mark on it for 8" to represent my "height above plate" (the rafter area just above the seat cut). I then measure from the ridge to the outer edge of the crown plate and whatever measurement that is is transferred to the upper tip of the new rafter down to wherever it meets up with the 8" mark on my jig. Strike a line there plus do a quick 90 degree line for seat cut. A couple quick cuts and voila, a rafter that fits perfectly, regardless of any variability in anything else.

Great job well explained wishing are young students inspiration on trying this on a simple structure like a dog house. We need more carpenters in this world today

This is a great explanation. Thank you! What if I need a 18” eave? Do I add 18” to the run and 6” to rise if I’m using 4:12 pitch and then use Pythagorean theorem with new units to calculate the rafter length?

Great example thank you

Greg, I am going to build a house similar to this. I am going to put 4' pony walls on the exterior wall and then put the rafters on top of the pony walls. I do not want the pony walls to push outwards. Can you guide me to a site which tells me where to locate my rafter ties? I would like a height of 6' 8" from floor to rafter tie. Any assistance would be welcomed.

good day. i am little bit confused. lets say we always have the length of our horizontal timber and to get our vertical we always use different numbers or there is a standard? or we take length of mid point and multiply with a specific number to get or vertical distance?

Convert everything to inches and when you find half the span take off thickness of ridge when you do your pitch and get the square root divide by 12 that gives u diagonal per inch of run then multiply by your run in inches and take it to the fourth decimal which is what a 1/16 is .0625 and your only off by a 1/16 thats the easiest way of course thats that top running length so you height above plate doesnt change anything and you add whatever overhang you need some people try to be to smart for their own good

Please explain slope & pitch

My head started spinning

The mathematics is mind-boggling

All you do is multiply 4/12×4/12=16/144add together =160 find square root=12.6491106040divide by 12 =1.0540925533×by 119.25 instead of 120 cause u take off 3/4 for thickness of ridge and you get 125.70053699take that round to fourth decimal =120inches and 11/16 cause thats 120.6875 that means you are within a 1/32 that is top running length so you would add your overhang of ccourse and whatever height above plate

how about a simple triangle calculator ? You know the botton lenght 10 ft you know two angles angle 90 degrees and the pitch angle you know the 40 inches measuement why do you complicate it ?