Unequal Slope Hip Rafter Calculations

[@smokiethebear3334]

Your videos are helping myself and a couple other apprentices get through our second terms of general carpentery in Southwestern Ontario! Thanks for the videos!

[@johntalo6082]

You are so kind brother to share your experiences and knowledge to a man like me who eager to learn building measurements.God bless you.

[@TersooJacob-tw7yj]

Weldon for the work and I appreciate you for your efforts for making some us to understand how hip roof being measured.Thank you and God bless you.

[@canadasalami]

As a former student preparing for the exam I can say these videos are very helpful!

[@johntalo6082]

I love your explanations very clear as Solomon Islander.pacific.

[@johntalo6082]

I love your channel brother.

[@carpentryandwoodwork2018]

Normally I would do this using degrees etc but Yes an interesting video!

[@gprooftheory]

That is all fine and dandy for a fine line drawing, when you add wood things change dramatically. To have the same over hang you have to raise the heal height of the steeper pitch to meet at the same time, therefore the hip will need to shift from the corner to make the hip plane at the wall plates at the Same point, also when you add a ridge board. your half span for the 5/12 would be 95.25 95.25 run/setback and for the 8/12 would be a 59.527 run/setback. The ridge board would be 97”, that is not a correct drawing for a wood framed roof weather it be hand cut or roof trusses having the same overhang. That drawing shows both the wall corner plate and Facia being in the same line, that does not work with having to make the heal height taller for the 8/12

[@scottfleming]

I appreciate the comment. It's tough to see in the video but the drawing clearly shows the hip offset from the corner. You can tell in the video that it does not run at 45 degrees. And yes, of course you need to pay attention to your height above plates (the heel). Often the difference is too great to simply adjust the birds mouth and the wall has to be built up on the steeper side. So I understand what you are saying but the drawing is fine. If your projection is equal then the fascia and corner of the building have to line up (2' out and 2' over for example), just the hip runs offset from 45.

[@OhJeezRanders]

Not sure if you still check the comments… thanks a lot for this. When we were learning this in class, we used a run of 15 for the hips instead of 16.971, could you explain to me where the 15 comes from? I understand that the hip run is the square root of the product of 12/12 for a 45 degree angle, just very confused where the 15 comes into play. Is this a common ratio between different slopes?

[@scottfleming]

I'm not sure where the 15 comes from. 13 is the Unit run of a hip on an octagonal roof. Maybe it was just a number that was picked to lay out the plumb cuts on an unequal hip/val with your framing square. It's all just proportional to the total run and total rise. So, what you use as the unit run for an unequal hip/val doesn't matter as long as it maintains a constant ratio with the total rise and run.

[@williamhospodor5246]

Can you do some videos on bastard roofs and matching facia on unequal pitches?

[@scottfleming]

Good idea!

[@E-E.ADVENTUREGEARS]

Which text book?

[@chiller19100]

So if you swing the hip rafter over to the steep side dd you make the height above plate the same as the commons on the steep side? or do you have to do something else to the hip rafter to get the hip in plane with the steep side and the shallow side? Thanks for any help

[@scottfleming]

Hi Dillon. Yes the height above plate is the same as the commons on the steep side. You'll have to "drop the hip" a little and because of the angle it runs at (not 45 degrees). So its not the same as equal slope. Remember that the theoretical measurements are to the centre and that your birdsmouth will be deeper because (typically) your hips are one lumber size up from your commons and jacks. JLC has a really good article on this topic here: www.jlconline.com/how-to/roofing/joining-unequally-pitched-roofs_o

[@Sherlockly]

What’s the equation needed to get to the hip true length if I have the hip run and rise?

[@scottfleming]

True or actual length is determined by shortening the theoretical length by the thickness of the ridge (and fascia, depending on where your measurements are taken from). It has to be shortened by the thickness measurement taken on the same angle as the hip - measured on the level and proportional. Alternatively, you could have the hips meet and shorten the ridge. Note- if your hip rise and run are actual measurements (inside of fascia to end of ridge) then the hypotenuse of those two will be the true length of the hip. When you lay it out remember that the layout lines are in the centre but the cheek cuts won't land in the centre due to the angle of the hip not being 45 degrees. Hope that makes sense!

[@williamhospodor5246]

What is the book called? I’m trying to find it online to buy?

[@scottfleming]

Carpentry by Vogt and Nauth, 3rd Edition

[@chiller19100]

Thanks a lot for this video it’s very helpful! Just curious, since the hips are not running at 45 degrees how would you know what angle they are running at so you could cut your Jack cuts. Thanks for any help.

[@chiller19100]

Or really I guess a better question would be is what is the pitch of the hips?

[@scottfleming]

@@chiller19100 The slope (pitch) of the hips is proportional to the total rise and run. Use ratio to find numbers that will fit on your framing square. In this example the total rise is 40" and run is 113.208". For the plumb cut, you could set your square at 8" for the rise and 22 5/8" for the run (just divide each number by 5). This is the equivalent to 4.24/12 slope. Plumb cuts for the jacks is the same as the commons for the side they are on (5/12 and 8/12). Side cuts are a different story!

[@chiller19100]

@@scottfleming that was very helpful and thanks for responding! Just one more question, would you have to raise the 8/12 plate height?

[@scottfleming]

Hi @@chiller19100 . Yes you do. The amount depends on the difference in slope and the projection to the fascia. In this example the projection is 1'. So the amount of rise on the 5/12 side at the plates is 5". The amount of rise on the 8/12 side is 8" so the plate needs to be built up by the difference of 3". If you make your the stand (amount of material left in the rafter at the birds mouth) equal for both slopes then just build up the plate by 3". If it was an 18" projection I would use ratio again to figure out the build up. 3" build up per foot (12") so 18 divided by 12 x 3 = how much we need to build up (4.5")

[@chiller19100]

@@scottfleming you have been extremely helpful! Thank you very much

[@gilbertososa5335]

Great video. As an educator, I see the need to teach this type of applied mathematics. This work would make a great student project in a geometry or Algebra 2 class. Can I get this sheet in a pdf form? Cheers!

[@scottfleming]

Sorry for the late reply. These drawings are from the text book I use in my shop so unfortunately I cannot share them.

[@gabecarr4037]

I know this is an older video but it's worth a long shot, thanks in advance. Building a one sided porch irregular hip roof, so this is what I got, need help with out end rafters and all pitch, Lenght is 23' + 1ft and each side for hangover From ridge face to the width is 74" + 1ft hangover The ridge is 16ft wide Between the outer wall height is 94" and top of my ridge is 108.5" With a difference of 14.5" between 74" Any help will be appreciated

[@gabecarr4037]

I'm thinking the front might have a 2/12 pitch or so

[@scottfleming]

@@gabecarr4037 I think I understand the situation. Don't forget that you have to consider the bird's mouth. With your total rise above plates 14.5" if you have a stand (Height Above Plates - or material left in the bird' mouth at the building line) of only 2 3/16" you will have a slope on the main (front) commons of 2/12. That would make the total rise from top of fascia to top of ridge 14 5/16" and a slope on the end commons of 3 3/16 / 12. The slope of the unequal hips are 1 11/16 / 12. You can change the stand of the main commons but that would change the slope from the 2/12 of the main commons. With a projection of 12" you'd be fine with a 2 3/16" stand. To the outside of fascia the length of your rafters are: Main commons 87 3/16" End commons 55 7/8" Hips 102 9/16" length of the jacks depends on your OC spacing and actual lengths of all need to be shortened proportional to the size of your fascia stock. I hope that helps...

[@gabecarr4037]

@@scottfleming that helps so much, thanks for replying, would it help if I cut down the ridge down a bit on each side, since it's a front porch, looking for a wider front look, thanks again

[@scottfleming]

@@gabecarr4037 happy to help! I think that's a great idea. I don't know how much you were thinking but if your ridge was 128" then you could have equal slope on all sides and your hips would run at 45 degrees making the layout and assembly easier. Plus it looks better from underneath if your rafters are exposed. I'm not sure you were thinking of taking that much off though... 32" from each end is a fair bit. Either way the slope is not too steep and a shorter ridge will give you more of a sweeping look.

[@gabecarr4037]

@@scottfleming I will do that, comes out to 10' 8"

[@nlrmtraindetailwalker2864]

I'm a union trade carpenter I been in trade now approximately 30 years now and I will like to take classes I live in Cincinnati Ohio If I may ask where do you live and do you actually teach how to step off with framing square ? I'm really interested in taking roof framing classes

[@scottfleming]

I do teach the step off method and have a video right here: kzbin.info/www/bejne/q17WZWOlpstsqJo I am in Peterborough Ontario

[@Alex-uf6su]

what would be the height of the roof?

[@scottfleming]

40" (total rise to ridge from fascia). Main roof is 5/12 slope and the span is 16' so the run is 8'. so we have 8 runs, each having a rise of 5". 5 x 8 = 40"