My question is regarding finding a common rafter length using the Construction Master IV calculator. I understand the key strokes involved. As an example, I have an 18′ wide building, with a 5/12 pitch. Using the users guide, the rafter length is: 18’/2=9′ 9′-3/4″(for ridge beam)=8′ 11 1/4″ (this is the run value). 5″=pitch, 9′ 8 3/16″ is the diagonal value. I am not sure I understand where to measure along the length of the rafter. Is the measurement from the long point of the head cut directly to the inside corner of the bird’s mouth (c-cut) or from the long point of the head cut along the top edge of the rafter 9′ 8 3/16″ then plumb down to the inside corner of the bird’s mouth (c-cut). It seems to me that either way I measure, the roof pitch will change from the desired 5/12.
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RTFM
Mr T
Happiness is a cold wet nose
Life is is never to busy to stop and pet the Doggies!!
hey T i bet i know what that means lol
joe fusco has the procedure using the construction calc on his website http://www.joesphfusco.org
Darkworksite4:
El americano pasado hacia fuera ase la bandera
That site should be http://www.josephfusco.org/
Take your measurement down the top edge of the rafter. Then draw your plumb-cut down (parallel to your head cut). Your seat cut will run perpendicular to this line you've drawn. What ever is left after you make this seat cut is your "heel stand". Only variable is the depth of seat cut which alters your heel stand measurement, which directly reflects on your ridge height. Make sense?
The heel stand or HAP (height above plate) is the distance, measured vertically up the plumb cut from the intersection of your bird's mouth cut to the top of your rafter. If you add this number to the number your CMIV gives you for a height, you will have the "actual" height of your ridge.
Hope that helps, have fun, and good luck.
Is the measurement from the long point of the head cut directly to the inside corner of the bird's mouth (c-cut) or from the long point of the head cut along the top edge of the rafter 9' 8 3/16" then plumb down to the inside corner of the bird's mouth (c-cut). It seems to me that either way I measure, the roof pitch will change from the desired 5/12.
The 9' 8-3/16" measurement is from the top long point of the head cut and down the top of the rafter which represents the outside of the top plate. Then plumb the line down and mark your seatcut towards the top plumbcut.
The roof pitch will not change at all either way you mark it when you lay out the rafter plumbcut and birdsmouth with a 5/12 pitch. If you mark it the wrong way towards the inside corner of the birdsmouth your rafter will be short.
If you draw a rafter on a piece of paper and mark the tops you can then draw a triangle and see the relationship the rafter has with it.
You can even mark the bottom of the rafters to lay it out the same 9' 8-3/16" and just draw your plumbcuts up to the top.
You can even layout your rafter to the inside of the plate but you would have to deduct the 3-1/2" thickness of your wall so your new run would be:
8' 11-1/4" - 3-1/2" = 8' 7- 3/4"
5 [inch] [pitch]
8' 7-3/4" [run]
[diag] = 9' 4-3/8" (Rafter Length)
Doing it that wat you would layout your seatcut the oppsite way, away from the top plumbcut. I don't want to confuse you but just trying to help you understand how the rafter is just a big triangle.
Joe Carola
That would be with a full bearing seat cut ::wink:: :-)
Erik,
Yes full bearing seat-cut as always, now you've made me even later for work ;-)
Joe Carola
You've got such a good way of explaining this stuff....you oughta be teaching it. I re-read my explanation, then I read yours and it's no longer a mystery to me why my guys just stare at me with blank looks on their faces!
>> ... my guys just stare at me with blank looks on their faces!
They're waiting for you to stick out your tongue again.
Thank you Dieselpig. You can say that we're all teachers being a boss or at least trying too teach the guys that work for us. Some get it and some don't. Some who get it quickly are the ones that really want too learn but sometimes the ones who don't get it quickly who really want too learn just have a little more trouble understanding at first. That is the reason why over the years trying too teach about roof framing I realized drawing it out whether on paper a sheat of plywood or the deck helps people understand so much easier about the roof framing.
Then again you get the guys when your trying too explain something about roof framing and they just stare at you with that blank look on their face and they just don't care about anything else other then nailing the rafters up on the marks and getting the roof framed which is good because they produce or just don't care either way other then getting paid for the day.
I'm telling you the truth about drawing it out on the plywood deck, when you actually draw the rafter as it's sitting on on wall and then draw a triangle under the rafter and draw a run and a rise, let's say for a 5/12 pitch and step out the 12" run mark and the 5" rise mark going up the hypotenuse line looking like your laying out a stair stringer, you will be surprised how the guys will say" Holy Sh!t, now I get it".
Same thing for figuring out the plywood angle for the gable end for sheathing the walls. I just taught the guys from the bottom of the left hand corner of the plywood for a 5/12 pitch roof we know for every 12" horizontal run we have 5" of vertical rise so if you mark 12" and then square up 5" from the bottom left plywood corner you can connect the two marks which would read 13" because that's the hypotenuse. That would be part of the angle and you can continue the line all the way up too the top of the sheat but I just showed them, why not come marking a 6' run on the bottom and using the T-Square marking 30" because 6' run x 5" rise is 30" then snap the chalk line straight through too the top of the plywood and you have your angle. What I've done in that explanation after snapping the line is show them the triangle again and it just seems too click when people see the triangle.
I know you know that and what I explained above sounds like a long explanation but in the end result my guys now when sheathing don't wait too get a sheat up on the wall and then measure over too get the angle they hook the tape on the corner and measure over and make two marks and snap a line in about 30 seconds and they have the angle.
Sorry for the long post but what I've also realized is that you have too have Patience when teaching something too someone and I have that. I see guys who will just start yelling because they're guys don't get it. Too me that's the wrong way because the one guy I use too work for years ago was like that until I told him I would throw him off the roof (the good old days). The way I teach on the job is like the way I teach my son Joey who will be 6 in August, you just have too be Patient and explain things. With Joey I don't just tell him too grab something and pick it up, I will tell him too grab the 2x4 with your Left hand or right hand so he gets too know which hand is his left or right.
You made me late for work now ;-)
Joe Carola