Rafter Table/span Question

bobbrown

doing a hip roof layover of a hip roof.
got the sleepers down - 5/12
now...when i measure between my sleeper edge points to get total span
to look up rafter length under the rafter tables do i measure from the long point to long point on the sleeper or from middle of rafter point to middle of rafter point. (middle of rafter point would be basically 3/4" up from long point)
thanks

bob
bob

joasis

Depending, I always use the long dimension. I have never thought about splitting it in the middle of the hypothetical line. Since I learned this on the job, I don't know the book method of doing this.

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K2

What's a layover?? What is a sleeper on a roof system?? I've framed with guys from all over the country and never heard these terms. But I havn't heard everything.

K2

If your looking for the length of your hip jacks, just take common pattern and find the "Diff in length of your valley or hip jacks" on your framing square and start subtracting. You shouldn't even have to do any math and you don't need a book.

Joe Carola

Bob,

Why do you need to measure in between the sleepers edge points to get the span?

Your ridge has to be in already. Pull your 16" centers from the last common 16" center and mark your sleeper to the long point or short point. There's no need to mark to the centers, it's a waste of time and an extra step once you get the center mark and then extend it to the long or short point.

What rafter tables are you looking up anyway. Are you looking at the common jack length differences on the framing square or a book? If your using a book, why are you using a book?

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Joe Carola

K2

Joe, what is a sleeper on a hip roof?? What is a layover?? Is this a hip system using trusses?? I need to know. Thanks.

joasis

Difference in terminology for area...I was guessing. I knew what he was asking, and had no idea why anyone would run any distance on a rafter that wasn't the top.

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bobbrown

there is an existing hip roof, but we are not dealing with the hip portion, just the common rafter portion. so an addition w/ hip roof has to go on forming a "t". you attach sleepers to the existing roof to form your bottom plate for the rafters. being that the addition is much wider than deep the end of the ridge can either end over the existing roof or you can frame a bastard hip. if i take the width of the addition and divide by 2 i get the ridge end point. this is not far from the roof edge, but is up the roof line a bit...still ok design/sight wise.
so i measure back from the addition line 1/2 the width of the addition and come to points on the existing roof at each end. now the sleeper is angling up at 5/12 and i have these points on the sleeper. if i measure between these two points (which is where i want the down roof portion of the rafter to end) i have the total span of the last common rafter portion of the new roof. i go to the rafter tables and get a reading and cut the rafters.
the question is will the down roof portion of rafter tails then fall exactly on the line or will the middle of the rafter fall on the line.
thanks for all the input.
bob
p.s. and the reason i'm using the rafter tables rather that doing a measure is the stinking project is 15 feet off the ground and i don't want to keep climbing up and down to get it right..plus i ought to be able to use the tables and get it right the first time.

K2

I'm reading this as a valley. Am I missing something??

joasis

From what I read, it is still the long dimension, not split.

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bobbrown

yes it is a valley created by the sleeper on the existing roof.
i really have to appol;ogize to the board for making this a lot more complicated than necessary.
couldn't see the forest for the trees and just state the simple question...do rafter tables make the tails fall on mid rafter line or lower edge rafter line (long point on compound cut) in a valley.
sorry to waste everyones time with all the added junk.
bob

TonyD

Mid rafter line

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K2

Got it. If your last common intersects the valley line at the point away from the valley then your tables or the square would be giving you long to long points. If your last common intersects on the side closest to the valley then you are using the long to short points. Measuring the center of the valley jack would be a difficult way to do it as the other guys already mentioned.

If you start your sheets of ply or osb out of the valley, the valley jacks can be a quarter inch off layout because your generally not breaking sheets there and there is not likely to be drywall underneath. Actually the small jacks can be more than a quarter off layout and no one would care but I uaually like to get them close.

Nick H

If I'm reading this right you dont have any "full" common rafters as your new hip lays back beyond the existing roof so you only have jack rafters. I've done a few like this recently and I reckon the easiest way to frame the new roof is to cut a pair of full common rafters and temporarily set these on your new wall plates as close as poss to the existing roof, then you can set the new ridge on these rafters, albeit the ridge is gonna be longer than necessary.
Once youv'e got the ridge set level you can cut another full common rafter and set this on your new wall plate but in the middle of the hip end, lay the top cut of this rafter alongside the ridge and you can mark where the ridge needs to be cut. From this mark you can measure back your 16" centres and put in your jacks, I usually measure the first one and then diminish the rest.
Once the jacks are in you can remove your pair of temporary rafters, cut the ridge to your mark, fix the centre hip end rafter, etc etc.
Trying to set the ridge with a pair of jacks sitting on the sleepers (we call them layer boards) just seems like real hard work and has too much room for error.
Thinking about it, how have you managed to get your sleepers in the right place without setting the ridge first ?

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bobbrown

thanks for all the input. things worked out just fine.
the lay out was pretty easy.
found the 2 end points at the valley ends.
measured total end point span. went to valley tables.
from both points measured valley length up roof and scribed a line. center where the lines intersected.
went back out and found mid point on exterior wall.
found mid point between valley points.
ran a string line from top roof point to mid point on wall.
plumbed down to see how close to mid point between valley points.
as luck would have it...right on...go figure.
even blind squirrel finds a nut every now and then.
then did exactly as suggested and did a temp support for the ridge.
attached at the top sleeper point and plumbed down to the confirmed center span line.
thanks again to all