Rafter stacking or hip & valley allign.
jimcco
| Posted in Construction Techniques on
I had always learned that jack rafters on both sides of hip or valley should be directly opposite on the hip or valley. We hear so much now about stacking I thought I would see how that works out in 3-d plan.
As you follow the “directly opposite” plan arround a complicated hip roof you are soon off from the stacking.
What do most of you do.
1) forget about stacking and make the jacks opposite.
2) forget about opposite and stack all rafters keeping them on spacing (ie 16 or 24)
3) make jacks opposite and add rafters to bring the commons back into stack alignment
(don’t want to hear about trusses)
Replies
Im a little confused. Do the rest of your rafters stack and its just the jack rafters?? If you are using the same spacing of rafters and studs ( 16 o.c. studs, 16 o.c rafters, etc.) you should be able to at least stack both sides on two of your corners, and one side on your other two corners.
A picture would help a lot here. If Ive got time later, Ill try and draw up what Im thinking. But to also answer your question, we always make the jacks opposite.
you have it right, I think he has simply encountered where on some of his corners he is not getting all to line up and stack at same time.
Think about this:
You have a room (area) with hip roof projecting from a long wall, then as you work around the area keeping jacks opposite on valley, hip, hip, & valley when you get back to the main roof the jacks are out of sync with the joists & studs that went thru the long wall area.
I'll cut a section from a model & paste it on later.
"as you work around the area keeping jacks opposite on valley, hip, hip, & valley when you get back to the main roof the jacks are out of sync with the joists & studs that went thru the long wall area."
that is because you you are laying your jacks out from the corner. if your studs are layed out from the same corner they will line up as will your common rafters. but if are working at the end of your stud layout unless the lengh of wall works out exactly wth your oc layout, then that end will not stack, if you are laying out the jacks layout from that corner, you have to follow the lay out from the other end, meaning the the smallest jack at end of run could end up being less than 16" ( or 24" for 2' layout ) from that corner. no big deal.
even if you lay it out with each hip or valley layed out from it's own corner, it's not a big deal if they dont' stack. if you do it that way, when you get to your commons, if you do not align with their layout, all that matters is that you are with in your oc. ie: 16" or less or 24" oc or less ( whatever your using). if you end up say at 30" oc where they meet up add one rafter in the middle.
when you turn your corner, it can change, with a different layout on that wall than was on the other. But dont' worry about it. align your jacks so that they oppose each other. stack your commons, and jacks if they work out that way.]
hope that makes sense
It's critical , that you bearing points line up (stack).
with 2 plates on top of walls, I wouldn't worry so much if common jacks stack or not. I'd rather have the jacks oppose each other, but even they can be offset if you have a heavy duty valley or hip rafter. ( some houses I've framed on have had a 2 ply 11 7/8 microlams for hips and valleys, which can easily handle offset jacks.) I could get into it more, but you'll be fine. long as you got your bearing points covered.
it is quite common to have a 16" layout for everything but the roof which often changes to a 24" oc layout.
i
I had always learned that jack rafters on both sides of hip or valley should be directly opposite on the hip or valley
That is considered good practice, but mathematicallyt, it doesn't work out when working with unequal pitches.
So, if it doesn't matter on unequal pitches, it doesn't matter on equal pitches, right?
It becomes a matter of aethetics and presentation. On some exposed roofs, the appearance might be critical. If so, the architect should draw it up with equal pitched slopes.
Sometimes, the old "rules of thumb" are just that and they don't make sense.
blue
With dbl. top plates stacking isn't needed.
Jacks meeting on the hip looks great but isn't needed.
You can solve the stacking problem ( if is a big deal to you ) before it starts if you lay out the end wall of the hip from the center instead of one end. Either allow for a king stud// rafter stack dead center (aligning with the main ridge), or lay out with equal distance off the the center to the two longest jacks.
On single pitch roofs I prefer to lay out my jacks so that I can use a sheathing drop on the opposite side of center.
just like dovetails look great but aren't needed :)
sorry couldn't resist.
*laffin here* Never have made or used one myself!