If ceiling joists are offset from each other, what about the rafters?
I am installing rafters and ceiling joists on a small house I am building and watched Larry Haun’s video and read his books as well. However there is one aspect of the process that is confusing.
In the video he says to overlap the ceiling joists and make allowances for this on the layout by putting the joists on one side of the line on one side of the house and the other side of the line for the other.
If the rafters are going to be attached to the ceiling joists wouldn’t they be offset from each other at the ridge? Aren’t rafters supposed to be in the same plane at the ridge? A block in between the ceiling joist and the rafter on one side of the house would fix this problem but is that up to code?
I have attached a drawing to make it a little clearer.
Thanks
Replies
I believe if there is a center partition, the joists can butt together and must be tied in accordance with your local building codes.
You could also use a block as you suggest as a spacer. It jus has to be long enough to meet the code for overlap and fastening.
Edit: Added sketch
I think you can rely on drywall to make up the difference. Drywall folks will prefer to run the sheets at right angles to the joists anyway.
The offset on ceiling joists is only in the inside of the house. Where they sit on the outside wall is not offset, but on the indicated side of the mark. this way all the rafters can offset directly at the ridge, and run straight, to be set upon the outside wall top plate, and secured to the adjacent ceiling joist.
So the ceiling joist layout on the outside walls would be exactly parallel to each other?
And the overlap on the inside would be directly underneath the middle of the rafters?
If the ceiling joist was long enough to span the entire distance, it would set straight.
A mark on the interior bearing wall made using a chalk line from the outside walls would be on one side of the long joist.
using two joists, overlapping at the center, the overlap joint would be moved half the thickness of the joist away from the chalk line.
the overlap line on the inside wall would end up 3/4 inch away from the edge of a line dropped from the joist side of the rafters, or in the same place the center line of a single long rafter would be.
This is my suggestion. it is different than what it looks like Larry is suggesting.
https://youtu.be/0Y6n6kf7vdY?t=418
he is laying out the joists square to the walls.
in this case, the rafters will end up offset some, between the wall and the ridge, to make them meet at the ridge.
depending on where you are, code will allow for some offset at the ridge, but if you make it too far, the ridge board will need to be beefier.
If you make the joists square and straight, and the rafters off a bit to meet at the ridge, the roof decking will make up the difference.
1.5 inches outside wall to outside wall is 3/4 inches to the ridge, and if the rafter length wall to ridge is 12 feet long, each 4 ft width of sheathing would see 1/3 of that, or 1/4 inch difference over the 4 ft wide sheathing. longer rafters would have less. roof sheathing pattern should be offset, and use clips to ensure gaps.
You also can make it all square, and use blocking to do so, or use framing straps to transfer the tension load between the joists laid end to end.
This is why people buy engineered roof trusses.