Offset Rafter Tie/Ceiling Joist
Offset Rafter Tie/Ceiling Joist
(OP)
I've got an existing building, with unreinforced multi wythe brick walls and a gable rafter roof. Client wants to raise the roof to increase the usable attic space.
We could take down the existing roof and replace with an increased pitch, giving us some more space. A different roof shape, such as a gambrel is another option.
Another option I'm considering is taking off the roof, building up new masonry knee walls, say 2-3 feet tall. and then replacing the roof. This would increase the space considerably by the time you are a couple feet out from the wall. In this case the attic floor joists would be offset from the rafters and so the roof kick out forces would have to be taken by the knee wall in bending. If I can get the capacity out of the wall section, rafters and bearing place connection, anyone see a specific issue with this sort of detail? It seems like it is kind of like a gambrel roof, just using masonry for the lower portion instead of more wood truss.
Thanks guys.
We could take down the existing roof and replace with an increased pitch, giving us some more space. A different roof shape, such as a gambrel is another option.
Another option I'm considering is taking off the roof, building up new masonry knee walls, say 2-3 feet tall. and then replacing the roof. This would increase the space considerably by the time you are a couple feet out from the wall. In this case the attic floor joists would be offset from the rafters and so the roof kick out forces would have to be taken by the knee wall in bending. If I can get the capacity out of the wall section, rafters and bearing place connection, anyone see a specific issue with this sort of detail? It seems like it is kind of like a gambrel roof, just using masonry for the lower portion instead of more wood truss.
Thanks guys.
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)





RE: Offset Rafter Tie/Ceiling Joist
I would be real concerned about this detail and developin g ny tension in the existing brick wall.
I would try to go with collar ties to limit any lateral kick to the existing wall and the need for the detail. The lower the better...
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Offset Rafter Tie/Ceiling Joist
How else is this sort of thing commonly accomplished? just trying to get more space in the attic. Dormers in the existing roof?
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Offset Rafter Tie/Ceiling Joist
Or possibly put a kicker (tension) in at the top of knee wall down to the floor at some angle?
EIT
www.HowToEngineer.com
RE: Offset Rafter Tie/Ceiling Joist
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)
RE: Offset Rafter Tie/Ceiling Joist
EIT
www.HowToEngineer.com
RE: Offset Rafter Tie/Ceiling Joist
M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)