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rafter cable ties

paulmars's picture

I cant understand this math. ive been over and over it. Each time I get a little further, then I loose it again.

How to calculate rafter thrust? -Help! at

Can someone help me figure cable load?


24" rafter spacing.

No rafter ties at all. A few existing collar ties.

ceiling joists run parallel to ridge.

house is 27' x 30'(ridge).

7/8" roof planking and asphalt shingles.


It's all about the squaw on (post #210138, reply #1 of 1)

It's all about the squaw on the hippopotamus.

Hint: Consider what happens if the rafters spread one inch -- how far does the ridge fall?  The spreading force is equal to the force on the ridge divided by how far the ridge falls (in inches).  For a 12/12 pitch the ratio is 1:1.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville