Collar ties designed primarily to resist wind uplift must be located in the upper third of hr.
Roof rafter thrust.
To resist thrust the irc calls for a structural ridge required for any roof with a pitch less than 3 12 or for each pair of rafters to be securely connected to each other by a continuous ceiling joist r802 3 2006 irc.
Rafter thrust occurs when the rafter tails the bottom of the roof members of a sloped roof where the roof meets the wall thrust outward and push the top of the wall outward.
Illustration of roof with rafter tie.
Connections can also pull apart.
This horizontal load or thrust can be considerable especially on a low pitched roof.
To resist thrust the irc calls for a structural ridge required for any roof with a roof pitch less than 3 12 or for each pair of rafters to be securely connected to each other at the lower end of the rafter by a continuous joist.
Figure 2 is an illustration of a roof constructed using rafter ties.
This can result in a bending outward at the top of the wall as well as a dropping of the roof ridge.