Roof Rafter Thrust

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.

Roof rafter thrust.

Collar ties designed primarily to resist wind uplift must be located in the upper third of hr. Figure 2 is an illustration of a roof constructed using rafter ties. Illustration of roof with rafter tie. This horizontal load or thrust can be considerable especially on a low pitched roof.

This can result in a bending outward at the top of the wall as well as a dropping of the roof ridge. Connections can also pull apart. 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. This thrust calculator gives rafter horizontal thrust at the plates l rafter span building width w load on rafter roof design load s rafter pitch t horizontal thrust wl 4 x run rise x on center spacing 12.