Roof Rafter Thrust

Tim healey in a roof with a non structural ridge rafter ties which resist the outward thrust of the rafters can be raised a maximum distance hc that is no more than one third the distance between the top of the supporting wall plates and the top of the ridge 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. 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. 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. 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.

Collar ties designed primarily to resist wind uplift must be located in the upper third of hr. 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. Illustration of roof with rafter tie.