Illustration of roof with rafter tie.
Roof rafter thrust.
Connections can also pull apart.
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.
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.
This can result in a bending outward at the top of the wall as well as a dropping of the roof ridge.
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.
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.
This horizontal load or thrust can be considerable especially on a low pitched roof.