Rafters And Roof Ridges Are Normally Under Tension

The roof framing mock up below shows a standard rafter tie.

Rafters and roof ridges are normally under tension.

Collar tie is a colloquial term for collar beam. Rafters are typically installed on 24 inch centers. It s an indication that you should look carefully for other problems in the roof framing. A rafter is one of a series of sloped structural members such as wooden beams that extend from the ridge or hip to the wall plate downslope perimeter or eave and that are designed to support the roof deck and its associated loads.

A tension tie in the upper third of opposing gable rafters that is intended to resist rafter separation from the ridge because of wind or unbalanced roof loads. If you see rafters installed on centers greater than 24 inches look for signs of failure such as sagging of the rafters. In many situations you ll find that ceiling joists installed parallel to the rafters are intended to function as rafter ties. A ridge beam carries the loads of the rafters connected to it and must be both strong enough to carry the weight and well supported at the bearing points at each end to transfer the loads down to the ground.

Mathematicians and engineers discussing collar ties and rafter ties explain that collar ties and rafter ties or ceiling joists under a gable roof are in enormous tension and that the mathematics of the roof forces are the same for collar ties and rafter ties. If you see sagging rafters recommend stabilization by a qualified contractor. A rafter tie is a tension tie in the lower third of opposing gable rafters that is intended to resist the outward thrust of the rafter under a load. A ridge board was not always required and the photo above of the attic in a 1920s era house shows a roof framed without one.