Rafters And Roof Ridges Are Normally Under Tension

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.

Rafters and roof ridges are normally under tension. A guarantee by a surety company that a roofing manufacturer will repair a roof membrane or covering under the conditions listed in the bonding contract. Also called collar tie. 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. Rafters are typically installed on 24 inch centers.

If you see sagging rafters recommend stabilization by a qualified contractor. That said i recommend having a local structural engineer come out and review the situation if you are not such an engineer yourself. Under the roofing paper felt along the rake edge. 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.

A horizontal timber uniting two opposing rafters at a point below the ridge usually in the upper half of the rafter length. As such i don t see significant risk here. A pair of rafters is called a couple in home construction rafters are normally made of wood exposed rafters are a feature of some traditional roof styles. Rafter tie a tension tie in the lower third of opposing gable rafters that is intended to resist the outward thrust of the rafter under.

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. Roof vents are required for roofs with unconditioned attic spaces. Roof sag or roof collapse forces. An attic with an area of 600 square feet with ridge and soffit vents should have a total vent area of square feet.

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. Flat roofs normally have venting systems. The roof framing mock up below shows a standard rafter tie. That s true for horizontal ties in the lower third of the roof.

Collar tie is a colloquial term for collar beam. If you see rafters installed on centers greater than 24 inches look for signs of failure such as sagging of the rafters. 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. This article describes explains the directions of forces in roof structures illustrating downwards force horizontal thrust and the causes of rafter sags rafters that disconnect from the ridge or top plate and why a sagging roof pushes the building walls outwards at the wall top.

We include photographs of collapsing wood framed roofs and photo sequences.