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.

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. A ridge board with the ceiling framing below acting as a tension tie is nearly non structural and of nowhere near the importance of a a true ridge beam. 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. 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.

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. That said i recommend having a local structural engineer come out and review the situation if you are not such an engineer yourself. 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. 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.

Under the roofing paper felt along the rake edge. 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. Collar tie is a colloquial term for collar beam. We include photographs of collapsing wood framed roofs and photo sequences.

An attic with an area of 600 square feet with ridge and soffit vents should have a total vent area of square feet. A horizontal timber uniting two opposing rafters at a point below the ridge usually in the upper half of the rafter length. If you see rafters installed on centers greater than 24 inches look for signs of failure such as sagging of the rafters. As such i don t see significant risk here.

Roof sag or roof collapse forces. It s an indication that you should look carefully for other problems in the roof framing. In many situations you ll find that ceiling joists installed parallel to the rafters are intended to function as rafter ties. 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.

Roof vents are required for roofs with unconditioned attic spaces. Flat roofs normally have venting systems. That s true for horizontal ties in the lower third of the roof. Also called collar tie.

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.