The ceiling joists are in “tension,” meaning that there are forces pulling on them from each end created by the roof loads. Ceiling rafters - Although their primary purpose is to provide a structure for supporting and attaching the ceiling, ceiling joists prevent the walls from the spreading apart by being connected to the rafters at each end of the span and creating a triangle.When a ridge board is used, there are several choices for containing the lateral pressure: One of the advantages of using a ridge beam instead of a ridge rafter is that the ridge beam carries the loads that would otherwise get transferred downward and then laterally to the end bearing walls, and exerts outward pressure at the top of the wall which, if not contained, will simultaneously cause the walls to splay and the ridge to drop lower.
#Flush cut rafter revit cracked
The ridge beam shown below, at the living room of a 1950s modern-style ranch house in Gainesville, has cracked at mid-span and is slowly heading towards failure after the crack opened further after a recent repair. While the joists commonly attach to the side of a ridge beam, they can also sit on top of it, as shown in the diagram below, which creates an interesting look when the roof structure is exposed as part of the design.īecause a ridge beam often carries a significant area of roof load, they can exhibit structural distress due to a defect in wood, impact on the roof, or use of an undersize beam. 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.Ī 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.
This means that the ridge board for 2圆 rafters, for example, must be more than the nominal 6-inch height of the rafters, because the diagonal cut at the ridge end of the rafter makes the vertical dimension of the face a larger dimension.
#Flush cut rafter revit full
The ridge board is usually just a nominal one inch or two inches wide (1x or 2x lumber) and must be tall enough so that the ends of the joists make full contact with it along their face. The ridge board is installed to provide a bearing point where the rafters meet, and it also helps with alignment along the ridge. The difference between them is that a ridge beam is a structural member that bears half of the live and dead loads of the rafters on either side of it, but a ridge board is not structural. A structural underlay (and draining membrane) is often required under the zinc to ensure air circulation to its underside.Yes, either a ridge board or a ridge beam is necessary, and required by the building code, where roof rafters meet at the the center of their span. Roofing application: The roof is either ventilated with a ventilating space of between 50 and 100mm (depending on rafter length) under the substrate, or installed in an unventilated (warm) roof design which includes suitable methods for condensation control. A simple breather membrane is normally installed between the zinc and the substrate to act as a separating layer. For buildings that require a non-combustible substrate for the zinc, trapezoidal metal sheet panels are used as a substitute for the wooden sheathing / boarding.įaçade application: The cladding is normally rear-vented behind the supporting sheathing / boarding with a ventilating space of at least 20mm (some countries require more). Sheathing / boarding to be laid flush, true and plumb, and its fasteners driven just below the surface. Shingles are fixed back to sheathing / boarding using hidden stainless steel clips secured at pre-determined centres (according to exposure) by stainless steel (A2 grade) fasteners. Cladding weight (zinc only) is between 6 and 7 kgs/m2. Normal shingle widths: 430, 530, and 600mm, nominal maximum length 2000mm. The shingles are made of 0,7 or 0,8mm thick elZinc ® titanium zinc rolled according to EN988 and ASTM B69-13. Zinc Flat lock traditional fully supported cladding composed of interlocking shingles.