Rafter straps
Two worked examples are provided here: one of gravity forces only, and one of a wind uplift scenario. Members may be selected from our database of standard sections, or a custom rectangular section may be defined with any species, grade, and dimensions.ĭesign can be a breeze by using our member selector or autosize features. The rafter member and each of the ties are set in the next sections. It is likely that none of this will need to be updated, as the default load magnitudes and rafter spacing are all pulled directly from the Project Defaults. The calculation is pre-filled with the roof loads, snow loads, and wind loads, an example of which is shown on the right. For the purpose of bearing calculations, the supports are assumed to be eclusively on the rafter, not any of the ties.
RAFTER STRAPS UPDATE
The diagram, an example of which is shown to the right, will update dynamically as each of the inputs are set. The first step in using the calculator is to input the overall geometry.
Ridge straps are not designed in this module, but may be added to control the uplift separation. However, a ridge strap has no effect upon gravity load scenario of the walls being pushed outward. However, a tie in any position will help in both scenarios.Īlternatively instead of a collar tie, a ridge strap can also be used to keep the rafters from separating at the ridge. A tie located in the bottom third of the roof, usually called a "rafter tie" (and which may also serve a dual purpose as a ceiling joist), is most efficient in preventing the walls from splaying outwards under downward loading. Ties prevent the walls from being pushed outwards by the roof under downward or gravity loads.Ī tie located in the top third of the roof, usually called a "collar tie" or "collar beam", is most efficient for preventing the rafters from separating at the ridge in uplift loading.Ties prevent the rafters from separating at the ridge in wind uplift loads and.In the design of a gable roof, ties serve two purposes, as illustrated in the graphic on the right: Using the calculator involves three essential steps, and one optional step in which the design can be fine-tuned. All load combinations are checked, and both uplift and downward forces are considered.
The wood roof ties calculator is capable of designing the ties and rafter for a gable roof having any combination of collar ties, rafter ties, or ridge straps. Wood Roof Ties to NDS 2018 - Usage & Theory Guide Using the Module