Note that, if there are two ties, it does not matter which tie is the 'first' or 'second', as long as it remains consistent throughout Depth of First/Second Tie : The depth of the collar and/or rafter tie from the roof ridge to the tie.If both are present, then select 'Two', otherwise select 'One'. Number of Ties Present : This refers to collar ties or rafter ties.Note that this module does NOT design the ridge strap itself it is simply assumed that the ridge strap is of sufficient strength to keep the rafters connected at the ridge under any uplift conditions. Ridge Strap Present? : A ridge strap is a metal strap which runs over the top of the roof and connects rafters on either side of the rafter.Roof Pitch : The rise over run pitch of the roof, given in the form of 'x:12'.This is the horizontal plan length, which will only equal the total rafter length if the roof pitch is zero (flat). Usually, this will be half the width of the roof, from eave to ridge. Rafter Plan Length : The horizontal length of a single rafter.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 andĢ. In the design of a gable roof, ties serve two purposes, as illustrated in the graphic on the right:ġ.

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.

Roof rafter tie rods