Using the Collar Tie Calculator involves several steps: This calculation considers factors such as the roof’s snow load, wind load, and the material properties of the collar tie itself. In general, collar ties are positioned a certain distance below the ridge beam and are sized to resist the anticipated forces.Ĭollar Tie Spacing: This is typically determined by local building codes and engineering specifications and may vary based on factors such as rafter size and span.Ĭollar Tie Size: The size of the collar tie is calculated to resist the bending forces that could cause the rafters to spread apart. The formula for calculating the dimensions and placement of collar ties is based on structural engineering principles and may vary depending on factors such as roof design, building codes, and the expected loads on the roof. It’s a valuable tool for ensuring the safety and durability of roofing systems. The Collar Tie Calculator assists carpenters and builders in determining the appropriate spacing, size, and location of collar ties based on specific roof design and load requirements. Correctly placed collar ties ensure that the roof remains structurally sound and doesn’t experience excessive sagging or movement. They serve to tie the rafters together and prevent them from spreading apart under the weight of the roof and other loads. Thanks, for everyone's time.Collar ties are typically horizontal framing members installed between opposing rafters in a roof system. If they're installed somewhere along the rafter span, they should be considered in your analysis and the impact on the rafter tie considered. If you want collar ties to only help with uplift resistance at the ridge, place them as high as possible. So, to summarize, collar ties see compression loads. I've seen and fixed lots of roofs where the rafter ties are too high. Below are the moments in the various members under the same loading conditions noted above: As the tie placement moves further up the rafter, the bending in the rafter increases significantly. Similar to collar ties, traditional rules-of-thumb would have them located anywhere in the bottom third of the rafter span ( ). Improperly located rafter ties can be even more dangerous. Yes, they'll go into tension in the event of uplift, but if they aren't designed to resist the appropriate compressive forces, the member or connection may be damaged and unreliable when it's needed in the uplift condition.

The frames at the bottom are for the rafter tie discussion to follow.Īs you can see, the collar tie goes into compression under load. Frames on the left have full snow on the roof, frames on the right have full snow on the left side, 50% snow on the right. Collar and rafter ties (where shown) are at the third points. Below are the axial loads in the members.

The span is 24', c/c, 4:12 slope, 50 psf snow, and i can't recall the dead load but it's not significant relative to the snow. This puts the collar tie in compression and increases the tension force in the rafter tie (the moment arm between the compression and tension forces in the collar and tie, respectively, decreases). However, when you add collar ties, you are introducing a lower point where the rafters can react against each other, like they do at the ridge. Common rule-of-thumb practice is to locate the collar ties in the top third of the rafters. Their intended purpose is primarily to prevent roofs from splitting at the ridge in the event of large uplift forces as the connection to the ridge is traditionally tenuous (end and/or toe-nails). I'm not a layman, so let's get it on! :)Ĭollar ties are common in residential roof construction. The thread has since been removed (layman question i suspect). I posted an unpopular fact in a thread the other day that i was hoping we could discuss a little more.

Roof rafter cross ties