Collar ties are important structural members in a rafter type roofing system. To be honest, most of the time they don’t look like much (many home inspectors don’t even take note of them), but without them, a rafter system would likely eventually fail to some degree or another.
If you look at the diagram you will see that short framing member near the top of the framing system. That right there is a collar tie. The technical term for it is actually “collar beam”, but not many people call it that. So for the sake of this blog, we will call it a collar tie.
Now that we know what it looks like, what does it do? Well, whenever I am on a home inspection here in Oklahoma and I see a sagged roof, one of the first things I look for is missing collar ties. That is because they help hold the roof framing together, and without them it can become horribly uneven and sag. Generally speaking, houses can go for extremely long periods of time without collar ties, but it is best practice to make sure they are in place and secure.
Read this great collar tie article by InterNACHI.