What Are Collar Ties in Carpentry?

Size and Specifications

• Ideally, your collar tie will be a 2-by-4 or a 2-by-6 piece of lumber. The ties should cross from rafter to rafter about two-thirds of the way up and run parallel to the ground. If a tie is longer than 8 feet, you will need bracing to keep the board from buckling.

Spacing Problems

• You need to have a collar tie between every pair of rafter posts. Unfortunately, this is a fairly new addition to code, and you will find older houses with collar ties every two or three rafter pairs. You will need to add ties so that you have one for every pair.

Required Slope

• You need a slope of at least one-third for collar ties to be effective. Let's say you are looking at a roof over a garage that is 30 feet wide. The rafter goes up across 15 horizontal feet to the ridge in the middle. For collar ties to work, the height at the ridge should be at least 5 feet (one-third of the horizontal distance) above the height at the point where the rafter meets the wall. If the slope is less, you will need knee walls or bigger rafters to brace the roof instead.

Exceptions

• If there are metal connectors between your house's rafters and the ridge beam, then you may or may not need collar ties, depending on the roof's pitch. Your home inspector or municipal code department will be able to answer that question for you, as laws vary by jurisdiction.