Purpose Of Roof Collar Ties

In the typical conventional roof frame of a home and some other type buildings collar ties and rafter ties are important and required structural components.

Purpose of roof collar ties. A collar beam or collar is a horizontal member between two rafters and is very common in domestic roof construction often a collar is structural but they may be used simply to frame a ceiling a collar beam is often called a collar tie but this is rarely correct. A collar tie is a tension tie in the upper third of opposing gable rafters that is intended to resist rafter separation from the ridge beam during periods of unbalanced loads such as that caused by wind uplift or unbalanced roof loads from snow. Collar ties rafter ties tension beams structural ridge beams. Further i was taught that what are commonly called collar ties are in fact rafter ties and that their purpose was to add rigidity to the apex of the roof rafter system.

Both are horizontal framing members that serve different purposes as they tie different components together and are both important to a properly framed roof. The most common reason for installing collar ties is to prevent rafters from spreading apart under load. Collar ties may take up space in the attic of your home but they are there for a reason. For rafter sag or to resist uplift you add in rafter jacks which tie the rafters to the joists typically midspan to midspan.

The upper collar tie does not experience the tension that the lower rafter tie is resisting if that tension is resisted in the upper third the roof is probably on the ground. In this collar tie roof storage space provided is less due to collar tie and limited head room for access to water storage cisterns. The rafter ties are incorrectly labelled as collar ties. This article describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings including definitions of collar ties rafter ties and structural ridge beams.

The 2015 international residential code does not require collar ties or collar beams. Where the rafter span is such that it requires support from underpurlins collar ties are fitted to opposing common rafters at a point immediately above the underpurlins. They supplement the ceiling joists and prevent the rafter couples spreading. A tie in building construction is an element in tension rather than compression and most collar beams are designed to work in.

Collar ties must be provided in all coupled roof construction. The purpose of the collar tie roof is to extend first floor rooms into the roof space and so limit the largely unused roof space. However in a conventionally framed peaked roof like the kind you describe collar ties would probably serve little or no function since the attic floor joists serve as ties to prevent the rafters from spreading.