Collar Ties

 

Collar ties are designed to tie together the tops of opposing rafters. This helps brace the roof framing against uplift caused by wind. Collar ties must be placed in the upper third of the roof.

Other facts about collar ties:

 

• They may or may not be required, depending on jurisdiction. InterNACHI inspectors should not call out lack of collar ties as a defect unless they know that collar ties were required in the jurisdiction in which the home is located at the time the home was built.
• Collar ties are probably not needed if metal connectors were used to fasten the rafters to the ridge.
• Where they are required, they should be installed on every other rafter where rafters are on 24-inch centers.  
• The 2006 International Residential Code (IRC) requires they have a minimum nominal dimension of 1-inch x 4-inch.
• Collar ties, contrary to popular belief, do not prevent walls from spreading.

  

Rafter Ties

 

Rafter ties are designed to tie together the bottoms of opposing rafters. This helps keep walls from spreading due to the weight of the roof. When the walls spread, the ridge will sag. A sagging ridge is one clue that the home may lack adequate rafter ties. Rafter ties form the bottom chord of a simple triangular roof truss. They should be placed as low as possible in the roof framing.

Other facts about rafter ties:

 

• Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses. A lack of rafter ties is a serious structural issue in a conventionally framed roof.
• In most homes, the ceiling joists also serve as the rafter ties.
• Where rafters are oriented perpendicular to the ceiling joists, rafter ties should be installed just above the ceiling joists. The ties usually rest on the joists.
• When rafters are installed on 24-inch centers, rafter ties are typically installed every other rafter.
• It’s not unusual to see rafter ties of either 2-inch by 4-inch or 2-inch by 6-inch. The 2006 IRC requires them to be at least 2-inch by 4-inch.

 

In summary, collar ties and rafter ties perform different functions but are both essential roof-framing members.