Replies

1. 
   Jim_Allen | Nov 02, 2007 06:32am | #1

   I've always called them wall ties. Typically, we put three of them (2x4) in a 20x20' garage. They hold the walls from spreading.

   FKA Blue (eyeddevil)

2. 
   Piffin | Nov 02, 2007 01:34pm | #2

   A rafter tie is in the lower third of the rafter span, typically also a ceiling joist. The higher they are raised up, the less they do to prevent wall spread and roof sag. In the upper third of the rafter, they are called collar ties and do almost noting in that regartd. In that poisition, the prurpose is to prevent roof hinging or openning at ridge in high winds

   re your final Q - they are ceiling joists if I understand you

    

    

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3. 
   Matt | Nov 02, 2007 02:16pm | #3

   Rafter ties form the base of the basic triangular element of a gable roof.

   On a normal stick framed gable roof the ceiling joists which also could be called the floor joists of the attic, serve also as the rafter ties that keep the rafter pairs from spreading and pushing the exterior walls outward.

   In a situation where the gable is to run the length of the building rather than the width, it may be a more efficient use of lumber to run the ceiling rafters perpendicular to the rafter pairs.  In this case separate rafter ties are installed just above the ceiling joists to keep the rafter pairs from spreading and pushing the walls out.  In this type of situation these rafter ties are often nailed not only to the rafter pairs but also to the perpendicular ceiling joists.

   This type of scenario might occur, for example on a 8'x 20' attached porch with a gable roof.  The 20' dimension is attached to the main house and the gable ridge runs perpendicular to the 20' dimension.   In this case, the choice would be to either 1) use 20' ceiling joists which would probably have to be 2x10s because their length, or 2) use 2x6-8' ceiling joists with maybe 3 rafter ties running the 20' length.  These rafter ties could be pieced together since they are not supporting a vertical load - they are only in tension, keeping the 8' ends of the porch from moving away from each other.  The ceiling joists are supporting the vertical load of the ceiling.

   Suggestion: don't use the word "truss" in reference to a stick framed roof.