![]() Those 12" "kneewalls" are going to push outwards at the top where the rafter tails are connected. Looking at the illustration I see a problem on the right end where it appears the loft is above an open porch. There is also a minimum size and number of nails listed in the IRC for the rafter tie to rafter connection. If the rafter tie is raised there may have to be adjustments to a larger size rafter to maintain rafter strength. A rafter tie may be raised up into the lower 1/3 of the rafter triangle. ![]() Rafter ties are often the ceiling joists. As such one can use a metal strap over the peak and nailed to the upper surface of the rafters to do the same thing. It is there to help keep the rafter peak together. A collar tie is properly installed in the upper 1/3 of the roof triangle. Collar ties do nothing to restrain the outward forces on the rafter tails. Obviously the header beam into either scheme requires some thought. Or if the exterior wall studs could extend up to the rafters, rather than the knee wall being framed separately, that'd work too. If your loft joists can extend through the exterior walls to meet the rafters, you don't need collar ties, except where the loft is open. Joists 12" below the top plate are sufficient.Ĭollar ties DO help prevent spreading walls, but their primary purpose is actually to keep rafters from spreading apart at the top. Collar ties I don’t believe do anything to resist outward force at the walls. I will use straps instead of collar ties. I think the formation of the triangle as a result of the rafter tie really stiffens up the roof, ie ridge in addition to supporting the walls from bowing. Do I need to actually tie the rafters together? Or is a wall that is tied by joists 12†below the top plate sufficient? I think it is.sufficient but it does have me thinking about it. if not, then a “TRUE†rafter tie will span the distance in the lower 1/3 of the rafter. If there is a gangway- a tie will be made through the gangway. Therefore there is a 10’ section with no ties at all. The lofts may or may not be joined by a small gangway. Yes- the joists are outside of the rafter triangle, but I THINK they are close enough (12†only) where they will still do the job of resisting outward force of the rafters. and the joists for the loft will span the entire width of the cabin- thereby tying the walls together. My lofts have kneewalls that are part of a continuous wall from the floor where 12†only will protrude above the floor of the loft- effectively creating a knee wall. Code is not required in MN where I am building. and the only real problem I am potentially worried about is the lack of rafter ties. I am building a cabin that I designed - 22’ wide x 28. Small Cabin Forum / Cabin Construction / Rafter ties? We had hundreds of roof failures this winter around my area, no doubt some of them caused by failure of rafter ties.- Forums - Register/Sign Up - Reply - Search - Statistics. In the unlikely event you received a significant snowfall, the combination of low pitch on the roof, limited rafter/collar ties, and the location of the ties at the midpoint of the rafter would allow for large outward forces on the walls, which could cause wall rotation or possibly roof collapse. I am not familiar with Alabama building practice, you may want to check with the building inspector before you remove every other frame. The rafter ties prevent the walls from spreading, which is the major issue where snow load dominates.īut you live in an area where there is little snow, so local framing practices are quite different. ![]() ![]() Where snow dominates, the collar tie has little structural significance, all it really does is equalize uplift loading on the roof during high wind events. It looks like your frame is at the midpoint between the wall and the rafter peak. ![]() Collar ties are typically at about the 2/3 point from the wall to the peak of the roof. Not terribly important, but in a truss all the members are either in tension or compression, there is no bending moment on any of them, whereas in your structure there will be bending moment on members that are part of the trapezoid.Īlso, rafter ties in the northeast are always in the lower third between the top of the wall and the peak of the roof. As a matter of terminology, you have a space frame, not a truss, because in a truss all of the structural members form triangles, and it looks like you have a trapezoid as part of your frame. In the Northeast, where snow loads are high, I have not seen this type of framing. It is always interesting for me to see local framing practice. ![]()
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